Data from: Spatial and temporal genetic structure at the fourth trophic level in a fragmented landscape

A fragmented habitat becomes increasingly fragmented for species at higher trophic levels, such as parasitoids. To persist these species are expected to possess life history traits, such as high dispersal, that facilitate their ability to use resources that become scarce in fragmented landscapes. If a specialized parasitoid disperses widely to take advantage of a sparse host, then the parasitoid population should have lower genetic structure than the host. We investigated the temporal and spatial genetic structure of a hyperparasitoid (fourth trophic level) in a fragmented landscape over 50 by 70 km, using microsatellite markers, and compared it with the known structures of its host parasitoid, and the butterfly host which lives as a classic metapopulation. We found that population genetic structure decreases with increasing trophic level. The hyperparasitoid has fewer genetic clusters (K=4), than its host parasitoid (K=15), which in turn is less structured than the host butterfly (K=27). The genetic structure of the hyperparasitoid also shows temporal variation, with genetic differentiation increasing due to reduction of the population size, which reduces the effective population size. Overall, our study confirms the idea that specialized species must be dispersive to use a fragmented host resource, but that this adaptation has limits.对于处于较高营养级（trophic level）的物种而言，已破碎的生境会进一步愈发破碎，以拟寄生者（parasitoid）为例。这类物种若要维持种群存续，理应演化出高扩散能力等生活史特征，以提升其在破碎化景观中利用稀缺资源的能力。倘若特化拟寄生者通过广泛扩散来利用稀少的寄主资源，那么该拟寄生者种群的遗传结构（genetic structure）理应弱于其寄主种群。本研究以一片跨度为50×70 km的破碎化景观中的第四营养级重寄生者（hyperparasitoid）为研究对象，借助微卫星标记（microsatellite markers）解析其时空遗传结构，并将其与已知的寄主拟寄生者、以及以典型集合种群（metapopulation）模式生存的寄主蝴蝶的遗传结构进行对比。研究结果表明，种群遗传结构随营养级升高而减弱：重寄生者的遗传簇（genetic clusters）数量（K=4）少于寄主拟寄生者（K=15），而寄主拟寄生者的遗传结构又弱于寄主蝴蝶（K=27）。此外，重寄生者的遗传结构还存在时间变异：种群规模缩减会导致有效种群大小（effective population size）降低，进而加剧遗传分化（genetic differentiation）。综上，本研究证实了这一假说：特化物种必须具备扩散能力以利用破碎化的寄主资源，但这类适应性演化存在其限度。