The expression of dietary conservatism in solitary and shoaling 3-spined sticklebacks Gasterosteus aculeatus

Dietary conservatism (DC) is a long-term, active avoidance of novel food by foragers, present in some (but not all) members of each forager population. Conservative prey choice by predators may exert strong selection pressure on prey populations because individuals with a novel appearance may be protected from predation by their novelty. Recent work has provided the first evidence of DC in a fish species, where novel-colored morphs of prey (Daphnia) were under predation by individual 3-spined sticklebacks Gasterosteus aculeatus. However, in this earlier study, sticklebacks were housed individually, whereas in the wild, they are a strongly shoaling species. Little is known about whether the social context may influence the expression of DC, but even if it does not, shoals are very likely to contain at least one nonconservative individual. Thus, most foraging shoals are expected to exert stronger selection against novel prey than are individual foragers. We found that DC, strong enough to drive a novel prey morph from initial rarity to fixation in a prey population, was evident among both single sticklebacks and shoals, but surprisingly, we found no evidence that isolated fish and shoals differed in the frequency with which they caused this to happen. Copyright 2011, Oxford University Press.