Male Polymorphism and Polyethism in Perdita texana (Hymenoptera: Andrenidae)

Ann. Entomol. Soc. Am. 85(5): 616-626 (1992) ABSTRACT Males of Perdita texana (Cresson), a communal, ground nesting, univoltine bee, show striking variation in head size and shape; larger males have disproportionately large heads and disproportionately undersized thoraces. As body size increases, the components of head shape that increase most strongly allometrically are the dimensions of the sites of attachment of the mandibular adductor muscles, the length of the mandibles, and the gap between the mandibular bases. Males also vary in where they spend the night. Some enter the nests of females during midto late afternoon, whereas others enter closed Opuntia flowers, where they remain until the next day. Males in nests leave early in the morning and join other males and females on flowers, where mating can be observed during the period of female foraging (1100-1400 hours [CST]). Head size-shape is not related to the site chosen for the night, but rather to male-male combat on flowers and the ability to grasp females during copulation. Larger-headed males were more successful in male-male combat on flowers and had higher reproductive success on flowers. Selection appears to favor large-headed males, but the persistence of small-headed males suggests a balanced polymorphism maintained either by temporally and spatially varying selection, or size-dependent differences in investment costs, such that small males, although lower in fitness, are cheaper for females to produce.