Comparative Linkage Mapping Suggests a High Recombination Rate in All Honeybees

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Abstract
Meiotic recombination is required for proper chromosome assortment, and accordingly, 1–2 chiasmata per chromosome are found in most species. However, observed recombination rates deviate in some cases from neutral expectations between and within genomes and may play an important role in adaptive evolution. One potentially important argument for an adaptive evolution of recombination rates is the exceptionally high genome-wide recombination rates of social Hymenoptera, in particular the Western honeybee, Apis mellifera . It has the highest metazoan recombination rate reported so far. Proximate or ultimate causes for this elevated recombination rate have not yet been resolved. In a comparative study, we investigated meiotic recombination in the red dwarf honeybee Apis florea . Microsatellite markers developed for A. mellifera were genotyped in a natural mapping population of A. florea . From these genotypes, we calculated local recombination rates, using the physical distances from A. mellifera . In addition to a few comparisons of intervals across the genome, we particularly focused on chromosomes 3 and 12. Confirming marker synteny, we found that recombination rates in A. florea are as high as or higher than those in A. mellifera . Our results are limited to select genomic regions but suggest that A. florea also exhibits an exceptionally high genome-wide recombination rate. This trait may thus occur genus wide. Although our study cannot identify a single explanation for the high rates of recombination in Apis , it favors hypotheses that apply to the entire genus. Furthermore, we conclude that the genome structure of the 2 species has been largely conserved, at least in the parts we investigated.

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