The effects of habitat- and diet-based cues on association preferences in three-spined sticklebacks

A number of recent articles have investigated the potential of familiarity preferences to influence group membership in free-ranging animals. However, it is not clear to which extent individual recognition or a more general recognition of a group odor is responsible for familiarity preferences. First, we tested the sensory basis of the recognition of familiars in stickleback. When allowed to choose between a familiar and a nonfamiliar stimulus shoal on the basis of both visual and chemical communication, visual communication only, and chemical communication only, the preference of focal fish for familiars was shown to depend on the presence of chemical cues. We subsequently investigated the effects of recent habitat and diet on shoaling preferences in the three-spined stickleback (Gasterosteus aculeatus). Experimental fish were divided into four treatment groups consisting of two water treatments (saline and freshwater) and two diet treatments (Daphnia spp. and bloodworm). Focal fish subsequently showed significant association preferences for groups of nonfamiliar fish that had undergone the same water or diet treatment as themselves. These data indicate that individual recognition is not a prerequisite for the expression of association preferences.