Competition from large males and the alternative mating tactics of small males of Dawson's burrowing bee (Amegilla dawsoni) (Apidae, Apinae, Anthophorini)

Abstract

Males of Dawson's burrowing bees (Amegilla dawsoni) search for virgin females at three locations: (1) open clay patches where females are emerging from underground brood cells, (2) the vegetated peripheral zone adjacent to emergence areas (through which females pass after emerging), and (3) clusters of flowering plants, which are often some distance from emergence areas. Males of Dawson's burrowing bees exhibit a size dimorphism with large major and small minors. Major males patrol only the open emergence sites, whereas minor males may be found in all three locations. Although most females are mounted and presumably mated immediately upon emergence, some are not, and these females make up a pool of potential mates for the small males patrolling the peripheral zone and flower patches. The density of males at emergence sites and the probability of male-male aggression change over the course of a day and over the entire flight season. When the level of competition is low, some minor males hunt for mates at emergence areas, where potential mates are relatively numerous. But when the presence of many large rivals makes it unlikely that a small male can avoid being displaced from emerging females, minors make the best of a bad job by shifting to areas where majors are absent.