Kin recognition and cannibalism in polyphenic salamanders

We investigated kin discrimination among larvae of Arizona tiger salamanders (Ambystoma tigrinum nebulosum) which occur as "typical" morphs that feed mostly on invertebrate prey and occasionally on conspecifics, and as "cannibal" morphs that feed primarily on conspecifics. When housed with smaller larvae that differed in relatedness, both cannibals and typicals preferentially consumed less-related individuals. Cannibals ate typicals much quicker when the choice was between nonkin and siblings than when the choice was between nonkin and cousins, indicating that cannibals could distinguish different categories of relatives. Cannibals were less likely to eat a larval sibling that was a cannibal morph than a sibling that was a typical morph. Occluding animals' nares temporarily eliminated kin discrimination, implying that olfaction is important in recognition. Larvae from different sibships varied considerably in their ability to discriminate kin, and the greater the probability that a larva from a given sibship would develop into a cannibal morph, the more likely the members of that sibship were to discriminate kin. Our results enable us to infer the functional significance of kin recognition in this species and to develop an evolutionary model of the mechanisms underlying the joint control of kin recognition and cannibalistic polyphenism.