Title: Metabolic rates in spiders
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Title: Metabolic rates in spiders
Physical Description: vi, 67 leaves : illus. ; 28 cm.
Language: English
Creator: Anderson, John F, 1936-
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 1968
Copyright Date: 1968
 Subjects
Subject: Spiders   ( lcsh )
Metabolism   ( lcsh )
Zoology thesis Ph. D
Dissertations, Academic -- Zoology -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
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Bibliography: Bibliography: leaves 64-66.
Additional Physical Form: Also available on World Wide Web
General Note: Manuscript copy.
General Note: Thesis - University of Florida.
General Note: Vita.
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Bibliographic ID: UF00097785
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000549682
oclc - 13272868
notis - ACX3978

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METABOLIC RATES IN SPIDERS















By


JOHN FRANCIS ANDERSON


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












UNIVERSITY OF FLORIDA
1968















ACKNOWLEDGEMENTS


I am deeply indebted to Dr. James L. Nation, under whose direction

the present research was conducted.

Dr. Robert M. DeWitt must be thanked for his liberal support in

providing the necessary supplies and equipment.

Grateful acknowledgement is given to Dr. Frank G. Nordlie, Dr.

Brian K. McNab, Dr. John D. McCrone, Dr. James L. Nation, and Mr.

Thomas Krakauer who gave most generously of their time in evaluating

some of my ideas.

My thanks go to Dr. Martin H. Muma, Dr. John D. McCrone, and Mr.

Cole Benton for supplying certain animals which otherwise would not

have been available. For aid in solving various statistical problems,

I am indebted to Miss Mary E. Glenn. Dr. Rodger Mitchell must be

thanked for his assistance in conducting the histological studies.

Financial support through appointment to research and teaching

positions was provided by Dr. Frank G. Nordlie and Dr. Lewis Berner

to whom I am grateful.

Dr. Nation, Dr. Nordlie, and Dr. McCrone must again be thanked

along with other members of my graduate supervisory committee, Dr.

Thomas J. Walker and Dr. Howard K. Wallace, who not only critically

reviewed the dissertation, but also provided support in solving the

many small but important problems that occurred during my tenure as a

graduate student.

Finally thanks are also due to Mrs. Lillian Ingenlath for typing

the manuscript.














TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS. . . . . . . . . ... ... ii

LIST OF TABLES. ............ .. . ... ..... . iv

LIST OF FIGURES . . . . . . . . ... . . v

INTRODUCTION . . . . . . . . . . . I

MATERIALS AND METHODS ............... . .. 5

RESULTS . . . . . . . . ... .... . . .. 14

Weight Changes . . . . . . . . ... . . 14
Temporal Variation in Oxygen Consumption . . ... 14
Loss of Temporal Variation in Oxygen Consumption . 19
Standard Metabolic Rates ................ .20
Respiratory Quotient .................. 23
Breathing Systems. ................ . . 23
Exoskeleton Weight, Metabolically Active Tissue
Weight, and Total Weight.... . . . . . 23
Oxygen Consumption and Temperature . . . . .... 23

DISCUSSION . . . ........ .... . ..... . 37

LITERATURE CITED. ............... ..... 64

BIOGRAPHICAL SKETCH ............... . . 67












LIST OF TABLES


Table Page

I LIST OF EXPERIMENTAL ANIMALS. . . . . . . . 6

2 WEIGHT CHANGES IN SPIDERS . . . . . . .... 14

3 AVERAGE OXYGEN CONSUMPTION OF ARACHNIDS AT 20 C . . 20

4 OXYGEN CONSUMPTION OF INDIVIDUAL ARACHNIDS AT
20 C. . . . . . . . . ... . . . . 21

5 CALCULATED SLOPES AND INTERCEPTS OF THE EQUATION
LOG METABOLISM = LOG K + n LOG WT . . . .... .22

6 RESPIRATORY GAS EXCHANGE SYSTEMS OF SPIDERS ...... 24

7 TOTAL WEIGHTS, EXOSKELETON WEIGHTS, AND ACTIVE
TISSUE WEIGHTS. . . . . . . . . ... ... 26

8 OXYGEN CONSUMPTION AT DIFFERENT TEMPERATURES. . . ... 29

9 AVERAGE WEIGHT, METABOLIC RATE AND BOOK-LUNG
SURFACE AREA IN ADULT SPIDERS . . . . . .... .50

10 CALCULATED RELATIONSHIPS BETWEEN EXOSKELETON
WEIGHTS AND METABOLICALLY ACTIVE TISSUE WEIGHTS
TO TOTAL WEIGHTS. . . . . . . .... ... . 57












LIST OF FIGURES


Figure Page

1 Oxygen consumption over 24 hours. Each point
represents the mean of N determinations. The
time interval indicated by the black stripe
represents the 12 hour dark period. (a) L.
lenta, N = 6; (b) f. hibernalis, N = 14. . . . .. 16

2 Oxygen consumption over 24 hours. Each point
represents the mean of N determinations. The
time interval indicated by the black stripe
represents the 12 hour dark period. (a) P.
regius, N = 6; (b) T. rufipes, N = 5; (c) A.
tepidariorum, N = 5. . . . . . . ... .. 18

3 Oxygen consumption of P. reaius versus
temperature. e 10 C acclimation; o 20 C
acclimation; e 30 C acclimation. Acclimation
time exposures are indicated in Table 8. . . . ... 31

4 Oxygen consumption at 30 C. Vertical lines
represent 95% confidence intervals of the
sample means. Spiders were exposed to 20 C
for three weeks prior to the start of this
experiment. (a) P. reqius; (b) F. hibernalis. . .. 34

5 Oxygen consumption at 10 C. Vertical lines
represent 95% confidence intervals of the
sample means. Spiders were exposed to 20 C
for three weeks prior to the start of this
experiment. (a) F. hibernalis; (b) L. lenta . . .. 36

6 Relationship between metabolic rate and
weight. (a) pooled regression line for all
arachnids; (b) theraphosid species (adults
and immatures); (c) F. hibernalis (adults);
(d) L. lenta (adults); (e) L. lenta (immatures);
(f) P. regius (adults); (g) P. reius (immatures);
(h) T. rufipes (adults); (i) P. otiosus (adults);
(j) T. sisyphoides (adult); (k) E. bilobatus (adults)
(1) A. tepidariorum (adults); (m) C. vittatus (adults)
(n) U. audouini (immature); (o) T. marginemaculata
(adults); and (p) C. hentzi (adults) . . . ... .41








7 Relationship between metabolic rate and weight.
(a) Hemmingsen's (1960) poikilotherm line;
(b) pooled arachnid line. Vertical lines
represent 95% confidence intervals . . . . .. 47

8 Relationship between book-lung surface area
and oxygen consumption in spiders. (a) L.
lenta; (b) P. reqius; (c) F. hibernalis;
(d) T. sisyphoides; (e) A. tepidariorum;
and (f) T. rufipes . . . . . . . . ... .52

9 Deviations of actual versus calculated values
of oxygen consumption and respiratory surface
area. Abscissa, surface area deviations.
Ordinate, oxygen consumption deviations.
(a) A. tepidariorum; (b) L. lenta; (c) P.
reaius; (d) T. sisyphoides; (e) T. rufipes;
and (f) F. hibernalis. . . . . . . . . 55

10 Relationship between temperature and standard
metabolism in P. reqius and F. hibernalis.
(a) minimal required energy expenditure at
20 C; (b) minimal required energy expenditure
at 30 C; (c) compensation at 30 C in P. reqius .... 62


Figure


Page













INTRODUCTION


The diversity of spiders is well known in terms of anatomy, be-

havior, and ecology. These aspects have been documented by Petrunke-

vitch (1933), Gertsch (1949), and Millot (1949). Although Anderson

(1966) studied the excreta of many different spiders, most other phys-

iological studies have dealt with a relatively small number of species.

