Shoal composition determines foraging success in the guppy

The composition of an animal group can impact greatly on the survival and success of its individual members. Much recent work has concentrated on behavioral variation within animal populations along the bold/shy continuum. Here, we screened individual guppies, Poecilia reticulata, for boldness using an overhead fright stimulus. We created groups consisting of 4 bold individuals (bold shoals), 4 shy individuals (shy shoals), or 2 bold and 2 shy individuals (mixed shoals). The performance of these different shoal types was then tested in a novel foraging scenario. We found that both bold and mixed shoals approached a novel feeder in less time than shy shoals. Interestingly, we found that more fish from mixed shoals fed than in either bold or shy shoals. We suggest that this can be explained by the fact that nearly all the cases where one fish was followed into the feeder by another occurred within mixed shoals and that it was almost always a shy fish following a bold one. These results suggest clear foraging benefits to shy individuals through associating with bold ones. Surprisingly, our results also suggest potential foraging benefits to bold individuals through associating with shy individuals. This study highlights a possible mechanism by which interindividual variation in behavioral types is maintained in a population.