Toad tadpoles associate preferentially with siblings

Abstract

Highly structured social systems can involve close kinship groups (eusocial insects¹, lion prides², helpers-at-the-nest in birds³). However, kinship generally has not been considered to be important or necessary for what seem to be merely gregarious phenomena, such as schooling behaviour⁴. In fact, Fisher first proposed kinship theory to explain the evolution of noxious taste in certain gregarious insect larvae. He reasoned that traits which at first may not be directly beneficial to the individual, such as distastefulness or warning coloration, might be selected for if they conferred advantage to siblings in the swarm⁵. Like some insect larvae, the tadpoles of many toads (genus Bufo) are conspicuously coloured, distasteful to predators and highly gregarious, forming densely packed schools in open areas along pond shores⁶. The tadpoles' aggregative behaviour may be important for feeding efficiency^7,8, thermoregulation⁹ or predator deterrence⁸, but their conspicuousness coupled with their distastefulness suggest that schooling may also serve an apose-matic function. Consistent with the predictions of a kin selection model, we report here that tadpoles of the American toad (Bufo americanus) preferentially associate with siblings in laboratory conditions.