Discrimination Between and Within Colonies of Social Insects: Two Null Hypotheses

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Abstract
Social insect workers sacrifice personal reproduction to help queens reproduce, and have evolved recognition abilities enabling biased cooperation toward relatives. Nestmatcs arc recognized, and non-nestmates discriminated against, by olfactory labels derived from any or all of several sources: their own genotypes, each other, their queen and their environment. Evolutionary scenarios and genetic models have been developed from the roles of different cue sources observed in studies of different species. Discrimination may also occur within colonies containing more than one genetic line, though the kin preferences reported in this context have been weaker than expected. However, we should be cautious in ascribing adaptive significance to laboratory results, in the absence of natural environmental odor sources and in col- onies of artificial genetic heterogeneity. The available evidence docs not rule out two null hypotheses: (1) While betwecn-colony discrimination is itself adaptive, the labels used in this context may be fortuitously based on any available odor idiosyncracies and not under selection. (2) Discrimination within colonies may be a nonadaptive side-effect of that between colonies.