Hatching plasticity and embryonic learning in chorus frog ( Pseudacris triseriata ) embryos in response to predatory burrowing crayfish ( Lacunicambarus chimera )

Crayfish represent a profound threat to amphibian populations worldwide, often acting as keystone predators that disrupt breeding success and contribute to local declines. In particular, voracious predation on eggs can consume substantial proportions of clutches, exacerbating vulnerability during this early life stage. We examined the palatability of chorus frog (Pseudacris triseriata) embryos to burrowing crayfish (Lacunicambarus chimera) and found that 28–60% of eggs were consumed, with higher rates when food was deprived. We then evaluated the hatching timing, size, and developmental stage of embryos exposed to the physical presence of crayfish or crayfish chemical cues alone. Embryos delayed hatching by ~ 0.5 day when in the physical presence of crayfish, while there were no differences in Gosner stage, total length, or snout-vent length between treatments. Recently hatched tadpoles from the kairomone-only and crayfish-exposed treatment showed reduced activity in behavioral assays compared to a control, indicating embryonic learning of predation risk. These findings suggest chorus frog embryos assess crayfish risk via mechanical cues, likely delaying hatching and learning antipredator behaviors embryonically to mitigate even more severe (relative to eggs) tadpole-stage vulnerability. These results demonstrate that chorus frogs have well-adapted defenses against crayfish, emphasizing the necessity of thorough, stage-specific assessments across the entire life history to accurately characterize native interactions and anticipate predation risk.