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 reptile species are nocturnal. We investigated the extent and behavioral mechanisms of temperature regulation in the nocturnal, rock-dwelling marbled gecko Christinus marmoratus during spring and summer During the daytime, we recorded body temperatures of lizards sheltering beneath rocks, as well as operative temperatures (the equilibrium body temperatures that animals would attain in given microclimates) beneath randomly chosen rocks available to the lizards. These measurements were compared with reference to the lizard's set-point (or target) temperature range (T-set), which we determined in a laboratory thermal gradient. In both seasons, Lizard body temperatures were closer to T-set than were randomly sampled operative temperatures, despite mean operative temperatures being 7 degreesC below and 6 degreesC above T-set in spring and summer, respectively. The mean body temperature of geckos was 7 degreesC higher, and the accuracy and effectiveness of temperature regulation were also much higher, during summer than during spring. The more severe physiological consequences of thermoconformity during summer, as well as a more constraining thermal environment during spring, are advanced as reasons for this seasonal pattern. At least two behavioral mechanisms allow C. marmoratus to achieve a regulated body temperature. First, operative temperatures within retreat sites selected by geckos were closer to T-set than were operative temperatures beneath available rocks, suggesting retreat-site selection as a thermoregulatory mechanism. Second, lizard body temperatures were closer to T-se than were operative temperatures at random positions within selected retreat sites. This observation, together with correlative evidence relating lizard body temperature to the maximum and minimum operative temperatures beneath selected retreat sites, indicates that positional and/or postural adjustments were also employed as thermoregulatory mechanisms. 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 and ecology of nocturnal ectotherms.