Data from: Evidence that microgynes of Myrmica rubra ants are social parasites that attack old host colonies

Ant microgynes are miniaturized queen forms found together with normal queens (macrogynes) in species occurring across the ant phylogeny. Their role is not yet fully understood: in some cases, they seem to be nonparasitic alternative reproductive morphs, in others incipient social parasites, and thus potential models for studying the evolution of social parasitism. Whether they are regarded as parasitic or not has traditionally been based on genetic differentiation from syntopic macrogynes and/or the queen/worker ratio of their offspring rather than measuring fitness traits. We confirmed previously reported genetic differentiation between microgynes and macrogynes of Myrmica rubra in a population studied for the first time. Further, we measured virulence and infectivity of M. rubra microgynes in a controlled laboratory experiment. Nests headed only by macrogynes (controls), only by microgynes, and naturally and artificially mixed nests were kept under identical conditions. We found reduction in worker numbers of both naturally and artificially mixed macrogyne/microgyne nests compared with controls, and strong reduction but also surprising variation in fitness of nests headed only by microgynes. Microgyne nests produced workers, males and microgynes. Microgynes did not themselves reproduce in artificially mixed nests, but reproduced most in naturally mixed nests that had lost their macrogyne queen. This, together with higher mortality of field-collected macrogyne queens from naturally infested colonies and greater estimated relative age of macrogyne queens in naturally infected nests, suggests that they preferentially exploit older host colonies. We conclude that M. rubra microgynes are intraspecific social parasites specialized on exploiting old host colonies.

蚂蚁微蚁后（microgynes）是体型小型的蚁后类群，与正常大蚁后（macrogynes）共存于遍布蚂蚁系统发育各分支的多个物种中。其生态功能尚未完全阐明：在部分场景中它们似乎是非寄生性的替代生殖型类群，而在另一些场景中则处于初期社会寄生状态，因此是研究社会寄生演化的潜在模型物种。传统上，判断微蚁后是否属于寄生类群，通常依据其与同域共存大蚁后的遗传分化程度，以及后代的蚁后/工蚁比例，而非通过适合度性状进行评估。本研究首次对某一野外种群展开调查，证实了此前关于红林蚁（Myrmica rubra）微蚁后与大蚁后间存在遗传分化的报道。进一步，我们通过可控实验室实验，测定了红林蚁微蚁后的毒力与侵染性。实验设置仅由大蚁后统领的蚁巢（对照组）、仅由微蚁后统领的蚁巢，以及天然混合和人工混合的蚁巢，所有蚁巢均置于相同环境条件下饲养。研究发现，与对照组相比，天然混合和人工混合的大/微蚁后蚁巢的工蚁数量均出现下降；而仅由微蚁后统领的蚁巢，其适合度不仅大幅降低，还存在出人意料的变异。微蚁后统领的蚁巢可产生工蚁、雄蚁及微蚁后。在人工混合蚁巢中，微蚁后自身并未进行繁殖，但在那些失去大蚁后的天然混合蚁巢中，微蚁后的繁殖率最高。结合野外采集的天然侵染蚁巢中大蚁后死亡率更高，且此类蚁巢中大蚁后的相对预估年龄更大这一结果，表明微蚁后会优先侵染成熟的宿主蚁巢。综上，红林蚁的微蚁后属于种内社会寄生者，特化于侵染成熟宿主蚁巢。