Dehydration-Induced Mortality and Premature Hatching in Gliding Treefrogs with Even Small Reductions in Humidity

Climate change is affecting rainfall patterns and increasing dry spells in the tropics. Although many environmental conditions can affect the hatching timing and survival of amphibian embryos, increased variation in rainfall and humidity can have particularly strong effects on species facing higher risk from dehydration, such as those with terrestrial eggs. Thus, it is important to understand how these environmental changes may affect the development, behavior, and immediate and long-term survival of amphibian embryos. We investigated whether Gliding Treefrog embryos (Agalychnis spurrelli) adaptively shift their hatching timing in response to dehydration risk, at the cost of smaller hatchling size. We raised embryos under three humidity levels and assessed egg and clutch hydration, hatching timing, and egg mortality. Mean humidity of 92% in Experiment I led to over 98% egg mortality by dehydration. A decrease from over 99 to 96% mean relative humidity in Experiment II induced premature hatching and reduced hatchling size across ages. Both clutch thickness and egg size increased at 99% and decreased at 96% humidity. Our results suggest that embryos of A. spurrelli are extremely dependent on consistent precipitation and particularly vulnerable to climate change. Although we did not directly measure differences in hatchling fitness, our results and previous findings suggest that small, premature hatchlings of A. spurrelli from dehydrated eggs would suffer higher mortality as tadpoles, thus embryos' self-defense against dehydration likely carries a delayed cost. These findings add to our understanding of how predicted climate changes may impact anuran early life stages.