Data from: Species mtDNA genetic diversity explained by infrapopulation size in a host-symbiont system

Understanding what shapes variation in genetic diversity among species remains a major challenge in evolutionary ecology, and it has been seldom studied in parasites and other host-symbiont systems. Here, we studied mtDNA variation in a host-symbiont non-model system: 418 individual feather mites from 17 feather mite species living on 17 different passerine bird species. We explored how a surrogate of census size, the median infrapopulation size (i.e., the median number of individual parasites per infected host individual), explains mtDNA genetic diversity. Feather mite species genetic diversity was positively correlated with mean infrapopulation size, explaining 34% of the variation. As expected from the biology of feather mites, we found bottleneck signatures for most of the species studied but, in particular, three species presented extremely low mtDNA diversity values given their infrapopulation size. Their star-like haplotype networks (in contrast with more reticulated networks for the other species) suggested that their low genetic diversity was the consequence of severe bottlenecks or selective sweeps. Our study shows for the first time that mtDNA diversity can be explained by infrapopulation sizes, and suggests that departures from this relationship could be informative of underlying ecological and evolutionary processes.

解析驱动物种间遗传多样性差异的核心机制，始终是进化生态学领域的重大挑战之一，而针对寄生虫及其他宿主-共生体（host-symbiont）系统的相关研究则极为匮乏。本研究聚焦于一个非模式宿主-共生体系统的线粒体DNA（mitochondrial DNA, mtDNA）变异：我们采集了寄生于17种不同雀形目鸟类的17种羽螨的418个个体样本。本研究探讨了种群普查规模的替代指标——寄种群（infrapopulation）中位数大小（即单只感染宿主所携带的寄生虫个体数中位数）对线粒体DNA遗传多样性的解释能力。结果显示，羽螨物种的遗传多样性与寄种群平均大小呈显著正相关，该相关性可解释34%的遗传多样性变异。基于羽螨的生物学特性，我们在多数研究物种中检测到了种群瓶颈效应信号；尤为特别的是，有3个物种的寄种群大小与其线粒体DNA遗传多样性水平严重不匹配，其遗传多样性极低。这3个物种的单倍型网络（haplotype network）呈星状结构（其余物种则多为网状结构），提示其极低的遗传多样性源于严重的种群瓶颈或选择性清除（selective sweep）事件。本研究首次证实，寄种群大小可有效解释线粒体DNA遗传多样性水平，同时提示，偏离该相关性的案例可用于揭示其背后潜在的生态与进化过程。