Abstract：
Isolation by environment (IBE) is a population genomic pattern that arises when ecological barriers reduce gene flow between populations. Although current evidence suggests IBE is common in nature, few studies have evaluated the underlying mechanisms that generate IBE patterns. In this study, we evaluate five proposed mechanisms of IBE (natural selection against immigrants, sexual selection against immigrants, selection against hybrids, biased dispersal, and environment-based phenological differences) that may give rise to host-associated differentiation within a sympatric population of the redheaded pine sawfly, Neodiprion lecontei, a species for which IBE has previously been detected. We first characterize the three pine species used by N. lecontei at the site, finding morphological and chemical differences among the hosts that could generate divergent selection on sawfly host-use traits. Next, using morphometrics and ddRAD sequencing, we detect modest phenotypic and genetic differentiation among sawflies originating from different pines that is consistent with recent, in situ divergence. Finally, via a series of laboratory assays-including assessments of larval performance on different hosts, adult mate and host preferences, hybrid fitness, and adult eclosion timing-we find evidence that multiple mechanisms contribute to IBE in N. lecontei. Overall, our results suggest IBE can emerge quickly, possibly due to multiple mechanisms acting in concert to reduce migration between different environments.
摘要：
环境隔离（IBE）是一种种群基因组模式，当生态屏障减少种群之间的基因流动时出现。尽管目前的证据表明IBE在自然界中很常见，很少有研究评估了产生IBE模式的潜在机制。在这项研究中,我们评估了五种拟议的IBE机制(针对移民的自然选择，对移民的性选择，对杂种的选择，偏向分散，基于环境的物候差异），可能会在红发松树的同胞种群中引起宿主相关的分化，Neodiprionlecontei,先前已检测到IBE的物种。我们首先描述了N.lecontei在现场使用的三种松树，发现寄主之间的形态和化学差异，这些差异可能会对锯蝇寄主使用性状产生不同的选择。接下来,使用形态计量学和ddRAD测序，我们检测到来自不同松树的锯蝇之间的适度表型和遗传分化，原位发散。最后,通过一系列实验室检测，包括评估幼虫在不同宿主上的表现，成年伴侣和宿主的偏好，混合健身，和成人羽化时间-我们发现证据表明，多种机制有助于N.lecontei中的IBE。总的来说,我们的结果表明IBE可以迅速出现，可能是由于多种机制协同工作以减少不同环境之间的迁移。
