NAVAS, C.A.; Universidade de S�o Paulo: Physiology of high-elevation amphibians: relationships with behavior and ecological challenge

A well supported macro-ecological trend is the reduction of biological diversity along altitudinal gradients. Although tropical amphibians conform to this pattern, this taxon exhibits various species, genera and families that are significantly represented at elevations higher than 3000 m. The multiple and independent colonization of high tropical elevations by amphibians poses diverse ecophysiological questions, including how they deal with low and variable temperatures and decreased oxygen availability. The data available suggest that the invasion of extreme altitudes by amphibians has occurred within the context of conserved general patterns of activity and limited capacity for behavioral thermoregulation. First, high elevation amphibians tend to be active at times of day that are typical for their genera, independently of whether such patterns reduce or increase the ecophysiological challenge experienced by individuals. Second, both amphibian skin morphophysiology and habitat traits constrain the effectiveness of thermoregulation at high altitudes. For example, basking high-elevation tree-frogs exhibit only modest increases in body temperature. The colonization of high-elevations by amphibians has basis on a very labile thermal physiology, leading to improved performance at low and variable temperatures. Oxygen seems not to constrain high-elevation tropical amphibians, as lungless salamanders are particularly specieose at high elevations, and improved oxygen uptake has been reported only for anurans at very extreme altitudes. Evidence from amphibians in other ecological settings, for example semi-arid regions, support the tendency of this taxa to extend their ecological range through evolutionary adjustments in physiology and rather changes in activity patterns.