The distribution of thelytoky, arrhenotoky and androgenesis among castes in the eusocial Hymenoptera

Abstract

Thelytokous parthenogenesis is the production of females from unfertilized eggs. In this review we categorize the known thelytokous eusocial Hymenopterans (mostly ants) by their modes of worker and queen reproduction. The resultant tabulation reveals that: (1) there are no species in which queens are thelytokous and workers are exclusively arrhenotokous (asexual production of males). (2) When workers are capable of thelytoky, there are no examples of species in which queens are strictly thelytokous. (3) Strict queen thelytoky is only present in species with irreversibly sterile workers. (4) Facultative queen thelytoky and sterile workers can lead to the evolution of androgenesis (males are clonal sons of their fathers). These associations are probably best explained by consideration of differing fitness benefits of thelytoky between workers and queens and suggest that some combinations are unlikely to evolve. We therefore predict that they will hold for all eusocial Hymenoptera. No examples of endobacterium-induced thelytoky are known for the eusocial Hymenoptera, whereas endobacterium-induced thelytoky is widespread in the solitary Hymenoptera. We argue that this is because species in which both queens and workers are thelytokous that are unlikely to persist over evolutionary time. Further, eusocial species have single-locus sex determination, which is not compatible with endobacterium-induced feminization that is typically based on genome duplication. Only two thelytokous eusocial bees are known, and their modes of reproduction are consistent with the associations seen in ants. Thus far, no thelytokous eusocial wasps have been identified.