DNA Studies Reveal Processes Involved in the Spread of New World African Honeybees

Abstract

African honeybees, imported to South America thirty-four years ago, have spread throughout most of the neotropics and have replaced the resident European bees. Two controversial views concern the nature of the neotropical African population. One view is that the African bees have spread primarily by paternal introgression into European colonies and the resulting population is mixture of all African-European hybrid genotypes. The other view is that the bees have spread primarily by maternal migration of feral African swarms and the feral population has retained, to a large extent, an African genetic integrity. Results from recent studies, using mitochondrial and nuclear DNA markers, support the latter view. Asymmetries in both maternal and paternal gene flow between feral African and managed European populations favor the African genotype. The replacement of the large extant European gene pool by a tiny introduced African gene pool could not have occurred if the African and European populations were panmictic and the African genotype were not favored by selective mechanisms. Some separation of the parental genotypes and/or selection against hybrid genotypes had to be realized. Superior fitness in a tropical environment is probably largely responsible for the African bee success, but reduced fitness of hybrids due to genetic factors may be involved also. As African bees approach temperate climatic regions where European bees are better adapted, a persisting hybrid zone may be established. With DNA markers, hybrid zone dynamics can be studied which may reveal the nature of selective processes.