Data from: Stepping-stone expansion and habitat loss explain a peculiar genetic structure and distribution of a forest insect

It is challenging to unravel the history of organisms with highly scattered populations. Such species may have fragmented distributions because extant populations are remnants of a previously more continuous range, or because the species has narrow habitat requirements in combination with good dispersal capacity (naturally or vector borne). The northern pine processionary moth Thaumetopoea pinivora has a scattered distribution with fragmented populations in two separate regions, northern and south-western Europe. The aims of this study were to explore the glacial and postglacial history of T. pinivora, and add to the understanding of its current distribution and level of contemporary gene flow. We surveyed published records of its occurrence and analysed individuals from a representative subset of populations across the range. A 633 bp long fragment of the mtDNA COI gene was sequenced and nine polymorphic microsatellite loci were genotyped. Only nine nucleotide sites were polymorphic in the COI gene and 90% of the individuals from across its whole range shared the same haplotype. The microsatellite diversity gradually declined towards the north, and unique alleles were found in only three of the northern and three of southern sites. Genetic structuring did not indicate complete isolation among regions, but an increase of genetic isolation by geographic distance. Approximate Bayesian model choice suggested recent divergence during the postglacial period, but glacial refugia remain unidentified. The progressive reduction of suitable habitats is suggested to explain the genetic structure of the populations and we suggest that T. pinivora is a cold-tolerant relict species, with situation-dependent dispersal.

解析种群高度零散分布的生物的演化历史，是一项极具挑战性的工作。这类物种呈现破碎化分布的原因不外乎两类：现存种群是此前连续分布范围的残遗类群，或是该物种对栖息地具有严格要求，但同时具备较强的扩散能力（自然扩散或借助媒介扩散）。北松列队蛾（Thaumetopoea pinivora）的分布零散，在北欧与西南欧两个独立区域内均存在破碎化种群。本研究旨在探究北松列队蛾的冰期及冰期后演化历史，以增进对其当前分布格局以及当代基因流水平的认知。我们调研了已发表的该物种分布记录，并对分布范围内具有代表性的种群个体展开分析。对线粒体DNA（mtDNA）COI基因的633 bp长度片段进行了测序，同时对9个多态性微卫星位点完成了基因分型。COI基因中仅存在9个多态性核苷酸位点，且整个分布范围内90%的个体共享同一单倍型。微卫星多样性随纬度向北逐渐降低，且仅在3个北部采样点与3个南部采样点中发现了特有等位基因。种群遗传结构并未显示区域间存在完全隔离，而是呈现出遗传隔离随地理距离增加而加剧的模式。近似贝叶斯模型选择结果显示，该物种在冰期后发生了近期分化，但其冰期避难所仍未被确定。研究结果表明，适宜栖息地的逐步缩减是该种群遗传结构形成的关键诱因，我们据此推测北松列队蛾是一种耐寒孑遗物种，其扩散能力随环境条件而异。