ABSTRACT Background: The sexually selected sperm hypothesis predicts that selection will favour female multiple mating by increasing the sperm competitive abilities of their sons. Hypothesis: Sons of multiply mated females should have higher sperm competitive abilities than sons of singly mated females. Organism: The bulb mite, Rhizoglyphus robini (Acari: Acaridae). Methods: Rhizoglyphus is a highly promiscuous species in which females gain no direct benefits from multiple matings. Virgin females were mated to one or six males. Sons of singly and multiply mated females were allowed to compete with each other for access to females' ova. Sperm competitiveness was estimated by the sterile male method. Results: Contrary to the predictions of the hypothesis, we found no difference in sperm competitiveness between sons of singly and multiply mated females. We suggest that non-genetic effects could explain this result
