Extreme tolerance for nocturnal emergence at low body temperatures in a high-latitude lizard: implications for future climate warming.

High-latitude lizards live in environments where ambient air temperature at night is frequently below retreat temperatures, which likely has implications for nocturnal emergence and activity. However, patterns of lizard activity at night under current temperate climates are poorly understood, a situation that limits our understanding of potential effects of climate change. We investigated patterns of nocturnal emergence and activity in the cold-adapted, viviparous gecko (Woodworthia 'Otago/Southland'). We measured operative environmental temperature (T e) available to geckos that emerged at night and simultaneously assessed nighttime emergence activity using time-lapse trail cameras. Also, we assessed field body temperature (T b) of emerged geckos of various life history groups at night using thermography to understand how current weather conditions affect field T b of emerged geckos. Our results show that Te , nocturnal emergence activity and field-active T b increased with nighttime air temperature. Nocturnal emergence was highest in spring and summer but also occurred in autumn and (unexpectedly) in winter. Geckos were active over a broad range of T b down to 1.4°C (a new record low for lizards) and on rock surfaces typically warmer than air temperature or T b. We conclude that this nocturnal, high-latitude lizard from the temperate zone is capable of activity at low winter temperatures, but that current climate limits emergence and activity at least in autumn and winter. Activity levels for cool-temperate reptiles will probably increase initially as climates warm, but the consequences of increased nocturnal activity under climate change will probably depend on how climate change affects predator populations as well as the focal species' biology.

Wind of change: a diurnal skink thermoregulates between cooler set-points and for an increased amount of time in the presence of wind.

Wind has the potential to dramatically alter the thermal landscape of habitats, and consequently, to affect how ectotherms thermoregulate. However, few studies have directly assessed if wind alters thermoregulation by ectotherms. We compared the thermoregulation of a heliothermic New Zealand skink under three treatments: no wind, wind at 2 m s-1 and wind at 6 m s-1. We provided captive skinks with housing in which their preferred body temperature was only achievable inside a wind tunnel. During experimental treatments with wind, airflow was generated through the wind tunnel while the maximum available operative temperature remained consistent among treatments. Skinks were able to move in and out of the wind tunnel. Using thermal bio-loggers, we recorded near-continuous skin temperatures of skinks over 90 min. Contrary to our expectations, more skinks tended to thermoregulate in the two wind treatments compared with the treatments without wind (P=0.062) and of the skinks that did thermoregulate, those in the two wind treatments thermoregulated for significantly longer than those in the treatment without wind. The set-point temperatures that skinks thermoregulated between became significantly cooler as windspeed increased, despite skinks having access to the same operative temperatures. Overall, our study suggests that wind has the potential to significantly change the temperatures selected by lizards, even when comparable temperatures are available; wind is therefore an important environmental parameter to consider when studying the thermal ecology of ectotherms, including in the context of climate change.

Hormone treatment does not reliably induce spermiation or mating in Hamilton’s frog from the archaic leiopelmatid lineage.

Amidst a global amphibian decline, captive breeding has become an important component of many conservation management programs. Some species fail to readily reproduce in captivity, including leiopelmatid frogs, an archaic lineage endemic to New Zealand. Assisted reproductive technologies can improve the reproductive potential and genetic management of captive programs. Herein we describe efforts to induce spermiation and mating in the threatened Hamilton's frog Leiopelma hamiltoni using a gonadotrophin-releasing hormone agonist and human chorionic gonadotrophin. The spermiation response was poor, with few individuals releasing spermatozoa and a low sperm concentration (mean (±s.e.) 27.4±8.5×103 spermatozoa mL-1 ) when spermiation was stimulated. The sperm concentration peaked 12-24h after hormone administration, suggesting this species may be slower to react than other anurans. Spermic urine was present in five males before hormone treatment. The sperm concentration was higher in this group (128.7±54.9×103 spermatozoa mL-1 ) than in the hormone-induced males. All spermatozoa observed exhibited no motility or, at most, a limited swaying movement with no forward progression. In separate hormone induction trials with 60 individuals (two males to one female per trial), no mating was exhibited during the 12h after treatment. Further studies to hormonally stimulate gamete release and mating are needed in leiopelmatids.

A nocturnally foraging gecko of the high-latitude alpine zone: Extreme tolerance of cold nights, with cryptic basking by day.

