Effects of mites on the physiology and performance of the Florida scrub lizard (sceloporus woodi)

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Effects of mites on the physiology and performance of the Florida scrub lizard (sceloporus woodi)
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Baldwin, Kevin S., 1963-
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Florida Scrub Lizard -- Physiology   ( lcsh )
Mites -- Diseases   ( lcsh )
Zoology thesis, Ph.D   ( lcsh )
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Thesis:
Thesis (Ph.D.)--University of Florida, 1999.
Bibliography:
Includes bibliographical references (leaves 122-141).
Statement of Responsibility:
by Kevin S. Baldwin.
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Typescript.
General Note:
Vita.

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EFFECTS OF MITES ON THE PHYSIOLOGY AND PERFORMANCE OF
THE FLORIDA SCRUB LIZARD (SCELOPORUS WOOD)









BY


KEVIN S. BALDWIN


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY



UNIVERSITY OF FLORIDA


1999











Copyright 1999

by

Kevin S. Baldwin













ACKNOWLEDGMENTS


Despite the emphasis on the individuality of research in our field, it is
remarkable how collective an enterprise it is. I owe a great debt to my
advisor Lou Guillette, who prodded me to think more mechanistically (no
mean feat). Other committee members included Rich Kiltie, who was
always available for statistical consultation; Carmine Lanciani who was a
great source of information; Buzz Holling who taught me to think big and
Jack Putz who supplied important perspective. I would also like to thank
Roger Anderson who has been a remarkable collaborator, mentor and
friend.
Within Zoology, Lou Guillette supplied lab space and equipment.
Harvey Lillywhite was always supportive of my efforts. Frank Nordlie
supplied the osmometer and his expertise. Pauline Lawrence and Marty
Crump always had great ideas. I owe thanks to Dave Evans and Kent Vliet
who through Biological Sciences provided most of my financial support
while at UF. Andy Rooney was extremely helpful in instruction of
histological techniques.
Across campus, Harvey Cromroy and Cal Welborn identified mites.
Jerry Butler gave advice on finding chiggers. Marilyn Spalding aided with
interpretation of histopathology.
Vince DeMarco, Harry Tiebout, Eleanor Mobley and Darcie Johnson
provided their insights from the field. Jim and Mary Buckner were
incredible sources of knowledge about scrub and first rate hosts in Ocala.
Laura Lowery, Carrie Sekerak, and Janet Hinchey of the USFS were
tremendous sources of information and support.
I have been aided by some exceptional undergraduates over the years.
Jen Gebo helped with the evaporative water loss measurements. Christine
Nielson did the bulk of the mite pocket measurements. Chris Kane did
amazing amounts of histology. Jen Gebo and Henry Villadiego helped
with the osmolarity and hematocrit measurements. David Smith helped








with the recovery time trials. Jen Gebo, Henry Villadiego, Chris Kane,
Leah Wojnar, Amy Mosseri, Krista Dietz and Katie Fontanessa helped
with behavioral observations and animal care.
I have been fortunate to have many friends who contributed
immeasurably to the quality of my life and ideas over the years. I owe
much to Dustin Penn, Ron Edwards, Susan Moegenberg, Lydia Flewelling,
Mark Stowe, Tim and Lydia Sweat-Young, and The Naked Apes.
Finally I would like to thank my parents, sister and grandparents who
were so supportive through this lengthy process. I am grateful to all.















TABLE OF CONTENTS

ACKNOWLEDGMENTS.................................................................................... iii

LIST OF TABLES....... .........................................................................................vii

LIST OF FIGURES.............................................................................................. iii

ABSTRACT..................... ...................................................................................... xi

CHAPTER 1 INTRODUCTION.............................................................................1
The Acarina and Reptiles.......................................................................2
Rationale for the Study..............................................................................5
Study Animals............................................................................................ 7
Study Area ....................................................................................................9

CHAPTER 2 CHIGGER INFESTATIONS, EVAPORATIVE WATER
LOSS AND THE POSSIBLE ADAPTIVE SIGNIFICANCE OF NUCHAL
POCKETS................. ................................................................................................ ..28
Introduction ................................................................................................ 28
Methods ....................................................................................................... 29
Results .......................................................................................................... 32
Discussion...................................................................................................33

CHAPTER 3 THE EFFECTS OF MITES ON THE MORPHOLOGY,
PHYSIOLOGY AND PERFORMANCE OF THE FLORIDA SCRUB
LIZARD, SCELOPORUS WOODI........................................................................42
Introduction................................................................................................ 42
Methods ....................................................................................................... 45
Results .......................................................................................................... 49
Discussion....................................................................................................54

CHAPTER 4 EFFECTS OF ADULT MITES ON LIZARD METABOLIC
RECOVERY FROM EXERCISE.............................................................................74
Introduction..........................................................................................74
Methods .......................................................................................................76
Results.............................................. .......................................................... 77
Discussion.......................................... .......................................................77




v








CHAPTER 5 SPATIAL AND TEMPORAL ASPECTS OF CHIGGER
AND MITE ABUNDANCE WITH SPECIAL REFERENCE TO
LANDSCAPE BURNING AND DISTURBANCE ...................................... ..81
Introduction....................................................... .........................................81
M methods ................................................................................... .....................84
Results....................................................... ........ .............................................86
D iscussion................................................................................... .........87

CHAPTER 6 CONCLUSIONS................................................................................105
Introduction ..................................................................................... ........105
The Evolution of Virulence...... ..............................................................108
Conservation Implications of the Evolution of Virulence.............. 112
Habitat Structure, Parasites and Scale............................... ...........115
Links Among Sublethal Effects............................................ ..............117
Prognosis.......................................... ........... ..........................................119

REFERENCES .........................................................................................................122

BIOGRAPHICAL SKETCH...................................................................................142






























vi














LIST OF TABLES

Table 1.1. Aspects of acari-reptile relationships..........................................21

Table 1.2. Duration of Eutrombicula alfreddugesi life history
stages ........................................................................................... ................. 26

Table 1.3. Geckobiella texana life history stages......................................26

Table 1.4. A comparison of scrub and high pine.....................................27

Table 3.1. Regressions of performance variables against
hematocrit values for S. woodi ..............................................................73

Table 3.2. Summary of average maximum performance values
for male and female S. woodi in July and August ................................74

Table 3.3. Average intensity of Geckobiella texana on Sceloporus
woodi during and after the reproductive season......................................74

Table 4.1. Effect of treatment with ivermecten on lizard
perform ance m measures. ............................................................................. 79

Table 5.1. Histories of sites in Ocala National Forest used to
assess m ite prevalence ............................................................................... 98

Table 6.1. Variables that affect virulence (after Ewald 1994).................121














LIST OF FIGURES

Figure 1.1. The life cycle of Eutrombicula alfreddugesi (after R.
Loomis, unpub. and Conant 1975). .........................................................13

Figure 1.2. Distribution of scrub (filled in black) in Florida, with
the Ocala National Forest and Big Scrub regions, where this
study was conducted, labelled with larger type (after Myers 1990).
...................................................................................................................... 14

Figure 1.3. Average maximum and minimum monthly
temperatures in Ocala, Florida (1961-1990).......................................15

Figure 1.4. Average monthly precipitation in Ocala, Florida
(1961-1990)...................................................................................................16

Figure 1.5. Coefficient of variation of average precipitation
(CVPPT) for Ocala, Florida........................................................................17

Figure 1.6 Marion County, Florida (shaded in black).............................18

Figure 1.7. Ocala National Forest within Marion County,
Florida .........................................................................................................19

Figure 2.1 Scanning electron micrograph (SEM) of a left nuchal
pocket of Sceloporus woodi at 50X magnification.................................37

Figure 2.2. Dehydration chamber for small lizards................................38

Figure 2.3. Stylostomes in longitudinal (left) and cross-section
(right) in a nuchal pocket of a Sceloporus woodi (1 cm = 40 gm). .......39

Figure 2.4. Eutrombicula alfreddugesi chiggerss) attached to the
nuchal pocket of Sceloporus woodi. Extensive inflammation
surrounds the stylostomes (1 cm = 40 gm).......................... ................39

Figure 2.5. Edge of nuchal pocket showing the localized
inflammatory response to chigger infestation........................................40


viii








Figure 2.6. Regression of evaporative water loss on mite
intensity ...................................................................................................... 41

Figure 3.1. The morphology-performance-fitness paradigm (after
Miles 1994 and Garland 1994)..................................................................61

Figure 3.2. Venn diagrams of model building strategies.......................62

Figure 3.3. Stylostome (feeding tube) of an adult female
Geckobiella texana into the thigh of Sceloporus woodi.......................63

Figure 3.4. Inflammatory reaction from the attachment of adult
Geckobiella texana behind the knees of Sceloporus woodi...................64

Figure 3.5. Inflammatory reaction from the attachment of adult
Geckobiella texana behind the knees of Sceloporus woodi...................65

Figure 3.6. Hematocrit for parasite-laden lizards after being
sprayed with a solution of ivermecten (mites-removed) or water
(m ites-retained)......................................................................................... 66

Figure 3.7. Plasma osmolarity for parasite-laden lizards after
being sprayed with a solution of ivermecten (mites-removed) or
w after (m ites-retained).............................................................................. 66

Figure 3.8. Turn-around distance (m) regressed against
hem atocrit ...................................................................................................... 67

Figure 3.9. Fast-run distance (m) regressed against hematocrit.............67

Figure 3.10. Endurance, as indicated by total distance (m) covered
by S. woodi individuals in a running trial, regressed against
hem atocrit ......................................................................................................8

Figure 3.11. The best performance of males in July as function of
adult mite intensity. Maximum speed declines with increasing
m ite load............................................................................................................68

Figure 3.12. Best performance (maximum speed m/s) of males in
A ugust ......................................................................................................... 69

Figure 3.13. Logistic regression of running tactic as a function of
mite intensity (number of mites per lizard host). ..................................70

Figure 3.14. Endurance of males in July as a function adult mite
intensity. ...................................................................................................... 71









Figure 3.15. Endurance of males in August as a function of adult
m ite intensity....................................................................... ...................... 71

Figure 3.16. Paired t-test of maximum speed in m/s before (pre-)
and after (post-) mite removal with ivermecten.......................................72

Figure 3.17. Paired t-test of total distance (endurance) before and
after mite removal....................................................................................73

Figure 3.18. The morphology-performance-fitness paradigm
extended..... ............................................ .......................................................73

Figure 4.1. Maximum endurance as a function of mite intensity.........79

Figure 4.2. Minimum recovery time as a function of mite
intensity. ............................................................ ....................... .................. 80

Figure 5.1. Longleaf pine at Kerr Island, ONF in May 1994 ..................95

Figure 5.2. Turkey oak at Kerr Island, ONF in May 1994.......................96

Figure 5.3. A typical edge between a young scrub and mature
sand pine.......................................................................................... ...........97

Figure 5.4. Chigger intensity (number of chiggers per lizard) of
Sceloporus woodi by habitat at Kerr Island in a) May, 1994.................99

Figure 5.5. Diel patterns of chigger activity, June 1997...........................100

Figure 5.6. Monthly intensity of chiggers on male lizards, 1996............101

Figure 5.7. Monthly intensity of chiggers on female lizards, 1996........102

Figure 5.8. Comparison of Geckobiella prevalence in roller-
chopped
(n = 4) and unchopped (n = 4) sites.............................................................103

Figure 5.9. Possible effects of roller-chopping on vegetation
spacing................................................................................................................104

Figure 6.1 Summary diagram...................................................................120














Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy


EFFECTS OF MITES ON THE PHYSIOLOGY AND PERFORMANCE OF
THE FLORIDA SCRUB LIZARD (SCELOPORUS WOODI)



By

Kevin S. Baldwin

May, 1999




Chairman: Dr. Louis J. Guillette, Jr.
Major Department: Zoology

Parasitology has enjoyed a renaissance in biology over the last decade
under the aegis of modern evolutionary theory. Much of this
reinvigoration is dependent on parasites causing measurable pathology,
which until recently was thought to be relatively rare because group
selectionist thinking predicted that parasites should evolve towards
benignness. Ectoparasites are model organisms for studying effects on
hosts because their intensities (number of parasites/host) are easily
manipulated. Although pathologies of mites and ticks on reptiles are well
documented, the mechanisms and implications of their non-lethal effects
have not.








I found that chiggers (Eutrombicula alfreddugesi) increase the evaporative
water loss of their lizard hosts, Sceloporus woodi, in north central Florida,
by causing inflammation that probably disrupts the water impermeable
lipid layer in their integument. The nuchal pockets of lizards may reduce
water loss by localizing chigger infestations in areas of the skin that form
enclosed spaces that become easily saturated with water vapor.
Geckobiella texana mites on Sceloporus woodi cause inflammation of
muscles and nerves around the knees where they tend to attach. Adult
females suck blood and appeared to increase the viscosity of the blood in
the lizards by reducing fluid volume. Osmolarity did not seem to be
affected. Both inflammation and blood loss may reduce host physiological
performance. Maximum sprint speed and endurance were reduced when
mites were present. Heavily infested lizards were more likely to turn
evasively than run away from a threat. Mites also reduced the ability of
lizards to recover from exhaustion.
Human activities affect chigger and mite populations. Fire suppression
may result in high chigger populations. Chiggers are dense at ecotones,
thus creating "edge" for deer may also create preferred habitat for chiggers.
Lizards had higher mite prevalence in roller-chopped sites than burned or
unchopped sites.
Habitat modification may select for high virulence of parasites by altering
transmission rates among hosts. When combined with stress, loss of
genetic variation, and decreased immunity from environmental
contaminants, high virulence may have greater effects on host
populations. By recognizing that virulence can evolve, we may be able to
select for less virulent pathogens.