This situation has resulted in a lack of information pertaining to

physiological diversity and,as such, precluded a fuller understanding

of the biology of these arachnids. I thought that respiration, as

measured by oxygen consumption, would be the most productive variable

to analyze in this regard, not only because of its ease of measurement,

but because it reflects the total energy requirement for all the meta-

bolic processes. This latter point was made by Benedict (1938), and

is supported by the wealth of literature where specific physiological

processes were studied using some aspect of respiration.

The major aim of this study was to determine whether interspecific

differences in oxygen consumption exist and, if so, to uncover some of

the causative factors in order to explore the consequences of these

differences in relation to the biology of spiders.

Interspecific differences have been detected in a number of

arachnids: they have been discovered in oribatid mites by Berthet

(1963); in harvestmen by Phillipson (1962); and in scorpions by Dresco-

Derouet (1964). In regard to spiders, Derouet (1953) found that a




2

cavernicolous species had a lower metabolic rate than one which nor-

mally lives outside caves.

A second aim of this study was to determine whether being a spider

is reflected in an energetic sense by comparing the metabolic rates of

spiders with those of other poikilotherms. There is some difficulty

in making these comparisons; the weights of the groups being compared

often differ, and the relationship between weight and metabolism is

not one of direct proportionality. While larger animals have a greater

total rate of metabolism than smaller ones, the converse is true when

metabolism is put on a per unit weight basis. The relationship be-

tween weight and metabolism has generally been represented by the

following equations:

metabolism = k weight

or

log metabolism = log k + n log weight

The logarithmic form of the equation is useful since most of the values

of n do not equal one, hence an arithmetic plot results in a curved

line. A double logarithmic plot of the equation for any value of n

does give a straight line. Consequently, to compare metabolic rates,

values of n and k are determined from experimental data. The equations

represented by these constants can then be compared with one another

as well as with standard curves. The latter have been constructed by

pooling data obtained from a wide variety of organisms. Examples of

such standards are Hemmingsen's (1960) unicellular, poikilotherm, and

homeotherm metabolism-weight regression lines.

I also thought it valuable to consider factors which might be

responsible for the size of n and k. Hemmingsen (1960) suggested that





3

the differences between levels of metabolism of poikilotherms and

homeotherms, i.e., different values of k, may be the result of an

increase in respiratory surface area in the latter group. Tenney and

Remmers (1963) demonstrated a relationship between lung surface area

and metabolic rate in a group of mammals ranging from bats to whales.

In poikilotherms, both Brown (1957) and Hemmingsen (1960) cite data

indicating that active fish have larger gill surface areas than sluggish

fish of the same weight. Whitford and Hutchison (1967) demonstrated

that above 15 C, lunged salamanders have a higher metabolic rate than

lungless species of the same weights. These findings indicated the

desirability of making interspecific comparisons of the relationship

between surface areas of book-lungs and metabolic rates in spiders.

In addition, I thought it of value to investigate metabolic rates

of those arachnids having only book-lungs or only trachea. The

Solifugae, as most insects, utilize only trachea while the Amblypygi

utilize only book-lungs as breathing organs. Thus, knowledge of

metabolic rates of solifugids and amblypygids may make comparison of

metabolic rates between spiders and insects more meaningful.

In the latest comprehensive review of the subject, Hemmingsen

(1960) claims that n, the slope of the metabolism-weight regression

equation, equals 0.75 and is quite uniform when large weight and taxo-

nomic ranges are considered. He claims the value of 0.75 has evolved

through orthoselection as the result of the struggle between propor-

tionality of metabolism to body weight and to surface functions.

Prosser and Brown (1961) and Hoar (1966) presented a more specific

hypothesis to explain the size of n. They suggest metabolism is not

directly proportional to weight because as animals get larger, a dis-




4

proportionate increase in supportive tissue is required. This hypoth-

esis assumes that supportive tissues such as the skeleton have low

rates of metabolism. I decided to zest this hypothesis by assuming

that the exoskeleton constitutes the bulk of tissue having a low meta-

bolic rate in spiders.

As a final consideration, the effect of temperature on metabolic

rate was studied in order to better evaluate any interspecific differ-

ences in metabolismo. !n general the rates of metabolism of poikilotherms

are governed by a logarithmic law relating the velocities of the various

component reactions to temperature. However, strict adherance to this

relationship is not always followed by poikilotherms. Some variations

in the metabolic response to temperature include the temperature com-

pensation response in individuals when exposed to new temperatures as

discussed by Bullock (1955), and the relatively new findings of Newel!

(1966) and Newell and Northcroft (1967, indicating temperature inde-

pendence to rapid temperature changes in quiescent animals.

With these possibilities in mind, a series of experiments was

designed to answer questions about the ability of spiders to remain

independent of rapid temperature fluctuations; the ability, degree,

and rate of temperature compensation; and the effect of previous thermal

history with regard to metabolic rate.













MATERIALS AND METHODS


To increase the probability of detecting interspecific physiolog-

ical differences, a diverse group of spiders was selected for study.

Two species of scorpions were included to aid in comparing spider

metabolism with that reported for scorpions by Dresco-Derouet (1964).

Adult females were used for the majority of observations as the relative

scarcity, short life span, and relatively high activity patterns of

males made them unsuitable for study. Immatures of a few species were

investigated. The species selected and site of their collection are

listed in Table I.

In general, metabolic rates of poikilotherms are measured under

conditions designed to obtain the lowest rate compatible with life

when all organs are at minimal levels of activity. Measurements so

obtained are termed standard metabolic rates. The conditions used to

maintain the arachnids in the laboratory and the conditions under which

measurements of standard metabolism were made are described in the

following paragraphs.

The arachnids were housed individually in glass containers of

appropriate size. Sheets of balsa wood were added to the cages of the

web building species and the salticids to provide a framework for webs

or the silken retreats of the latter. The cages of the other arachnids

were partially filled with moist sand.

lhe arachnids were kept at a temperature of 20 C except during the







TABLE I

LIST OF EXPERIMENTAL ANIMALS


Order
Family Species Collection Site


ARANEIDA


Lycosidae


Salticidae


Filistatidae


Theridi idae


SCORPIONIDA


Buthidae


Ummidia audouini (Lucas)


M species


H species




G species


Lycosa lenta Hentz


Phidipppus reqius (C.L. Koch)


Phidippus otiosus Hentz


Filistata hibernalis (Hentz)b


Achaearanea tepidariorum
(C.L. Koch)

Theridion rufipes Lucas


Tidarren sisyphoides
(Walckenaer)



Centruroides hentzi (Banks)


Ctenizidae



Theraphosidaea


Torreya Ravine,
Liberty Co.,
Florida

12 miles north of
Colima, Colima,
Mexico on Highway
110

5 miles west of
Puebla, Puebla,
Mexico on Highway
150

Tehuantepec, Oaxaca,
Mexico

Gainesville, Alachua
Co., Florida

Gainesville, Alachua
Co., Florida

Gainesville, Alachua
Co., Florida

Gainesville, Alachua
Co., Florida

Gainesville, Alachua
Co., Florida

Gainesville, Alachua
Co., Florida

Gainesville, Alachua
Co., Florida



Gainesville, Alachua
Co., Florida




7

TABLE 1 (Continued)


Species


Centruroides vittatus (Say)


Collection Site


Alabama ?


SOLFUGAE

Eremobatidae

AMBLYPYGI

Tarantul idae


Eremochelis bilobatus (Muma)



Tarantula marqinemaculata
(C.L. Koch)


Portal, Arizona



Plantation Key,
Monroe Co., Florida


aThe confused state of taxonomy of this group prevented species deter-
mination.

bLehtinen (1967) places this species in the genus Kukulcania.


Order
Family




8

experiments dealing with the effects of temperature change. This

temperature was selected because it approximates the average temperature

where most of the arachnids were collected. It is also a temperature

commonly used in measuring metabolic rates of poikilotherms; thus it

facilitates the comparison of data with those of other workers.

