Cytogenetic basis of thelytoky in Apis mellifera capensis

Abstract

Haplodiploid insects reproduce both sexually and asexually; haploid males arise from unfertilized eggs, while diploid females arise from fertilized eggs. Some species can also produce female offspring by thelytokous parthenogenesis. For example, queenless workers of the Cape honey bee, Apis mellifera capensis, of South Africa can produce diploid female offspring from unfertilized eggs. Genetic evidence suggests that in A. m. capensis, diploidy is restored in zygotes by the fusion of two maternal pronuclei, the haploid descendants of the two alternate products of meiosis I. Here, we confirm this genetic evidence by direct cytological observation of pronucleus fusion. We also provide a description of how the fusion occurs at 4.5–5 h post oviposition and describe the meiotic events that lead up to and follow the fusion. Finally, we document numerous departures from the typical meiotic patterns, which likely explain some of the anomalous A. m. capensis individuals that have been previously identified genetically.