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Variation in Southeast Asian anurans


This dissertation reports studies of variation in Southeast Asian frog species as it affects their ability to respond to environmental change. First, using museum specimens of Bornean anurans, I found that clutch size did not increase with altitude, as expected from studies of other ectotherms. Second, a comparative study of genetic, call, and morphological data in two distant populations (Singapore and Thailand) of each of three wide-ranging species, showed that the distant populations of two (Microhyla heymonsi and Rana erythraea) are conspecific, but the third (Polypedates leucomystax) has diverged in call and morphology, indicating that they may represent incipient cryptic species. Third, comparing reproduction in these three species in Singapore (where frogs breed year-round) with that in central Thailand (where reproduction is limited to six months) I found that clutch size varied significantly between sites, indicating that these three species compensate for shortened breeding time by producing more offspring in a given breeding event. Fourth, I report the results of field experiments to test the ability of tadpoles to respond to drying of their aquatic habitat; their inability to develop more rapidly when faced with desiccation suggests they may not adapt well to some climate change associated with global warming. Finally, I report field observations on the reproductive behavior and larval development of two species of Thai anurans. The initial goal of these studies was to examine patterns of reproductive variation in wide- ranging tropical species as a first step towards predicting how species may respond to climate change. Collectively, these results show that there is potential for some species to adjust reproductive parameters in response to climate change (different clutch sizes at different latitudes), but that adjustments may not occur as predicted from studies on temperate anurans (e.g., an inability of tadpoles to speed up development in response to desiccation) and that trends observed in other ectotherms (clutch size variation across altitude). Clearly, much remains to be learned about the evolutionary ecology of tropical anurans

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