Plasticity for the kin and conspecific preferences in the frog tadpoles (Rana ornativentris)

In vertebrates, little is known of kin recognition systems and their plasticity. Even in well-studied anuran larvae (tadpoles), the determinants and effects of prior experience have not been clarified. This study evaluates the plasticity of kin and conspecific discrimination in tadpoles of the Japanese montane brown frog Rana ornativentris. We raised tadpoles under two different sibship conditions: the pure line, comprising only siblings, and the mixed line, comprising both siblings and non-siblings. The association preference by a subject tadpole to unfamiliar ("stimulus") tadpoles was assessed through binary-choice tests using a 2 × 2 × 2 factorial design among each kinship line (pure and mix), subject ontogeny/size (early stage/small and late-stage/large), and stimuli ontogeny/size. Contrary to our expectations, kin preference was confirmed only in early developmental small tadpoles from mixed line, and only with a small stimulus. Furthermore, tadpoles from mixed line did not exhibit size preference for unrelated conspecifics. These results suggest that different prior associations have modulated kin templates along tadpole ontogeny and that the presence of non-kin would enhance the learning of kin/non-kin. This study provides the first example that plasticity of kin recognition affects not only kin-biased association but also conspecific recognition along ontogeny in tadpoles.