Thermoregulation and thermal performance of crested geckos (Correlophus ciliatus) suggest an extended optimality hypothesis for the evolution of thermoregulatory set‐points

Abstract

Crested geckos (Correlophus ciliatus, formerly Rhacodactylus ciliatus) were rediscovered in New Caledonia 25 years ago and despite being common in the pet trade, there is no published information on their physiology. We measured thermoregulation (preferred body temperature, thermal set‐point range, and voluntary limits) and performance (thermal performance curves [TPC] for 25 cm sprint speed and 1 m running speed) of adult and juvenile crested geckos in the laboratory to describe their thermal tolerances, differences among life stages, correlations between behavior and performance, and correlations with natural temperatures. Despite lacking special lighting or heating requirements in captivity, crested geckos displayed typical thermal biology for a lizard with no difference among life stages. They thermoregulated to a narrow set‐point range (TSET, 24–28°C), that broadly overlaps natural air temperatures in New Caledonia, during activity. Somewhat surprisingly, the optimal temperature for performance (TOPT, 32°C) was substantially above preferred body temperatures and approximated the average maximum temperature voluntarily experienced (VTMAX, 33°C). Preferred body temperatures, by contrast, corresponded to the lower threshold temperature (Td) where the TPC deviated from exponential, which we suggest is the temperature where performance is optimized after accounting for the costs of metabolic demand and overheating risk. Our results demonstrate that despite their lack of specific requirements when housed in human dwellings, crested geckos actively thermoregulate to temperatures that facilitate performance, and have thermal biology typical of other nocturnal or shade‐dwelling species. Additionally, crested geckos appear at little risk of direct climate change‐induced decline because increased temperatures should allow increased activity.

Thermal adaptation revisited: How conserved are thermal traits of reptiles and amphibians?

“…Thermal preferences in two species of racerunner lizards (genus Eremias ) were higher in adults than in juveniles (Tang et al, 2013; Xu & Ji, 2006). In contrast, no difference in T pref was observed between adults and juveniles of the six‐lined racerunner ( Aspidoscelis sexlineatus ; Paulissen, 1988) and no differences in thermoregulatory behaviors or thermal performance curves for sprint speed were found between juvenile and adult crested geckos ( Correlophus ciliates ; Aparicio Ramirez et al, 2020).…”

Introduction to the special issue–Beyond CTMAXand CTMIN: Advances in studying the thermal limits of reptiles and amphibians

“…That traits interact to shape evolutionary patterns is exemplified in the “extended optimality hypothesis” for the evolution of thermal set‐points proposed by Aparicio Ramirez et al (2020). In this study, the optimum temperature for sprint performance in crested geckos ( C. ciliatus ) far exceeded PBT and instead corresponded to the maximum temperature tolerated.…”

“…Perhaps unsurprisingly, free‐living stages that primarily differ only in size can have similar thermal biology. For example, Aparicio Ramirez et al (2020) found no difference in PBTs or thermal performance curves between juvenile and adult crested geckos ( Correlophus ciliatus ) despite individuals differing in size by an order of magnitude. Similarly, Ginal et al (2020) demonstrate similar thermal performance curves for running/swimming between aquatic adult and tadpole African clawed frogs ( Xenopus laevis ) despite differences in both size and morphology.…”

Oxygen environment and metabolic oxygen demand predictably interact to affect thermal behavior in a lizard, Sceloporus occidentalis

“…CT MAX , and the voluntary maximum temperature (VT MAX ; max T b ) correlates closely with CT MAX resulting from selection to maintain high organismal performance (Aparicio Ramirez et al, 2020;Camacho et al, 2018;Martin & Huey, 2008). When exposed to a novel oxygen environment, the body temperatures selected by an animal should indicate their perception of how the oxygen environment affects thermal performance.…”

“…Thermoregulatory behavior provides insights into how organisms perceive the thermal environment and can be used to assess the impact of varied environmental conditions on thermal tolerance. Lizards typically prefer body temperatures (T b ) a few degrees below CT MAX , and the voluntary maximum temperature (VT MAX ; max T b ) correlates closely with CT MAX resulting from selection to maintain high organismal performance (Aparicio Ramirez et al, 2020; Camacho et al, 2018; Martin & Huey, 2008). When exposed to a novel oxygen environment, the body temperatures selected by an animal should indicate their perception of how the oxygen environment affects thermal performance.…”