CHAPTER 1
INTRODUCTION


Over the last decade and a half, the study of parasites has enjoyed a
renaissance in the ecological and evolutionary sciences (Lehmann 1993).
Parasites have been linked to the evolution and maintenance of sex (Lively et

al. 1990; Moritz et al. 1991), and many aspects of sexual selection (e.g.,
Hamilton and Zuk 1982; Meller 1990; Lefcort and Blaustein 1991; Folstad and

Karter 1992). Careful application of individual selection theory has led to

critical thinking on mode and frequency of pathogen transmission in the
evolution of virulence (Ewald 1983, 1994). Parasites and disease that were
once thought to evolve toward benignness "for the good of the species" can in
fact evolve towards extreme virulence. The emergence of new diseases (e.g.,
HIV, Ebola, Hanta virus, and Lyme disease) and the reemergence of old ones

(e.g., tuberculosis, cholera, and malaria) have biologists in many disciplines
thinking seriously about pathogens and parasites again (Garrett 1994).
Ectoparasites are model systems for studying host-parasite interactions

because they are relatively easy to study, can cause pathologies with ecological

and evolutionary consequences, and have the potential to interact with other
parasites by acting as vectors. Ectoparasites are also relatively amenable to
experimental manipulation. The first part of this introduction is a review of

what is known about acarine (i.e., tick and mite) interactions with reptiles. It
is modeled after other reviews (Reichenbach-Klinke and Elkan 1965; Frank
1981), but rather than taking an acarine systematist's point of view, it focuses








on types of interactions among acari, reptiles and other parasites or
pathogens. The second part of this introduction presents a rationale for this
study by way of a "classification" of acarine-lizard studies that attempts to
encapsulate what has been done and points to some gaps in our
understanding. Finally, the third part of the introduction includes some
background information on the species and landscape involved in this study.


The Acarina and Reptiles

The Acarina are found in nearly all habitats available to plants and
animals. They can be found in terrestrial, aquatic (including hot springs) and
marine habitats, living internally and externally on both vertebrates and
invertebrates (Baker and Wharton 1952). Among the metazoa, perhaps only

nematodes are more ubiquitous.

Within the reptilia, for example, ticks have been reported on marine
iguanas (Amblyrhynchus cristatus), (Vercammen-Grandjean 1965) and sea
snakes (Laticauda spp., Zann et al. 1975). Entonyssid mites are found in the
lungs and trachea of snakes (Reichenbach-Klinke and Elkan 1965). The mite
Mabuyonyssus parasitizes the nostrils of reptiles (Reichenbach-Klinke and
Elkan 1965). The aptly named cloacaridae are found in the cloacal mucosa of
turtles and are probably venereally transmitted (Frank 1981). The majority of
ticks and mites on reptiles are found externally.

Some ectoparasitic mites are very host specific (e.g., Geckobiella mites
have only been found on lizards of the genus Sceloporus). Others are
generalists: e.g., the chigger, Trombicula batatas in the US infests about 100
species of vertebrates including reptiles and amphibians (Frank 1981). The
chigger, Eutrombicula alfreddugesi, has been observed on 126 vertebrate
species (Benton 1987). Different stages in the life cycle frequently specialize on








different foods. As juveniles and adults, ticks are blood feeders. As larvae and
nymphs, mites are tissue feeders. As juveniles and adults, some are blood

feeders, whereas others, like trombiculid mites, are free-living.
Table 1.1 summarizes the different kinds of relationships and

pathologies attributed to mites and ticks on reptiles. Much of its content is
outlined below.


Direct Impacts

Host dehydration, blood loss, anemia and even death by
exsanguination (Mader et al. 1986) are common effects of ectoparasites (Frank

1981; Salvador et al. 1996; Dunlap and Mathies 1993). Ticks facilitate feeding by

engaging in host manipulation with salivary secretions that include
immunosuppressants, analgesics, anticoagulants and antiplatelet aggregatory

compounds (Bowman et al. 1996). Because ticks are essentially giant mites,
mite saliva probably has similar components with like effects. Heavy
infestations of mites can present serious challenges to their hosts not only in

terms of what is removed, but also in what is added.

Despite these manipulations by the ticks, inflammation, integumental
lesions, dermatitis and granuloma formation do affect the reptilian host

(Arnold 1986; Bauer et al. 1990; Goldberg and Bursey 1991a, 1993; Goldberg and

Holshuh 1992). Tick saliva can cause paralysis in some reptiles (Frank 1981)
and irritation caused by mite saliva of experimentally applied mites has even
induced tail autotomy in geckos (Oliver and Shaw 1953). Ixodes asanumai
ticks on the skink Eumeces okadae has been reported to cause limb muscle
atrophy (Hayashi and Hasegawa 1984a).
Heavy infestations also lead to behavioral changes in the host.
Anorexia has been documented (Klingenberg 1993; Mader et al. 1986; pers.








obs.). Effects may even be seen in the next generation. Sorci et al. (1994) found
alterations of behavior and performance in offspring of infested females.


Mites and Ticks as Vectors

Mites and ticks are efficient vectors of disease. The bacteria Aeromonas
hydrophila, which causes a fatal, hemorrhagic septicemia in snakes, is

transmitted by Ophionyssus mites (Camin 1948). Ixodid and argasid ticks can
transmit the spirochete that causes Q-fever (Frank 1981). Viruses and

protozoans are also transmitted by mites and ticks (Sekevoya et al. 1970; Frank

1981). Klein (1985) was able to infect Sceloporus undulatus with the
coccidium Shellackia by force feeding it Geckobiella texana mite vectors.

Leishmania and Hepatozoon sauromali, a hemogregarine, can infect

chuckwallas via Hirstiella mites (Lewis and Wagner 1964). The protozoan
Karyolysus is transmitted by gamasid mites, Sauronyssus saurarum (Svahn,

1974), whereas Leukocytozoon, a hematozoon is transmitted by macronyssid

mites (Frye 1981). Even parasitic worms can be transmitted; the argasid tick
Ornithodorus talaje transmits the haemofilarian, Macdonaldius oschei
(Reichenbach-Klinke and Elkan 1965; Frank 1981).


Interactions with Other Variables

Dunlap and Mathies (1993) found that nymphal ticks alone had little
impact on hosts but when hosts also had malaria, their body condition
declined significantly. Similarly, captive animals with heavy mite loads are
more likely to develop bacterial infections (Klingenberg 1993; pers. obs).
Stress can interact with immunity via hormones to affect the health of hosts
(for review see, Guillette et al. 1995). The stresses resulting from parasitic

infections and vice versa are not well understood.





5

In at least one case, the ectoparasite can benefit from its interaction
with a host in a nontraditional manner; that is, its host actually eliminates a
bacterial infection in the parasite. Lane and Quistad (1998) found that an
unknown compound in lizard blood actually rids nymphal ticks of infections

of Borellia burgdorferi bacteria, and argued that large populations of
Sceloporus lizards limit the spread of Lyme disease in western North
America.
Phoresy (passive attachment of a commensal to the host) has been
documented between mites and reptiles. Ophiomegistus (Paramigistidae) can

parasitize skinks and snakes but typically infests insects and myriapods.

Reptiles may acquire these mites as they consume their insect hosts.
Elkan reported a slow-worm (Anguisfragilis) infested by the sarcoptiform

mite Caloglyphus sp. (Reichenbach-Klinke and Elkan 1965). Phoresy may be a
minor cost entailed by feeding.

Mites can also be a source of food for lizards. Burrage (1966) found that

Uta stansburiana ate Ophionyssus sp. mites from one another. One

potential negative side-effect of this is the possible transmission of protozoans
(see above).


Rationale for the Study

Between the extremes of death and phoresy, there are large holes in

our understanding of the effects of ectoparasites on reptiles. To better
appreciate these gaps, I will construct a crude classification of the types of
studies that have been done. At the foundation of any biological study is
proper identification of the organisms of interest. A large portion of the
literature is devoted to a-taxonomy (e.g., Lawrence 1936; Cunliffe 1949;
Powder and Loomis 1962; Loomis and Crossley 1963; Newell and Rykman








1964; Lucas and Loomis 1968; Loomis and Spath 1969; Loomis 1971; Bennett
1977; Bennett and Loomis 1981) and documenting the association of hosts and
parasites (e.g., Jelison 1934; George 1960; Mather 1979; McAllister 1980;
Simonsen and Sarda 1985). There is also some documentation of geographic
and elevational variation in ectoparasite loads of different reptilian
populations (e.g., Allred and Beck 1962; Spoecker 1967; Loomis and Stephens
1973; Gadsden 1988; Zippel et al. 1996). In addition to this spatial component,
seasonal variation in parasite load has been recorded in some reptilian
populations (Mohr et al. 1964; Spoecker 1967; Loomis and Stephens 1973).
Additional studies describe where ticks and mites attach to their hosts
(Powder and Loomis 1962; T. Auffenberg 1988; Auffenberg 1981, 1988, 1994;
Pearson and Tamarind 1973; Hayashi and Hasegawa 1984b; Oliver et al. 1993),
when mites attach in the life-cycle of the lizard (Goldberg and Bursey 1994)

and the duration of this attachment (Jameson 1972; Goldberg and Bursey
1991b, 1993). Local pathology caused by mites and ticks has been examined
histologically (Bauer et al. 1990; Goldberg and Bursey 1991a; Goldberg and
Holshuh 1993). Finally, in recent years there has been some attention paid to
the physiological (Dunlap and Mathies 1993) and performance effects of (Sorci
et al. 1994) ectoparasitism.
A look at the dates of the studies cited in Table 1.1 reveals that the

topics in this classification have developed in roughly chronological order. In
as much as this time-line can be construed as a "phylogeny" of lizard-
ectoparasite studies, the following chapters represent an ontogeny of my own
thinking about these relationships. This study begins by recapitulating the

phylogeny of lizard-ectoparasite studies and extends this descriptive work to
an understanding of the implications of mite infestations for the physiology
and whole-organism performance of the hosts. Finally, this study explores








some conservation oriented links among host populations, parasites and
landscape-level modifications of habitat.

Study Animals


The Lizard Host

The Florida scrub lizard, Sceloporus woodi, is a small, grayish, spiny-
scaled lizard (Figure 1.1) and is the only member of its genus not found west
of the Mississippi River. It is a Florida endemic and is almost always restricted
to sand pine scrub, a plant association with a highly disjunct distribution (see
Figure 1.2). In addition to the Ocala National Forest-Big Scrub complex, where
this study was conducted, S. woodi also occurs along the coast in isolated
populations from Merritt Island south to Jonathan Dickinson State Park and
Marco Island. Inland, there are populations at the Archbold Biological Station
and the Lake Wales Ridge.

Sceloporus woodi is a forest edge species that prefers open, sandy areas
adjacent to sand pine scrub and sandhill associations of long leaf pine and
turkey oak (DeMarco 1992). Because of its narrow habitat requirements, the
fragmented nature of scrub, and the rapid conversion of scrub into
agricultural lands or housing developments, Sceloporus woodi is federally
listed as threatened.

This species is sexually dimorphic for size and color (Figure 1.1). Adult
females average 4-5 mm longer than males and retain dark undulating bands
on the dorsum characteristic of juveniles, whereas males lose this pattern to
achieve a uniform dorsal gray color. Males have bright blue patches on each
side of the belly and black and blue patches under their throats. Some females








have faint blue patches in these areas, but generally tend to be light colored on
the underside.
Females mature at about 47 mm SVL and can begin vitellogenesis as
early as March, if they are in their second reproductive season (DeMarco
1992). Females in their first reproductive season typically yolk follicles in
April or May. Courtship and mating occur from March June. Females
typically lay three clutches per season (DeMarco 1992) though some estimates
are as high as five per season for larger individuals (Jackson and Telford
1974). Clutch size ranges from 2-8, averages 4, and increases with body size.
Reproduction is over by the end of August. Eggs take about 2.5 months
to develop (depending on temperature) with hatchlings emerging from late
June to early November at 20-25 mm SVL and around 0.40 gm mass
(DeMarco 1992). Hatchlings reach maturity in as little as 6-10 months (Jackson
and Telford 1974; DeMarco 1992; Hartmann 1993), depending on when they
hatch.
Hartmann (1993) studied population demographics of a population of
S. woodi on the Lake Wales Ridge and found that this species is essentially
an annual species, with survivorship ranging from 2.5-22% depending on
hatching date. DeMarco (1989) documented interannual variation of the
seasonal shift in egg and clutch size.

The Parasitic Mites

To better understand how landscape level modifications could affect
ectoparasite populations one must first understand the life cycles of the
ectoparasites and how they interact with their hosts and habitat. Eutrombicula
alfreddugesi is a trombiculid mite. Only the larval stage (commonly known
as chiggers or red bugs) of mites in this family is parasitic on vertebrates. It








has been observed on 32 mammals (including humans), 52 birds, 39 reptiles
and 3 amphibians (Benton 1987). The juveniles and adults are free-living in
the soil and eat small arthropods and their eggs in the leaf litter (Figure 1.1).
Duration of the life stages for E. alfreddugesi is shown in Table 1.2. In
contrast, the pterygosomid mite Geckobiella texana lives its entire life cycle
on its lizard host (Goodwin 1954; Table 1.3). Geckobiella has only been found
on lizards of the genus Sceloporus (Lane 1954; Jack 1959). I have observed

larvae, juveniles, and adults moving from one lizard host to another in
captivity. Geckobiella can be involved in the transmission of disease.
Bonorris and Ball (1955) implicated Geckobiella in the transmission of
Shellackia. Klein (1985) experimentally infected Sceloporus undulatus by
force feeding them Geckobiella texana infected with Shellackia occidentalis.


