Male dimorphism in Perdita portalis (Hymenoptera, Andrenidae) has arisen from preexisting allometric patterns

Abstract

Allometric scaling coefficients were quantified using principal components analysis for eight species of closely related Perdita bees. The coefficients were mapped onto a cladogram and male dimorphism in P. portalis was found to be the derived state, whereas polymorphism was ancestral. The phylogeny explained 87.4 ± 1.1% of the variation in male head allometry among taxa, indicating that the evolution of head allometry is highly congruent with the cladogram. These results were used to place Perdita male head allometry in the context of adaptive phenotypic plasticity. Wheeler's (1991) model for the evolution of discrete alternative castes in ants is applied to the morphometric data in Perdita. We argue that the developmental rules that govern the evolution of caste polymorphism in social insects can be applied to the evolution of alternative male mating tactics in other Hymenoptera.