Lizards that inhabit high-latitude alpine zones are exposed to extreme temperatures and long winters and most are diurnal heliotherms. Yet some poorly known nocturnal species exist in such locations, including several viviparous geckos from New Zealand. We studied the orange-spotted gecko (Mokopirirakau 'Roy's Peak'), a cryptic, nocturnal and viviparous lizard known only from the alpine zone (1150-1800 m a.s.l.) in the South Island (~44°S). Our field study investigated (1) the influence of female reproductive condition and sex on daytime body temperatures, including relationships with microhabitat rock temperatures, (2) the influence of temperature and other weather conditions on gecko emergence by night and day, and (3) the thermal microclimates available year-round to orange-spotted geckos. Building a better understanding of these lizards aids in species conservation efforts, for example in developing monitoring programmes, and provides insights into the evolution of thermal mechanisms in cold environments. Reproductive females maintained higher daytime body temperatures than non-reproductive females and males, suggesting pregnancy-related thermophily. On summer days, all reproductive groups reached similar body temperatures to New Zealand geckos from lower elevations, suggesting similar thermal preferences. Using trail cameras, we obtained evidence of geckos openly basking during the day (previously undocumented for this species) when temperatures of exposed lizard models (=Texp) were 3.2-39.3 °C. We also observed emergence at night at low Texp (-0.8-14.6 °C), when some Tbs were probably 0-6 °C. Diurnal activity increased as Texp rose to peak at ~30 °C before dropping again at higher temperatures, whereas nocturnal activity unexpectedly decreased with increasing Texp. Our study provides evidence of diurnal activity in a 'nocturnal' gecko that may be essential to squamate viviparity at high-latitude, high-elevation sites. It also suggests remarkable capacity for locomotor activity at extremely low Tb.

Thermal heterogeneity of selected retreats in cool-temperate viviparous lizards suggests a potential benefit of future climate warming.

Rocky retreats are limited and geologically constrained resources for rock-dwelling nocturnal lizards. Such lizards should seek retreats that offer thermoregulatory benefits without the risk of overheating during the day, and that protect from predation. For cold-adapted species where air temperature is frequently lower than optimum temperature for performance, factors influencing retreat-site selection and whether future warmer conditions will force superficial rock slabs to be abandoned on hot days remain poorly known. Here, we predicted that retreats selected by a nocturnally foraging, cool-temperate gecko from southern New Zealand would be thermally heterogeneous and that future warmer temperature will force lizards to abandon daytime retreats on hot days. We sampled loose rock slabs (potential retreats) in a tussock-grassland site in all seasons. We measured seasonal rock temperature profiles and field body temperature (Tb) of captured geckos using thermography and quantified the physical characteristics of each potential retreat. We found that both physical characteristics and rock temperatures determine choice of retreats. Field Tb of lizards positively correlated with retreat and air temperatures. Also, retreat temperatures, including those of the substrate below the rock slabs, showed complex heterogeneity enabling lizards to choose microsites within retreats to achieve preferred body temperatures intermittently. Observed seasonal shifts in characteristics of occupied rocks imply that lizards choose retreats to maximise warmth in spring, minimise risk of overheating (remain below voluntary thermal maximum, VTmax) in summer and avoid freezing over winter. Our study demonstrates the importance of microclimatic conditions in influencing retreat-site selection. Climate warming might lead to seasonal changes in use of rock slabs and possibly be beneficial initially, but longer-term implications need to be examined.

Heat and water loss versus shelter: a dilemma in thermoregulatory decision making for a retreat-dwelling nocturnal gecko.

Understanding the interaction between upper voluntary thermal limit (VTmax) and water loss may aid in predicting responses of ectotherms to increasing temperatures within microhabitats. However, the temperature at which climate heating will force cool-climate nocturnal lizards to abandon daytime retreats remains poorly understood. Here, we developed a new laboratory protocol for determining VTmax in the retreat-dwelling, viviparous Woodworthia 'Otago/Southland' gecko, based on escape behaviour (abandonment of heated retreat). We compared the body temperature (Tb) at VTmax, and duration of heating, between two source groups with different thermal histories, and among three reproductive groups. We also examined continuous changes in Tb (via an attached biologger) and total evaporative water loss (EWL) during heating. In the field, we measured Tb and microhabitat thermal profiles to establish whether geckos reach VTmax in nature. We found that VTmax and duration of heating varied between source groups (and thus potentially with prior thermal experience), but not among reproductive groups. Moreover, geckos reached a peak temperature slightly higher than VTmax before abandoning the retreat. Total EWL increased with increasing VTmax and with the duration of heating. In the field, pregnant geckos with attached biologgers reached VTmax temperature, and temperatures of some separately monitored microhabitats exceeded VTmax in hot weather implying that some retreats must be abandoned to avoid overheating. Our results suggest that cool-climate nocturnal lizards that inhabit daytime retreats may abandon retreats more frequently if climate warming persists, implying a trade-off between retention of originally occupied shelter and ongoing water loss due to overheating.

