Data from: Extreme polyandry aids the establishment of invasive populations of a social insect

Although monandry is believed to have facilitated the evolution of eusociality, many highly eusocial insects have since evolved extreme polyandry. The transition to extreme polyandry was likely driven by the benefits of within-colony genetic variance to task specialization and/or disease resistance, but the extent to which it confers secondary benefits, once evolved, is unclear. Here we investigate the consequences of extreme polyandry on the invasive potential of the Asian honey bee, Apis cerana. In honey bees and other Hymenoptera, small newly founded invasive populations must overcome the genetic constraint of their sex determination system that requires heterozygosity at a sex-determining locus to produce viable females. We find A. cerana queens in an invasive population mate with an average of 27 males (range 16–42) that would result in the founding queen/s carrying 75% of their source population’s sex alleles in stored sperm. This mating frequency is similar to native-range Chinese A. cerana (mean 29 males, range 19–46). Simulations reveal that extreme polyandry reduces the risk, relative to monandry or moderate polyandry, that colonies produce a high incidence of inviable brood in populations that have experienced a founder event, that is, when sex allele diversity is low and/or allele frequencies are unequal. Thus, extreme polyandry aids the invasiveness of A. cerana in two ways: (1) by increasing the sex locus allelic richness carried to new populations with each founder, thereby increasing sex locus heterozygosity; and (2) by reducing the population variance in colony fitness following a founder event

Thelytokous Parthenogenesis in Unmated Queen Honeybees (Apis mellifera capensis): Central Fusion and High Recombination Rates

The subspecies of honeybee indigenous to the Cape region of South Africa, Apis mellifera capensis, is unique because a high proportion of unmated workers can lay eggs that develop into females via thelytokous parthenogenesis involving central fusion of meiotic products. This ability allows pseudoclonal lineages of workers to establish, which are presently widespread as reproductive parasites within the honeybee populations of South Africa. Successful long-term propagation of a parthenogen requires the maintenance of heterozygosity at the sex locus, which in honeybees must be heterozygous for the expression of female traits. Thus, in successful lineages of parasitic workers, recombination events are reduced by an order of magnitude relative to meiosis in queens of other honeybee subspecies. Here we show that in unmated A. m. capensis queens treated to induce oviposition, no such reduction in recombination occurs, indicating that thelytoky and reduced recombination are not controlled by the same gene. Our virgin queens were able to lay both arrhenotokous male-producing haploid eggs and thelytokous female-producing diploid eggs at the same time, with evidence that they have some voluntary control over which kind of egg was laid. If so, they are able to influence the kind of second-division meiosis that occurs in their eggs post partum

Workers’ sons rescue genetic diversity at the sex locus in an invasive honey bee population

The hallmark of eusociality is the division of labour between reproductive (queen) and non‐reproductive (worker) females. Yet in many eusocial insects, workers retain the ability to produce haploid male offspring from unfertilized eggs. The reproductive potential of workers has well‐documented consequences for the structure and function of insect colonies, but its implications at the population level are less often considered. We show that worker reproduction in honey bees can have an important role in maintaining genetic diversity at the sex locus in invasive populations. The honey bee sex locus is homozygous‐lethal and, all else being equal, a higher allele number in the population leads to higher mean brood survival. In an invasive population of the honey bee Apis cerana in Australia, workers contribute significantly to male production: 38% of male‐producing colonies are queenless, and these contribute one‐third of all males at mating congregations. Using a model, we show that such male production by queenless workers will increase the number of sex alleles retained in nascent invasive populations following founder events, relative to a scenario in which only queens reproduce. We conclude that by rescuing sex‐locus diversity that would otherwise be lost, workers’ sons help honey bee populations to minimize the negative effects of inbreeding after founder events and so contribute to their success as invaders

Cytogenetic basis of thelytoky in Apis melligera capensis

CITATION: Cole-Clark, M. P. et al. 2017. Cytogenetic basis of thelytoky in Apis melligera capensis. Apidologie, 48:623–634, doi:10.1007/s13592-017-0505-7.The original publication is available at https://www.springer.com/journal/13592Haplodiploid 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.Publisher's versio

Queenless colonies of the Asian red dwarf honey bee (Apis florea) are infiltrated by workers from other queenless colonies

In all honey bee species studied thus far, 2--4% of the workers were not born in the sampled colony. These unrelated (nonnatal) workers are thought to arise via orientation errors while returning from foraging trips. Interestingly, in colonies of the red dwarf honey bee, Apis florea, the proportion of nonnatal workers increases significantly when the colonies become queenless, and these workers are more likely to have active ovaries and lay eggs than natal workers. As a result, queenless colonies are heavily parasitized with the eggs of nonnatal workers, but the origin of the parasitizing workers is currently unknown. Here we show that workers from queenless A. florea colonies are far more likely to leave their colony and join another colony compared with workers from queenright colonies. Choice experiments showed that these drifted workers are much more likely to join a queenless colony than a colony with a queen. Perhaps surprisingly, not many workers from queenright colonies joined queenless colonies despite the opportunity for direct reproduction in queenless colonies. We suggest that the inclusive fitness benefits of remaining in the natal colony in the presence of the queen exceed the benefits of direct reproduction in an unrelated queenless colony. Copyright 2009, Oxford University Press.