An evaluation of daily, seasonal and population-level variation in the thermal preference of a group-living lizard, Ouroborus cataphractus (Sauria: Cordylidae)
2014
Truter, Johannes Christoff | Truter, Johannes Christoff | van Wyk, Johannes Hendrik | Truter, Johannes Christoff | van Wyk, Johannes Hendrik | Mouton, Pieter le Fras Nortier
Ectotherms are known to function optimally within a specific range of body temperatures, bordered by two set-point values (i.e. preferred temperature range; Tp). Preferred body temperature stands central in understanding behavioural thermoregulation in a thermally dynamic temperate environment. In this study we determined Tp for the group-living cordylid lizard, Ouroborus cataphractus, during the respective annual peak periods in food availability and scarcity. Body temperatures were recorded in ecologically realistic photo-thermal gradients using body-mounted, modified iButtons. In addition to studying seasonal and spatial variation in Tp we also assessed daily variation and among-day repeatability of Tp estimates. The mean Tp among populations and across seasons was 29.8 ± 2.3°C (range: 26.8-32.6°C) and represents the lowest mean Tp and range recorded for any cordylid lizard to date. Literature reports on the seasonal activity patterns and micro-spatial variation in thermal habitat quality of O. cataphractus suggest that the low Tp minimizes thermoregulatory costs during summer, autumn, late winter and spring. The low Tp is therefore expected to relax energy budgets and function as part of the adaptive strategy of the species to survive seasonal food stress in a semi-arid environment. The among-day repeatability of mean Tp varied among populations and across seasons despite exposure conditions that were kept constant. The results of the present study suggest that Tp estimates based on short term laboratory trials may be inaccurate due to potential high among-day individual variation and low repeatability in thermal preference.
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