Pregnancy reduces critical thermal maximum, but not voluntary thermal maximum, in a viviparous skink.

Upper thermal limits are commonly measured in ectotherms; however, the effects of life-history stages, and in particular pregnancy in viviparous species, are rarely considered. In this study, we examined whether two measures of upper thermal tolerance varied among life-history stages in a viviparous New Zealand skink (Oligosoma maccanni). First, we measured voluntary thermal maxima (VTmax) and critical thermal maxima (CTmax) for four groups: late-pregnant females, newly postpartum females, males, and neonates. Second, we examined whether exposing skinks to their CTmax in late pregnancy affected success of pregnancies or size and performance of offspring. We found that both VTmax and CTmax differed among the four groups, although only CTmax differed enough to detect specific pairwise differences. Pregnant skinks and neonates had a significantly lower CTmax than postpartum skinks, and pregnant skinks also had a lower CTmax than males. Effect sizes were very large between groups, where CTmax differed significantly, and borderline large for VTmax between male and neonate skinks and between postpartum and pregnant females. Pregnancy success, and the size and sprint speed of resulting neonates were not affected by thermal-tolerance tests on late-pregnant females. The reduction in CTmax we observed in pregnant skinks could indicate that at high temperatures, pregnant skinks do not have the same ability to keep up with oxygen demands as non-pregnant skinks-possibly reflecting reduced ventilation capacity simultaneous with high oxygen demands from embryos as well as maternal tissues. These findings are consistent with some studies, showing that reduced oxygen availability can reduce thermal tolerance in reptiles.

Accuracy of an inexpensive, compact infrared thermometer for measuring skin surface temperature of small lizards.

Studies of thermal sensitivity in ectotherms require accurate measurements of body temperature using a reliable device, including in field situations. In this study, we tested the accuracy of a compact and inexpensive mini-infrared thermometer (mini-IRT, 22.3 g) at close distance (within 5 mm) for measuring skin surface temperature of small lizards or their models (painted copper bars). First, we used copper bars to assess the effect of model width on the accuracy of the measurement. We placed the heated models on a cool background, and then surface temperatures were measured with a mini-IRT for comparison with a thermogram from an infrared camera (IRC). We also assessed the accuracy of the mini-IRT for measuring skin temperature for two species of small lizards in the laboratory and in the field, in comparison with the skin surface temperature measured with the IRC and with cloacal temperature measured with a thermocouple thermometer. Our results with inanimate models show that the accuracy of the mini-IRT at a distance within 5 mm is biologically acceptable (within ±1.0 °C of the mean value obtained using a more expensive, calibrated device) when the width is ≥ 7 mm. For live lizards, we observed highly significant relationships between skin surface temperature measured with the mini-IRT and temperatures measured with the two other devices. The mean discrepancies between the mini-IRT and other devices were acceptably small for geckos but larger for the smaller and more slender skinks. Taken together, our results suggest that skin temperature measured with the mini-IRT at a close distance is acceptable for field studies on lizards with an abdominal width ≥7 mm, serving as an inexpensive proxy for core body temperature in situations where portability and affordability of equipment and minimal animal handling are paramount. Nonetheless, calibration of mini-IRTs before use is strongly recommended.

Effects of Warm Temperatures on Metabolic Rate and Evaporative Water Loss in Tuatara, a Cool-Climate Rhynchocephalian Survivor.

