Differential reproductive success among subfamilies in queenless honeybee ( Apis mellifera L.) colonies

Abstract

With very rare exceptions, queenright worker honeybees (Apis mellifera L.) forego personal reproduc- tion and suppress reproduction by other workers, prefer- ring to rear the queen's sons. This is in stark contrast to colonies that have lost their queen and have failed to rear a replacement. Under these conditions workers activate their ovaries and lay many eggs that develop partheno- genetically into a final brood of males (drones) before the colony perishes. Interestingly, not all workers contribute equally to this final generation of drones in queenless colonies. Some subfamilies (workers that share the same father) contribute a disproportionately greater number of offspring than other subfamilies. Here we explore some of the mechanisms behind this reproductive competition among subfamilies. We determined the relative contribu- tion of different subfamilies present in colonies to laying workers, eggs, larvae and pupae by genotyping samples of all life stages using a total of eight microsatellite loci. Our colonies were headed by free-mated queens and com- prised 8-17 subfamilies and therefore differed signifi- cantly from colonies used in an earlier study investigating the same phenomena where colonies comprised an artificially low number of subfamilies. We show that, first, subfamilies vary in the speed with which they activate their ovaries after queen-loss and, second, that the survival of eggs to the larval stage is unequal among subfamilies suggesting that some subfamilies lay eggs that are more acceptable than others. However, there is no statistically significant difference among subfamilies in the survival of larvae to pupae, indicating that ovary activation and egg survival are the critical components to reproductive competition among subfamilies of queenless honeybee workers.