Thermal ecology in the Aegean Wall Lizard (Podarcis erhardii): Microclimate may be more important than genetic impoverishment

Background/Question/Methods

The effects of global climate change will be particularly severe for populations that already live close to the upper critical temperature threshold (CT­_max), and for populations that have been reduced and isolated through habitat fragmentation, an important mechanism of human-caused biodiversity loss. Despite the worldwide occurrence of both processes, we have a poor understanding of how habitat fragmentation (and the associated loss in genetic diversity) renders species increasingly susceptible to climate change. Elucidating this relationship is important if we are to conserve global biodiversity. In this study, we examined thermal ecology and physiology across landbridge island populations of the Aegean Wall Lizard (Podarcis erhardii). Landbridge islands are model systems for studies of long-term habitat fragmentation effects. Lizard populations on the Cyclades islands group have been isolated since island formation and show a predictable gradient of genetic diversity according to island size and age. P. erhardii is also considered model ectotherm for studies of thermal ecology. We quantified environmental conditions (T_e), field body temperatures (T_b), preferred temperatures (T_pref), critical thermal maxima and minima (CT_min and CT_max) and evaporative water loss (EWL) across populations that differed in either site environmental characteristics or in lizard population genetic diversity.

Results/Conclusions

Our findings suggest that although genetic diversity does not appear to underlie differences in physiology or variability in thermal ecology, environmental differences between study sites create differences across the lizard populations. Notably, we found differences in water loss rates between populations, which correspond to differences in habitat dryness. We have also found evidence that these differences may be heritable, although plasticity in osmoregulation, which may be very important for lizard survival in the event of future increases in habitat aridity, remains to be determined. These results have important implications for fragmented species in the face of a rapidly changing climate.