The thermal sensitivity of physiological rates is a key characteristic of organisms. For tuatara (Sphenodon punctatus), the last surviving member of the reptilian order Rhynchocephalia and an unusually cold-tolerant reptile, we aimed to clarify responses in indices of metabolic rate (oxygen consumption [[Formula: see text]] and carbon dioxide production [[Formula: see text]]) as well as rates of total evaporative water loss (TEWL) to temperatures at the warmer end of the known tolerated range; currently, patterns for metabolic rate are unclear above 25°C, and TEWL has not been measured above 25°C. We first established that metabolic rate was lowest during the photophase and then measured [Formula: see text], [Formula: see text], and TEWL at six temperatures (12°, 20°, 24°, 27°, 29°, and 30°C) during this phase. Consistent with our predictions, we found that mass-adjusted [Formula: see text], [Formula: see text], and TEWL increased at least 3.5-fold between 12° and 30°C (at 30°C, rates were 2.509 mL g-1 h-1, 2.001 mL g-1 h-1, and 1.829 mg-1 g-1 h-1, respectively). Temperature coefficients (Q10 values) for mass-adjusted [Formula: see text] and TEWL showed thermal dependence between 12° and 29°C but with a reduced increase or thermal independence between 29° and 30°C. There was no observed effect of egg incubation temperature (inferred sex) on the subsequent metabolic rates of juveniles. The respiratory exchange ratio implied a switch from carbohydrate metabolism at <22°C to lipid metabolism at >27°C. The rigorous measurement of [Formula: see text] and TEWL provides a basis for future studies to predict the thermal sensitivity of tuatara to human-mediated climate change.

Further miniaturisation of the Thermochron iButton to create a thermal bio-logger weighing 0.3 g.

Thermochron iButtons are commonly used by thermal biologists to continuously measure body temperature from animals. However, if unmodified, these devices are of a size that limits their use with very small animals. To allow iButtons to be used to study smaller species, methods to miniaturise them by 61% have been previously described. We present a method to reduce iButton mass by a further 71%. The modified devices have a shorter battery life, but the minimum size of vertebrates able to carry the devices is reduced from 28.9 g to 6.6 g, if the arbitrary, yet widely cited, maximum of 5% body mass for attached devices is adhered to. We demonstrate the application of our method by recording surface temperatures of captive and wild skinks and show that captive cockroaches weighing 0.8 g are also able to carry the device. We believe this to be the first time that temperature data have been recorded from an insect in this way.

Sexual Dimorphism of Digit-Length Ratio in a Viviparous Lizard: Influence of Age, but not Preservation State or Sex of Interuterine Twin.

The existence of sex differences in digit-length ratio (especially between the second and fourth digits, 2D:4D) is well established for humans from fetal life onwards, and has been linked with later performance. In rodents, the ratio is affected prenatally by exposure to androgens and estrogens, with some research suggesting an influence from sex of the neighbouring intrauterine fetus. However, the ubiquity and ontogenetic development of sexual dimorphism in digit ratios is not well established among wild amniotes. We report the first digit ratios for a gekkotan lizard, representing a speciose lineage in which viviparity has evolved independently from mammals and other reptiles. For the gecko Woodworthia "Otago/Southland", in which up to two embryos develop in separate uteri, we found: (1) significant sexual dimorphism in adults in 2D:3D of the right hindlimb only (larger in males), but not in 2D:4D for any limb; (2) no dimorphism in ratios for young juveniles, with no influence of sex of the interuterine twin, and no relationship with sprint speed; (3) in preserved tissues of the same juveniles, no sexual dimorphism in ratios, but a change in relative lengths of some digits with preservation. The ontogenetic pattern might be explained by altered sex-steroid exposure at the transition to adulthood rather than during prenatal development. Our results support a phylogenetic hypothesis that sauropsids (birds and reptiles) differ from mammals in the direction of sex difference, if present. Experiments are needed to establish the roles of androgens and estrogens in establishing these sex differences in lizards. Anat Rec, 301:1169-1178, 2018. © 2018 Wiley Periodicals, Inc.

Glucocorticoids in tuatara (Sphenodon punctatus): Some influential factors, and applications in conservation management.

Glucocorticoid (GC) hormones promote basic life processes, regulate life-history transitions, and help individuals cope with challenges and stressors, thereby playing an important fitness role. Here, we review recent evidence for several factors that influence plasma concentrations of corticosterone (CORT), the main GC in tuatara (Sphenodon punctatus), and discuss the application of CORT as a physiological tool to monitor conservation efforts. Observational studies show an association between CORT concentrations and seasonal reproductive activity, ambient temperature, and ecological habitat parameters (including presence of rats/seabird abundance, sex-ratio, and genetic diversity), and experimental studies show a positive influence of acute temperature increase on the CORT response. Recently, CORT physiology has been applied as a monitoring tool in tuatara translocation programmes. No signs of chronic stress in CORT profiles were observed during standard short- and long-term translocation and rat eradication procedures, giving confidence that current conservation efforts are supportive in population recovery. These results provide a foundation for comparative understanding of stress physiology in reptiles, and will be critical for managing future population viability of tuatara in a changing environment.

