Alpine viper in changing climate: thermal ecology and prospects of a cold-adapted reptile in the warming Mediterranean

In a rapidly changing thermal environment, reptiles are primarily dependent on in situ adaptation because of their limited ability to disperse and the restricted opportunity to shift their ranges or evolve. However, the rapid pace of climate change may surpass these adaptation capabilities or elevate energy expenditures. Therefore, understanding the variability in thermal traits at both individual and population scales is crucial, offering insights into reptiles' vulnerability to climate change. We studied the thermal ecology of the endangered Greek meadow viper (Vipera graeca), an endemic venomous snake of fragmented alpine-subalpine meadows above 1600 m of the Pindos mountain range in Greece and Albania, to assess its susceptibility to anticipated changes in the alpine thermal environment. We measured preferred body temperature in artificial thermal gradient, field body temperatures and the availability of environmental temperatures in five populations encompassing the entire geographic range of the species. We found that the preferred body temperature (T_p) differed only between the northernmost and the southernmost populations and increased with female body size but did not depend on sex or the gravidity status of females. T_p increased with latitude but was unaffected by the phylogenetic position of the populations. We also found high accuracy of thermoregulation in V. graeca populations and variation in the thermal quality of habitats throughout the range. The overall effectiveness of thermoregulation was high, indicating that V. graeca successfully achieves its target temperatures and exploits the thermal landscape. Current climatic conditions limit the activity period by an estimated 1278 hours per year, which is expected to increase considerably under future climate change. Restricted time available for thermoregulation, foraging and reproduction will represent a serious threat to the fitness of individuals and the persistence of populations in addition to habitat loss due to mining, tourism or skiing and habitat degradation due to overgrazing in the shrinking mountaintop habitats of V. graeca.