Adaptive, caste-specific changes to recombination rates in a thelytokous honeybee population

The ability to clone oneself has clear benefits—no need for mate hunting or dilution of one's genome in offspring. It is therefore unsurprising that some populations of haplo-diploid social insects have evolved thelytokous parthenogenesis—the virgin birth of a female. But thelytokous parthenogenesis has a downside: the loss of heterozygosity (LoH) as a consequence of genetic recombination. LoH in haplo-diploid insects can be highly deleterious because female sex determination often relies on heterozygosity at sex-determining loci. The two female castes of the Cape honeybee, Apis mellifera capensis , differ in their mode of reproduction. While workers always reproduce thelytokously, queens always mate and reproduce sexually. For workers, it is important to reduce the frequency of recombination so as to not produce offspring that are homozygous. Here, we ask whether recombination rates differ between Cape workers and Cape queens that we experimentally manipulated to reproduce thelytokously. We tested our hypothesis that Cape workers have evolved mechanisms that restrain genetic recombination, whereas queens have no need for such mechanisms because they reproduce sexually. Using a combination of microsatellite genotyping and whole-genome sequencing we find that a reduction in recombination is confined to workers only.

Genetic diversity and population structure of two subspecies of western honey bees (Apis mellifera L.) in the Republic of South Africa as revealed by microsatellite genotyping

Apis mellifera scutellata and Apis mellifera capensis, two native subspecies of western honey bees in the Republic of South Africa (RSA), are important to beekeepers in their native region because beekeepers use these bees for honey production and pollination purposes. Additionally, both bees are important invasive pests outside of their native ranges. Recently, whole mitogenome sequencing and single nucleotide polymorphisms were used to study their genetic diversity. To add to our knowledge of the molecular ecology of both bees, we tested the ability of microsatellites to be used as a tool to discriminate between A.m. capensis and A.m. scutellata. We analyzed the genetic variability and overall population structure of both bee subspecies and hybrids of the two by genotyping individuals collected from RSA (N = 813 bees from 75 apiaries) at 19 microsatellite DNA loci. Overall, populations averaged between 9.2 and 11.3 alleles per locus, with unbiased heterozygosity values ranging from 0.81 to 0.86 per population. Bayesian clustering analyses revealed two distinct evolutionary units, though the results did not match those of earlier morphometric and molecular analyses. This suggests that the microsatellites we tested were not sufficient for subspecies identification purposes, especially for Cape and hybrid bees. Nevertheless, the microsatellite data highlight the considerable genetic diversity within both populations and a larger-than-expected hybridization zone between the natural distributions of A.m. capensis and A.m. scutellata.

Social Parasitism in the Honeybee (Apis mellifera) Is Not Controlled by a Single SNP

The Cape bee (Apis mellifera capensis) is a subspecies of the honeybee, in which workers commonly lay diploid unfertilized eggs via a process known as thelytoky. A recent study aimed to map the genetic basis of this trait in the progeny of a single capensis queen where workers laid either diploid (thelytokous) or haploid (arrhenotokous) eggs. A nonsynonymous single nucleotide polymorphism (SNP) in a gene of unknown function was reported to be strongly associated with thelytoky in this colony. Here, we analyze genome sequences from a global sample of A. mellifera and identify populations where the proposed thelytoky allele at this SNP is common but thelytoky is absent. We also analyze genome sequences of three capensis queens produced by thelytoky and find that, contrary to predictions, they do not carry the proposed thelytoky allele. The proposed SNP is therefore neither sufficient nor required to produce thelytoky in A. mellifera.