Maternal basking regime has complex implications for birthdate and offspring phenotype in a nocturnally foraging, viviparous gecko.

Maternal basking regime can affect gestation length in viviparous squamates, but effects on offspring phenotype in species with extended pregnancies and ability to delay the birth season are unclear. We investigated the effects of three maternal basking regimes on maternal thermoregulation, gestation length, pregnancy outcome and offspring phenotype in the gecko Woodworthia 'Otago/Southland'. This long-lived (30+ years), nocturnal forager has field pregnancies lasting up to 14 months, with fully developed offspring maintained in utero over winter. Within regimes, we also compared outcomes for spontaneous (early) deliveries with those from induced (late) deliveries to test the 'adaptive prolongation of pregnancy' hypothesis. Although a cool regime significantly extended gestation, the effect was reduced by increased maternal basking, and embryonic development under the cool regime was just as successful. Offspring from spontaneous births (but not induced births) were smaller and grew more slowly when from the cool regime. However, induced offspring did not differ in consistent ways from those delivered spontaneously and offspring from all groups had high viability, similar use of warm retreat sites and similar sprint speeds. Thus, consistent evidence for adaptive prolongation of pregnancy was lacking. Unusually for squamates, pregnant females can begin vitellogenesis before giving birth, and a profound drop in maternal body temperature near the end of pregnancy (∼6.3°C, confirmed under the warm regime) may assist survival of embryos in utero Female lizards that maintain fully developed embryos in utero have the potential to make complex trade-offs among birthdate, offspring phenotype and future reproduction.

Adherence to Bergmann's rule by lizards may depend on thermoregulatory mode: support from a nocturnal gecko.

Bergmann's rule predicts an increase in body size with decreasing environmental temperature; however, the converse pattern has been found in the majority of lizards studied to date. For these ectotherms, small body size may provide thermal benefits (rapid heat uptake when basking), which would be highly advantageous in cold environments. Yet such an advantage may not exist in nocturnal lizards (which do not avidly bask), in which Bergmann's rule has not been closely studied. We have examined whether the body size of a primarily nocturnal gecko, Woodworthia "Otago/Southland" changed with elevation and operative temperature (determined using physical copper models). In a laboratory study, we investigated whether thermoregulatory mode (heliothermy or thigmothermy) alters the effect of body size on heating and cooling rates. This gecko followed Bergmann's rule, thereby showing the opposite of the dominant pattern in diurnal lizards. Size at maturity, maximum size of adults and size at birth were larger at higher elevations and at lower operative temperatures. Using physical models, we found that large body size can confer thermal benefits for nocturnal lizards that remain within diurnal retreats. Bergmann's rule should not be dismissed for all lizards. Our results clearly support Bergmann's rule for at least one thigmothermic species, for which large body size may provide thermal benefits. Future studies on Bergmann's rule in lizards should consider thermoregulatory mode. We advocate that this ecogeographic rule be examined in relation to operative temperature measured at field sites. Finally, we predict that climate warming may weaken the relationship between body size and elevation in this gecko.

Moving house: long-term dynamics of corticosterone secretion are unaltered in translocated populations of a rare reptile (the tuatara, Sphenodon punctatus).

Translocations are an important conservation tool used to restore at-risk species to their historical range. Unavoidable procedures during translocations, such as habitat disturbance, capture, handling, processing, captivity, transport and release to a novel environment, have the potential to be stressful for most species. In this study, we examined acute and chronic stress (through the measurement of the glucocorticoid corticosterone) in a rare reptile (the tuatara, Sphenodon punctatus). We found that: (i) the acute corticosterone response remains elevated during the initial translocation process but is not amplified by cumulative stressors; and (ii) the long-term dynamics of corticosterone secretion are similar in translocated and source populations. Taken together, our results show that translocated tuatara are generally resistant to cumulative acute stressors and show no hormonal sign of chronic stress. Translocation efforts in tuatara afford the potential to reduce extinction risk and restore natural ecosystems.

Modulation of corticosterone secretion in tuatara (Sphenodon punctatus): Evidence of a dampened stress response in gravid females.

