Monandry and polyandry in three species of North American bumble bees (Bombus) determined using microsatellite DNA markers

Abstract

Polyandry, or multiple mating by females, is widespread in insects, and generally females need to mate more than once to achieve maximum fertility and fecundity. However, although monandry by queens (mating with a single male) is the general rule in the eusocial Hymenoptera, polyandry does occur in many species. Since there are associated costs, numerous hypotheses have been proposed to account for its evolution. Two hypotheses are particularly applicable to bumble bees: the genetic load (cost of diploid male production) hypothesis, which predicts monandry in bumble bees, and the resistance to disease hypothesis, which predicts polyandry. We used four DNA microsatellite markers to determine mating frequencies of queens of three species of North American bumble bees: Bombus (Pyrobombus) perplexus Cresson, 1863, Bombus (Bombus s. str.) occidentalis Greene, 1858, and Bombus (Bombus s. str.) terricola Kirby, 1837. No multiply-mated queens were found in either B. terricola (n = 21 colonies) or B. occidentalis (n = 23 colonies). However, 2 out of the 24 B. perplexus colonies were found to have twice-mated queens. This is consistent with other studies which indicate that bumble bees are mostly monoandrous, but that species of the subgenus Pyrobombus Dalla Torre, 1880 are likely to show some degree of polyandry.