Integrative effects of thermal tolerance and dehydration in the early life stages of Neotropical treefrogs

Abstract

Climate change is increasing both environmental temperatures and droughts around the world. Anurans are a group particularly sensitive to these environmental changes, due to their ectothermic condition and the requirement of water bodies for reproduction. Many tropical anurans lay terrestrial eggs, relying on environmental moisture for embryonic development. These eggs are vulnerable to dehydration, which may alter development or cause mortality. However, in some species, embryos can hatch prematurely to escape from drying eggs. Hatching responses to heat have only been examined in one species to date; embryos of the red-eyed treefrog, Agalychnis callidryas, can hatch in response to heating. Moreover, our preliminary results with A. callidryas suggest that dehydration reduces the magnitude and duration of thermal tolerance, leading embryos to hatch more rapidly and at lower temperatures. However, these data need to be expanded and compared with other species that present other oviposition strategies that can play an important role during embryonic development. Nor do we know if other species phylogenetically close to A. callidryas, such as phyllomedusid species that wrap clutches with leaves, also have the same response mechanisms against high temperatures and dehydration. Therefore, this project proposes a comparative study to evaluate the interactive effects of dehydration and high temperatures on the embryos of Neotropical treefrogs that deposit open clutches with those of treefrogs that deposit the clutches wrapped with leaves. For this, we will use A. callidryas, a Neotropical species whose embryonic development and behavior has been well studied. Also, we propose to use Phyllomedusa distincta, an endemic treefrog from Brazil for which nothing has been documented in this regard and which deposit their clutches wrapped with leaves. For both species, we will measure the thermal tolerance (VTMax) of embryos within dehydrated and completely hydrated clutches. In addition, to evaluate the role of clutch and plant structures surrounding eggs (e.g. jelly, leaf protection), we will measure the VTMax of embryos of both species in eggs isolated from their clutch and reared under conditions of hydration and dehydration. We hope that our project can demonstrate a convenient behavioral assay for thermal tolerance of terrestrial anuran embryos and reveal interacting effects of dehydration and high temperatures at an early life stage. Depending on results, this work could potentially be expanded to either a larger comparative study of more species with open and wrapped clutches and/or experimental tests of how the parental clutch-wrapping strategy affects the thermo and osmoregulation environment of their embryos. Such ecophysiological information can improve our understanding of the vulnerability and self-defense mechanisms of terrestrial anuran clutches facing hydric and thermal stress due to climate change. (AU)