Behaviour and Genetics of Social Insects Lab, School of Biological Sciences A12, University of Sydney, NSW 2006, Australia.
Evolution. 2011 Mar;65(3):860-8. doi: 10.1111/j.1558-5646.2010.01164.x. Epub 2010 Nov 5.
The honey bee population of South Africa is divided into two subspecies: a northern population in which queenless workers reproduce arrhenotokously and a southern one in which workers reproduce thelytokously. A hybrid zone separates the two, but on at least three occasions the northern population has become infested by reproductive workers derived from the southern population. These parasitic workers lay in host colonies parthenogenetically, resulting in yet more parasites. The current infestation is 20-year old--surprising because an asexual lineage is expected to show a decline in vigor over time due to increasing homozygosity. The decline is expected to be acute in honey bees, where homozygosity at the sex locus is lethal. We surveyed colonies from the zone of infestation and genotyped putative parasites at two sets of linked microsatellite loci. We confirm that there is a single clonal lineage of parasites that shows minor variations arising from recombination events. The lineage shows high levels of heterozygosity, which may be maintained by selection against homozygotes, or by a reduction in recombination frequency within the lineage. We suggest that the clonal lineage can endure the costs of asexual reproduction because of the fitness benefits of its parasitic life history.
北方种群中无蜂王的工蜂进行孤雌生殖，而南方种群中的工蜂则行产雌孤雌生殖。一个杂交区将它们分开，但至少有三次，北方种群被南方种群衍生的生殖工蜂所侵袭。这些寄生工蜂在宿主群体中进行孤雌生殖，导致更多的寄生虫。目前的疫情已经持续了 20 年——令人惊讶的是，由于杂合度的增加，一个无性系预计会随着时间的推移而表现出活力下降。这种下降预计在蜜蜂中会很严重，因为性位点的纯合性是致命的。我们调查了疫区的蜂群，并在两组连锁微卫星基因座上对疑似寄生虫进行了基因分型。我们证实，有一种单一的寄生虫无性系，表现出由重组事件引起的微小变异。该无性系表现出高度的杂合性，这可能是由于对纯合子的选择，或由于该无性系内重组频率的降低而维持的。我们认为，由于其寄生生活史的适应性好处，无性系的寄生虫能够承受无性繁殖的代价。
