Patterns of seasonal plasticity in evaporative water loss and preferred temperature in three geckos of the wet-dry tropics.

Abstract

Seasonal physiological plasticity (acclimatisation) facilitates homeostasis in changing environments and has been studied extensively with respect to thermal biology and metabolism. Less is known about seasonal changes in evaporative water loss (EWL) in response to changing water availability and humidity. The wet-dry tropics of northern Australia experience moderate seasonal temperature changes, but substantial changes in rainfall and humidity. We studied three gecko species (Amalosia rhombifer, Heteronotia binoei and Hemidactylus frenatus) in the wet and dry seasons with respect to their EWL, preferred body temperatures (T_pref), and their choice between a dry and humid refuge at and below T_pref. EWL was significantly lower in the dry season (66% of wet season values). T_pref for two of the species did not change seasonally, but A. rhombifer selected lower T_pref during the warmer wet season. Given a choice of refugia, the humid refuge at low temperatures was never preferred over the warm microhabitat. When both refugia were at the preferred temperature, only A. rhombifer showed a preference for the humid microhabitat. These results demonstrate that although thermoregulation is prioritised in the short term, hydroregulation (physiological plasticity in EWL) is adjusted in the longer term, with shifts occurring on a seasonal scale. However, it is possible that shifts in EWL may occur in response to prevailing weather conditions on a shorter timescale. Before broad generalisations can be drawn about the phenomenon of EWL plasticity, measurements need to be taken from more species in different climatic regions at ecologically relevant timescales.