Relative humidity was kept near 100% by the addition of a few drops of

water to the cages at frequent intervals. In addition, a shallow tray

of water was kept in the incubator. A high relative humidity was

maintained since it was discovered that certain lycosid spiders tended

to reduce their oxygen consumption when the humidity was lowered to

10%. In essence, these conditions were used to prevent undue stress on

the animals. A 12 hr light and dark cycle was maintained in the in-

cubator with illumination provided by a 40 w bulb or a 40 w fluorescent

tube. The arachnids were fed various types of living insects once a

week. The purpose of the feeding schedule was to maintain constant

body weights. The efficacy of the feeding schedule was tested by

monitoring individual weights. Oxygen consumption for the purpose of

obtaining standard metabolic rates was measured at 20 C, 100% relative

humidity, and at a point of minimal activity. ?hillipson (1962) dem-

onstrated temporal variations in oxygen consumption in harvestmen.

Phanuel (1967) and Dresco-Derouet (1961) detected patterns in oxygen

consumption corresponding to activity cycles in certain salticid

spiders and scorpions, respectively. These results pointed to a

potential problem of defining the time of day when metabolism should

be measured. Consequently the oxygen consumption of a number of species

was measured over a 24 hr period at 20 C, 1007, relative humidity, and

a 12 hr light and dark cycle to find the time of day when the metabolic





9

rates were consistent with the definition of standard metabolism.

Once determined for each species, this time period was used for all

subsequent measurements.

Since my definition of standard metabolism depended on the exis-

tence and maintenance of a daily rhythm of activity where I could measure

oxygen consumption at a time whe'n.the arachnids were not active, I

thought it valuable to set up a control experiment to detect possible

sources of error if the acclimation conditions inadvertently produced

a loss of rhythm. Individuals of L. lenta, a species which from field

observations and preliminary studies of oxygen consumption was known

to exhibit temporal variations in activity and oxygen consumption,

were kept under constant darkness at 20 C and 100% relative humidity

for three weeks. The oxygen consumption of this experimental group

of L. lenta was then measured in the evening, a time when they are

normally active in nature. The results were compared with standard

metabolic rates of a control group of L. lenta that had been kept at

20 C and 100% relative humidity but under a 12 hr light and dark cycle

to see if loss of the temporal pattern of oxygen consumption occurred,

and also to see whether the rates of oxygen consumption obtained for

the experimental group were comparable to standard metabolic rates for

this species.

Observations were made on individuals after they were exposed to

20 C, 100'/ relative humidity, and the 12 hr light and dark cycle for

three weeks. Metabolic rates were not measured on any individual

until six days after their last feeding to preclude variations in

metabolic rates due to the absorption of food from the gut.

Actual oxygen consumption was measured using a Gilson differential




10

respirometer. Warburg flasks of about 15 ml capacity were used to

house the arachnids in most instances. Some of the larger lycosids

and all the theraphosids required the use of 125 and 200 ml flasks.

About 0.2 ml of a 10% (w/v) KOH solution was placed in the center wells

of the flasks to absorb the expired carbon dioxide. Granular soda

lime, (a mixture of NaOH and Ca(OH)2), was used for this purpose in the

case of the larger flasks. About an inch of the soda lime was layered

at the bottom of the flasks and covered with several thicknesses of

plastic screening to prevent contact with the animals. One-half ml of

water was placed in the side arms to produce a water saturated atmos-

phere within the flasks. For those spiders whose oxygen consumption

was measured under conditions simulating daylight, 75% of the flask

was covered with black plastic tape to minimize the effect of bright

light. All measurements were converted to ul of dry gas at 760 mm Hg

and 0 C.

An estimate of the respiratory quotient of the arachnids was re-

quired to compare oxygen consumption data with data of other workers

whose results are reported in kilocalories. This estimate was obtained

using P. reqius. Twenty-five specimens were.placed individually in

Warburg flasks as usual except that no KOH was added to the center

well. A 30 minute reading was made. Since no KOH was present, any

changes in the level of the manometric fluid reflected both oxygen

consumption and carbon dioxide production. A second 30 minute reading

was made with KOH in the center well. As the expired carbon dioxide

was absorbed by the KOH, this second measurement reflected only oxygen

consumption. By assuming oxygen consumption was constant for the two

30 minute intervals, I calculated carbon dioxide production and sub-

sequently the resoi~-,;orv co"ier'.





li

Estimates of book-lung surface area were made from measurements

of scaled drawings of serial cross-sections of spider abdomens. The

histological procedures used were described by Mitchell (1964). The

sections were 8 u thick and stained with a Chlorazol black E saturated

solution of 70% (v/v) ethyl alcohol. Drawings of sections of a book-

lung were made with the aid of a split image drawing tube. Every

fifth or tenth section was drawn depending on the size of the spider,

hence estimates of surface area and volume were made from 10 or 20%

of the total number of sections. The volume of a book-lung was esti-

mated from measurements made using a polar planimeter, while total

respiratory surface area was estimated from measurements of individual

lamellae in the drawn sections. The lamellae refer to the leaves of

the book-lung as they appear in cross-section. Since the spiders

investigated have a pair of book-lungs, both volume and surface area

values were doubled to provide estimates for the whole spider.

The extent of development of the tracheal systems was obtained

by examination of specimens after they had been boiled in a 10% (w/v)

solution of KOH.

The relationship between exoskeleton weight and total weight was

calculated from data obtained as follows. Live spiders were weighed

one week after they had fed. The spiders were killed and the viscera

were removed from the exoskeleton by scraping with a scalpel. The

contents of the legs were removed by rolling a glass cylinder down the

length of the legs so as to force extrusion of their contents from the

detached proximal ends. The exoskeleton was dried at 105 C until a

constant weight was obtained.

To study effects of temperature, members of a species were kept





12

at 20 C, 100% relative humidity, and a 12 hr light and dark cycle for

three weeks. The metabolic rate was measured at 20 C. The temperature

was then changed to 30 C and oxygen consumption monitored until a

stable set of readings was obtained. This reading represents the

metabolic rate at 30 C after acclimation to 20 C. The spiders were

kept at 30 C for six days with oxygen consumption measured daily to

detect temperature compensation effects. On the sixth day, after

completion of the 30 C reading, the temperature was changed first to

20 C and then to 10 C. Oxygen consumption was measured at both tem-

peratures. The rates obtained at 30 C, 20 C, and 10 C on the sixth

day were assumed to represent metabolic rates at the respective tem-

peratures after acclimation to 30 C. The actual time required to

effect a temperature change of 10 C varied between 15 to 20 minutes.

Once the new temperature had been reached, one to three hours was

required to obtain a stable metabolic rate at the new temperature.

The entire procedure was repeated to study acclimation at a

temperature of 10 C. Individuals of a species were acclimated to 20 C,

100% relative humidity, and a 12 hr light and dark cycle for three

weeks. At the conclusion of the acclimation period, metabolic rates

of these individuals were measured at 20 C. The temperature was

changed to 10 C and oxygen consumption monitored until a stable meta-

bolic rate was obtained. This reading represents the metabolic rate

at 10 C after acclimation to 20 C. The spiders were kept at 10 C for

eight days with oxygen consumption measured daily. On the eighth day,

after completion of the 10 C reading, the temperature was changed to

20 C and then to 30 C. The spiders were kept at these two temperatures

until a stable metabolic rate was obtained. A time interval of one to




13

three hours was required at each temperature. The rates obtained on

the last day at 10 C, 20 C, and 30 C were assumed to represent metabolic

rates in response to acclimation to 10 C.

The temperature range of 10 to 30 C was selected as one the animals

might normally encounter in nature.












RESULTS


Weight Changes: The results obtained from weight measurements are

summarized in Table 2.


