Selective Oviposition by Oriental Fire-bellied Toads in Temporally Fluctuating Environments

Abstract

Selective oviposition is widespread in anurans because it significantly affects the survivorship of their offspring, especially when environmental conditions are heterogeneous and potentially unfavorable. In the present study, we aimed to determine whether female oriental fire-bellied toads (Bombina orientalis) selectively lay eggs to increase their progeny's survival. We studied the Jeju Island population because the streams on this island are ephemeral, so the timing and site of egg-laying can be important for the survival of their progeny. We surveyed all pools in a specific area of an ephemeral stream for two years to determine whether female B. orientalis selectively lay eggs in certain pools to increase their progeny's survival. The characteristics of pools in our study sites varied especially in size that ranged from 0.01 to 36 m(2) in surface area. We found that female B. orientalis avoid laying eggs in very small pools where the risk of desiccation or over-heating of water is high. However, unexpectedly, they also avoided large pools and primarily laid eggs in the pools that are not very small or large. In terms of timing, egg-laying took place in association with the timing of rain: the number of pools with egg clutches decreased as the number of days since the last rainfall increased. Females also avoided laying eggs in pools that were already occupied by tadpoles. Field experiments demonstrated that the degree of cannibalism on eggs by conspecific tadpoles is intense in this species. These findings collectively indicate that B. orientalis that live in a fluctuating environment show complicated oviposition behavior that mediate both desiccation and cannibalism risks.