Anton Christian, Zeisset Inga, Musche Martin, Durka Walter, Boomsma Jacobus J, Settele Josef
Helmholtz-Centre for Environmental Research - UFZ, Department of Community Ecology, Theodor-Lieser-Strasse 4, D-06120 Halle, Germany.
Mol Ecol. 2007 Sep;16(18):3828-38. doi: 10.1111/j.1365-294X.2007.03441.x.
Habitat fragmentation may interrupt trophic interactions if herbivores and their specific parasitoids respond differently to decreasing connectivity of populations. Theoretical models predict that species at higher trophic levels are more negatively affected by isolation than lower trophic level species. By combining ecological data with genetic information from microsatellite markers we tested this hypothesis on the butterfly Maculinea nausithous and its specialist hymenopteran parasitoid Neotypus melanocephalus. We assessed the susceptibility of both species to habitat fragmentation by measuring population density, rate of parasitism, overall genetic differentiation (theta(ST)) and allelic richness in a large metapopulation. We also simulated the dynamics of genetic differentiation among local populations to asses the relative effects of migration rate, population size, and haplodiploid (parasitoid) and diploid (host) inheritance on metapopulation persistence. We show that parasitism by N. melanocephalus is less frequent at larger distances to the nearest neighbouring population of M. nausithous hosts, but that host density itself is not affected by isolation. Allelic richness was independent of isolation, but the mean genetic differentiation among local parasitoid populations increased with the distance between these populations. Overall, genetic differentiation in the parasitoid wasp was much greater than in the butterfly host and our simulations indicate that this difference is due to a combination of haplodiploidy and small local population sizes. Our results thus support the hypothesis that Neotypus parasitoid wasps are more sensitive to habitat fragmentation than their Maculinea butterfly hosts.
如果食草动物及其特定的寄生生物对种群连通性降低的反应不同，栖息地破碎化可能会中断营养级相互作用。理论模型预测，营养级较高的物种比营养级较低的物种更容易受到隔离的负面影响。通过将生态数据与来自微卫星标记的遗传信息相结合，我们以瑙氏黄斑蛱蝶及其专性膜翅目寄生蜂黑首新羽角姬小蜂为对象，对这一假设进行了验证。我们通过测量一个大型复合种群中的种群密度、寄生率、总体遗传分化（theta(ST)）和等位基因丰富度，评估了这两个物种对栖息地破碎化的敏感性。我们还模拟了当地种群间遗传分化的动态，以评估迁移率、种群大小以及单双倍体（寄生蜂）和双倍体（寄主）遗传对复合种群持续性的相对影响。我们发现，对于黑首新羽角姬小蜂来说，距离最近的瑙氏黄斑蛱蝶寄主种群越远，寄生频率越低，但寄主密度本身不受隔离的影响。等位基因丰富度与隔离无关，但当地寄生蜂种群之间的平均遗传分化随着这些种群之间距离的增加而增大。总体而言，寄生蜂的遗传分化远大于蝴蝶寄主，我们的模拟结果表明，这种差异是由单双倍体和当地种群规模较小共同导致的。因此，我们的结果支持了这样一个假设，即新羽角姬小蜂寄生蜂比它们的瑙氏黄斑蛱蝶寄主对栖息地破碎化更敏感。