TABLE 2

WEIGHT CHANGES IN SPIDERS



Species Number of Avg Original Avg Final Interval Between
Individuals Wt t SE Wt + SE Measurements
Measured (mg) (mg) Minimum Maximum


F. hibernalis 23 594 27 537 t 23 1 week 6 months

L. lenta 13 925 + 54 943 + 75 2 weeks 6 months

P. reqius 24 577 + 23 555 + 24 1 week 2 months

T. rufipes 12 28 2 28 + 2 2 weeks 1 month


aOnly mature females were used in this part of the study.

bNo initial weighing were made until the spiders had been held under
acclimation conditions for at least three weeks.


There were no statistically significant differences between average

initial and final weights in the species tested. On the basis of this

evidence I assumed that the feeding procedures were adequate to maintain

a constant body weight in all the experimental animals.

Temporal Variation in Oxygen Consumption: The average oxygen con-

sumption over a 24 hr period is shown in Figures 1 and 2 for individual

species. Sample sizes are indicated in each figure. Temporal variation



























Figure 1. Oxygen consumption over 24 hours. Each point represents
the mean of N determinations. The time interval indicated
by the black stripe represents the 12 hour dark period.
(a) L. lenta, N = 6; (b) F. hibernalis, N = 14.



































0


0 __ __ __ _


1900


TIME OF DAY






b


* 0 0 0 0
e0


*0 0


*
* 0 *


~I0700 o
0700 1 00 0700


TIME OF DAY


200


0700


6700




























Oxygen consumption over 24 hours. Each point represents the
mean of N determinations. The time interval indicated by the
black stripe represents the 12 hour dark period.
(a) P. reqius, N = 6; (b) T. rufipes, N = 5; (c) A. tepidar-
iorum, N = 5.


Figure 2.





18







8


* *


S0 0 0


120




80




40


0 0
0O 0 0


1900


TIME OF DAY



C


0 0 0 0 *
0


1900


TIME OF DAY


1900 07 00

TIME OF DAY


)700


* *


* C


0700


0700


40 ,


0 *


0
0


0700


=-- 13 M
o0,





19

was evident for L. lenta and P. reqius with the highest rates of oxygen

consumption occurring at a time when each species is active in nature.

Subsequent measurements for obtaining standard metabolic rates were

made in the evening for P. reqius and during the daytime for L. lenta

when their respective rates reached minimal levels. Temporal variation

was not detected in the other species. Their metabolic rates appear

to be slightly higher at night, but the variation between the hourly

readings and the relatively small magnitude of the rise at night pre-

vented making a firm decision about the existence of a daily pattern

of oxygen consumption in these species. Measurements of oxygen con-

sumption over a 24 hr period were not made on the other arachnids.

I felt the close correspondence between the patterns of oxygen con-

sumption with the normal activity rhythms of L. lenta and P. reqius,

as well as a knowledge of the activity cycles of the other arachnids

studied, justified measurement of oxygen consumption of the latter

group during that part of their activity cycle when physical activity

was known to be minimal.

Loss of Temporal Variation in Oxygen Consumption: The control

group of 17 individuals of L. lenta that had been exposed to an alter-

nating 12 hr light and dark cycle had a mean standard metabolic rate

of 81 ul 02/gm/hr with a SE of t 3. The experimental group of 11

individuals, whose metabolic rates were measured during the evening

after they had been exposed to constant darkness for three weeks, had

a mean rate of 81 ul 02/gm/hr with a SE of + 6. The correspondence of

the metabolic rates of the control group measured during the daylight

and the experimental group measured during the evening when members of

this species are normally active suggests that constant darkness extin-





20

guished the temporal variation in oxygen consumption. It also suggests

that standard metabolic rates would be obtained even though acclimation

conditions extinguished any metabolic rhythm.

Standard Metabolic Rates: The standard metabolic rates of the

various arachnids tested are listed in Tables 3 and 4. Individual data

are reported in Table 4 since small sample sizes did not make it feasi-

ble to pool data in certain species. The relationship between weight

and metabolic rate for individual species and various groupings of

species has been computed, and the parameters associated with the re-

gression equation that describes the relationship,as well as correlation

coefficients,are reported in Table 5.

TABLE 3

AVERAGE OXYGEN CONSUMPTION OF ARACHNIDS AT 20 C



Species Number of Avg Wt + SE Avg Metabolic Avg Wt Specific
Individuals (mg) Rate + SE Metabolism + SE
Measured (ul 02/hr) (ul 02/gm/hr)


F. hibernalis 81 571 15 29 + 2 50 t 2

P. reqius 78 568 35 54 + 2 93 1 4

P. otiosus 13 337 + 30 48 + 5 147 + 19

L. lenta 80 970 27 90 + 5 94 + 5

A. tepidariorum 7 73 11 25 3 356 33

T. rufipes 51 25 1 5 + 1 201 + 11

C. hentzi 15 212 + 18 9 I 43 + 6


aOnly mature females were used in this part of the study.







TABLE 4

OXYGEN CONSUMPTION OF INDIVIDUAL ARACHNIDS AT 20 C


Species Specimen Wt Metabolic Wt Specific
(mg) Rate Metabolism
(ul 02/hr) (ul 02/gm/hr)


T. sisyphoides

U. audouini

Theraphosid
species

M series adults



M series immatures



H series adult
H series immatures


G series adult
G series immatures


C. vittatus


E. bilobatus


T. marqinemaculata


110

379


M-9
M-1O
M-ll
M-13
M-12
M-15
M-16

H-77
H-75
H-76

G-2
G-9
G-10

CV-la
CV-2

SO-1
SO-2

T-l
T-2a


23,120
19,230
22,150
22,500
3,600
1 ,960
5,130

9,770
2,900
4,060

14,290
5,100
2,640

359
451

63
109

456
290


426
420
284
642
128
49
109


males












I-
C






4)
O
u
14-


() >-
U
CL
- 0



Cr1o
O>




C 0
o0 >D











U II
L

C >
--


OC

vn


co r- .D
000




oNCO Co
m03 -T


--- F


















--0
r- \. co
S00










***















-0
Lr\












000








Lnco
C- C C
- -


- C0 -T f CO -
- Co) m r- -


in


-
- f


- c\ o


000















I I I
m-- r.cr

















Ooo




0-c













I I
000
-.I- -






















0--0
- re-,













































000
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Co C 0


CNJ


In


*-I0)


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rn ru

LUI I-


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r-



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II

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4-1

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0Q









>-
n?





23

Respiratory Quotient: The average respiratory quotient of 25

individuals of P. regius was 1.02 with SE equal to + 0.04. On the

basis of these measurements, the conversion ratio of 5.05 kilocalories

per liter of oxygen was used to convert oxygen consumption values to

kilocalories for all the species studied. The conversion made possible

comparison of the metabolic rates of the arachnids studied with the

data reported by Hemmingsen (1960).

Breathing Systems: Surface area and volume estimates of book-

lungs for individuals, as well as a description of the degree of devel-

opment of the tracheal system on the species level are given in Table 6.

Exoskeleton Weight, Metabolically Active Tissue Weight, and Total

Weight: Individual exoskeleton weights, total weights, and estimates

of weights of metabolically active tissue are reported in Table 7. The

estimates of active tissue weights were obtained by subtracting exo-

skeleton weights from total weights.

Oxygen Consumption and Temperature: The rates of oxygen consump-

tion obtained at different temperatures are listed in Table 8. Figure

3 provides a graphic illustration of the relationship between oxygen

consumption and temperature in P_. reqius.

The sensitivity of metabolism to temperature change is evident

when rates of oxygen consumption at different temperatures within the

same temperature acclimation regimen are compared.

