Freezing Risk in Tropical High-Elevation Anurans: An Assessment Based on the Andean Frog Pristimantis nervicus (Strobomantidae)

Diverse anuran lineages have colonized a tropical high-elevation Neotropical ecosystem called páramo, which is located above the tree-line and below the snow and characterized by low and variable temperatures on a daily basis. Amphibian species apparently become exposed to the freezing temperatures in the páramo, particularly at elevations above 3500 m.a.s.l. (meters above sea level). If the body temperatures of these amphibians indeed reach freezing levels during the night, amphibian survival in the páramo would require permanent (as opposed to seasonal) physiological tolerance to freezing. However, such physiological studies would be justified only with evidence that microhabitat temperatures reach subzero temperatures for periods long enough to induce partial tissue freezing. Therefore, the purpose of this work is to investigate whether páramo amphibians are exposed to freezing. We focused on Pristimantis nervicus, an amphibian that is active at night in exposed microhabitats, making it potentially vulnerable to all aspects of the páramo climate. We recorded body temperatures and used plaster models to evaluate operational temperatures along diverse transects located at 3500 m.a.s.l. in the Eastern Andes of Central Colombia. We found that, regardless of the substrate where this species is present, individuals are at risk of freezing. The body temperatures recorded were as low as -1.05°C and the operational temperatures estimated values slightly lower than -5.0°C These data suggest the existence of cryoprotection mechanisms in this, and possibly other páramo anuran species.