A test of alternative hypotheses for kin recognition in cannibalistic tiger salamanders

The function of kin recognition is controversial. We investigated the adapt ive significance of kin discrimination in cannibalistic tiger salamander la rvae, Ambystoma tigrinum. Previous laboratory experiments show that canniba ls preferentially consume less related individuals. We hypothesized that th is example of kin recognition (1) is a laboratory artifact, (2) is a by-pro duct of sibship-specific variation in escape responses, because cannibals f rom families with rapid responses may be more likely to cannibalize slowly escaping non-kin, (3) is an epiphenomenon of species recognition, (4) funct ions in disease avoidance, because kin may be more infectious than non-kin, or (5) is favored by kin selection. We evaluated these five hypotheses by using laboratory and field experiments to test specific predictions made by each hypothesis. We rejected hypotheses 1-4 above because (1) kin recognit ion was expressed in the wild, (2) escape responses did not reliably predic t whether a cannibal would ingest kin or non-kin, (3) kin recognition was n ot most pronounced in populations where tiger salamanders co-occur with oth er species of salamanders, and (4) non-kin prey were more likely than kin t o transmit pathogens to cannibals. However, we established that the necessa ry condition for kin selection, Hamilton's rule, was met. Thus, our results implicate kin selection as the overriding reason that cannibalistic tiger salamanders discriminate kin.