The existence and degree of temperature compensation of individ-

uals of a species at a relatively high temperature of 30 C can be

determined by comparison of the values obtained at 30 C to acclimation

temperatures of 20 and 30 C. All the species tested, except F. hibernalis,

show an appreciable reduction in oxygen consumption during a six day












In
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('4"






TABLE 7

TOTAL WEIGHTS, EXOSKELETON WEIGHTS, AND ACTIVE TISSUE WEIGHTS



Species Total Wt Exoskeleton Wt Wt of Active Tissue
(mg) (mg) (Total Wt minus Wt
of Exoskeleton)
(mg)


Theraphosid species
M series

A. tepidariorum











P. reqius















L. lenta


21,264


22,000

103
74
33
99
34
81
58
88
77
111
110

1,086
904
269
91
286
212
52
322
278
581
71
403
311
217
138

1,281
462
560
811
886
1,229
1 ,092
1,152
714
1 ,024


1 ,012
807
241
88
260
204
49
285
246
539
66
360
288
199
128

1,172
433
531
757
823
1,161
1 ,019
1 ,079
661
951






TABLE 7 (Continued)


Species Total Wt Exoskeleton Wt Wt of Active Tissue
(mg) (mg) (Total Wt minus Wt
of Exoskeleton)
(mg)


L. lenta


















F. hibernalis


















T. rufipes


25
33
112
137
121
336
141
174
203
100
273
51
72
1 ,049
1,144
772
967
1,162


30
133
32
110
57
156
164
163
149
375
246
734
295
350
509
437
452
375


1
2
5
6
7
16
8
11
14
4
21
3
3
127
148
103
76
85

2
8
1
6
5
11
12
6
8
22
15
28
24
27
28
30
21
22

1
2
2
2
1


24
31
107
131
114
320
133
163
189
96
252
48
69
922
996
669
891
1 ,077

28
125
31
104
52
145
152
157
141
353
231
706
271
323
481
407
431
353

12
27
11
23
24






TABLE 7 (Continued)


Species Total Wt Exoskeleton Wt Wt of Active Tissue
(mg) (mg) (Total Wt minus Wt
of Exoskeleton)
(mg)


T. rufipes 40 2 38
37 2 35
15 1 14
32 2 30
18 1 17
29 2 27
30 1 29
23 2 21
23 2 21
24 1 23
17 2 15












f2 Lf\ -3:00 Wr- WO L\ P%0




Coo Lr Loo tLt o oD m m0 -0oo
\.O 0o 0o r r- L% Lt> L t Ci O

E I I I I l I I I I I 0
S00 on ncd CN4 C4- CMJ4f


L
S N -n C- - - n


a)
C


0




O -


S--- a0 .D'D I I
S I I I I I I I I I I -
< > 00N \cO4D L(N00 \\ Qe\ L 0




0 0C


o 06 >-
f) I UI C- -C



Lu ( O 4- N 44 -en- C 0)
- cco n r 0-- ---) CL E
I CD 0








L > 11 0)0
-1 0 I I C N



< < o-'e- -N CNJ l U) L
Q- C4 --M - 0 )
0 0O-c rIOOO -1OU C -O
LLJ u ca - ^- ^-^ -^) 0















0- NNN n N- v 0
> I I I I I I I I
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4-U >-0> >.0 > 0 > 0 0
0 C




2 0 0)

S0 U -a 0-

= u 0 > Do


S-0- 000 00 00 00 0 00 m C \-o '
-0 -N I I n
_c -a E







-- m U -
2L > U I I 1 1 1 1|- O,
































Sa 0O
-a 0 C 0M C> C (C M C M (D | | -o 0 U



*- m E 0 0 v
E0 D 00
u E











V) 4a 0 4-
I- 1n CI CLV-




























/ Figure 3.


Oxygen consumption of P. reqius versus temperature.
* 10 C acclimation; o 20 C acclimation; 0 30 C
acclimation. Acclimation time exposures are in-
dicated in Table 8.






























































I -T---


TEMPERATURE


2.0














1.0





32

exposure to 30 C. Statistically significant differences at the 5%

level are apparent in the case of P. regius and T. rufipes. The effects

of 30 C over time in the metabolic rates of P. reqius and F. hibernalis

are indicated in Figure 4. Comparison of the oxygen consumption rates

obtained at 10 C after acclimation to 10 and 20 C does not reveal any

statistically significant increase in oxygen consumption during an

eight day exposure to 10 C. In fact F. hibernalis shows a decrease in

oxygen consumption indicating a type of inverse compensation. The

time course of measurements at 10 C is indicated in Figure 5 for F.

hibernalis and L. lenta.




























Oxygen consumption at 30 C. Vertical lines represent 95%
confidence intervals of the sample means. Spiders were
exposed to 20 C for three weeks prior to the start of this
experiment. (a) P. reqius; (b) F. hibernalis.


Figure 4.






























B I I


TIME (days)


6 7,--


TIME (days)


300.


200





100



























Figure 5. Oxygen consumption at 10 C. Vertical lines represent 95%
confidence intervals of the sample means. Spiders were
exposed to 20 C for three weeks prior to the start of this
experiment. (a) F. hibernalis; (b) L. lenta.


















*


o0 1 24 5 6
TIME (days)








b


TIE (days)
TIME (days)













DISCUSSION


Although the study of variation in oxygen consumption over a 24

hr period was conducted for the practical purpose of determining when

this measure represented standard metabolic rate, the results have some

theoretical import.

Of the five species tested, the two hunting spiders, L. lenta and

P. reggius, displayed a definite temporal variation in oxygen consump-

tion. Since these observations were recorded over a single 24 hr

period, some objection might be made to calling this variation a

circadian rhythm. However, studies of oxygen consumption in harvest-

men by Phillipson (1962) and those on locomotory activity patterns ;n

salticid spiders reported by Phanuel (1967), where measurements were

recorded over two or more 24 hr cycles, support the conclusion that

the two spiders have a definite rhythm of oxygen consumption which

corresponds to periods of activity in nature. It is doubtful, however,

that the measured oxygen consumption of these hunting spiders during

their active locomotory phases accurately reflects the oxygen consump-

tion maintained during such phases in nature. While the high rates

obtained in the laboratory probably correspond to the time these spiders

are active in the field, the magnitude of such measurements may be a

reflection of the animals struggling within the confines of a small

flask.

Cloudsley-Thompson (1960) suggests the adaptive functions of these





38

rhythms may partially reside in the avoidance of harsh physical factors.

This function is probably of some significance in the case of nocturnal

species such as L. lenta. However, the biotic function of synchronizing

activity of spiders with the time of greatest prey availability cannot

be excluded as a possibility.

A definite temporal pattern in oxygen consumption is not apparent

from the results graphed in Figures Ib, 2b, and 2c. The species in-

volved are all web builders; therefore it follows that any rhythmic

increases in energy expenditure probably would be associated with

building and/or repair of webs. The lack of detection of a rhythm may

be an artifact in that the spiders were placed in the Warburg flasks

24 hr prior to measuring oxygen consumption. Webs were built during

this time and should have remained in good repair during the course

of the experiment.

I am tempted to speculate that the energy spent in the building

and maintenance of webs serves the same function, namely prey capture,

as that spent during the increased locomotory activity of the hunting

species. Certainly the web increases the effectiveness of its owner

in sampling the environment for prey, but there may be an added advan-

tage related to energy conservation in those spiders which do not make

a new web every day. Once the web is constructed its owner does not

have to raise his metabolic rate on a daily basis to insure capture

of prey, while hunting spiders must expend energy daily to emerge from

their retreats and move about in search of food. Unfortunately this

study does not provide data that would support this conjecture for

reasons discussed previously.

The importance of light as a Zeitqeber was demonstrated by the





39

correspondence between the standard metabolic rate of L. lenta with the

metabolic rate of an experimental group of this species which had been

kept in constant darkness. The results also suggest that even though

the conditions used to maintain the arachnids in the laboratory extin-

guished metabolic rhythms, measured rates of oxygen consumption would

be compatible with standard metabolic rates. The correspondence of

oxygen consumption values obtained under constant darkness with those

obtained from organisms when they are in an inactive phase under an

alternating light and dark cycle, if substantiated by future research,

suggests maintaining organisms under constant conditions to alleviate

the necessity of measuring metabolic functions at inconvenient times

in order to obtain standard metabolic rates.

