Wintertime tales: How the lizard Liolaemus lineomaculatus endures the temperate cold climate of Patagonia, Argentina.

In temperate, polar and montane environments, ectotherms must find ways to endure throughout the coldest months of the year. Lizards search for microsites where temperatures remain warm or alter their biochemical balance to tolerate freezing or avoid it by supercooling. We evaluated the cold hardiness and potential winter refuges of two populations of Liolaemus lineomaculatus, from a temperate site (42°S) and a cold site (50°S). We analysed the role of possible cryoprotectants by comparing a group of cooled-down lizards with a control group of lizards that were not exposed to cold. The populations of this study are not freeze tolerant and the biochemical analysis showed no evidence of metabolites significantly changing concentration after exposure to cold. However, the species remained several hours at their Supercooling Point (SCP), suggesting they can supercool. The analysis of potential winter refuges showed that lizards using these potential refuges would spend almost no time at all at temperatures close to or below their SCP. Furthermore, lizards from the cold site were able to survive below 0°C temperatures with a lower SCP than lizards from the temperate site. Liolaemus lineomaculatus developed physiological mechanisms that can help them survive when temperatures drop sharply, even when lizards are in suitable shelters.

Is thermal sensitivity affected by predation risk? A case study in tadpoles from ephemeral environments.

Changes in environmental temperature may induce variations in thermal tolerance and sensitivity in ectotherm organisms. These variations generate plastic responses that can be analyzed by examining their Thermal Performance Curves (TPCs). Additionally, some performance traits, like locomotion, could be affected by other factors such as biological interactions (e.g., predator-prey interaction). Here, we evaluate if the risk of predation modifies TPCs in Mendoza four-eyed frog (Pleurodema nebulosum, Burmeister, 1861) and Guayapa's four-eyed frog (Pleurodema guayapae, Barrio, 1964), two amphibian species that occur in ephemeral ponds in arid environments. We measured thermal tolerances and maximum swimming velocity at six different temperatures in tadpoles under three situations: control, exposure to predator chemical cues, and exposure to conspecific alarm cues. TPCs were fitted using General Additive Mixed Models. We found that curves of tadpoles at risk of predation differed from those of control mainly in thermal sensitivity parameters. Our work confirms the importance of biotic interactions have in thermal physiology.