Thermoregulation strategies and microhabitat structure as determinants of susceptibility to heat waves in two sympatric Mediterranean lizards.

Abstract

Heat waves are becoming common climatic phenomena in the western Mediterranean. Ectotherms are sensitive to rapid climatic shifts owing to the intrinsic dependence of their physiology on environmental temperature and humidity. Assessing microclimatic trends in behaviour, physiology, immunology, and susceptibility to infestations in lizard species with dissimilar thermal preferences can contribute to understanding differences in susceptibility to heat waves of these ectotherms. We investigated Acanthodactylus erythrurus and Psammodromus algirus. Two active thermoregulator lizards, with the former species sustaining a warmer body temperature. We investigated their response at multiple levels in two habitat plots differing in microclimatic environments and predicted that the more thermophilic species would better tolerate heat waves. We sampled 420 lizards during most of their annual activity period in two consecutive years with heat waves. The hydric environment appeared to be a major determinant explaining behavioural, cellular, and endocrinological responses in both lizard species. Maximum relative humidity (rain events) was associated in both species with a reduction in thermoregulatory effort and total white blood cells (an important component of the immune system). Faecal glucocorticoid metabolites concentration was lower in both species upon environments of high relative humidity stochasticity. The high temperature associated with heat waves also explained some of the responses. The rise of nocturnal temperatures increased mite loads in both species and was associated with a significant decrease in total white cells only in P. algirus, the less thermophilic species. Moreover, the increase of maximum diurnal temperatures and thermal stochasticity explained a significant increase of ectoparasitic mites only for P. algirus, a species with an overall higher mite prevalence and load. The results suggested that heat waves can incur higher costs on less thermophilic lizard species in terms of a higher exposure to ectoparasites and a reduction in circulating white blood cells.