To illustrate the interspecific variations in metabolic rates of

arachnids, the species metabolism-weight regression lines, and,where

appropriate, average metabolic rates versus weights were plotted in

Figure 6. In addition, the metabolic rates of all the arachnids were

combined and a pooled arachnid metabolism-weight line constructed in

Figure 6 as a reference line for the purpose of comparison.

With the exception of one point representing the average metabolic

rate of the solfugid, E. bilobatus, all of the values above the pooled

arachnid line represent spiders. They include L. lenta, P. reqius,

P. otiosus, A. tepidariorum, and T. sisyphoides. Immature stages of

P. reqius and L. lenta as well as adult T. rufipes have metabolic rates

which fall on the pooled arachnid line. The values below the pooled

arachnid line represent the metabolic rates of the amblypygid T.

marginemaculata; scorpions, C. hentzi and C. vittatus; three species

of theraphosid spiders; the trap-door spider, U. audouini; and the













c n





fu -4-1'I
L- O E


L C .J E

.- i


00 -



--- 0
---' -
4) -J 4-' n



Q 0 0|
LOE, 3








00) -
I 0:- u-'
( QI f
m vi -I .- .


0 &- -O



- *- I 4
S-C -I

L .n 3 *-



O -U --
c3




C-- V1 *n .- N











3U -C: u
4a -- 1 (E
.C in 0 ol-






L 0l
OO C
va --









o -o U L

)-0.- .- IC
4-e C --- 4O T



U 4i 3 a|




4 C- + E4


0 t0 - 1 3
3 UO (0 0







T.*- I- 1 TO
CL) -




C L .---





O30 vi Ti
4 4 *-' T
g .c -----I (o









Cl ^ ru 0

- .-

TO 3
)-Q TO C O

*a





41




a








+
0









-a


+++







0-3

-3






'e
























o o
--























0-

I I
N --O













+ + +
0 0 0 0




(J4/ O ) 31V1 3 O170 V[3H 901





42

cribellate spider F. hibernalis. The data on three species of scorpions

reported by Dresco-Derouet (1964) agree with the metabolic rate values

I obtained for scorpions.

Pooled regression lines were calculated for adult arachnids whose

metabolic rates are on or above the pooled regression line and for

those whose metabolic rates fall below the line in an attempt to

estimate the statistical significance of the difference in metabolic

rates of these groupings. Analysis of covariance, as described by

Snedecor (1956), was used for this purpose. Unfortunately the slopes

of the two lines were shown to be unequal thus preventing further

testing of the difference in elevation between the two lines. In a

partial attempt to circumvent this problem, the same test was conducted

on metabolic rate values of a pair of species, P. reqius and F.

hibernalis. The metabolism-weight regressions of these species fall

above and below the pooled arachnid line, respectively. The suitabil-

ity of using data obtained from these two species can be seen in

Figure 6: their weight ranges and slopes of their regression lines

coincide. With I and 156 degrees of freedom, the calculated f ratio

is 117.74 indicating that the difference between their respective

rates of oxygen consumption is statistically significant well beyond

the 1% level.

In considering these two groupings, i.e., arachnids with a high

or low metabolic rate as evidenced by the position of metabolic rate

values in respect to the pooled arachnid line, I came to the conclu-

sion that the various levels of the metabolic rate in arachnids are

associated with their evolutionary history, particularly in regards

to the fact that arachnids are predators. The arguments leading to

this conclusion are developed in the following paragraphs.





43

The composition of the group with a low metabolic rate includes

species that are representatives of primitive orders or are primitive

species within a more advanced arachnid order. I use the word primi-

tive in the sense that organisms so described are the most conservative

anatomically of their respective taxa. Whether an arachnid was con-

sidered primitive or not was made on the basis of information supplied

by Millot (1949), Stdrmer et al. (1955), and Lehtinen (1967). Assuming

that physiological conservatism would be correlated with anatomical

conservatism, I thought it valuable to discuss the evolution of

metabolic rates in arachnids. Since arachnids were one of the first

groups to move from an aquatic to a terrestrial habitat, they as

predators probably faced the problem of having an inconsistent food

supply. A low metabolic rate in this situation would certainly be of

value. Even in extant species, a low rate of energy expenditure would

be of selective advantage in that it would permit an animal to live in

an unstable environment with regard to prey density and/or an environ-

ment where the high rate of water loss concomitant with high metabolic

rates would be detrimental.

While a plausible argument may be constructed to explain the

adaptive significance of a low metabolic rate, the fact that certain

arachnids have relatively high metabolic rates deserves some attention.

Assuming that during the colonization of the terrestrial habitat prey

availability became more and more reliable, the metabolic rates of

arachnids could have increased beyond a required minimal level in

response to different selective pressures associated with increased

activity patterns, rapid rates of development, and increased reproduc-

tive potential. I am assuming that these physiological components





44

require a relatively high rate of energy expenditure and that maximum

metabolic rates are a function of standard metabolic rates in the sense

that the higher the standard metabolic rate, the higher the maximal

metabolic rate. With the exception of the solfugid, the arachnids

with relatively high metabolic rates are generally considered to have

undergone more evolutionary change than those arachnids with low

metabolic rates, at least in so far as the species used in this study

are concerned.

The association of a low metabolic rate with predatory habits and

relative lack of evolutionary change is not contradicted by reports

in the literature. Harvestmen are not solely dependent on living prey

as an energy source and represent one of the most advanced orders of

arachnids. A comparison of the metabolic rates obtained at 16 C for

two species of harvestmen, as reported by Phillipson (1962), with my

pooled arachnid line indicates that harvestmen have a rate of metabolism

three to four times higher even though my measurements were made at

20 C. I would argue that harvestmen evolved a relatively high metabolic

rate in response to some unknown selection pressure, and one of the

requisites of this high metabolic rate is a flexibility in terms of

accepting food sources in addition to living prey.

The fact that Dresco-Derouet (1967) reported a low metabolic rate

for the harvestman, Ischyropsalis luteipes Simon does not contradict

this line of reasoning since this species normally lives in caves.

As Frost (1959) points out, one of the main characteristics of a cave

environment is a scarcity of food. Derouet (1953) and Dresco-Derouet

(1960) also demonstrated that a low metabolic rate is associated with

a cavernicolous habitat in spiders.




45

Hemmingsen's (1960) study was selected as a basis for comparison

of arachnid metabolic rates with those of other polkilotherms because

of the comprehensive nature of the review. The values of the slopes

of the regression equations describing the relationship between weight

and metabolism of arachnids, as indicated in Table 5, do not differ

significantly from 0.75, a value that has been computed by Hemmingsen

(1960) from data obtained from a wide variety of organisms. To

detect any difference between levels of metabolism, the metabolic

rates of all the arachnids were pooled and then converted to their

caloric equivalents. A respiratory quotient of one was obtained from

experiments with P. reqius and was used to convert oxygen consumption

values to kilocalories. The comparison of the pooled arachnid line

and Hemmingsen's (1960) standard poikilotherm line is shown in Figure

7. The average metabolic rate of the arachnids sampled in this study

is about 40 to 50% lower than that of other poikilotherms over the in-

dicated weight range. I mentioned previously that certain spiders

had relatively high metabolic rates for arachnids, however, while

these rates approach Hemmingsen's (1960) standard poikilotherm line,

they still fall below it. Again I would argue that the low rate of

metabolism in the arachnids studied in comparison with other poikilo-

therms is the result of adaptation to a relatively inconsistent food

supply. Further remarks concerning the adaptive significance of high

and low metabolic rates will be made below where the results of the

effect of temperature on metabolic rate are discussed.