Study Area

This study was conducted in Ocala National Forest (ONF), Marion
County, Florida (Figure 1.2). The Big Scrub complex, which lies within and
around the ONF, is the largest inland scrub in Florida (Myers 1990). The Ocala
region has an average minimum temperature of 14.8 OC, an average
maximum temperature of 28.3 OC (Figure 1.3) and averages 1309 mm
precipitation per year (Figure 1.4). The bulk of the precipitation falls between
May and September (Southeastern Regional Climate Center 1998). Variation
in precipitation from year to year is largely dependent on month. The
coefficient of variation of average precipitation is highest in March and
lowest in July (Figure 1.5).
The Ocala region is primarily a matrix of two upland ecosystems: scrub
and high pine. The Florida scrub ecoystem is perhaps best summarized by
(Myers 1990, p. 151) as "mature forests of tall, twisted leaning sand pines








(Pinus clausa) rising above an inpenetrable mass of evergreen scrub oaks;
rusty lyonia; rosemary; unusual varieties of holly, bay; and hickory; and an
array of inconspicuous species, many with restricted distribution." An
estimated 40-60% of plant species are endemic. Scrub is pyrogenic and
maintained by fires that occur every 15-100 years. The "varieties" of scrub
patches seen today reflect their different fire histories (Myers 1990). Embedded
in these extensive areas of scrub are islands of high pine consisting of open
woodlands of longleaf pine (Pinus palustris) over a cover of wiregrass
(Aristida stricta) and several hundred other species, and occasional clumps of
turkey oak (Quercus laevis) or other oak species. High pine is maintained by
fires recurring every 1-15 years. In the absence of fire, oaks and sand pine
invade and begin to dominate.
Despite their physiognomic differences, scrub and high pine are

strongly associated with one another as they both occur on dry, infertile
uplands whose soils are derived from the same parent material, both are
maintained by fire, and the ignition of scrub depends on flammable high pine
(Myers 1990). A comparison of scrub versus high pine plant species
composition and fire regimes is made in Table 1.4.
Unfortunately, both scrub and high pine ecosystems have been reduced
to a fraction of their historic ranges. Longleaf pine has decreased from a nearly
continuous expanse of 25 million hectares to a handful of sites that
collectively contain less than 1000 hectares of old growth (Noss 1989). Much
of Florida's historic sand pine scrub depicted in Figure 1.2 has been reduced or
fragmented by development. The largest remaining tracts are in ONF, which
like much of the managed xeric pineland in the southeastern coastal plain of
the U.S., is oriented for timber production. Harvest schedules have been
accelerated since the the early 1980s with the result that uncut sand pine scrub








has been reduced to 25% of its original area within the ONF (Anderson and
Tiebout 1993).
LANDSAT images are especially useful for characterizing large scale

landscape changes over time (FGDL 1998) and can give some indication of the
nature of management changes on the ONF. The LANDSAT series of

satellites uses a Multi-Spectral Scanner (MSS) sensor with 60 m resolution.
Three of the 4 spectral bands detected by the MSS are shown here to render a
false color infrared image. Band 4 is near infrared, bands 2 and 1 correspond to

the red and green portions of the visible spectrum. Multiple images were
stitched together to form an image mosaic to cover the geographic extent of

Marion County, Florida (Figure 1.6), the eastern half of which is depicted in

Figure 1.7. The 3 different MSS images (Figures 1.7a, b, c) respectively, are
from 1973, 1986 and 1991, plus or minus one year (FGDL 1998).

The patchwork nature of scrub and high pine habitats with various cut

and burn histories on the ONF has created a series of what can be thought of

as replicated plots of habitat. These are amenable to establishing patterns, and

generating and testing hypotheses about the interactions among lizard hosts,
their acarine parasites, and the landscape.
The first part of this thesis explores physiological effects of parasitism. If

chiggers puncture the integument, can they increase evaporative water loss?
Do the nuchal pockets of these lizards decrease the degree of water loss? Can
blood-sucking mites affect the speed, endurance, behavior, and recovery
ability of the lizards?
The second part of this thesis explores whether microhabitat and
habitat affect chigger abundance. Does burn frequency affect chigger and other
arthropod abundance? Does roller-chopping following clear-cutting of sand
pine scrub alter the population biology of mites on lizards? Answers to these





12


questions will be addressed in an attempt to better understand the

interactions among a host, its ectoparasites, and their landscapes.




















_- --~ w*


I Enoaria
*-^


S-)SG


(1,


1 1 1, -I* i ) I* I t -, P Y P


Figure 1.1. The life cycle of Eutrombicula alfreddugesi (after R. Loomis,
unpub. and Conant 1975).


3;r


,Y -J^


SLC -~ --

J-

















St. Vincent


Cedar Key Scrub


ila National Forest

"Big Scrub

~ Merritt Island


Lake Wales Ridge


State Park


Marco Island


Figure 1.2. Distribution of scrub (filled in black) in Florida, with the Ocala
National Forest and Big Scrub regions, where this study was conducted,
labelled with larger type (after Myers 1990).














I I I I I I I I I I I I


30 -


1-1




f 20
W
EL
a)
H


10 *-


Jan Feb Mar Apr May Jun


Jul Aug Sept Oct Nov Dec


MONTH
Figure 1.3. Average maximum and minimum monthly temperatures in
Ocala, Florida (1961-1990); (Southeastern Regional Climate Center 1998).













200








150








100








50
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

MONTH
Figure 1.4. Average monthly precipitation in Ocala, Florida (1961-1990);
(Southeastern Regional Climate Center 1998).











100


90


80


70


60


50


40


30


20
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

MONTH
Figure 1.5. Coefficient of variation of average precipitation (CVPPT) for
Ocala, Florida, where the coefficient of variation is the standard deviation of
monthly precipitation divided by the average monthly precipitation
(Winsberg, 1990).


























-4


Figure 1.6. Marion County, Florida (shaded in black). LANDSAT
scenes in Figure 1.7 are of the eastern half of Marion County, which is
primarily composed of sand pine scrub and long-leaf pine in Ocala
National Forest.









Figure 1.7. Ocala National Forest within Marion County, Florida. The sigmoid towards the upper-left hand
comer is the Ocklawaha River. The black U-shaped area in the upper right is Lake Kerr. The large undisturbed
patch (in all scenes) in the middle of the eastern edge of the scene is the Juniper Wilderness. The circle that
appears in Figures b and c in the lower right delineates the Naval bombing range.

Figure 1.7 a. Ocala National Forest, 1973. Much of the Forest appears dark red, which represents mature sand
pine. Light colored areas have been recently clear cut, medium patches are several years old. The horizontal
banded areas to the west of Lake Kerr on Kerr Island, and the vertical bands in Hughes Island to the south of
Lake Kerr show the results of a Forest Service experiment to generate edge for deer with alternating bands of
turkey oak and long-leaf pine.

Figure 1.7 b. Ocala National Forest, 1986. The once continuous blocks of mature blocks sand pine have been
logged in sections of 8-25 ha (Greenberg 1993). The shading of patches gives some indication of the age of the
cut with the lightest being the most recent.

Figure 1.7 c. Ocala National Forest, 1991. As before, shading gives some indication of the age of the cut with the
lightest being the most recent. Careful inspection of the image from 1986, (Figure 1.7 b) can reveal the degree of
regrowth in what were then young cuts.









































a. ONF, 1973 b. ONF, 1986


c. ONF, 1991








Table 1.1 Aspects of acari-reptile relationships

Ectoparasite Host Pathology / Notes Reference
(Family) (duration of attachment)


Pathologies
Hirstiella sp.
(Pterygosomidae)


Neotrombicula california
(Trombiculidae)


Geckobiella texana
(Pterygosomidae)

Ixodes pacificus
(Ixodidae)


Eutrombicula lipovskyana
(Trombiculidae)



chiggerss"


Ophionyssus serpentium


Sceloporus jarro



Uta stansburiana


Uta stansburiana
Sceloporus graciosus



Uta stansburiana

Sceloporus graciosus

Sceloporus jarroi




Rhacodactylus sp.


acute dermatitis, death



epidermal necrosis
integumental lesions
(7 days)


(28 days)
(5 days)


blood loss, acute fibrinoid reaction
integumental lesions
(16days)


(8 days)


focal ulcerative dermatitis
inflammation
granuloma formation
(52 days in mite pockets,
shorter elsewhere on lizard)
tissue damage


pruritis (=itching) and dermatitis


Goldberg & Holshuh 1993



Goldberg & Bursey 1991a



Goldberg & Bursey 1991b
Goldberg & Bursey 1991b



Goldberg & Bursey 1991b

Goldberg & Bursey 1991b

Goldberg & Holshuh 1992




Bauer et al. 1990


Mader et al. 1986









Table 1.1 (continued)

Ectoparasite Host Pathology / Notes Reference
(Family)


Hirstiella trombidiformes Sauromalus obesus
(Pterygosomidae)
"mites" Gehyra mutilata


Ixodes asanumai
(Ixodidae)

Physiology and
Performance
"mites" (Lealapidae)


Eumeces okadae




Lacerta vhipara


acariasis, anemia, death

mites transferred from
Hemidactylus garnotti
caused tail autotomy

muscle atrophy




altered performance &
dispersal in offspring


Mader et al. 1986

Oliver & Shaw 1953


Hayashi & Hasegawa
1984



Sorci et al 1995


gervaisi Varanus sp.


suck blood


Auffenberg &
Auffenberg 1990


Ixodes pacificus
(Ixodidae)


Ixodes ricinus
(Ixodidae)


Sceloporus occidentalis



Psammodromus algirus


reduced hematocrit,
reduced "condition" in lizards
also infected with malaria

lowered hematocrit and hemoglobin,
increased intensity in T-implanted
males


Dunlap & Mathies 1993



Salvador et al. 1996


Aponomma
(Ixodidae)









Table 1.1 (continued)

Ectoparasite Host Pathology / Notes Reference
(Family)


Vectors
Bacteria
Ophionyssus serpentium snakes
(Macronyssidae)
Ixodes pacificus Sceloporus occidentalis
(Ixodidae)


Ixodes
(Ixodidae)


vector of Aeromonas hydrophila


Camin 1948


reservoir host of Borrelia burgdorferi Lane 1989


transmit spirochaete Q-fever


Frank 1981


Ornithodorus talaje transmit spirochaete Q-fever
(Argasidae)


Hirstiella trombidiformes Sauromalus obesus


vector for Leishmania


Mader et al. 1986


Protozoans


Hirstiella pyrformis
(Pterygosomatidae)

Geckobiella texana
(Pterygosomatidae)


Sauromalus various


Sceloporus
S. undulatus

S. undulatus


vector of Hepatozoon
a hemogregarine


occidentalis


Ophionyssus natricis
(Macronyssidae)
Ophionyssus saurrum Lacerta agilis
(Macronyssidae) Lacerta vivipara


sauromali,


transmits Shellackia occidentalis,
transmits Shellackia occidentalis
via ingestion of mite,
probably vectors of hemogregarine


vector of protozoan Karyolysus;
no symptoms


Lewis & Wagner 1964;
Newell & Ryckman 1964

Bonorris & Ball 1955
Klein 1985

Frank 1981


Svahn 1974










Ectoparasite Host
(Family)

Liponyssus saurarorum Lacerta
(Macronyssidae)

Neoliponyssus saurarum lizards
(Macronyssidae)

Ophionyssus serpentium snakes
(Macronyssidae)

Worms
Ornithodorus talaje

(Argasidae)

Ixodes ricinus Lacerta
(Ixodidae) Lacerta

Phoresy
Caloglyphus sp.
(Sarcoptiformes) Anguis


No Described Effect
Aponomma hydrosauri
(Ixodidae)

Ixodes ricinus
(Ixodidae)


Table 1.1 (continued)

Pathology / Notes


murals


vector ot Karyolysus lacertarum


transmit coccidia (Shellackia)


Leukocytozoon
hematozoons


transmit Haemofilaria

(Macdonaldius oschei)

vector of tick-borne encephalitis


viridis



frag is
ftagilis


Trachydosaurus


Lacerta agilis
Lacerta vivipara


phoresy for non-feeding lavae



none noted
finds host by its odor & disturbance

no effects on host mortality


rugosus


Reference


.. r r


Grell, in Noble et al.
1989

Frank 1981


Frye 1981
Marcus 1981


Reichenbach-Klinke
1965
Frank 1981

Frank 1981
Sekeyova et al. 1970



Elkan in Reichenbach-
Klinke 1977


Downes 1984


Bauwens et al. 1983









Table 1.1 (continued)

Ectoparasite Host Pathology / Notes Reference
(Family)

Geckobiella texana Sceloporus jarrovi none noted Goldberg & Holshuh 1992
(Pterygosomidae)

Possible Benefit
Ophionyssus natricis Uta stansburiana, Uta ate mites off one another & Burrage 1966
(Macronyssidae) Sceloporus occidentalis Sceloporus, which had lower
incidence of disease

Ixodes asanumai Eumeces okadae deticking behavior Hayashi & Hasegawa
(Ixodidae) 1984








Table 1.2. Duration of Eutrombicula alfreddugesi life history stages.



Stage mean duration (days) range in duration (days)



egg 6 15-20 (egg + deutovum)
deutovum 7
unfed larva 1 up to 24
feeding 3 1-4
engorged larva 2 1-8
protonymph 6 9-10
nymph 11 12-32
tritonymph 17 5-10
adult 12 52
Total 55 67-98
Source Jenkins 1947 Wolfenbarger 1952



Table 1.3. Geckobiella texana life history stages.


Female Male
Stage Duration (days) Duration (days)

egg 6 6 days
deutovum 11-16 11-16
larva feed 3-4 days posthatch, feed 3-4 days posthatch,
engorge 4-5 days engorge 4-5 days
nymphochrysalis 4-7 (small chrysalis)
nymph engorge 7-15 days
imagochrysalis 4 7-10 (large chrysalis)
adult engorge 7-10 days engorge 7-10 days
Total 46-67 38-51
(after Goodwin 1954)
Note: Males skip the nymphochrysalis and nymph stages










Table 1.4. Comparison of scrub and high pine.


