Ontogenetic isolation favours sibling cannibalism in mites

Inclusive fitness theory suggests that cannibalistic individuals should preferentially eat unrelated prey when given a choice between related and unrelated individuals. Using the predatory mite Phytoseiulus persimilis, I investigated whether having contact with siblings during a sensitive ontogenetic phase or not determines whether cannibalistic protonymphs tend to eat more sibling or nonsibling larvae in choice situations. Cannibals reared with siblings preferentially ate nonsibling larvae when these had been reared in a sibling group but showed no preference when the larvae had been reared in isolation. Cannibals reared in isolation showed no preference when the larvae had been reared in a sibling group and preferentially ate sibling larvae when these had been reared alone. The occurrence of preferential sibling cannibalism when both cannibal and prey had been reared in isolation suggests the use of self-referent phenotype matching to distinguish between siblings and nonsiblings.