Experimental warming and drying act independently on developmental responses for two amphibian species

Abstract

Abstract Climate change is affecting freshwater habitats worldwide through multiple, interacting pressures that influence the survival, distribution, and persistence of freshwater organisms. Temporary freshwater habitats, or those that dry seasonally, can exhibit wide‐ranging variability in temperature and drying regimes. Aquatic organisms with complex life cycles (e.g., aquatic and terrestrial life stages) often rely on temporary freshwaters to complete their life cycles and have specific adaptations to cope with these dynamic environments. However, climate change is altering the temperature and drying regime of many temporary freshwater habitats worldwide, often resulting in warmer habitats available for shorter durations of time. The ways in which climate‐mediated changes to temporary freshwaters affect development and life history of aquatic organisms, particularly those with complex life cycles, remains poorly understood. We investigated larval development, growth, survival, and relationships among them for two amphibian species, wood frogs (Lithobates sylvaticus) and spring peepers (Pseudacris crucifer), in response to warming and drying in a mesocosm experiment. Over 13 weeks in the spring and summer of 2019, we manipulated temperature and water levels in 48 outdoor pond mesocosms to produce four treatments: control (ambient conditions), drying alone, warming alone, and drying + warming. We predicted reduced survival, body size, and time to metamorphosis for both species in response to warming and drying, with the effect being stronger on wood frogs due to their more specialised habitat use and shorter breeding period. Warming treatments were on average 2°C higher than controls, and drying treatments decreased water depth by 2.5 cm each week. We found that warming temperature shortened larval time to metamorphosis, and drying decreased body size at metamorphosis. Surprisingly, we also found that, across all treatment groups, individuals with early metamorphosis tended to be larger in size and from mesocosms with generally higher survival. Our study indicates that warming and drying may act independently on different developmental responses for amphibians. Our results echo recent calls for a better understanding of the nuanced, often unpredictable, relationships among climate‐mediated environmental pressures and the developmental traits they influence, particularly for organisms with complex life cycles that depend upon dynamic habitat for growth and survival. Understanding these relationships and the mechanisms that drive them will be key to predicting the response of freshwater organisms to climate change.