Characteristic Scrub High Pineland

Pines Pinus clausa (Sand pine) Pinus palustris (Longleaf pine)
Hardwoods Q. myrtifolia (Myrtle oak) Quercus laevis (Turkey oak)
Q. geminata (Sand live oak) Q. incana (Bluejack oak)
Q. chapmanni (Chapman's oak) Q.falcata (Southern red oak)
Lyonia ferruginaea (Rusty lyonia) Q. margaretta (Sand post oak)
Ceratolia ericoides (Rosemary) Q. marilandica (Blackjack oak)
Persea humilis (Silk bay)
Foliage evergreen deciduous
Herbs sparse abundant
Ground cover litter, lichens, bare sand grasses, forbs
Aspect dense thicket open woodland
Fire Frequency infrequent (15-100 years) frequent (1-15 years)
Fire Intensity high low


after Myers, 1990










CHAPTER 2
CHIGGER INFESTATIONS, EVAPORATIVE WATER LOSS AND THE
POSSIBLE ADAPTIVE SIGNIFICANCE OF NUCHAL POCKETS


Introduction

Reptiles are generally assumed to have impermeable integuments.
Tight intercellular junctions, fibrous polymer layers of protein, and lipid
layers in the integument all contribute to this impermeability (Lillywhite and
Maderson 1988). The mesos layer just below the outer layer of (-keratin is of
primary importance in creating a barrier to water (Lillywhite and Maderson
1982). Given the importance of this water-tight integument, one should not
be surprised to see features and behaviors of reptiles that would serve to
maintain its integrity. Likewise, dramatic effects as a result of compromising
its integrity would be expected.
One issue in lizard biology is whether the small skin invaginations

(integumentary pockets) in areas such as the neck, axilla, groin and
postfemoral regions are adaptations to minimize the impacts of ectoparasites.
Arnold (1986, 1993) and Benton (1987) argue that these pockets are adaptive
features that benefit the host by concentrating mites in areas where their
deleterious effects can be minimized. Bauer et al. (1990), and Bauer (1993)
argue that pockets are merely facultatively exploited by mites.
If pockets are adaptations, then one prediction would be that
parasitized animals with blocked pockets would have higher evaporative
water loss than those with unblocked pockets because on animals with
blocked pockets, ectoparasites would resort to using other locations on the
body with a consequential increase in evaporative water loss. There are solid








biophysical reasons to predict this. Pockets, by creating a small enclosed space
around the chiggers, should reduce evaporative water loss by creating a
microenvironment that has a higher relative humidity than the surrounding
environment. Some plants have a similar structure as well. Oleander
(Nerium sp.), has stomatal crypts in which the stomata are sunk deeply into a
thick "multiple epidermis" (Salisbury and Ross 1992).
Though the histopathology of mites on reptile integument has been
well documented (Arnold 1986; Bauer et al. 1990; Goldberg and Bursey 1991a;
Goldberg and Holshuh 1992, 1993), its implications for water balance, as well
as other physiological and ecological aspects of the host, have not been
examined. This paper will describe the histopathological effects of chiggers
(Eutrombicula alfreddugesi ) on the integument of the Florida scrub lizard
(Sceloporus woodi ) and link that pathology to increases in evaporative water
loss. These results will then be extended to test if the prominent nuchal
pockets on this species can reduce integumental water loss in parasitized
animals.

Methods

Scanning Electron Microsopy

Scrub lizards were collected in Ocala National Forest (Marion County,
Florida) in 1995-6. Three animals were euthanized with a 9:1 solution of
water to sodium pentobarbitol (Nembutal@ Sodium). Fresh tissue from the
mite pockets was fixed in Bouin's alcoholic fluid for one week, followed by
dehydration in an alcohol series and hexamethyldisilazane. A gold sputter
coat was applied to the tissue which was then viewed with a Hitachi scanning
electron microscope at 50X. Photographs were taken with Polaroid type 52
film which was then scanned at 300 dpi (see Figure 2.1).








Histology

Scrub lizards were collected in Ocala National Forest (Marion County,

Florida) in 1995-6. Three animals were euthanized with a 9:1 solution of
water to sodium pentobarbitol (Nembutal@ Sodium). Fresh tissue from the
mite pockets and behind the knees was fixed in Bouin's alcoholic fluid for
one week. Tissue was embedded in paraffin following dehydration in an

alcohol series and exposure to Hemo-D@ (Fisher Scientific) for 2 h. Tissue was
then sectioned at 7 p.m and stained with a modified Masson's trichrome stain

(Presnell and Schreibman 1997). Histopathology was examined using light
and differential interference contrast (DIC) microscopy. Photographs were
made at 200x magnification with slide film. Images were digitized with a slide

scanner.


Evaporative Water Loss

Lizards were captured by noose in Ocala National Forest, Marion
County, Florida. The number of chiggers on the lizards were counted under a
dissecting microscope or with the aid of a hand lens. Lizards were placed in a

60 cc syringe that was fitted with a nylon exit valve. Air was pumped through

the syringe after being dried by passage through a column of silica gel (Fisher

Scientific); air was passed through a flowmeter to ensure a constant rate. A

second column of silica gel was used to collect moisture lost by the lizard
(Figure 2.2). Both the lizards and the collecting gel column were weighed
before and after each 2 h run to the nearest 0.0001 g using a Mettler balance.
All runs were done at 25 OC. From these data, evaporative water loss (EWL) in

mg/g/h was derived. Lizard EWL was remeasured several days after the
chiggers had finished feeding and dropped off. If an animal was actively








moving in the chamber during the measurement of EWL, that run was

dropped from the analysis, in order to minimize the effects of activity level
on the results. Linear regression was used to derive the relationship between
EWL and chigger intensity (number of chiggers per lizard).

Nuchal Pockets and EWL

To test if nuchal pockets reduced evaporative water loss of parasitized

hosts, 14 lizards (4 females, 10 males) were measured without mites (using
the above techniques), and then remeasured following reinfestation with
mites. The animals were divided into two groups of 7 lizards each. One group

had its nuchal pockets blocked with Testors enamel paint and the other had
same-sized dots of paint applied just above the pockets on the back of the
neck. The blocked group had 4 males and 3 females, while the unblocked

group had 6 males and 1 female (this difference in sex ratio resulted from
matching the animals for size). Lizards were reinfested with mites by being
placed overnight in metal troughs that had been lined with freshly collected
leaf litter from Ocala National Forest. I found that litter from forest edges that
contained rosemary (Ceratolia ericoides ) duff and lichens (Cladina sp. and
Cladonia sp.) usually contained many chiggers. A repeated measures
ANCOVA was performed with post-chigger EWL as the dependent variable,
pre-chigger EWL, and pocket treatment (blocked or unblocked) as the
independent variables, and intensity as the covariate. The assumption of
homogeneity of slopes was checked using the treatment*pre-chigger EWL
interaction term and supported (F = 0.21, p = 0.66), so it was valid to do a
repeated measures ANCOVA.









Results


Scanning Electron Microsopy

The chiggers congregated in the nuchal pockets, which were not

covered with scales (Figure 2.1). The skin in the pocket had a granular
appearance.


Histology

Where the chigger attaches to the lizard, a stylostome (literally, feeding

tube) is formed by the interaction of parasite saliva and host tissues (Figure

2.3). Pockets where chiggers attached showed marked inflammation with
lymphocytic infiltration concentrated around the stylostome (Figure 2.4). The

concentric layering of lizard cells around the stylostomes is consistent with

early granuloma formation. Areas where chiggers had not attached showed
no inflammation. Where infestation had occurred, the stratum corneum

separated from the underlying stratum germinativum in 2 out of 3 cases. In

uninfested areas it remained attached (Figure 2.5).

Evaporative Water Loss

Chigger intensity of wild caught lizards ranged from 8 454 chiggers/
individual. The EWL ranged from 1.52 to 7.78 mg/g/h. The least-squares

regression of EWL on intensity yielded the following relationship: (EWL =
0.015 (intensity) + 1.52) and explained nearly 75% of the variation in EWL
(Figure 2.6). After the chiggers reached repletion, they dropped off the lizards.
Once the lizards had a few days to recover from the infestation, EWL








averaged 1.47mg/g/h, s.d. = 0.52, N=16, not significantly different than the y-
intercept for the regression of EWL on intensity (p = 0.397).

Nuchal Pockets and EWL

Following reinfestation, lizards with blocked pockets had higher

evaporative water loss (1.66 mg/g/h) than those with unblocked pockets (1.22

mg/g/h), correcting for differences in intensity. The whole model explained
52% of the variation in EWL after chiggers attached (F = 5.74, p = 0.015).
Intensity was the strongest predictor (F = 7.73, p = 0.019), followed by
treatment (F = 3.68, p = 0.089 and pre-chigger EWL (F = 2.28, p = 0.13). Though
males tended to have slightly higher evaporative water loss than females,
gender, or interactions of gender with intensity did not contribute
significantly when added to this model and, in fact, reduced the adjusted r2 to
46%.


Discussion


Histology

The inflammatory response to chigger infestation in the nuchal
pockets was distinct and localized around the stylostomes. Some have argued
that the immune response is akin to host manipulation by the parasite, as the
chiggers appear to feed on the mixture of lymph and cellular debris created by
the reaction to their saliva (Hase et al. 1978; Arnold 1986).
The separation of the stratum corneum from the underlying
connective tissue in infested areas could indicate that the compounds in mite
saliva are capable of weakening the lipid-rich mesos layer (H.B. Lillywhite,








pers. comm.). This response could contribute to increased evaporative water
loss through the areas of affected integument (Lillywhite and Maderson 1982).
On two occasions, when I noosed heavily infested animals, the 2 lb test
monofilament line actually cut into the weakened integument in the nuchal
pocket. The wound appeared to ooze lymph. This andecdotal evidence
supports the histological observations.

Evaporative Water Loss

Evaporative water loss was strongly correlated with chigger intensity
(numbers of chiggers per lizard). Increased EWL could significantly reduce the
time it would take an animal to reach its vital limit of dessication in dry
conditions. Crowley (1987) found that dessicated Sceloporus undulatus in
enclosures selected significantly lower body temperatures than did hydrated
lizards, chose body temperatures that were negatively correlated with degree

of dessication, and showed decreased activity by remaining buried in the
substrate. In a different study, Crowley (1985) found that sprint running
performance of S. undulatus was relatively insensitive to the effects of
dessication. In contrast, Wilson and Havel (1989) found that dehydration
reduces the endurance running capacity of Uta stansburiana.

Nuchal Pockets and EWL

The one-tailed prediction that animals in the blocked pocket treatment
group would have greater evaporative water loss was supported (p = 0.089,
a=0.10). This result lends credence to the idea that the nuchal pockets could
have adaptive value. Arnold (1986) has already suggested that nuchal pockets
localize tissue damage and the immune response of swelling and








inflammation. Reduction in evaporative water loss is another potential
benefit of pockets.
One other aspect of the chigger-concentrating effects of nuchal pockets
is that they could create "badges" of status for the lizards. If home range size is
correlated with intensity of infestation, then many chiggers would coalesce in
the pockets to create a visually striking indicator of territory size. Males have
home ranges that are about twice the size of females (G. Hokit, pers. comm.,
pers. obs.). Larger individuals tend to have more chiggers. In lieu of bright
integument, males could use chiggers as indicators of territory quality. It
would be interesting to manipulate chigger numbers and see if it affects
mating success.
If nuchal pockets are an adaptive feature of lizards, it is worth asking
what advantages chiggers gain from going into them. Chiggers tend to

aggregate in the pockets where there might be an advantage of being in a
"selfish herd" (Hamilton 1971), and they are better able to resist abrasion and

shedding of skin. S. woodi routinely dive and shimmy into sand as part of
their everyday activities (pers. obs.). Cyamid copepods ("whale lice"), are
associated with the slits and pleats on whales apparently as a way of avoiding
high velocity gradients (Vogel 1994). Chiggers may be doing the same thing by
seeking out pockets on their sand-swimming lizard hosts. Multiple
perforations of the lizard integument by the chigger mouthparts allow skin to
slough off around groups of chiggers rather than pull them off as individuals
(pers. obs.). The Allee Effect [positive density dependence (Ehrlich and
Roughgarden 1987)], in which feeding efficiency increases with higher density
(up to a point), may facilitate chigger growth and development. The trade-off
here is whether the increased per capital feeding of grouped chiggers is still
better than reduced per capital feeding over a wider area of the lizard. If








pockets create a "win-win" situation for both parasite and host, they could be
an evolutionarily stable solution (Maynard Smith 1982) to the problems
presented by ectoparasites.
Past studies have documented histopathology of lizards and their
acarine parasites. This study was prompted by a need to place the pathology in
a physiological and ecological context. In future studies it might be possible to
reduce the response to infestation with anti-inflammatory agents and
measure if evaporative water loss decreases. Testosterone has long been
recognized as an immune suppressor. Are there qualitiative differences in
pathology between male and female hosts or juvenile and adult hosts?
This study was host-centered, but it could be profitable to examine the

host-parasite relationship from the parasite's perspective. Hase et al. (1978)
suggested that inflammation around the stylostome enhances feeding by
breaking down tough dermal tissue. The administration of anti-
inflammatories to the host would be expected to reduce the feeding efficiency
and hence growth of the ectoparasites.
Finally, another way to explore the relationship between chiggers and
nuchal pockets on lizards would be to use the comparative method. There is
much variation in the depth of nuchal pockets within the genus Sceloporus
(pers. obs.). Species found in arid western North America, tend to have
deeper pockets than S. woodi, which is only found in Florida (pers. obs.). If
nuchal pockets are a feature that has been selected to concentrate chiggers and
create areas of high humidity and hence low evaporative water loss, then this
pattern of pocket depth would be consistent with that adaptationist
hypothesis. A study that measured pocket depth in several species of
Sceloporus or a wide-ranging species like S. undulatus and attempted to











correlate it with climate in the areas where the animals were caught could be
illuminating.


Figure 2.1 Scanning electron micrograph (SEM) of a left nuchal pocket of
Sceloporus woodi at 50X magnification. The Eutrombicula alfreddugesi
chiggers are clustered together towards the center of the pocket, which is
devoid of scales.

































Figure 2.2. Dehydration chamber for small lizards. Room air at 25 oC is passed
by an aquarium pump through a column of dessicating silica gel, through a
flow meter and over a lizard (head first). Moisture from the lizard chamber is
collected in a second column of silica gel.





























_- _




Figure 2.3. Stylostomes in longitudinal (left arrow) and cross-section (right
arrow) in a nuchal pocket of a Sceloporus woodi (1 cm = 40 jim).



