Bagley Robin K, Sousa Vitor C, Niemiller Matthew L, Linnen Catherine R
Department of Biology, University of Kentucky, Lexington, KY, 40506, USA.
cE3c - Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, 1749-016, Lisboa, Portugal.
Mol Ecol. 2017 Feb;26(4):1022-1044. doi: 10.1111/mec.13972. Epub 2017 Jan 27.
Divergent host use has long been suspected to drive population differentiation and speciation in plant-feeding insects. Evaluating the contribution of divergent host use to genetic differentiation can be difficult, however, as dispersal limitation and population structure may also influence patterns of genetic variation. In this study, we use double-digest restriction-associated DNA (ddRAD) sequencing to test the hypothesis that divergent host use contributes to genetic differentiation among populations of the redheaded pine sawfly (Neodiprion lecontei), a widespread pest that uses multiple Pinus hosts throughout its range in eastern North America. Because this species has a broad range and specializes on host plants known to have migrated extensively during the Pleistocene, we first assess overall genetic structure using model-based and model-free clustering methods and identify three geographically distinct genetic clusters. Next, using a composite-likelihood approach based on the site frequency spectrum and a novel strategy for maximizing the utility of linked RAD markers, we infer the population topology and date divergence to the Pleistocene. Based on existing knowledge of Pinus refugia, estimated demographic parameters and patterns of diversity among sawfly populations, we propose a Pleistocene divergence scenario for N. lecontei. Finally, using Mantel and partial Mantel tests, we identify a significant relationship between genetic distance and geography in all clusters, and between genetic distance and host use in two of three clusters. Overall, our results indicate that Pleistocene isolation, dispersal limitation and ecological divergence all contribute to genomewide differentiation in this species and support the hypothesis that host use is a common driver of population divergence in host-specialized insects.
长期以来，人们一直怀疑宿主利用分化会推动植食性昆虫的种群分化和物种形成。然而，评估宿主利用分化对遗传分化的贡献可能很困难，因为扩散限制和种群结构也可能影响遗传变异模式。在本研究中，我们使用双酶切限制性内切酶相关DNA（ddRAD）测序来检验以下假设：宿主利用分化导致红头松叶蜂（Neodiprion lecontei）种群间的遗传分化，红头松叶蜂是一种广泛分布的害虫，在北美东部的整个分布范围内利用多种松树宿主。由于该物种分布范围广，且专门以已知在更新世期间广泛迁移的宿主植物为食，我们首先使用基于模型和无模型的聚类方法评估总体遗传结构，并识别出三个地理上不同的遗传簇。接下来，我们使用基于位点频率谱的复合似然方法和一种最大化连锁RAD标记效用的新策略，推断种群拓扑结构并确定到更新世的分歧日期。基于对松树避难所的现有认识、估计的种群统计学参数以及叶蜂种群间的多样性模式，我们提出了一个关于红头松叶蜂的更新世分歧情景。最后，我们使用Mantel检验和偏Mantel检验，发现在所有簇中遗传距离与地理之间存在显著关系，在三个簇中的两个簇中遗传距离与宿主利用之间存在显著关系。总体而言，我们的结果表明，更新世隔离、扩散限制和生态分化都导致了该物种全基因组的分化，并支持宿主利用是宿主专一性昆虫种群分歧的常见驱动因素这一假设。
