Ecological implications of behavior and physiology in high-elevation neotropical anurans

The purpose of this study is to understand the behavioral and physiological mechanisms by which some anuran species, most likely derived from lowland tropical forms, have been able to colonize the harsh and cold environments of the high Andean elevations. To answer this question I used a comparative approach in which pairs of congener species, one high-elevation and one low-elevation, were contrasted in different aspects of the thermal biology. The genera studied were Atelopus, Bufonidae; Colostethus, Dendrobatidae; Eleutherodactylus, Leptodactylidae; and Hyla, Hylidae. I found that the activity temperatures of terrestrial and nocturnal frogs were lower than those of other ecotypes, and their thermal ecology was more dramatically affected by an increase in altitude. Body temperatures of active high-elevation frogs were mainly determined by the interaction between microhabitat selection and time of the day. High-elevation Colostethus and Eleutherodactylus used temporal shifts in the patterns of activity to reduce the exposure to low temperatures during activity. In high-elevation amphibians body temperature constrained only energetically demanding activities, such as calling at high rates, but had little effects on short bursts of activity or activities that are performed at low rates. All high-elevation species exhibited a distinctive capacity for locomotion through a broad temperature range, whereas lowland forms showed little ability to move at low temperatures. The activity metabolic rates and the metabolic scopes at low temperatures were always higher in the upland frogs, but the differences disappeared at warmer temperatures. None of the species exhibited a capacity for metabolic acclimation. Success at high tropical elevations appears to involve complex interactions among metabolic physiology, behavior, and habitat selection, that vary from species to species. However, the similarity of metabolic traits among unrelated genera, suggests convergent evolution favoring an increased capacity for activity in high Andean frogs.