-. "-
-

















oipocket of Sceloporus woodi. Extensive inflammation surrounds the



stylostomes (1 cm = 40 im).










40















Ir
t -_













Figure 2.5. Edge of nuchal pocket showing the localized inflammatory
response to chigger infestation. The stratum corneum has separated from the
inflamed pocket on the left edge of the figure. There is no inflammation on
the right side of the figure, where chiggers were not attached (1 cm 40 m)
r







^^s-^5^^ -.-^


Figure 2.5. Edge of nuchal pocket showing the localized inflammatory
response to chigger infestation. The stratum corneum has separated from the
inflamed pocket on the left edge of the figure. There is no inflammation on
the right side of the figure, where chiggers were not attached (1 cm = 40 pim).























0 50 100 150 200 250 300 350 400 450 500
Chigger Intensity
(# chiggers per animal)

Figure 2.6. Regression of evaporative water loss on mite intensity; (y =
0.015x + 1.521; Adj r2 = 0.75, F = 51.78, p = 0.0001). The adjusted r2 of a 2nd
order polynomial regression was actually lower (0.735) than for the linear
regression model.










CHAPTER 3
THE EFFECTS OF MITES ON THE MORPHOLOGY, PHYSIOLOGY
AND PERFORMANCE OF THE FLORIDA SCRUB LIZARD,
SCELOPORUS WOODI


Introduction


Though relationships between morphology and behavior or ecology
are well documented (e.g., Darwin's Finches), until recently they have largely
neglected the intermediate step of organismal performance (Wainwright and
Reilly 1994; Garland and Losos 1994). The conceptual framework for including
performance in studies linking morphology to ecology was first laid down by
(Arnold 1983) in a quantitative genetics context, and has been elaborated on by
Miles (1994) and Garland and Losos (1994), (see Figure 3.1). Physiology and
biochemistry, like morphology, can be considered as aspects of phenotype, as
they are all sub-organismal in their level of biological organization. They can
interact among one another. Behavior is seen as a potential filter between
selection and performance in this expanded scheme (Garland et al. 1990a;
Garland and Carter 1994). However, some workers prefer to view behavior as
a category of morphology (Emerson and Arnold 1989).
From within the morphology-performance-fitness paradigm, a series of
lizard indoor racetrack studies has emerged. Huey and Hertz (1982) and
colleagues (Garland 1985) used computers to record light beams being
occluded by lizards as they ran down the racetrack to make precise
measurements of speed and acceleration. The results have been used to test
repeatability of performance (Van Berkum et al. 1989), inter-familial variation
in sprint speed (Van Berkum and Tsuji 1987), and to generate large








comparative data sets (Garland 1994; Bennett and Huey 1990) that have been
used in phylogenetic analyses of performance. Though these studies have
provided new insights into the evolution of performance, they have tended
to favor precision over realism. Levins (1966) argued that models of the world
can only emphasize two out of three components (precision, generality, and
realism) at a time (Figure 3.2). Previous studies have been conducted in
laboratory situations on small (2 m long), indoor tracks with unnatural

substrates (see Huey and Hertz 1982; Garland 1985, 1994; Van Berkum and

Tsuji 1987; Van Berkum et al. 1989). The result has been precise, repeatable
measurements of performance over short distances, that do not, however,
include complex behaviors.

In more realistic studies, precision and control over environmental

parameters, such as temperature afforded by a laboratory-based investigation,
are sacrificed. However, with a large track in the field on natural substrate, a

more ecologically relevant environment is obtained. We hypothesized a
more realistic situation would generate maximal performance data that more
clearly reflects what the animals are capable of in situations where natural

selection operates. We predicted that a more natural situation would allow
collection of data that are usually difficult to obtain or analyse, e.g.,
behavioral decisions such as turning around. Previous studies have had

difficulty dealing with such behavioral data and eliminated them from

analysis (see Miles 1994).
Little attention has been paid to the effects of parasites within the
morphology-performance-fitness paradigm. Sorci et al. (1994) found maternal
mite load resulted in increased sprint speed of offspring in the viviparous
lizard Lacerta vivipara. Schall (1990; Schall and Dearing 1987) has focused on

malaria in Sceloporus occidentalis, and found both positive and negative








effects on male competition for mates. Infected males have darker ventral
coloration and so appear older, an advantage for social displays. However
they also suffer reduced stamina. This study documents the effects of

ectoparasitic mites on the morphology, physiology and performance of a
lizard.
The Florida scrub lizard, Sceloporus woodi, is a small, grayish, spiny-

scaled lizard that is a Florida endemic and is almost always restricted to sand

pine scrub, a plant association with a highly disjunct distribution. S. woodi is
a forest edge species (like many of its congeners) that prefers open, sandy areas

between sand pine scrub and sandhill associations of long leaf pine and
turkey oak (DeMarco 1992). It has already been identified as a species that is
unusually fast for its size (Miles 1994).

S. woodi is sexually dimorphic in size with adult females averaging 4 -
5 mm longer than males in snout-vent length (SVL). Females mature at

about 47 mm SVL and can begin vitellogenesis as early as March. Courtship

and mating occur from March-June. Females typically lay three clutches per
season of 2 8 eggs (mean = 4). The reproductive season is over by late August
(DeMarco 1992).

The pterygosomid mite Geckobiella texana lives its entire life cycle on
its lizard host and larvae, nymphs and adults of both sexes feed on blood

(Goodwin 1954). G. texana has only been found on lizards of the genus

Sceloporus (Lane 1954; Jack 1959). Juveniles and adults can move from one
lizard host to another in captivity (pers. obs.).
This study documents the effects of Geckobiella on the morphology,

physiology, and several measures of performance of S. woodi, including
maximum speed, endurance, and behavioral tactics. This study also describes








effects of reproductive season and gender on performance. All performance
measures were made at a large outdoor racetrack on natural substrate.


Methods



Morphology/Histopathology

Scrub lizards were collected in Ocala National Forest (Marion County,

Florida) in 1995-6. Three animals were euthanized with a 9:1 solution of

sodium pentobarbitol (Nembutal@ Sodium). Fresh tissue from the mite

pockets and behind the knees was fixed in Bouin's alcoholic fluid for one
week. Tissue was embedded in paraffin following dehydration in an alcohol
series and exposure to Hemo-D (Fisher Scientific) for 2 h. Tissue was then
sectioned at 7 itm and stained with a modified Masson's trichrome stain
(Presnell and Schreibman 1997). Histopathology was examined under light

microscopy using DIC microscopy. Photographs of histological sections were

made onto slide film and images were digitized with a film scanner.


Physiologyev

To determine the effects of mites on hematocrit and osmolarity, lizards
were maintained in aquaria and sprayed with a 1% sterile solution of

ivermecten [(Ivomec@, Merck & Co., Inc., Rahway, NJ), 0.5 mL Ivomec@/liter
H20, after Abrahams 1992] to remove mites or water as a control treatment.

Blood was sampled from post-orbital sinuses (Frye 1981) with 10 p.1 capillary
tubes (Drummond Scientific Co., Broomall, PA) and spun in a micro-

centrifuge for 10 min to separate it into fractions of packed red blood cells and
plasma. The lengths of the red blood cell (RBC) column and the entire








column (packed RBC's + plasma) were measured to the nearest 0.5 mm and
divided by one another to calculate hematocrit. Plasma osmolarity was
measured with a Wescor 5100B vapor pressure osmometer (Wescor Inc.,
Logan, UT).
Data were analyzed with JMP In statistical software (SAS Institute 1996).
Homogeneity of variance across groups was assessed with Levene's test,
which compares the average absolute values of the within group residuals
from the mean (Sall and Lehmann 1996). Data were checked for normality
with the Shapiro-Wilk W test. Variables that violated assumptions of
normality were compared with the Wilcoxon rank sum test. Relationships

between hematocrit and performance were assessed with linear regression.


Performance

An outdoor racetrack was constructed in Ocala National Forest, near
Ocala, Florida at the edge of a stand of mature sand pine (Pinus clausa ) and a
stand that burned and was cleared in 1989 (site YB in Anderson and Tiebout
1993). The track had sides composed of 24" wide aluminum flashing held in
place by cable-ties wrapped around stakes driven into the ground. The surface
of the track was made of packed sand available in situ. The track was 28.5 m
long and 60 cm wide (wide enough for a researcher to run inside the track to
chase the lizards). Vegetation (1 m high) was placed at 12 m from the starting
line and at the far end of the track so as to provide a source of cover to
encourage a subject to run quickly and continuously towards these
landmarks. Lizards were caught at several sites in Ocala National Forest and
brought to the track.
Lizards were weighed to the nearest 0.01 g and snout vent length was
measured to the nearest 0.5 mm. We used the residual of mass over SVL as








an operational measure of "condition", assuming more robust individuals
are healthier. Locations and intensities of Eutrombicula alfreddugesi

chiggerss) and Geckobiella texana (mites) on the lizards were recorded. The
lizards were housed in 50 mm diameter x 110 mm long plastic vials that were
covered with tape so that they could not see out of them. Animals were post-
absorbtive but well hydrated. Approximately 0.5 h prior to the sprint- trials,
the vials were placed in a portable, temperature-controlled chamber (Igloo
Koolmate 36, Peltier-type cooler-heater) and heated to the active body

temperature for these lizards (33-38 OC; R. A. Anderson, unpubl. data).
Immediately before a sprint-trial, the cooler was opened, a vial removed, the

lizard removed from the vial and its temperature taken with a Schultheis

cloacal thermometer. Animals that struggled for more than 1 s were not run
immediately and placed back into the cooler to be run at least 20 min later. A
team of two researchers was required to run the lizards. One researcher

chased the lizard and marked any critical locations, such as slow-down or
turn-around points in the sand. The other researcher observed from beside
the track, but behind the lizard and lizard-chaser, with 2 stopwatches (with

split-time capabilities) in hand. Typically a run would proceed as follows: The
chaser would hold the lizard in hand at the starting point and slowly show
both eyes of the lizard the vegetation landmarks down the track, then would
set the lizard down on the track and let it go. The lizard usually remained

motionless for 1-2 s then would sprint away from the chaser towards the
vegetation. In some trials, the lizard would double-back on itself and run
through the legs of the chaser, who would mark the turn-around distance
(TAD) and confirm with the timer that the turnaround had in fact occurred.
Whether the lizard turned around it would eventually slow down. The

slowdown point was distinctive and was identified as a rapid reduction in








stride frequency and running velocity, sometimes accompanied by
exaggerated side-to-side movement of the anterior abdomen and forelimbs
(wiggling). The chaser would mark this fast-run distance (FRD) which was
also timed and then continue to chase the lizard until it could no longer

move. This last interval was defined as the final distance/time. The turn-
around (if applicable), slowdown and final distances and times were summed

to determine a total distance (TD) and time for each run. Running rates for
each interval and the entire run were calculated by dividing the distances by
the appropriate durations. Nearly 100 lizards were run in this manner and 3-5

runs per individual were logged to obtain a reasonable estimate of maximum
effort. Maximum speed was defined as the fastest leg of any of the runs.
Animals that did not move at least 1 m/s were deleted from the analysis.

Animals were run during the breeding season (at the end of July) and post-
breeding season (late August, early September) to determine if there were
reproductive/seasonal effects on performance and interactions between

seasonality, parasite load and performance. Animals were run with mites and
then re-run several days after the mites had been removed with a spray
application of ivermecten (Abrahams 1992).

Data sets were checked for normality with the Shapiro-Wilk W test and
analyzed using JMP In software (SAS Institute 1996). Linear and multiple

regression were used to assess relationships between mite load, body
temperature, condition (residuals of body mass regressed on SVL), and the
performance measures: maximum speed (MAXQUAL) and turnaround
distance (TAD). Animals that turned around were labelled as "evaders",
whereas animals that ran continuously towards the end of the track were
labelled "runners." Logistic regression was used for predicting a categorical
behavioral response (run or evade) from a continuous predictor, mite








intensity (number of mites per lizard). A paired-t test was performed on the

data obtained in the mite removal experiment.


Results


Morphology/Histopathology

Adult Geckobiella tended to congregate behind the knees of the lizards.

Occasionally, (< 10% of the time) 1 or 2 would attach in the nuchal pockets or

the axilla. In the areas behind the knees, the Geckobiella mites made deep
stylostomes (Figure 3.3). Inflammation in the form of lymphocyctic

infiltration extended into the thigh musculature, filling the interstices

between muscle bundles (Figure 3.4). Inflammation also extended around the

femoral nerve and layers of surrounding connective tissue (Figure 3.5).

Heavily infested lizards tended to push their feet along the surface of

the sand rather than dig them into the substrate as they ran in performance
trials (pers. obs.). Whether this "sliding" was due to discomfort, swelling, or

mechanical interference by the mites is not known. It certainly could have

contributed to decreased running performance.


Blood Parameters

The hematocrit and osmolarity data violated assumptions of

normality, so a Wilcoxon rank sum test was used. The "mites-removed"
lizards had significantly lower hematocrit than the "mites retained" lizards

(Figure 3.6; S = 85, Z = 2.65, P < 0.0081). Plasma osmolarity was not
significantly different between treatments (Figure 3.7; S = 57, Z = -0.21, P <

0.83). Total body water was not measured.








Turn-around distance range was 1.5 11.0 m (mean = 8.11 m, s.d. =
3.92), and was normally distributed (Shapiro-Wilk W = 0.97, P < 0.92). Fast-
run distance (FRD), (distance until slowing) range was from 0 15.25 m
(mean = 8.04 s.d. = 4.52), and was normally distributed (Shapiro-Wilk W =
0.97, P < 0.91). Total distance (TD) run by each lizard ranged from 12 31.5 m
(mean = 20.0, s.d. = 6.41), and was normally distributed (Shapiro-Wilk W =

0.92, P < 0.29).
Performance measures were negatively correlated with increasing

hematocrit (Figure 3.8 3.10). Least squares regression yielded the
relationships in Table 3.1. After the Bonferroni adjustment for multiple
comparisons (a = 0.05/3 = 0.017), only fast-run distance (FRD) was
significantly correlated (inversely) with hematocrit.



