Data from: Dispersal and gene flow in the rare, parasitic Large Blue butterfly Maculinea arion

Dispersal is crucial for gene flow and often determines the long-term stability of meta-populations, particularly in rare species with specialized life cycles. Such species are often foci of conservation efforts because they suffer disproportionally from degradation and fragmentation of their habitat. However, detailed knowledge of effective gene flow through dispersal is often missing, so that conservation strategies have to be based on mark–recapture observations that are suspected to be poor predictors of long-distance dispersal. These constraints have been especially severe in the study of butterfly populations, where microsatellite markers have been difficult to develop. We used eight microsatellite markers to analyse genetic population structure of the Large Blue butterfly Maculinea arion in Sweden. During recent decades, this species has become an icon of insect conservation after massive decline throughout Europe and extinction in Britain followed by reintroduction of a seed population from the Swedish island of Öland. We find that populations are highly structured genetically, but that gene flow occurs over distances 15 times longer than the maximum distance recorded from mark–recapture studies, which can only be explained by maximum dispersal distances at least twice as large as previously accepted. However, we also find evidence that gaps between sites with suitable habitat exceeding ∼20 km induce genetic erosion that can be detected from bottleneck analyses. Although further work is needed, our results suggest that M. arion can maintain fully functional metapopulations when they consist of optimal habitat patches that are no further apart than ∼10 km.

扩散对基因流动至关重要，且通常决定了集合种群（metapopulation）的长期存续稳定性，对于拥有特化生活史的稀有物种而言尤为如此。这类物种往往是保育工作的核心关注对象，因其栖息地的退化与破碎化会对其造成远超其他类群的严重威胁。然而，学界目前仍缺乏关于通过扩散实现的有效基因流动的详细认知，导致保育策略不得不依赖标记重捕法（mark–recapture）的观测数据——但这类数据被认为难以准确预测长距离扩散事件。这类研究局限在蝴蝶种群的相关研究中尤为突出，因为微卫星标记（microsatellite markers）的开发难度极大。本研究借助8个微卫星标记，对瑞典境内的大蓝蝶（*Maculinea arion*）的遗传种群结构开展了分析。近数十年来，该物种种群在欧洲全域出现大幅衰退，英国本土种群彻底灭绝后，科研人员从瑞典厄兰岛（Öland）引入源种群实施再引入计划，如今该物种已成为昆虫保育的标志性类群。研究结果显示，该蝶种群存在高度的遗传结构分化，但基因流动的发生距离可达标记重捕法观测到的最大扩散距离的15倍之多——这一现象仅能通过至少两倍于此前学界公认的最大扩散距离来解释。不过，本研究同时发现，当适宜栖息地斑块之间的间距超过约20公里时，会引发可通过瓶颈效应（bottleneck）分析检测到的遗传侵蚀。尽管仍需开展更多后续研究，但本研究结果表明，当大蓝蝶的适宜栖息地斑块间距不超过约10公里时，其种群可维持功能完整的集合种群结构。