BackgroundGlobal warming has been frequently demonstrated to increase growth rate in larval amphibians that have considerable phenotypic plasticity; this may lead to an increase in larval survival because large larvae are less likely to be captured by gape-limited predators. This study is to test whether warming could improve tadpole growth and thereby enhance the tadpole survival in plateau frog Rana kukunoris.MethodologyWe conducted an experiment involving growing tadpoles under two contrasting temperatures, i.e. ambient temperature vs. warming by 3.8°C, with and without their major predators – the gape-limited predaceous diving beetles Agabus sp. in eastern Tibetan Plateau, in a factorial arrangement. We recorded the survival and measured body fresh weight and morphological characteristics of the tadpoles.Principal FindingsWarming significantly increased body fresh weight in the presence of predators after three weeks of treatments. However, the predators imposed significant and similar effects on the survival of tadpoles under both ambient and elevated temperatures, with the effects mostly occurring in the first three weeks of the experiment. Changes in the body form, i.e. the greater whole length at a given fresh weight and the longer tail at a given body length, could have acted as mechanisms of defense and escape for the tadpoles.Conclusions/SignificanceWarming did not increase tadpole survival with or without presence of predators. Moreover, an increased growth rate (due to warming in the presence of predators) was not a major factor contributing to the tadpole survival. We postulate that even if warming increases the tadpole growth rate in the plateau frog, it does not necessarily improve their survival in the presence of gape-limited predators.

Global warming may induce significant changes in species life history traits particularly in amphibians, which are characterized by complex and plastic life cycles. Because both warming and predators are often suggested to reduce size at metamorphosis in amphibians, we hypothesized that the size at metamorphosis was further reduced by experimental warming in the presence of predators. We conducted a factorialdesigned experiment involving two factors and two levels (warmed vs. ambient, lethal predator absence vs. presence, resulting in four treatments) using Rana kukunoris tadpoles in the eastern Tibetan Plateau, and we examined its behavioral, growth, and developmental responses to warming in the presence and absence of predatory beetles (Agabus sp.) for 13 weeks. During the course of the experiment, a similar level of tadpole mortality due to the diving beetles was found between ambient and warmed treatments, but the warming effect on size at metamorphosis depended on whether the predators were present or absent. In the absence of predators, warming did not significantly increase tadpole growth but advanced the timing of metamorphosis, such that size at metamorphosis of forelimb emergence and tail resorption was much reduced in terms of body fresh weight. In the presence of predators, warming increased tadpole growth rate much more than the development rate (as reflected by duration of the tadpole stage), and therefore the size at metamorphosis was significantly increased. The significant effect of the interaction between predator and warming on the size at metamorphosis could be attributed to the tadpole response in the frequencies of feeding, resting, and swimming to the predator activity level, which was in turn increased by warming. We suggest that warming-induced changes in life history traits should be studied in relation to species interaction so as to accurately predict ecological response of amphibians to the future warmed world.

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