Asiatic Herpetological Research[April 1990Vol. 3, pp. 54l9]

Thermal Sensitivity of Sprinting and Clinging Performance in the TokayGecko (Gekko gecko)

JONATHAN B. LOSOS
1

1

Museum of Vertebrate Zoology and Department of Integrative Biology,
University of California, Berkeley, CA 94720 USA

Abstract. -The thermal sensitivity of sprinting and clinging ability was measured in tokay geckos(Gekko gecko). Sprinting performance was maximal at high (35-4 1°C) temperatures, as is the case forother nocturnal lizards, but the optimal temperature for clinging was considerably lower (approximately
17°C). These different optima could be adaptive if maximal sprinting and clinging capabilities are needed atdifferent temperatures. Alternatively, they could result from constraints on adaptive evolution.

Key Words: Reptilia, Sauria, Gekkonidae, Gecko gecko, thermal sensitivity, optimal performance.

Introduction

Most physiological processes areEctothermic
temperature-dependent.
animals, which do not maintain a constantfrequently experience in nature (Bennett1980); however, nocturnal lizards appear
exceptional (Huey and Bennett 1987; Hueyetal. 1989). The thermal sensitivity of few

otherwhole-organism

locomotor

subject tofluctuation in the rate at which they canperform many vital tasks. By regulating
body temperature behaviorally, however,

performance measures has been determined
for lizards.
Here I report the thermal
sensitivity of tokay geckos (Gekko gecko)

many reptiles can maximize performancemaximum sprinting and clinging capability.

body temperature,

are thus

capability (Huey 1982a).

Insome cases,

maximal performance temperature might
For example, awealth of behavioral data indicates thatmany lizards and snakes increase their bodydiffer for different tasks.

temperature after feeding, which suggeststhat digestion has a higher optimal
temperature than other activities (reviewedin HueyI

ask whether

maximum performancecapability occurs at the relatively low
temperatures most commonly experienced

by geckos (Huey et al. 1989) and whether
the optimal temperature is the same for thetwo performance measures.

Methods

1982a).

Early work centered on the thermal
dependence of sub-organismal traits (e.g.,
enzyme activity, muscle contractile speed[Huey and Stevenson 1979]). In manycases, however, the effect of temperatureon the functional capacities (e.g., sprint
speed, critical thermal maximumtemperature) cannot be predicted by study
at sub-organismal levels (e.g., LichtMarsh[Fig. 1] for two ecologically relevant tasks,and1967;

Bennett

1985, 1986).
Consequently, recent studies have focusedon whole-organism performance. The
thermal dependence of sprinting ability has
been studied in great detail. Maximum
sprinting speed and/or endurance in many
species occurs at the temperature they most1990 by Asiatic Herpetological Research

Tokays are relatively large geckos foundon trees and walls throughout southeastern
Asia (Smith 1935). Lizards were captured
on Phuket Island, Phuket Province,
Thailand, and transported to the Universityof California, Berkeley in late September
1987. They were maintained in 30 x 17 x 9cm

shoeboxes at ambient
plastic
temperatures and provided with water andcrickets ad libitum. An ontogenetic series
was used in this study (11 individuals;
snout-vent length: 85-180 mm; mass: 10140 g).
All trials were conducted in a walk-in
environmental chamber in the Museum ofVertebrate Zoology, University ofApril 1990

FIG. 1.

Asiatic Herpetological ResearchVol. 3, p. 55

Gekko gecko from Phuket Province, Thailand.

California, Berkeley, within a month ofcapture. Lizards were placed in the chamber

one hour prior to performancemeasurement. Humidity, which could not
be regulated, was determined on several
occasions using a Bacharach slingat least

psychrometer.

Clinging capability was measured byplacing lizards on a plexiglass plate and, at
a gradual and steady rate, lifting the end of
the plate so that the lizard was clinging withits head directed down. The angle at which
the lizard fell from the plate was recorded(protocol modified from Emerson and Diehl
1980; Alberch 1981). Lizards that jumped
from the plate were not included in thefrom the experimental plate.

One trial per lizard was conducted perPerformancetemperature.

atninetemperatures (12, 16, 17, 22, 24, 31 [three35, 41; the order oftemperatures
presented in figure 2) wasmeasured over a six-day period. On somedays, two trials were conducted.
times],

34,

isSprint capability was measured byplacing lizards at the end of a 2.25
trackway covered with a rough rubber
surface and inducing them to run bymanalysis.

repeated taps to the tail (protocol following
Huey 1982b; Huey et al. 1989; Garland1985). As the lizard ran, it interrupted lightbeams stationed every 0.25 m. The time

There was noevidence that temperature affected thelizards' efforts to prevent sliding and falling

elapsed during each interval was computedby a Compaq personal computer, the fastest
single interval during four trials, conductedat hourly intervals, was considered themaximum speed for that lizard at thatAs lizards began to slide, theyusually attempted to maintain their grip bymoving and re-applying their toe pads
regardless of temperature.

