Climate change and invasive species are significant threats to biodiversity and ecosystems around the globe, including freshwater wetlands and their associated communities. We assessed the effects of climate change on the larvae of a well-known invasive amphibian species, the American bullfrog (Lithobates catesbeiana), in three laboratory experiments. Our overarching hypothesis was that bullfrog tadpoles would respond to changes in temperature and hydroperiod via a stress response, resulting in behavioral, morphological, and developmental changes. Hydroperiod treatments were applied via weekly water removal while temperature was manipulated using aquarium heaters. Experiment 1 examined the effects of hydroperiod alone on the development and activity of bullfrog tadpoles by comparing individuals exposed to reduced hydroperiod conditions with individuals in a stable hydroperiod. Experiment 2 examined the effects of future climate (decreased hydroperiod and increased temperature) and food availability on the growth, developmental stage and gut length of bullfrog tadpoles. Experiment 3 examined the effects of decreased hydroperiod and increased temperature on the survival, growth, and development of tadpoles of a native species, Pacific chorus frog (Pseudacris regilla) paired with a conspecific or a bullfrog tadpole.
Results/Conclusions
No response to reduced hydroperiod was observed in experiment 1. Percent time active and developmental stage were similar among individuals at the end of 60 days regardless of hydroperiod treatment (activity: ANOVA, p=0.73; development: ANOVA, p=0.83). No differences in developmental stage or growth were observed between treatment groups in experiment 2 (development: two-way ANOVA, pclimate=0.11, pfood=0.47, pinteraction=0.82; growth: two-way ANOVA, pclimate=0.75, pfood=0.23, pinteraction=0.84). Analysis of gut length is ongoing. In the final experiment, native Pacific chorus frog tadpoles survived longer when paired with a single bullfrog tadpole compared to when paired with a single conspecific under future climate conditions (Weibull survival analysis, pinteraction= 0.007), but no differences in growth or development were observed. Overall, the results obtained in all three experiments did not conform to our predictions. Our findings suggest that American bullfrog tadpoles may have limited responses to reduced hydroperiod and increased temperature and, more surprisingly, that the presence of bullfrog tadpoles may provide some benefit to native tadpoles during thermal and hydroperiod stress. Our results highlight the importance of understanding invasive species’ responses to climate change, as some invasive species may be less successful under future, more variable, climates.