Polyandry in social Hymenoptera — disunity in diversity?

Abstract

Multiple mating by queens occurs in many species of social Hymenoptera despite its likely costs. Hypotheses to explain multiple mating include a need for more sperm than provided by a single male, the convergence of queen and worker sex-allocation optima and various genetic diversity hypotheses. For some species the sperm need hypothesis fails since queens retain only a single male’s worth of sperm. In other cases, sperm store does increase with the number of matings. Similarly for the sex-allocation and genetic diversity hypotheses, data from some species are in support, those from others are not. Comparative analysis reveals a negative correlation between level of genetic diversity (of which queen mate number is an important determinant) and parasite load; findings in the best-studied case are complex: monandry and higher levels of polyandry are each selectively favored over moderate polyandry. Out of 14 identifiable hypotheses five are judged most useful for future work. Unfortunately, the search for a simple unitary model to explain all cases seems futile. A model encompassing all of these factors is desirable for studies on single species, but would be complex. Comparative analyses remain desirable, but should encompass the likelihood that different factors predominate in different groups