Gehyra Geckos Prioritize Warm Over Humid Environments

Abstract

Maintaining stable hydric and thermal states are dual challenges for reptiles that inhabit terrestrial environments with variable conditions across time and space. Under some conditions, reptiles face a conundrum where both physiological parameters cannot be simultaneously maintained at preferred levels by behavioral or physiological means. Prioritization of behavioral regulation of hydric or thermal state, and at which point this prioritization changes, was tested for nine species of congeneric tropical geckos by assessing their use of microhabitats with distinct thermal and hydric conditions in a controlled environment. Gehyra geckos were presented with two crevices of contrasting humidity levels, and time spent in either crevice was recorded across three ambient temperature treatments of 32°C, 27°C, and 22°C. Temperatures in the humid crevice matched ambient air temperature, whereas temperature in the dry crevice was maintained at 32°C. In these trials, all species showed greater use of the dry (and warm) crevice in the 27°C and 22°C treatments, while there was no strong preference for the humid or dry crevice in the 32°C treatment. Thus, Gehyra geckos prioritized thermoregulation and maintained thermal state through behavioral responses, and humid microhabitats were not selected even when it did not compromise the animal's thermal state. Although selection for preferred thermal conditions was prioritized in the short term, this does not preclude the possibility that hydric state can be regulated on a seasonal time scale.

Keywords: Gehyra; geckos; hydroregulation; reptile; thermoregulation.

Figure 1

Set‐up of microhabitat selection experiments across three temperature treatments (nominally, 32°C, 27°C, and 22°C). The humid crevices used a water‐soaked terracotta tile coated with a layer of acetate and rubber to prevent drying, resulting in a mean relative humidity ±1 standard deviation of 98.8 ± 2.02%. The measured temperatures in the humid crevices were: 32.0 ± 0.65°C, 27.1 ± 0.55°C, and 21.4 ± 0.76°C. The dry crevice had dehydrated air pumped into the cavity at a low rate (resulting in a mean relative humidity of 35.0 ± 8.77%), and a heat mat was used to maintain a temperature of 32.4 ± 0.87°C.

Figure 2

Proportion of experiment time Gehyra species spent in crevices across temperature treatments (humid crevices were at treatment temperature, whereas the dry crevices were maintained at 32°C). Points are raw values (white = day, black = night), bars are predicted proportional time with confidence intervals. (a) Gehyra australis, (b) G. gemina, (c) G. koira, (d) G. lapistola, (e) G. minuta, (f) G. moritzi, (g) G. nana, (h) G. paranana, (i) G. purpurascens.

Figure 3

Proportion of crevice time Gehyra species spent in the humid crevice (vs. the dry crevice) across temperature treatments (humid crevices were at treatment temperature, whereas the dry crevices were maintained at 32°C). Points are raw values (white = day, black = night), bars are predicted proportional time with confidence intervals. (a) Gehyra australis, (b) G. gemina, (c) G. koira, (d) G. lapistola, (e) G. minuta, (f) G. moritzi (g) G. nana, (h) G. paranana, (i) G. purpurascens.