Maximum Performance

Average maximum speeds ( 2.08 + 0.51 m/s) were similar to those
recorded previously for this species (Miles 1994; i.e., ~2.25 m/s). However,
highest maximum speeds were nearly 70% faster, (4 animals clustered around

3.0 0.15 m/s). Our subjective impression is that lizards did not reach these
high speeds until they had been running for > 5 m. For an average-sized (50

mm SVL) S. woodi, a speed of 3 m/s is about 60 body-lengths/s. The fastest
run we recorded had a lizard averaging 3.8 m/s over the entire 28.5 m length
of the track. This is 76 body-lengths/s, or 13.7 km/h!

Male Speed

Maximum speed of male lizards tended to decline with increasing mite
levels. The maximum velocity (MAXQUAL) of males in July with no mites








averaged nearly 2.25 m/s (Figure 3.11). The best performing male ran nearly 3
m/s. A male with 21 mites ran less than 1 m/s. Collectively, body
temperature, mite intensity, and the residual of mass regressed on SVL
statistically accounted for nearly 70% of the variation in maximum running
velocity (body temperature: F = 15.86, P = 0.001; adult mite intensity: F = 16.98,
P = 0.007, resid. mass: 23.53, P = 0.0001; Adj. R2 = 0.69, F = 16.32, P<0.0001). Mite
intensity alone statistically accounted for 31% of the variation in maximum
velocity in July.

Running performance among males in August showed a weak inverse
relationship between mite load and maximum speed (maxrunqual = 2.34 -
0.032 mites; Adj. R2 = 0.048, F = 1.95, P = 0.18), (Figure 3.12a). The residual of
mass over SVL ("condition") and body temperature no longer contributed
significantly to the regression equation, so they were dropped from the
multiple regression. The range of body temperatures was narrow, therefore
no correlation of running performance was expected. When the outlying
point (indicated by the arrow in Figure 3.12b), was dropped from the analysis,
mite intensity statistically accounted for nearly 23% of the variation in
maximum running velocity in August and was the only significant predictor
of performance, (maxrunqual = 2.36 0.052 mites, Adj. R2 = 0.23, F = 6.23, P
= 0.023, see discussion regarding the outlier).



Female Speed

Neither mite intensity nor temperature had any apparent effect on the
maximum speed of females, which was 1.55 0.46 m in July and 2.05 0.37 m
in August. The only significant correlate was the residual of mass on SVL
(condition), which accounted for 15% of the variation in running speed in








July and 27% in August. Female sample size in July was n = 7 (most females
were gravid and reluctant to run, hence they were not used), so it is difficult
to assess the significance of the between month difference in speed.

Turnaround Tactics

There was a direct correlation between mite load and the tendency for
males to turn around during running trials in July (n= 29). Probability of
turnaround was about 30% with no mites and was nearly 100% with
intensities greater than 10 mites (Figure 3.13). The logistic regression model
was highly significant (p = 0.011, df = 1), and mite intensity statistically
accounted for 17% of the tendency to turn around (p = 0.063, one-tailed test).
There was no effect of mites on tendency for females to turn around in the
July trials, but this may be an artifact of small sample size (n = 7). There was
no trend in the probability of evading with increasing mite load in August for
either males or females.

Endurance

The total distance (TD) the males ran in July was negatively correlated
with mite intensity (TD = 23.77 0.56*mites; Adj. R2 = 0.28, F = 8.04, p = 0.011).
According to the regression equation, average TD was nearly 24 m with no
mites but declined to < 12 m at intensities of 20 mites (Figure 3.14). Mite
intensity explained 28% of the variation in total distance run. In July, the best
performing male (i.e., fastest leg of either turnaround or fast-run distance) ran
nearly 30 m before reaching exhaustion.
In August, the relationship between mite intensity and endurance was
much weaker, with mites explaining only 3% of the variation in endurance
(Adj. R2 = 0.033, p < 0.23, df = 17). Four of the males in August ran farther








than the best performing male in July. In August, the best performing male
ran nearly 45 m before reaching exhaustion (Figure 3.15).
The only strong predictor for endurance of July females was their
residuals of mass/SVL which accounted for 47% of the variation in running
distance (p = 0.053, df = 7). None of the variables measured were significant
predictors for endurance of females tested in August.

Speed and endurance of males and females increased from July to
August (Table 3.2). Both measures of performance are similar between the
sexes in both months, with both sexes showing performance improvement in
August, after the period of reproductive activity.

Mite Intensity

Table 3.3 shows that the average intensity (number of mites per lizard)
was 4-5 mites per lizard. The average intensity of G. texana on S. woodi was
not significantly different between males and females either during or after
the reproductive period.

Mite Removal

If mites had no effect on performance, then upon re-running
individuals after mite removal, 50% would be expected to run faster or
farther and 50% would be expected to run slower or less far. In fact, 2-3 days
after mite removal, all but three of the lizards ran faster and farther.
Following removal of mites, the lizards ran an average of 0.73 m/s faster
(Figure 3.16); (t = 3.91, df = 15, p < 0.0014) and 4.5 m farther (Figure 3.17); (t =
2.16, df = 17, p < 0.046).








Discussion


Morphology, physiological parameters and performance of lizards were
all affected by mite infestation. The effects and their implications will be

discussed below.

Morphology /Histopathology

Muscle tissue behind the knee joint was clearly inflamed. Goldberg and
Bursey (1991a) also found that in response to mite infestation, skeletal muscle
was infiltrated by an inflammatory response that included histiocytes,

heterophils, fibroblasts, and lymphocytes. The proliferation of lymphoid cells
into the leg musculature and nerves with the resulting myositis and neuritis

could be painful and cause the observed decrease in running performance.

Swelling could reduce the speed and angle of limb motion. The physical
presence of the mites alone could interfere with flexion at the knee joint.

Hematocrit and Osmolarity

Lizards with mites had higher hematocrit than lizards for which the

mites were removed with ivermecten. This result was not expected because

host blood loss, anemia (Mader et al. 1986), and even exsanguination are
common effects of ectoparasites (Frank 1981; Dunlap and Mathies 1993;
Salvador et al. 1996). Mader et al. (1986) documented an extreme case of
parasitism of captive chuckwallas (Sauromalus obesus) by the mite Hirstiella
trombidiformes. The other cases involved ticks, which are much larger than

mites and are capable of consuming more blood per individual parasite. In

the case doumented here, with levels of parasitism comparable to those
observed in the field (pers. obs.), the lizards were apparently able to avoid








anemia. However, this story can be turned around. It may be that with mites
attached, the lizards were unable to maintain plasma volume. This is
contrary to studies of desert lizards in which homeostasis of plasma volume

is achieved despite significant losses of body water to evaporation (Bradshaw
and Shoemaker 1967; Nagy 1972; Lemire et al. 1982), and suggests that mites
have an impact that is fundamentally different than dehydration due to
evaporation. Perhaps under stressful conditions (like parasitism), lizards can,
via the sympathetic nervous system release blood cells stored in the spleen or

liver. In humans, release of blood cells from the spleen can raise hematocrit

one to two per cent, and in so called lower animals, blood storage is even
greater (Guyton 1991).

Despite the differences in hematocrit, there was no difference in

plasma osmolarity between the experimental and control groups. If
dehydration were an effect of ectoparasitism, then higher plasma osmolarity

would be expected in the experimental group. Perhaps the lizards are able to

respond to reduced blood volume and still maintain plasma osmolarity.
Chuckwalla lizards (Sauromalus hispidus) on islands in the Gulf of
California, were able to maintain osmotic homeostasis despite losing 20% of

their total body water and consuming a high potassium diet (Smits 1985).
Regardless, the probable major effect of higher hematocrit is increased

viscosity of blood.

Performance and Hematocrit

Lizard performance was negatively correlated with hematocrit levels,
with slow-down distance showing the strongest relationship. If blood
viscosity is higher, then its flow must be lower because, according to
Poiseuille's equation, fluid flow through a tube is inversely proportional to








its viscosity (Schmidt-Nielsen 1983). The rate of lactate clearance from
muscles would be reduced proportionally with the decrease in blood flow.
Lactate concentrations would rise faster in lizards with increased hematocrit,
and this could account for the decrease in the slow-down distance. The weak

negative correlation of turn-around distance with hematocrit is consistent
with Crowley (1985) who found that sprinting performance of Sceloporus
undulatus was relatively insensitive to the effects of dehydration. The strong

negative correlation between slow-down distance and hematocrit is
consistent with Wilson and Havel (1989), who found that dehydration
(determined by % mass loss) reduced the endurance of Uta stansburiana.

Thus, there is a compelling chain of causation from parasitism, increased
hematocrit, increased blood viscosity, decreased lactate clearance, and
decreased endurance. With a larger species it would be possible to measure
lactate concentrations (e.g., Gleeson 1991).


Maximum Performance

The average maximum speeds we found were similar to those
recorded in (Miles 1994); but the highest maximum speeds we observed were
nearly 70% faster. These results are substantially higher than those obtained
in the lab and illustrate the limitations of previous lizard racetrack studies.
The relationships among speed, endurance, and mite loads were quite strong,

but not consistently so (see below). The outlier in Figure 3.13b showed a
phenomenal performance. We decided to eliminate that animal in one
calculation of the regression relationship between maximum performance
and mite load because it was so unusual. We suspect that its mites may have
just all emerged as adults and attached. Another possibility is that particular
individual was extremely agitated. This individual does force us to think








about "motivation" as a factor in performance studies. On the other hand,
mites may simply not be as debilitating following the reproductive season
when testosterone levels are lower, energy budgets are decreased, and
relatively more energy is devoted to maintenance (see below).


Seasonal Effects on Performance

The strong negative correlations between mite intensity and
performance (speed and endurance) during the breeding season decreased or

disappeared as the breeding season ended. This is not surprising as
reproductive activity has a huge energetic cost. A clutch of eggs represents

about 8 kJ of energy (unpubl. data), which is equivalent to 2 weeks worth of a
daily energy budget of 0.68 kJ/(animal day), with 88% converted to
reproduction (from Nagy 1983). We expected tests of maximal performance
during reproduction to be more likely to show effects of parasitism. Though

mite intensities remained constant, average speed increased 12% for males

and 25% for females, and average endurance increased by 5 m following the

reproductive season. The seasonality of effects may be one explanation for

why costs of parasitism have been difficult to measure consistently in the
past.

Condition

Condition (the residual of mass regressed on SVL) consistently showed
some predictive value for performance. Relatively heavy animals ran slower
and for shorter distances. This type of relationship has been documented for
pregnant female lizards (Shine 1980d; Bauwens and Thoen 1981), and recently
fed snakes (Garland and Arnold 1983; Ford and Shuttlesworth 1986). This is

not surprising either, as it takes more work to move more mass. However, its








implications for trade-offs in life histories are intriguing. Condition is
generally assumed to be a monotonically increasing function, i.e., the fatter
the better. This assumption may reflect evolutionary ecology's temperate-
zone, homeotherm biases. The results of the current study suggest that rather
than being a linear function, condition can asymptote or even decrease with
respect to fitness. There are performance (i.e., speed and endurance) costs to
being heavy and they may have some interesting implications for

morphology (e.g., body shape and fat storage) and seasonality of reproductive
strategies. Do animals have the ability to store more fat than they actually do?
Is the risk of not having enough energy to overwinter balanced against the

likelihood of being too heavy and slow? Detailed studies that examine
tradeoffs between condition and performance within individuals over time

could be quite illuminating.


Turn Tactics

Changes in behavior may compensate for reduced locomotor ability
(Garland and Losos 1994). If an animal is debilitated by parasites, it may be
risky for it to attempt to run away from a predator. An evasive strategy could

be more effective for avoiding capture. That the effect of mites on behavior
was observed in males only during the breeding season is consistent with
existing hypotheses about effects of testosterone (T) (see below). However, the

lack of an effect in July females could be an artifact of small sample size or
simply the swamping of any variation or correlation by the massive effects of
gravidity.

Behavioral changes have been documented in response to other
stressors besides parasites. Ectotherms tend to be more wary when they are
below their optimal temperature (pers. obs.). Females reduce their cost of








reproduction by changing behavioral tactics. Gravid female skinks (Eumeces
laticeps), for example, tend to be less active and less conspicuous on the
surface than when they are post-reproductive (Cooper et al. 1990). Likewise,
gravid female Lacerta vivipara allow closer approach by observers apparently
as a way of increasing crypsis (Bauwens and Thoen 1981), as do gravid garter
snakes (Brodie 1989).


Sexual Dimorphism

Testosterone is a well documented immune suppressor (Salvador et al.
1996; Saino et al. 1995), and could reduce the immune response in males,
making damage from the mites worse. This could explain the decrease in
effects of mites on male lizards between July and August. With reduced T in
August, males could be healthier. Additionally, allocation of energy for
maintenance could be reduced under the effects of T (Salvador et al. 1996). A
male could devote so much energy to territoriality and reproductive
behaviors that little energy remains for maintenance, repair, and immunity.
Marler and Moore (1991) found that males with artificially elevated T could
only be maintained in the field with dietary supplementation because their
levels of reproductive activity were so high. More detailed studies of
pathology that examine both adult male and female hosts and/or compared
them to juveniles could be interesting, as could manipulations of T levels as
in Salvador et al. (1996).

The lack of an effect of mites on female Sceloporus speed could reflect
that they are not burdened by immunosuppressive effects of T. Also, female
reproductive effort, particularly relative clutch mass (RCM = clutch
mass/total female mass), could be so great as to overwhelm the effects of
mites.








Extending the Paradigm

Maximal whole-animal performance abilities, defined as what animals
can do when pushed to their limits, may in fact best be observed in natural or
seminatural field environments (contra Garland and Losos 1994). Studies in
which the scale of the observations allows subjects to reach their full potential
and display behavioral options provide valuable information. Field
observations also aid in the assessment of the relevance of lab studies to the
field [see Schlesinger et al. (1993), which documents "lizard-fall" in the field
with regard to the agility documented in a laboratory setting (Sinervo and
Losos 1991)]. A trade-off with field studies vs. lab studies is that because of the
increased variation in environmental variables in the field, sample sizes
must be larger to achieve the necessary statistical power. This may be
impractical for certain species or situations.

