Department of Biological Sciences, University of Denver, Denver, CO, USA.
Department of Biology, Syracuse University, Syracuse, NY, USA.
Mol Ecol. 2019 Sep;28(18):4317-4334. doi: 10.1111/mec.15218. Epub 2019 Sep 26.
Population divergence can occur due to mechanisms associated with geographic isolation and/or due to selection associated with different ecological niches. Much of the evidence for selection-driven speciation has come from studies of specialist insect herbivores that use different host plant species; however, the influence of host plant use on population divergence of generalist herbivores remains poorly understood. We tested how diet breadth, host plant species and geographic distance influence population divergence of the fall webworm (Hyphantria cunea; FW). FW is a broadly distributed, extreme generalist herbivore consisting of two morphotypes that have been argued to represent two different species: black-headed and red-headed. We characterized the differentiation of FW populations at two geographic scales. We first analysed the influence of host plant and geographic distance on genetic divergence across a broad continental scale for both colour types. We further analysed the influence of host plant, diet breadth and geographic distance on divergence at a finer geographic scale focusing on red-headed FW in Colorado. We found clear genetic and morphological distinction between red- and black-headed FW, and Colorado FW formed a genetic cluster distinct from other locations. Although both geographic distance and host plant use were correlated with genetic distance, geographic distance accounted for up to 3× more variation in genetic distance than did host plant use. As a rare study investigating the genetic structure of a widespread generalist herbivore over a broad geographic range (up to 3,000 km), our study supports a strong role for geographic isolation in divergence in this system.
种群分歧可能是由于与地理隔离相关的机制或与不同生态位相关的选择导致的。选择驱动物种形成的大部分证据来自对使用不同宿主植物物种的专门昆虫食草动物的研究；然而，宿主植物利用对一般食草动物种群分歧的影响仍知之甚少。我们测试了饮食广度、宿主植物物种和地理距离如何影响秋粘虫（Hyphantria cunea；FW）种群的分歧。FW 是一种分布广泛、极端的广义食草动物，由两种形态型组成，有人认为它们代表两种不同的物种：黑头和红头。我们在两个地理尺度上描述了 FW 种群的分化。我们首先分析了宿主植物和地理距离对两种颜色类型在广泛的大陆尺度上遗传分歧的影响。我们进一步分析了宿主植物、饮食广度和地理距离对以科罗拉多州红头 FW 为重点的更精细地理尺度上分歧的影响。我们发现红头和黑头 FW 之间存在明显的遗传和形态差异，科罗拉多 FW 形成了一个与其他地点不同的遗传集群。尽管地理距离和宿主植物利用都与遗传距离相关，但地理距离解释的遗传距离变化是宿主植物利用的三倍多。作为一项罕见的研究，调查了广泛分布的广义食草动物在广泛的地理范围内（最多 3000 公里）的遗传结构，我们的研究支持地理隔离在该系统分歧中的重要作用。
