Morphological Alterations in Rana japonica Tadpoles Induced by Predation Risk From Hynobius setouchi Salamander Larvae

Anuran tadpoles demonstrate morphological alterations in response to predation risk, thereby developing predator-specific defensive morphologies that enhance survivorship, compared to tadpoles without such defenses. In aquarium experiments, we assessed whether <i>Rana japonica</i> tadpoles demonstrated morphological changes when exposed to the salamander larvae <i>Hynobius setouchi</i>. They are gape-limited predators that coexist with these tadpoles in natural environments. In the presence of <i>H. setouchi</i> larvae, some <i>R. japonica</i> tadpoles were swallowed tail-first, and smaller individuals demonstrated damaged tail fins because of predator attacks, whereas larger tadpoles had intact tail fins. Tadpoles developed larger body sizes and deeper tail fins only when they were in close proximity to <i>H. setouchi</i> larvae, and smaller tadpoles demonstrated relatively larger tail-to-body ratios. These results imply that larger body sizes and deeper tail fins serve as inducible defense mechanisms, potentially improving swimming ability to evade predators and reducing the likelihood of tail-first ingestion.