Another aspect of extending the paradigm of performance studies is the
inclusion of parasitized animals. Lab studies in which animals have had
parasites removed would not tell the full story of how traits related to
performance evolve. Performance decrements can be directly caused by
parasites or at least be correlated with their presence; therefore they should be
included in the morphology-performance-paradigm (Figure 3.18). A caveat is
that the inclusion of parasites in these studies also increases variation in the

measured sample populations (see comments about sample size and
statistical power above).
Variation in a trait is a necessary precondition for natural selection to
result in evolution (Endler 1986). If there is a heritable component in
susceptibility to parasitism (e.g., Moller 1990), then including parasites in
performance studies could be important. Even if there is no heritable








component to likelihood of parasitism, there could be heritable rules for
behavioral tactics when parasitized or faced with any conditional stressor (see
turning tactics above). There are obvious implications of the effects of
parasitism for studies of natural selection and both components of sexual
selection: mate choice and male-male competition. Links between
performance and social dominance in reptiles have already been made
(Garland et al. 1990b). Adding parasites to these studies will take longer and
require more effort; however because of their emphasis on realism and
variation, they should be quite rewarding.












Morphology

Physiology ---PERFORMANCE -- Behavior --Fitness
f
Biochemistry



Figure 3.1. The morphology-performance-fitness paradigm (after Miles 1994
and Garland 1994).









a.





Realism Precision





Generality







b.





Realism Precision





Generality







Figure 3.2. Venn diagrams of model building strategies
(after Levins 1966). Models may simultaneously possess only two of the
three properties of realism, generality and precision.
a) this model sacrifices realism for precision.
b) this model sacrifices precision for realism.























~-s~Bx
r --*1
-t -


9
, 4

I '


sc: td -n


Figure 3.3. Stylostome (feeding tube) of an adult female Geckobiella texana
into the thigh of Sceloporus woodi. Only female mites are blood feeders
(Goodwin 1954); (1 cm = 40 gm).


.




















-i,


-


i
t~t- 4:


- / t t
$1 *s -'


Figure 3.4. Inflammatory reaction from the attachment of adult
Geckobiella texana behind the knees of Sceloporus woodi. Lymphocytes
extend well into the thigh musculature, filling the interstices between muscle
bundles on the left side of the figure (1 cm = 40 gpm).


-


T6 ak




























'I, & i

U .-. .. S i -


i* ,* *5-;-
-, w U'
*b- -'.- .A


-.
Cr f:' .-


C.: .'-4 ...
ii b..
r .~-,.


I'


-~ ~ ~ ~ ~~Z ,-- -.*<-
--
..-'- f
5 .S



E "i
'' "'

'-* 1 P1'jZ1v
*'/


-.- /.


Figure 3.5. Inflammatory reaction from the attachment of adult

Geckobiella texana behind the knees of Sceloporus woodi. Lymphocytes

surround and extend into the femoral nerve (see arrow); (1 cm = 40 gm).


r rr-




f-g
~. ^ :


II
-^
- r


B-

'~ 7


f *
t


X










40-


S35-





25-



20- .
ts_________
(0-------------------


ivermecten


water


treatment


Figure 3.6. Hematocrit for parasite-laden lizards after being sprayed with a
solution of ivermecten (mites-removed) or water (mites-retained). Symbols
represent means (large dots) with standard error bars.


AI-M-


400-

380-

360-

340-


320-

300-


ivermecten


water


treatment


Figure 3.7. Plasma osmolarity for parasite-laden lizards after being sprayed
with a solution of ivermecten (mites-removed) or water (mites-retained).
Symbols represent means (large dots) with standard error bars.


T .. it ... .... .... ...











15.0-


S12.5-
U

S10.0-


d 7.5-


S5.0-


r 2.5-


o~-
0.0 -
.20


* I 1 '
.25 .30
Hematocrit


.40
.40


Figure 3.8. Turn-around distance (m) regressed against hematocrit. As
hematocrit increases, the distance covered by the lizard before it turns around
decreases.


1 I I I 1
.20 .25 .30 .35 .40
Hematocrit


Figure 3.9. Fast-run distance (m) regressed against hematocrit. As
hematocrit increases, the distance covered by the lizard at a fast run
decreases.


U
U

U U

U



U


U


I.











- Y


IU) I I 1 I 1
.20 .25 .30 .35 .40
Hematocrit


Figure 3.10. Endurance, as
woodi individuals in a


indicated by total distance (m) covered by S.
running trial, regressed against hematocrit.


2 nA-


2.5-



2.0-



1.5-



1.0-


I I I I I
0 5 10 15
adult mites/lizard


20
20


Figure 3.11. The best performance of males in July as function of adult
mite intensity. Maximum speed declines with increasing mite load.


U
U

U







U

U
















3.0-




2.5-




2.0-


1.5-


3.0 -


2.5 -


2.0-


0 5 10 15

adults mites/lizard


1.5-


I I I I I
0 5 10 15
mites(adults)


Figure 3.12. Best performance (maximum speed m/s) of males in
August with the outlier (indicated by arrow) a) included and
b) removed from regression calculation.


U
U U
*

a
U



I
U
U
U
U
* U
U
U

U


U
U U
U

U
U





70


1-
run

0.75-


0.5- .

S_. evade
& 0.25- ..


0 I I I I I
0 5 10 15 20
Mite Intensity
(number of adult mites/lizard)

Figure 3.13. Logistic regression of running tactic as a function of mite
intensity (number of mites per lizard host). The curve represents the
probability of the lizard trying to evade capture. With no mites, lizards are
likely to evade about 40% of the time (and run, 60% of the time). With 20
mites, lizards are likely to evade nearly 100% of the time. Highly infested
animals are more likely to evade rather than run away from a perceived
threat.





















U
U
a
U
U
U
U U

U

U U
* U
U
U
I I
U


-5 0 5 10

mites(adults)


- Mean Fit

-Linear Fit


Figure 3.14. Endurance of males in July as a

intensity.


1I "
15 20


function adult mite
function adult mite


Figure 3.15. Endurance of males in August as a function of adult mite

intensity.


A I----------------------


1


-------------------
~---------------------------,


-----------------------------------


--------------













,3.0

~ 2.5

2.0

.I5-

1.0

0.5- pe a0
.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
pre-maxqual


Figure 3.16. Paired t-test of maximum speed in m/s before (pre-) and after
(post-) mite removal with ivermecten. The heavy line represents the null
hypothesis of no difference. The thin line represents the line of fit through
the sample. The dashed lines around the thin line represent the 95%
confidence intervals for the difference in means. Because the heavy line lies
outside the confidence interval, there is a significant difference between the
speeds before and after mite removal. Following removal of mites, the lizards
ran an average of 0.73 m/s faster, (t = 3.91, df = 15, p < 0.0014).


I __












45-


S-35

S25

S15-


5 10 15 20 25 30 35 40 45 50 55 60
pre-Total Distance (m)

Figure 3.17. Paired t-test of total distance (endurance) before and after mite
removal. For interpretation, see above. Following the removal of mites, the
lizards ran 4.5 m farther (t = 2.16, df = 17, p < 0.046).




JOMorphology

PARASITES -' Physiology ---PERFORMANCE --Behavior --Fitness

Biochemistry /


Figure 3.18. The morphology-performance-fitness paradigm extended.


__I _








Table 3.1. Regressions of performance variables against hematocrit values for
S. woodi.

performance
variable a regression equation Adj. R2 F-statistic pb

TAD = 11.97 15.54 Hct 0.069 0.55 0.49
FRD = 24.12 52.90 Hct 0.52 11.81 0.0074
TD = 38.24 66.48 Hct 0.39 7.35 0.024

a. TAD is turnaround distance;
FRD is fast-run distance;
TD is total distance
b. Pa = 0.017, due to Bonferroni correction



Table 3.2. Summary of average maximum performance values for male and
female S. woodi in July and August.

July August
sex maxqual Total Dist. maxqual Total Dist.
(m/s) (m) (m/s) (m)
male 1.89 .68 21.43 6.94 2.16 .50 26.07 8.43
female 1.55 .46 20.14 9.82 2.05 .37 25.03 5.93


Table 3.3. Average intensity of Geckobiella texana on Sceloporus woodi
during and after the reproductive season.

July August
sex mite intensity mite intensity
male 4.39 1.28 (n = 26) 3.96 0.99 (n = 24)
female 5.57 2.46 (n = 7) 4.33 0.99 (n = 24)
P 0.67 0.79











CHAPTER 4
EFFECTS OF ADULT MITES ON LIZARD METABOLIC RECOVERY FROM
EXERCISE

Introduction
Mites are commonly found on free-living reptiles and they frequently
become a problem for captive animals because they can reach high intensities
and enjoy increased transmission rates among stressed hosts with decreased
immunity. Histopathological response to mites (Goldberg and Bursey 1991a;
Goldberg and Holshuh 1992), and mite prevalence in both space (Allred and
Beck 1962; Spoecker 1967) and time (Loomis and Stephens 1973) have been
documented for lizards. However, there have been few studies documenting
the effects of ectoparasites on the physiology of lizards. Dunlap and Mathies
(1993) found that tick larvae significantly reduced the hematocrit and body
condition of lizards that were also infected with malaria. Effects of mites on
performance have been addressed previously (Chapter 3); but there is another
aspect of performance that is frequently overlooked: metabolic recovery from
exercise.

The significance of anaerobic metabolism to the natural histories of
amphibians and reptiles has been well documented. It is a major source of
energy for intense burst activities such as predator escape, intraspecific
combat, and subduing large prey items (Pough and Andrews 1985a; Gatten
1985). As glycogen is depleted in muscles, lactate accumulates, resulting in
reduced strength and endurance. In order to regain their full capabilities, the
animals replenish levels of muscle glycogen via gluco- or glyco-neogensis
(Gleeson 1991; Gatten and Clark 1989). Gleeson (1982) found that
replenishment of muscle glycogen through these mechanisms can take up to








2.5 h at 35 C in Sceloporus occidentalis following exhaustion. This recovery
period is a cost of anaerobiosis that must be repaid following any intensive

activity, and is a function of many factors [e.g., body size, temperature
(Gleeson, 1980; Wagner and Gleeson, 1997), epinephrine and glucagon, which
stimulate lactate removal (Gleeson et al. 1993; Scholnick et al. 1997), and

seasonality (Gleeson, 1985)].
Any factor that increases this recovery time could be of ecological

importance. The adult female pterygosomid mite Geckobiella texana, sucks

blood from its Sceloporus hosts (Goodwin 1954). The potential for anemia,
reduced blood volume, and dehydration due to parasitism by mites requiring

blood-meals, provided an excellent opportunity to examine physiological and

ecological effects on the recovery time of the host following intense exercise.
In this study I tested whether Geckobiella texana mites reduce endurance and

increase recovery time of the Florida scrub lizard Sceloporus woodi.


Methods
Lizards were captured in Ocala National Forest, Marion County,

Florida and maintained in a colony at the University of Florida, Gainesville,
Florida. Animals were kept in terraria illuminated with full-spectrum

fluorescent lighting, and provided with mealworms every day and water ad

libitum. These trials were run in the Fall of 1997, when animals were post-
reproductive. A total of 12 females and 8 males were used over the course of
the study. At 25 OC, lizards were chased on a circular indoor track, 4 m in
circumference with a natural sand substrate, until they lost their righting
response [for further discussion of this technique, see Huey et al. (1984)]. This
duration, measured in seconds, was defined as "endurance." The exhausted
lizards were then placed on their backs in terraria and timed until they








righted themselves and began moving and behaving normally. This duration
was defined as "recovery time." The number of adult Geckobiella texana

mites on each lizard was counted and defined as "mite intensity." The

maximum duration and minimum recovery time for each level of intensity
was to used to better delineate the limits of lizard performance. Lizards were

later sprayed with ivermecten [a 1% sterile solution of Ivomec@, Merck & Co.,
Inc., Rahway, NJ diluted with water (0.5 ml Ivomec/ liter H20), after

Abrahams (1992)] to remove the mites and then one week later were again

subjected to the endurance and recovery trials.

To analyze the data, I used linear regression with mite intensity as the

independent variable and the maximum endurance, and minimum recovery

time for each level of intensity as the dependent variables. Data were checked

visually for normality and analyzed using JMP In software (SAS Institute

1996). I performed a Wilcoxon signed-rank test (the non-parametric

equivalent of the paired-t test) with the pre- or post- treatment recovery

times.


Results

Endurance declined from about 2 min with no mites to 0.5 min with

an intensity of 35 adult mites (Figure 4.1). Maximum endurance was
negatively correlated with mite intensity. Minimum recovery time increased

from 2.5 min to 12.5 min, (Figure 4.2) and was positively correlated with mite

intensity.
In trials conducted after mites were removed from the lizards, the

average recovery time decreased 40%, from 10.3 min to 6.5 min (Table 4.1). A

Wilcoxon signed-rank test indicated that the 3.8 min in recovery time

difference between the two treatments was highly significant (Z = 22.5, P =








0.02, df = 9). None of the other performance variables were significantly
different between treatments.


