Evolutionary Genetics of Division of Labor in Colonies of the Honey Bee (Apis mellifera)

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Abstract
We observed division of labor in worker honey bees from three genetically distinct sources (two selected strains and a wild-type source) in a common colony environment. We demonstrate a genotypic component to variability in those elements of individual behavior necessary for the evolution of the individual and colony-level behavioral phenotype-variability in task specialization and variability in the age-based system of division of labor. We present a model for individual behavior that integrates the effects of variability in individual genotypes with the current model of age and environmental determinism. Sources of variation involving interaction of genotype and environment are not individually specified, but an analysis of foraging behavior shows that such interactions can be significant. This conflicts with the traditional view of the colony environment as a source of behavioral resemblance among workers. The colony environment may, in some cases, actually amplify phenotypic differences among individuals beyond that expected on the basis of their additive genotypes. Interactions among workers or among subfamilies may significantly affect the expression of genotypic variability in worker behavior, resulting in facultative specialists that perform tasks with increased efficiency. Conversely, genotypic diversity within a colony may reduce colony fitness. Workers with different response thresholds may operate less efficiently as a group than workers with similar values if this variability results in conflict among nestmates over how an activity should be performed. Worker behavior is characterized by two elements: the proportion of time spent performing specific tasks (task specialization) and the temporal pattern of task performance (temporal division of labor). Analysis of the evidence presented here suggests that these components may be independent of one another. Further, we show that variation in the temporal pattern of performance of nest activities is independent of variation in the ontogeny of foraging behavior. Both of these findings reveal considerable flexibility in the evolution of energetically efficient task groups.

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