Data from: Convergent reversion to single mating in a wasp social parasite

While eusociality arose in species with single-mating females, multiple mating by queens has evolved repeatedly across the social ants, bees, and wasps. Understanding the benefits and costs of multiple mating of queens is important because polyandry results in reduced relatedness between siblings, reducing kin-selected benefits of helping while also selecting for secondary social traits that reduce intracolony conflict. The leading hypothesis for the benefits of polyandry in social insects emphasizes advantages of a genetically diverse workforce. Workerless social parasite species (inquilines) provide a unique opportunity to test this hypothesis, since they are derived from social ancestors but do not produce workers of their own. Such parasites are thus predicted to evolve single mating because they would experience the costs of multiple mating but not the benefits if such benefits accrue through the production of a genetically diverse group of workers. Here we show that the workerless social parasite Dolichovespula arctica, a derived parasite of wasps, has reverted to obligate single mating from a facultatively polyandrous ancestor, mirroring a similar reversion from obligate polyandry to approximate monandry in a social parasite of fungus-farming ants. This finding and a comparison with two other cases where inquilinism did not induce reversal to monandry support the hypothesis that facultative polyandry can be costly and may be maintained by benefits of a genetically diverse workforce.

尽管真社会性（eusociality）起源于实行单配偶制的雌性类群，但蚁后多雄交配（polyandry）在社会性蚂蚁、蜜蜂与胡蜂中已多次独立演化。理解蚁后多雄交配的收益与成本至关重要：多雄交配会降低同胞间的亲缘系数，削弱基于亲缘选择的利他行为收益，同时也会催生可减少社群内部冲突的次生社会性状。针对社会性昆虫中多雄交配的收益，主流假说强调了遗传多样的工职种群所具备的优势。无工职社会性寄生类群（inquilines）为验证该假说提供了独特契机——这类物种虽起源于社会性祖先，却无法产生自身的工职种群。因此，此类寄生虫被预测会演化出单配偶制：若多雄交配的收益来源于遗传多样的工职种群，那么它们将仅承担多雄交配的成本，却无法获得相应收益。本研究表明，作为胡蜂衍生寄生类群的无工职社会性寄生物种*Dolichovespula arctica*，已从兼具多雄交配能力的祖先类群退回至专性单配偶制，这与切叶蚁社会性寄生类群从专性多雄交配向近似单雄交配的反向演化现象一致。结合对另外两例社会寄生并未引发单配偶制逆转的案例的比较，这一发现支持了以下假说：兼性多雄交配模式可能存在成本，且其得以维持的原因或许正是遗传多样的工职种群所带来的收益。