Asiatic Herpetological ResearchVol. 3, p. 56

1551.50.25

1.00

2030

Temperature

April 1990

AsiaticApril 1990

Herpetological Research

Eremiascincus fasciolatus (Huey andBennett 1987). Clinging capability, thethermal dependence of which has neverpreviously been investigated, is maximal atconsiderably

lower(approx.

17°C)

Vol. 3, p. 57

evolve high critical thermal maxima. The
high sprint performance maximum might bea correlated effect of this physiological
adaptation to high temperatures and not be
adaptive per se (Huey et al. 1989).

temperatures.
Itisdifficult to envision

how suchdifferent optima could evolve adaptively.
Most lizards sprint maximally attemperatures close to those they normallyexperience (Huey 1982a; Huey et al.
1989). The low optimal temperature forclinging matches the field temperatures ofmany active nocturnal geckos (Huey et al.
1989). However, many nocturnal geckos
bask and/or are active to some extent during
the day (Bustard 1967, 1968; Werner andWhitaker 1978; Nagy and Knight 1989).
Consequently, the high optimal temperaturefor sprinting seen in many nocturnal lizards
might represent adaptation for diurnal
capability (Huey and Bennett 1987; Huey et1989). Nonethless, it seems implausiblethat one aspect of locomotion, sprint

Clinging capability depends upon both
physical and physiological processes.
Geckos cling to smooth surfaces by dry
adhesion. The subdigital lamellar pads ofgeckos are covered with millions of
microscopic setal hairs. When the pads areadpressed to a surface, these hairs form
intermolecular bonds with molecules on thesurface of the substrate (Hiller 1975). If
the surface energy (a measure of thenumber of free electrons on the surface ofthe substrate) is relatively high, thenenough bonds can form to support thelizard. Because these bonds result from theactivity of electrons, the forces theoreticallyshould be temperature-independent over therange of temperatures in this study.

al.

performance, should be selected at hightemperatures, whereas another importantcomponent of effective movement,clinging, should be favored at considerably
lower temperatures.

As an alternative explanation, thedifferences in thermal optima might result
from differences in evolutionary lability ofthe two performance capabilities and thus
represent constraints on adaptive evolutionin either sprinting or clinging ability. To
understand why these performance abilities
are affected differently by temperature, abetter understanding is needed of theirunderlying physical and physiologicalbases (e.g., Garland 1984, 1985; Marshand Bennett 1985, 1986). In many speciesof lizards, sprint performance is maximal attemperatures close to the critical thermalmaximum (Huey and Bennett 1987; Huey
et al. 1989). The cause for this linkage isunclear. However, if geckos must be able
to survive diurnal temperatures (either

because they intentionally maintain hightemperatures to maximize other processes,
or because environmental conditions
preclude the maintenance of lower
temperatures), then they would have toHowever, geckos have an elaborate
muscular and vascular system for the
adpression and removal of their toe pads
(Russell 1975); the thermal dependence of
these muscles has not been investigated.
The poor clinging performance of geckos at10-12°C is clearly the result of

At thatphysiological incapacitation.
weregenerally
temperature, geckos
inactive, moved slowly and infrequently,and even rarely bit or barked whenhandled. In contrast to trials at higher
temperatures, the lizards did not attempt toadjust their pads or posture when the plate
was tilted and quickly lost their hold. Moreresearch is required to determine whether
the performance decline at temperatures
above 17-1 8°C results from decreased
capability of the muscles and enzymes
involved in clinging.

One possible confounding effect in theclinging experiments is the variation in
Moisture might
absolute humidity.
decrease the formation of high-energy
intermolecular bonds. Absolute humidity
the environmental chamber wasmeasured at several temperatures andincreased from 8.5 Barrs at 11.9°C to 25.1
Barrs at 34.3°C (relative humidity,in

Vol. 3, p. 58

Asiatic Herpetological Research

however, was greatest

atintermediatetemperatures). Consequently, the greater
absolute humidity at higher temperatures inthe environmental chamber might havecaused a decrease in clinging ability.
Further research is needed to investigate towhat extent humidity affects clinging.

Although different processes may often
be maximized at different temperatures,
rarely is the difference as great as isobserved between sprinting and clinging intokay geckos (Huey 1982a). One would
not expect these geckos to need maximum
ability at these aspects of locomotion atsuch different temperatures, but neither
would one expect the physiologicalsensitivity of different systems to be sodifferent. Interestingly, the optimal
temperature for hearing sensitivity in the
tokay gecko is intermediate between thesprinting and clinging optima (Werner
Further research is required to1976).
understand the processes shaping andconstraining performance evolution.