Although the preceding discussion is concerned with the adaptive

significance of the various levels of standard metabolism, no mention

had been made of the morphological factors which determine the various

















C(



c
L.
i-


O













U
_c

















4- -
0












0ro
L














CO-
0






















U) 0)
u
0 C






oo
- U


cn
*- o



rc



4-1 L.








(U





ui-







47




















CDJ
+






+






0









E
o -







0

C-









0




cl











~ 2









0 31V0 0110OV 3W 00





48

rates of oxygen consumption for a given organism. Those arachnids

that have metabolic rates above the pooled arachnid line of Figure 6

carry out external respiration by means of book-lungs and/or trachea

whereas those arachnids with relatively low metabolic rates utilize

only book-lungs for this function. The implication that a tracheal

system is a factor associated with a high metabolic rate is supported

by certain evidence. The two individuals of T. marginemaculata, which

respire by means of book-lungs, had a metabolic rate of 41 and 23 ul

02/gm/hr while the two individuals of E. bilobatus, which use only

trachea, had measured rates of 246 and 249 ul 02/gm/hr. The spiders

that utilize both book-lungs and trachea have a higher metabolic rate

than those spiders that utilize only book-lungs. The latter group in-

cludes F. hibernalis, a spider having rudiments of a tracheal system.

It is doubtful, however, that this system functions in gas exchange in

this species. Even the spiders which have a relatively high metabolic

rate have rates inferior to those of insects as cited by Hemmingsen

(1960). The latter group utilize only trachea. The high metabolic

rates of the harvestmen also fit this scheme as they respire solely

by means of a tracheal system. This evidence suggests that a tracheal

system is more efficient in delivering oxygen to cells than is a book-

lung system associated with a circulatory system. However, considering

just spiders, the answer is not clear cut. Davies and Edney (1952)

demonstrated in the wolf spider, Lycosa amentata, that respiration

took place mainly through the book-lungs. Blocking of the spiracular

opening of the tracheal system with celloidin did not reduce the

oxygen consumption of these spiders. Dresco-Derouet (1960) repeated

this experiment on different spiders and obtained the same results. As




49

indicated in Table 6, P. regius has a well developed tracheal system

in addition to book-lungs, yet this spider has a weight specific

metabolic rate which closely approximates that of L. lenta, a spider

which has book-lungs and a poorly developed tracheal system. The

hypothesis advanced by Levi (1967) merits consideration at this point.

He suggests the tracheal system is probably important in reducing water

loss. As the rate of oxygen consumption increases there is a concomi-

tant increase in respiratory water loss, an intolerable consequence for

a small terrestrial organism if not corrected. The trachea may function

as a means of reducing this water loss because of a longer diffusion

distance and/or smaller spiracles relative to those associated with

book-lungs. The one spider with an extensive tracheal system, P.

regius, has its highest metabolic rate during the daytime when it would

be exposed to conditions conducive to high rates of water loss, i.e.,

relatively high temperatures and low relative humidities. On the

other hand, L. lenta, a spider with a poorly developed tracheal system,

is active at night when low temperatures and high relative humidities

would not be as conducive to high rates of water loss.

in summary, I suggest that a tracheal system is associated with

high metabolic rates because of its efficiency in transporting oxygen,

and perhaps more importantly because it reduces water loss. On the

basis of experiments of Davies and Edney (1952) and Dresco-Derouet (1960),

as well as my analysis of the association between metabolic rates and

tracheal systems of P. reqius and L. lenta, I concluded that in spiders

the tracheal system functions mainly during the active phases of the

daily cycle of the spider and not, at least to any great extent, when

the spider is quiescent.





50

If the latter assumption is true, then analysis of the respiratory

surface area of only the book-lungs is justified from the standpoint

of associating standard metabolic rates with respiratory surface areas.

Since estimation of the surface area of a book-lung requires an exces-

sive amount of time, the analysis of the effect of this measure on

metabolic rates was conducted interspecifically rather than intraspe-

cifically. Table 9 summarizes the data used in this analysis while

Figure 8 shows a graph of metabolism versus respiratory surface area.


TABLE 9

AVERAGE WEIGHT, METABOLIC RATE AND
BOOK-LUNG SURFACE AREA IN ADULT SPIDERS



Species Avg Wt Avg Metabolic Rate Avg Book-Lung Surface
(mg) (ul 02/hr) area
(mm2)


L. lenta 970 90 333

P. reqius 568 54 258

F. hibernalis 571 29 142

A. tepidariorum 73 25 39

T. sisyphoides 110 17 49

T. rufipes 25 5 14




The results listed in Table 9 indicate a general correspondence

between metabolic rate and respiratory surface area, i.e., the larger

the surface area the higher the rate of metabolism. However, the

weight component complicates the analysis as there are only two species,

F. hibernalis and P. reqius, which have roughly the same average weight.

























Figure 8. Relationship between book-lung surface area and oxygen
consumption in spiders. (a) L. lenta; (b) P. reqius;
(c) F. hibernalis; (d) T. sisyphoides; (e) A. tepidariorum;
and (f) T. rufipes.






52






















oa





.C

o

2n
C-


-c,
10



10
-J R




0





10
S2











10P0 S E ( 02


LOG RESPIRATORY SURFACE AREA (mm2)




53

Regression lines describing the relationships of metabolism and surface

area to weight were calculated using the average values listed in

Table 9 to provide standards in an attempt to correlate deviations in

the metabolism-weight relationship with deviations in the respiratory

surface area-weight relationship. The logarithemic form of these equa-

tions are:

log metabolism = 0.6320 (log wt) 0.0408 and

log surface area = 0.9398 (log wt) 0.0127

The sample correlation coefficients for these relationships are 0.91

and 0.99, respectively. These equations were used to calculate ex-

pected metabolic rates and surface areas at the average weights for

each species. The calculated values were then compared with the ob-

served values to see whether the deviations between calculated and

observed values of metabolic rate corresponded to deviations between

calculated and observed values of surface area. The results of these

procedures are shown in Figure 9. In every case, where there is a

metabolic rate higher than predicted on the basis of the metabolism-

weight regression equation, there is a larger than predicted surface

area. The converse situation also holds. This analysis suggests that

the rate of oxygen consumption is a function of the respiratory surface

area of the book-lungs. To ascertain the degree of statistical signifi-

cance of the relationship between metabolic rate and respiratory surface

area, a sample partial correlation was computed. This method of analy-

sis eliminates the effect of weight. The calculated sample partial

correlation is 0.86 which, with 3 degrees of freedom, is significant

at the 10% level but not at the 5% level. The hypothesis that the

greater the amount of surface area the higher the metabolic rate does

not imply that other factors such as cardiac output and properties



























Figure 9. Deviations of actual versus calculated values of oxygen
consumption and respiratory surface area. Abscissa, surface
area deviations. Ordinate, oxygen consumption deviations.
(a) A. tepidariorum; (b) L. lenta; (c) P. reqius; (d) T.
sisyphoides; (e) T. rufipes; and (f) F. hibernalis.




















+1.5








+1.0.








+0.5.


-I .


-1.0.


-1.5.


C
0


+1.0


I I


I


-u.b





56

of respiratory pigments may not be important in regulating the level

of oxygen consumption. The former is certainly of some importance

since Sherman and Pax (1968) discovered marked variations in heart rate

corresponding to levels of locomotory activity in the spider Geolycosa

missouriensis.

The hypothesis that disproportionate increases in supportive

tissues that occur as animals get larger is responsible for the rate of

increase in metabolic rate with an increase in weight is not validated

by the results of this study. Regression equations describing the

relationships of exoskeleton weight and metabolically active tissue

weight to total weight were calculated, and are reported in Table 10.

In the case of the three species investigated, the weight of metaboli-

cally active tissue increases in direct proportion to total weight,

i.e., the slope of the equation describing this relationship approxi-

mates a value of one. If the hypothesis were to hold, the slopes of

the regressions of weights of netabolically active tissue and rates of

metabolism to total weight should equal one another. Comparisons of

these values reported in Tables 5 and 10 indicate this is not the case.

