Living in the mountains: thermal ecology and freezing tolerance of the lizard Abronia taeniata (Squamata: Anguidae)

Description

The impact of daily and seasonal variation in environmental temperature on lizards is important, since their physiological processes are body temperature dependent. Lizards that occupy mountainous areas must have been favoured to colonize such habitats through selection on thermal biology traits to thermoregulate effectively; these lizards can maintain their activity near their minimum critical temperature and even have antifreeze mechanisms. Tolerance of freezing is related to the biosynthesis of cryoprotective molecules, such as glucose, whose concentration may increase after freezing. The aims of the present work were: (1) study the thermoregulation of the viviparous lizard Abronia taeniata, and (2) determine its survival and/or tolerance to freezing. This species occurs in pine forests, pine-oak forests, and mountain mesophilic forests in areas that reach freezing temperatures. We recorded air, substrate, and body temperatures at capture time of the lizards. In the laboratory, we determined the species' preferred temperature, crystallization point of the individuals and their blood glucose level before and after freezing. In addition, we recorded the operative temperatures with null models in the study area. We found out that A. taeniata sustains activity in a wide range of temperatures, is a moderate thermoregulator during autumn and winter and actively avoiding thermally favourable microhabitats in spring. In A. taeniata, the body temperatures are tightly linked to air and substrate temperatures. Seasonality had an effect over body temperature, preferred temperatures and thermoregulatory effectiveness indices. When exposed to temperatures below zero, A. taeniata showed an increase in blood glucose levels, which aided them in surviving freezing. Taken together, our results suggest that A. taeniata may sustain activity at low environmental temperatures, due to an effective behavioural thermoregulation, and in case temperatures of its habitat go below zero, is also capable of tolerate freezing.

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