EMERSON, S. B., AND D. DIEHL.

thank T. Papenfuss and R. Macey forproviding the geckos, R. Jones forassistance with equipment, R. Huey foradvice on racing geckos, J. Herron forproviding me with a pre-publication
manuscript, and A. Bauer, H. Greene andR. Huey for constructive comments on aprevious version of this paper.
I

Literature Cited

ALBERCH, P.
infoot1981. Convergence and parallelism
morphology in the neotropical

1980.

Toe padmorphology and mechanisms of sticking in
Biological Journal of the Linnaenfrogs.
Society 13:199-216.

GARLAND, T., JR.

1984. Physiological correlatesof locomotory performance in a lizard: an
American Journal ofallometric approach.
Physiology 247:R806-R815.

GARLAND, T., JR.

1985.

Ontogenetic andindividual variation in size, shape and speed in
the Australianagamid lizard Amphibolurusnuchalis. Journal of Zoology, London (A)207:425-439.

HILLER, U.

1975.

Comparative studies on thefunctional morphology of two gekkonid lizards.

Journal of the Bombay Natural History Society

73:278-282.

HUEY, R. B.

1982a. Temperature, physiology,
and the ecology of reptiles. Pp. 25-91. In C.
Gans and F. H. Pough (Eds.), Biology of theReptilia, Vol. 12. Academic Press, New York,USA.

HUEY, R. B.
Acknowledgments

April 1990

1982b.

andPhylogenetic

ontogenetic determinants of sprint performancein some diurnal Kalahari lizards. Koedoe 25:43-48.

HUEY, R. B., AND A. F. BENNETT.

1987.

Phylogenetic studies of coadaptation: preferredtemperatures versus optimal performance
temperatures of lizards. Evolution 41:10981115.

HUEY, R. B., P. H. NIEWIAROWSKI, J.
KAUFMANN, AND J. C. HERRON. 1989.
Thermal biology of nocturnal ectotherms: issprint performance of geckos maximal at low

body temperatures?

Physiological Zoology

62:488-504.

salamander genus Bolitoglossa. I. Function.

HUEY, R. B., AND R. D. STEVENSON.

Evolution 35:84-100.

BENNETT, A. F.

The thermal dependence ofAnimal Behavior 28:752-762.

1980.

lizard behavior.

BUSTARD, H. R.

1967.
intheActivity cycle andAustralian gecko,thermoregulation
Gehyra variegata. Copeia 1967:753-758.

BUSTARD, H. R.

1968.

The ecology of theAustralian gecko Heteronotia binoei in northern

1979.

Integrating thermal physiology and ecology ofectotherms: a discussion of approaches.

American Zoologist 19:357-366.

LICHT, P.

1967.

Thermal adaptation

intheenzymes of lizards in relation to preferred bodytemperature.

Pp. 131-145.

In C. L. Prosser(Ed.), Mechanisms of Temperature Adaptation.
American Association for the Advancement ofScience, Washington, D. C.

New South Wales. Journal of Zoology, London156:483-497.

MARSH, R. L., AND A. F. BENNETT.

1985.

Asiatic Herpetological Research

April 1990

Thermal dependence of isotonic contractile
properties of skeletal muscle and sprint

RUSSELL, A. P.

Vol. 3, p. 59

1975.

A contribution to theperformance of the lizard Dipsosaurus dorsalis.

functional analysis of the foot of the Tokay,
Gekko gecko (Reptilia: Gekkonidae). Journal of

Journal of Comparative Physiology B 155:541-Zoology, London 176:437-476.

551.
1935. The Fauna of British India,
Vol. 2
Sauria.
andAmphibia.
Reptilia
Taylor and Francis, Ltd., London. 440 pp.

SMITH, M. A.

MARSH,R. L., AND A. F.

BENNETT.

1986.

Thermal dependence of contractile properties ofskeletal muscle from the lizard Sceloporus
occidentalis with comments on methods forfitting and comparing force-velocity curves.
Journal of Experimental Biology 126:63-77.

NAGY, K. A., AND M. H. KNIGHT.

1989.

Comparative field energetics of a Kalahari skink(Mabuya striata) and gecko (Pachydactylus
bibroni). Copeia 1989:13-17.

—WERNER, Y. L.

1976. Optimal temperatures forinner-ear performance in gekkonid lizards.
Journal of Experimental Zoology 195:319-352.

WERNER, Y. L., AND A. H. WHITAKER.

1978.

Observations and comments on the bodytemperatures of some New Zealand reptiles.
New Zealand Journal of Zoology 5:375-393.