Unfortunately, the lack of information pertaining to the biochemical

composition of spiders precludes testing the assumption that the

exoskeleton constitutes the bulk of metabolically inactive tissue.

The apparent anomaly where exoskeleton weight increases disproportion-

ally with an increase in total weight while active tissue weight in-

creases in direct proportion, at least in the case of L. lenta, is

resolved when these relationships are analyzed. The form of the equa-

tions are determined by two variables, namely the slope and the inter-

cept. While exoskeleton weight may increase disproportionally with an















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58

increase in total weight, the mathematical relationship between active

tissue weight and total weight can be one of direct proportion due to

the higher intercept in the latter. These relationships are indicated

in Table 10.

The results pertaining to the effect of temperature on metabolic

rate, as recorded in Table 8, indicate oxygen consumption in spiders

is not independent of rapid changes in temperature. The calculated

average Qi0 values for temperature ranges of 10 to 20 C and 20 to 30 C

are 3.3 and 2.4, respectively. These values are in contrast with the

findings of Newell (1966). He claimed the metabolic rates of poikilo-

therms are largely independent of rapid temperature fluctuations with

resulting Q10 values ranging from 1.2 to 1.3 provided that metabolic

rates of quiescent organisms were measured at frequent intervals. My

experimental procedures agree with these requirements in that oxygen

consumption was measured at 10 to 15 minute intervals after a rapid

10 C temperature change at a time of day when the spiders were inactive.

The correspondence of my results with those of Tribe and Bowler (1968)

suggests temperature independence in poikilotherms is not as wide-

spread as Newell (1966) implies.

The results recorded in Table 8 indicate previous thermal history

does have an effect on metabolic rate when measured at a new temperature.

In every case, except F. hibernalis, acclimation to a low temperature

of 10 C resulted in a significantly higher metabolic rate at 30 C than

would be produced when the spiders were acclimated at 20 C or 30 C.

This situation is depicted graphically in Figure 3 where the metabolic

rate-temperature curves show a rotation around 20 C. Tiis phenomenon

appears to be associated with the ability of individual species to





59

compensate at high temperatures by lowering their metabolic rates

after exposure to the new high temperatures. For example, individuals

of P. regius, when acclimated at 20 C for three weeks, have an initial

average metabolic rate of 237 ul 02/gm/hr at 30 C. After a six-day

exposure to this temperature, the average metabolic rate decreased to

151 ul 02/gm/hr. In each case where compensations to a high temperature

were detected, the degree of compensation was not complete because the

rate of oxygen compensation did not decrease to the level recorded at

20 C. The magnitude of decrease in metabolic rate corresponds to what

Precht (1958) terms a 'type 3' compensation. The degree of compensa-

tion, computed from the average metabolic rates initially obtained at

30 C after acclimation for three weeks at 20 C and those obtained at

30 C after a six-day exposure to this temperature, involve reductions

of 20%o for L. lenta, 36% for P. regius, and 31% for T. rufipes. In all

cases, the maximal compensation was reached by the third day of exposure

to 30 C.

In trying to relate the findings of the temperature studies to

standard metabolic rates, I noticed the spiders which showed a decrease

in oxygen consumption during exposure to 30 C all had relatively high

metabolic rates at 20 C as indicated in Figure 6. The one spider which

did not demonstrate compensation at 30 C had a relatively low metabolic

rate at 20 C. This correlation suggests homr'ostatic potential in

regards to temperature is perhaps limited by the relative rate of metab-

olism. Making the assumption there is a certain minimum level of energy

expenditure required to keep arachnid protoplasm in a healthy statc,

it seems reasonable to have a standard metabolic rate at this relatively

low level under certain conditions. As mentioned previously, I suspect





60

the movement from an aquatic to a terrestrial habitat that arachnids

made in the geological past presented the problem of a limited food

supply. However, as time passed and more and more organisms colonized

the terrestrial habitat, the luxury of a high metabolic rate was not

selected against, on the contrary it probably possessed certain adaptive

adjuncts. One of these adjuncts may relate to'the relatively large

temperature fluctuations inherent in a terrestrial environment.

Consider a spider that has a low metabolic rate at an intermediate

temperature. This animal is living close to its minimal level of re-

quired energy expenditure. A rise in environmental temperature of 10 C,

through its effects on the kinetics of enzyme systems, would result in

roughly two fold increases in both minimal and standard metabolic

rates. Since the new minimal and standard metabolic rate approximate

one another in this case, any reduction in energy expenditure, which

might well be desirable from the standpoint of the limitation of energy

resources, would be incompatible with maintaining life. On the other

hand, a spider with a relatively high metabolic rate at the intermediate

temperature, that is to say its standard metabolic rate is appreciably

above minimal requirements, when exposed to a higher temperature would

also increase its required minimal and standard metabolic rates. How-

ever, since this new rate would be above minimal requirements, a

decrease in oxygen consumption could take place. This reduction in

energy expenditure would be advantageous when the amounts of food re-

quired to support the different levels of metabolism are considered.

This model is depicted graphically in Figure 10 using the data obtained

from F. hibernalis and P. reqius. I must admit that this explanation

is speculative. The major difficulty stems from the acceptability of



























Figure 10. Relationship between temperature and standard metabolism
in P. regius and F. hibernalis. (a) minimal required energy
expenditure at 20 C; (b) minimal required energy expenditure
at 30 C; (c) compensation at 30 C in P. reqius.



























_m 200
E
en

c P. reqius










7 100
LI
o











F. hibernalis

a






0
20 C o c

TEMPERATURE




63

the assumption that there is a certain minimal level of energy expen-

diture which may be different in certain cases from that defined as

the standard metabolic rate.

The lack of compensation to the 10 C temperature is not surprising.

As predators of insects it would be of little value for spiders to

increase their metabolic rate at low temperatures since the low temper-

atures would also reduce the activity of their prey. I would even

suggest that the inverse compensation exhibited by F. hibernalis, a

web builder, reflects an adaptation to the greater inhibitory effect

of low temperature on flying versus walking insects.













LITERATURE CITED


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17:973-982.

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Berthet, P. 1963. Mesure de la consommation d'oxygene des Oribatides
(Acariens) de la litiere des forts. p. 18-31. In J. Doeksen and
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Brown, M. E. 1957. The physiology of fishes, Volume I. Metabolism.
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Cloudsley-Thompson, J. L. 1960. Adaptive functions of circadian
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Derouet, L. 1953. M6tabolisme compare de deux Araignees, I'une
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some allied families, with notes on the evolution of the suborder
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Tardigrades, Arthropodes, Trilobitomorphes, Chelicerates. P-P.
Grass (ed.). Masson et Cie. Paris. 979 p.

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and H. R. Northcroft. 1967. A re-interpretation of the
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BIOGRAPHICAL SKETCH


John Francis Anderson was born July 25, 1936, at Hartford,

Connecticut. He graduated from Bulkeley High School in June, 1954.

From 1954 until 1958, Mr. Anderson served in the United States Marine

Corps. Following his release from active duty he entered Central

Connecticut State College at New Britain, Connecticut, where he re-

ceived his Bachelor of Science degree with honors in June, 1962.

In September, 1962, he entered the Zoology Department at the University

of Florida where he received his Master of Science degree in April,

1965. He continued graduate studies toward the degree of Doctor of

Philosophy at the University of Florida while serving as a research

and teaching assistant.

Mr. Anderson is married to the former Marjorie Ann Barrett. He

is a member of the American Society of Zoologists and Sigma Xi.







This dissertation was prepared under the direction of the chair-

man of the candidate's supervisory committee and has been approved by

all members of that committee. It was submitted to the Dean of the

College of Arts and Sciences and to the Graduate Council, and was

approved as partial fulfillment of the requirements for the degree of

Doctor of Philosophy.


December, 1968


Dean, Graduate School


Supervisory Committee:



SChai rman

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