The role of learning by a predator, Rivulus hartii, in the rare-morph survival advantage in guppies

Negative frequency-dependent selection (NFDS), where rare types are favoured by selection, can maintain diversity. However, the ecological pro- cesses that mediate NFDS are often not known. Male guppies (Poecilia reticu- lata) exhibit extreme diversity of colour patterning and, in a previous field experiment, rare morphs had a survival advantage. Here, we test the hypothesis that predators impose NFDS because they are efficient at captur- ing familiar prey morphs, but are less efficient at capturing unfamiliar mor- phs. Over a series of trials, we presented Rivulus hartii, a natural predator of guppies, with male guppies with the same colour patterning (A trials); then, for a second series of trials, we presented the rivulus with guppies with a new colour pattern (B trials). The success of rivulus at capturing guppies on the first attack increased over successive A trials. First attack success decreased significantly for the early B trials, and then increased during suc- cessive B trials, eventually reaching the same level as in the best A trials. This experiment demonstrates that learning, perhaps through long-term search image formation, plays a role in predation success on familiar vs. unfamiliar prey morphs. These results support the hypothesis that predator learning contributes to the maintenance of the extreme male guppy poly- morphism seen in nature.