Baseline and stress response glucocorticoid (GC) secretion can be modulated by individuals to support activities and physiological functions connected with reproduction (migration, mating, oviposition and/or parturition, care of young). Corticosterone (CORT) is the primary GC in reptiles and, in accordance with other vertebrates, an adrenocortical stress response is observed. Modulation of CORT secretion occurs in several reptile species, such that elevated baseline CORT concentration and/or a dampened CORT response are common during reproductive life-history events. We investigated CORT secretion after 24 h capture-restraint in the oviparous tuatara (Sphenodon punctatus), the last living rhynchocephalian, and tested whether gravid females have a dampened CORT response compared with non-gravid females. We also included males as a comparison. We confirmed that gravid females have significantly higher baseline plasma CORT concentrations than non-gravid females, suggesting increased CORT secretion during nesting. Furthermore, we found that gravid females exhibit a dampened CORT response compared to non-gravid females and males. Our results demonstrate that female reproductive condition influences CORT secretion in tuatara, and suggest that gravid females modulate CORT secretion during nesting to maintain homeostasis, effectively increasing chances of reproductive success and promoting overall fitness.

Securing the demographic and genetic future of tuatara through assisted colonization.

Climate change poses a particular threat to species with fragmented distributions and little or no capacity to migrate. Assisted colonization, moving species into regions where they have not previously occurred, aims to establish populations where they are expected to survive as climatic envelopes shift. However, adaptation to the source environment may affect whether species successfully establish in new regions. Assisted colonization has spurred debate among conservation biologists and ecologists over whether the potential benefits to the threatened species outweigh the potential disruption to recipient communities. In our opinion, the debate has been distracted by controversial examples, rather than cases where assisted colonization may be a viable strategy. We present a strategic plan for the assisted migration of tuatara (Sphenodon punctatus), an endemic New Zealand reptile. The plan includes use of extant populations as reference points for comparisons with assisted-colonization populations with respect to demography, phenotypic plasticity, and phenology; optimization of genetic variation; research to fill knowledge gaps; consideration of host and recipient communities; and inclusion of stakeholders in the planning stage. When strategically planned and monitored, assisted colonization could meet conservation and research goals and ultimately result in the establishment of long-term sustainable populations capable of persisting during rapid changes in climate.

Effects of early postnatal environment on phenotype and survival of a lizard.

Nutritional and thermal regimes experienced early in life can strongly influence offspring quality and ultimately adult life histories, especially in ectotherms. However, the importance of the interaction between diet and temperature during postnatal development and the effect on offspring quality are unknown. We compared offspring quality (size, shape, speed, behavior, and survival) of juvenile McCann's skinks (Oligosoma maccanni) housed outdoors under variable thermal conditions (under shelter, but exposed to daily and seasonal variations in light and temperature) with those housed indoors under more stable thermal conditions (controlled temperatures providing 30-40% more basking opportunity) and with a control group (open field conditions). For those caged in captivity (indoors and outdoors), we also compared outcomes between those fed a restricted diet and those fed ad libitum. By comparing individuals raised under different environmental regimes, we aimed to determine whether direct effects of temperature or indirect effects of food supply are more important for offspring quality. Individuals provided with food ad libitum grew faster, and attained larger sizes than those raised on a restricted diet or in the field. Activity rates were higher in individuals exposed to stable rather than variable thermal conditions. Survival post release in the field was highest for larger neonates, and lowest in individuals raised under stable thermal conditions and a restricted diet. We found little evidence for effects of an interaction between feeding and thermal regimes on most factors measured. However, the conditions experienced by young animals (especially diet) do influence important traits for population persistence, such as survival, and may influence key reproductive parameters (e.g., age and size at maturity), which could have implications for conservation management. Further research, including the ultimate influence of early environmental conditions on fecundity and life expectancy, is urgently needed.

Thermal dependence of locomotor performance in two cool-temperate lizards.

Temperate-zone ectotherms experience varying or very low ambient temperatures and may have difficulty in attaining preferred body temperatures. Thus, adaptations to reduce the thermal dependence of physiological processes may be present. We measured the optimal temperature range for sprint speed and compared it with the selected body temperatures (T (sel)) of two sympatric, cool-temperate lizards: the diurnal skink Oligosoma maccanni and the primarily nocturnal gecko Woodworthia (previously Hoplodactylus) "Otago/Southland". We also investigated whether time-of-day influenced sprint speed. Contrary to results for other reptiles, we found that time-of-day did not influence speed in either species. For each species, the optimal temperature range for sprinting and T (sel) overlapped, supporting the 'thermal coadaptation' hypothesis. However, the optimal range of temperatures for speed is not always attainable during activity by either species, which have limited opportunities to attain T (sel) in the field. The thermal sensitivity of sprint speed in these two species does not appear to have evolved to fully match their current thermal environment. More data on cold-adapted species are needed to fully understand physiological adaptation in ectotherms.