Do nocturnal ectotherms thermoregulate? A study of the temperate gecko Christinus marmoratus

Current paradigms relating to reptilian temperature regulation are derived almost entirely from data on diurnally active species, although many reptil e species are nocturnal. We investigated the extent and behavioral mechanis ms of temperature regulation in the nocturnal, rock-dwelling marbled gecko Christinus marmoratus during spring and summer During the daytime, we recor ded body temperatures of lizards sheltering beneath rocks, as well as opera tive temperatures (the equilibrium body temperatures that animals would att ain in given microclimates) beneath randomly chosen rocks available to the lizards. These measurements were compared with reference to the lizard's se t-point (or target) temperature range (T-set), which we determined in a lab oratory thermal gradient. In both seasons, Lizard body temperatures were cl oser to T-set than were randomly sampled operative temperatures, despite me an operative temperatures being 7 degreesC below and 6 degreesC above T-set in spring and summer, respectively. The mean body temperature of geckos wa s 7 degreesC higher, and the accuracy and effectiveness of temperature regu lation were also much higher, during summer than during spring. The more se vere physiological consequences of thermoconformity during summer, as well as a more constraining thermal environment during spring, are advanced as r easons for this seasonal pattern. At least two behavioral mechanisms allow C. marmoratus to achieve a regulated body temperature. First, operative tem peratures within retreat sites selected by geckos were closer to T-set than were operative temperatures beneath available rocks, suggesting retreat-si te selection as a thermoregulatory mechanism. Second, lizard body temperatu res were closer to T-se than were operative temperatures at random position s within selected retreat sites. This observation, together with correlativ e evidence relating lizard body temperature to the maximum and minimum oper ative temperatures beneath selected retreat sites, indicates that positiona l and/or postural adjustments were also employed as thermoregulatory mechan isms. This study suggests that nocturnal lizards are capable of regulating body temperature to an extent that is comparable to that of diurnal lizards . Our findings have implications for understanding the thermal physiology a nd ecology of nocturnal ectotherms.