Who follows whom? Shoaling preferences and social learning of foraging information in guppies

Preferences of fish for different types of shoals may influence the transmission of novel information through them. We investigated the factors influencing the preferences of guppies, Poecilia reticulata, for different shoals in order to shed some light on how information transmission occurs. Adult subjects were given a choice between swimming with two diverging shoals of conspecifics that differed with respect to key characteristics. In six choice experiments, subjects discriminated between shoal partners on the basis of: (1) shoal size, subjects preferring a shoal of 10 to a single fish; (2) size of shoaling fish, small fish preferring small conspecifics rather than an equal number of large fish, while large fish showed no preference; (3) local foraging experience of shoaling fish, shoals containing fish that had previously been repeatedly fed in the experimental tank being preferred to shoals with no such experience; and (4) familiarity of shoaling fish, guppies preferring familiar rather than unfamiliar conspecifics. No discrimination on the basis of colour or hunger was observed. In addition, following a shoal to a food site on just three trials allowed guppies to learn a route, or food site, preference. Guppies were considerably more likely to learn to adopt the behaviour shown by members of a shoal of several demonstrators than an alternative behaviour shown by a single conspecific demonstrator. The relationship between preferences for different shoals and the social transmission of information is discussed in the light of these findings. The results suggest that shoaling preferences may strongly influence-the social transmission of novel foraging information or feeding preferences through fish populations, and imply that learned information may diffuse through fish populations in a nonrandom, or directed, manner. (C) 1998 The Association for the Study of Animal Behaviour.