Discussion

Florida scrub lizards (Sceloporus woodi ) infested with adult mites

(Geckobiella texana ) showed decreased running endurance and increased
recovery times. The decline in endurance is concordant with the results

presented in Chapter 3. The increase in time to recover from exhaustion is

strong, though the mechanism behind it is not clear. Perhaps the muscle
inflammation shown in histological sections (Chapter 3) interferes with

glyconeogenesis that occurs in skeletal muscle (Gleeson et al. 1993). An
increase in hematocrit is correlated with mite parasitism, and the associated
increased viscosity of blood could reduce the rate of lactate clearance from

muscle tissue.
Recovery is a frequently underappreciated aspect of ectotherm whole-

organism performance. For sit-and-wait predators such as phrynosomatid

lizards, short, rapid, anaerobic sprints for food capture and territorial displays

are the most common type of activity (Pough and Andrews 1985a). The
advantages of anaerobic sprint capability is its relative insensitivity to

temperature and dehydration (Crowley 1985). The disadvantages include
accumulation of lactate and hydrogen ions in muscle tissue that must be
cleared and "processed" before anaerobic capacity can be regained. Animals

that are paying off an oxygen debt do not engage in foraging or social
activities. They also could be vulnerable to predation. The inescapable cost of
this debt may be factored into the behavioral decisions animals make (e.g., the
turnaround distance measured in the previous chapter). Animals in excellent
condition may be able to recover from a sprint in a fraction of the time it takes








animals in poor condition to do so. A lizard faced with sprinting away from a
predator at full speed or making short, evasive maneuvers to escape, may
choose the latter if the cost of recovery time from an extended sprint is high
and either tactic is equally successful in avoiding predation. The cost of
increased recovery time caused by parasites could shift the point at which that

behavioral switch from "flee" to "evade" is made.

The fivefold increase in metabolic recovery time from exhaustion in
heavily parasitized individuals compared to unparasitized individuals, and

the 40% decrease in average recovery time following mite removal suggest

that parasitism may significantly reduce the time available for other activities

in lizard time budgets. The effects of parasitism by mites may be more

substantial for their lizard hosts than previously appreciated.


Table 4.1. Effect of treatment with ivermecten on lizard performance
measures.

Performance Difference Signed-Rank P-value
Variable from Zero Statistic

endurance -2.8 2.5 0.82
recovery time 3.78 22.5 0.02















150'




* 100

xi


-5 0 5 10 15 20 25 30 35 40
Mite Intensity


Figure 4.1. Maximum endurance as a function of mite intensity. As
mite intensity increases, endurance declines (y = 108.78 2.60*Mite
Intensity, n = 14, Adjusted R 2 = 0.39, F = 9.44, P = 0.0097).


15- -


..


- 10.0-
-


7.5-
Q-

0
8 5.0-


2.5-


S nn-


S-5 0 5 10 15 20 25 30 35 40
Mite Intensity


Figure 4.2. Minimum recovery time as a function of mite intensity.
As number of mites per lizard increases, the time required for full
recovery from exhaustion increases (y = 3.18 + 0.22*Mite Intensity,
n=14, Adjusted R 2 = 0.60, F = 20.84, P = 0.006).


a N


a -


__ __ _______I


I .













CHAPTER 5
SPATIAL AND TEMPORAL ASPECTS OF CHIGGER AND MITE
ABUNDANCE WITH SPECIAL REFERENCE TO LANDSCAPE BURNING
AND DISTURBANCE



Introduction


The Florida scrub was unique.... There was perhaps no similar region
anywhere.... The soil was a tawny sand, from whose parched fertility
there reared, indifferent to water, so dense a growth of scrub pine...that
the effect of the massed thin trunks was of a limitless, canopied
stockade.... It seemed inpenetrable... .Wide areas, admitted of no
human passage. ... In places the pines grew more openly, the sunlight
filtered through and patches of ground showed bald and lichened .... A
random patch of moisture produced, alien in the dryness, a fine stand
of slash pine or long-leaf yellow. These were known as pine islands. To
any one standing on a rise, they were visible from a great distance.
-Marjorie Kinnan Rawlings, South Moon Under


As described by Rawlings (1933), the Ocala region is primarily a matrix
of two upland ecosystems: scrub and high pine. The Florida scrub ecosystem is

perhaps best summarized by (Myers 1990, p. 151) as "mature forests of tall,
twisted leaning sand pine (Pinus clausa) rising above an impenetrable mass
of evergreen scrub oaks; rusty lyonia, rosemary; unusual varieties of holly,
bay; and hickory, and an array of inconspicuous species, many with restricted
distribution." An estimated 40-60% of its species are endemic, making scrub
Florida's most distinctive ecosystem (Myers 1990). Scrub is pyrogenic and
maintained by fires that occur every 15-100 years. The "varieties" of scrub
patches seen today reflect their different fire histories (Myers 1990).








Embedded in these extensive areas of scrub are islands of high pine
consisting of open woodlands of longleaf pine (Pinus palustris) over a cover
of wiregrass (Aristida stricta), and occasional dumps of turkey oaks (Quercus
laevis). High pine is maintained by fires recurring every 1-15 years. In the

absence of fire, turkey oak begins to dominate in sandhills. Despite their
difference in appearance, scrub and high pine are strongly associated with one

another as they both occur on dry, infertile uplands whose soils are derived
from the same parent material, both are maintained by fire, and the ignition
of scrub depends on flammable high pine (Myers 1990).
In Ocala National Forest, long leaf pine islands are burned on a regular
basis to mimic what is thought to have been the natural burn cycle. This burn

cycle is used to prevent the pine islands from being overgrown by hardwoods
and sand pine. However, to create "edge" for deer, land managers have

allowed some clumps and stands of oak to persist in the pine islands. Kerr
Island, for example, has alternating patches long leaf pine and turkey oak in
some areas.

In much of Ocala National Forest, sand pine (Pinus clausa) is managed
for pulpwood production. To protect this asset, U.S. Forest Service personnel
normally quickly extinguish fires in sand pine scrub Accidental burns are

salvage logged. Clear cuts of unburned sand pine (typically 8-25 ha) leave tree
slash and crushed shrubs throughout the site. Site preparations for new sand
pine plantings include roller-chopping, which disturbs 100% of the soil
surface to 15 cm depth or "bracke" seeding which disturbs about 30% of the
soil surface by drilling and depositing seeds at fixed intervals (Greenberg
1993).

Campbell and Christman (1982) argued that clear cutting mimics
wildfire by creating a similar habitat structure. Similarities between clear-cuts








and wildfire include above-ground tissue death, biomass removal, and bare-
ground exposure. These effects are why many scrub plants (Greenberg et al.
1995b), birds (like the Florida scrub jay, Aphelocoma coerulescens, a
disturbance specialist; Greenberg et al. 1995a), and reptiles (Greenberg et al.
1994) respond similarly to fire and clear-cuts. There are however differences
in nutrient cycling, coarse woody debris and standing dead biomass
(Greenberg 1993).
This study was undertaken to 1) assess whether fire frequency affects
chigger densities in long leaf pine/turkey oak habitats and chigger intensities
on Florida scrub lizard (Sceloporus woodi) populations associated with these
patches having different fire histories, 2) identify microhabitat preferences of
chiggers, 3) identify daily and seasonal patterns of chigger activity, and 4)
identify if there are any patterns of ectoparasite distribution associated with
United States Forest Service (USFS) silvicultural practices.
To better understand how landscape level modifications could affect
ectoparasite populations I reviewed the life cycles of the ectoparasites and
their interactions with hosts and habitat. Eutrombicula alfreddugesi is a
trombiculid mite. Only the larval, "chigger" stage in this mite family is
parasitic on vertebrates; however they are not host specific. E. alfreddugesi
has been found on 126 species (Benton 1987). The juveniles and adults are
free-living in the soil and eat small arthropods and their eggs in the leaf litter.
Because of the juveniles' and adults' dependence on leaf litter arthropods, I
hypothesized that any landscape modification that affected leaf litter would
have an impact on chigger intensity. In contrast, the pterygosomid mite
Geckobiella texana lives its entire life cycle on its lizard host and has been
found only on lizards of the genus Sceloporus (Lane 1954; Jack 1959). I have
observed larvae, juveniles and adults moving from one individual lizard








host to another in captivity. Because they are so tightly bound to their lizard
host for their entire life cycle, I predicted that any landscape modifications
that affected lizard densities or frequency of interactions would also affect
Geckobiella prevalence on the lizards.


Methods

Microhabitat: Longleaf vs. Turkey Oak

To determine densities of chiggers in habitats with different burning

frequencies, I surveyed plots in Kerr Island, Ocala National Forest, Marion

County, Florida. Kerr Island is an island of high pine (Pinus palustris)
embedded in an alternating matrix of turkey oak (Quercus laevis). High pine
habitat is shown in Figure 5.1. Turkey oak habitat is shown in Figure 5.2. In

May of 1997, I randomly placed two sets of fifteen, 10 cm square black ceramic

tiles in each the two different habitat types and examined them for chiggers
after 10 min (Williams 1946).


Lizards

To determine the intensity of chigger infestations on Sceloporus
woodi, I captured animals by noose, noted the habitat type (long leaf pine or
turkey oak) at the site of capture and did total body counts with the aid of a
hand lens. Comparisons among sites were made with the Wilcoxon rank
sum test.


Diel Cycles

To determine daily patterns of chigger activity, I placed fifteen 10 cm
black square tiles out in the field (Williams 1946) and examined them for








chiggers every hour from 0800-2000 h on 29 June 1997 at a site 2 km E. of Mill
Dam Lake, on the south side of State Road 40 (SR40). The tiles were divided
into 3 groups of 5 tiles each. Each of the groups was placed within 5 m of the
other. One group was placed along an edge between an old (> 10 yrs) sand pine

stand and the U.S. Forest Service road ringing a young (6-9 yrs) sand pine
stand. A second group was placed in open, sandy areas between the road and
the young scrub. The third group was placed at the edge of the young scrub
and the open sandy areas. A typical edge between a young scrub and mature

sand pine is shown in Figure 5.3.


Annual Cycles

To determine seasonal patterns of chigger activity, I made monthly
surveys of chigger intensity by noosing lizards at a site 2 km E. Mill Dam Lake,

on the south side of SR40 (same site as above) and counting all chiggers on
them. This site was clear cut and reseeded in 1988. I did not sample the habitat
for chiggers on a monthly basis.


Silvicultural Practices

To assess the potential effects of silvicultural practices on Geckobiella
texana populations, I determined the prevalence of Geckobiella mites on

Sceloporus woodi at 8 sites that had well documented histories and were
either roller-chopped (n = 4) or not roller-chopped (n = 4). Histories and
localities of these sites are given in Table 5.1.









Results

Microhabitat

In 1997, examining two 15 tile plots of each habitat type (n = 60 tiles), I
found no chiggers in the longleaf pine habitat using the tile method. Chiggers
averaged 0.4/tile (40 chiggers/m2) in the turkey oak habitat. There was a
highly significant difference in chigger density between the habitat types
(Kruskal-Wallace rank sum, S = 1020, Z = 2.77, P > I Z I = 0.0055).


Lizards

The intensities of chiggers on Sceloporus woodi was related to habitat
type in which they were found. In May of 1994, in longleaf pine habitat, the
average intensity was 13.4 chiggers per lizard (n = 13). In turkey oak, the
average intensity was 68.8 chiggers per lizard (n = 12), (Figure 5.4a). The
intensities were significantly different, (Kruskal-Wallace rank sum, S = 225, Z
= 3.73, P > I Z I = 0.0002). In May of 1997 in different plots of longleaf pine
habitat, the average intensity was 26 (n = 7). In turkey oak habitat, the average
intensity was 53 (n = 8), (Figure 5.4b ). The intensities were significantly
different, (Kruskal-Wallace rank sum, S = 35, Z = -2.38, P > I Z I = 0.017).


Diel Cycles

There was a pronounced diel cycle of activity for the chiggers. They
were active just after dawn and very active especially around dusk (Figure
5.5). There was also a spatial component to their activity. No chiggers were
ever found on the road. There were more chiggers active along the mature
sand pine outer edge than the young scrub inner edge.








Annual Cycles

There was a definite seasonality of chigger intensities with peaks in the
summer (Figures 5.6 and 5.7). Male lizard chigger intensity peaked in May,
whereas on females, August was the peak month of chigger infestation.
Intensities were essentially zero from December to February. Males had
higher intensities than females for every month except for August.


Silvicultural Practices

There is some indication of a relationship between silvicultural
practices and prevalence of Geckobiella texana. Roller-chopped sites had
uniformly high prevalences (> 60% of lizards sampled were infested),
whereas unchopped sites had a bimodal distribution of mites, with both high

and low prevalences (Figure 5.8).


Discussion

Fire and Microhabitat

The long leaf pine at Kerr Island and other pine islands in Ocala Forest
is burned on a regular schedule of 2-3 years (Laura Lowery, USFS, pers.
comm.). The turkey oak habitats within Kerr Island exist because these areas
are not burned. Because of differences in fire regime, conditions on the
ground in the two habitat types are quite different. In the long leaf pine areas
there is less shade and a thin (2-3 cm), homogeneous ground cover of pine
needles that is depauperate of arthropods (pers. obs.). The ground cover of
pine needles is reduced following a fire, and with frequent fires, never
accumulates to be more than a centimeter or two. Chiggers in long leaf pine








are probably limited by a lack of food for juveniles and adults. In contrast, the
turkey oak areas have more shade and a thicker (5-6 cm), heterogeneous layer
of leaf litter that hosts a diverse assemblage and high density of arthropods
upon which the juvenile and adult Eutrombicula alfreddugesi can feed.


Fire and Pest Control

Fire has long been used to control arthropod pests in agricultural, range
and pasture lands (Komarek 1970). In the first half of this century, north
Floridians used to burn areas around their homes on a regular basis in part to
reduce chigger and tick populations (R. Franz, pers. comm.).
Wilson (1986) found reduced abundance of Ixodes dammini adult ticks

by up to 88% for as long as 6 months after a burn. Mather (1993) found that
the abundance of Ixodes dammini nymphs was reduced by 49% in burned
wood lots as compared to unburned ones. However, the risk of encountering
nymphs infected with the spirochete, Borrelia burgdorferi, which causes
Lyme Disease, was the same because different subpopulations of nymphs
(feeding on rodents or deer) were disproportionately affected by the fire.
Reed et al. (1977) reported a 91% reduction in chigger populations 2
days after a burn. The populations recovered to reflect just a 22% reduction
within a month. Rapid increases in the populations following the burn led
them to conclude that gravid female mites and/or eggs in the soil were not as
heavily affected by fire. Stressing the dynamics of the situation, they also
pointed out that if hosts were attracted to the burn, replete chiggers detaching
from them could actually increase the chigger population in subsequent years.