Data from: Flickers of speciation? Sympatric color morphs of the arc-eye hawkfish, Paracirrhites arcatus, reveal key elements of divergence-with-gene-flow

One of the primary challenges of evolutionary research is to identify ecological factors that favor reproductive isolation. Therefore, studying partially isolated taxa has the potential to provide novel insight into the mechanisms of evolutionary divergence. Our study utilizes an adaptive color polymorphism in the arc-eye hawkfish (Paracirrhites arcatus) to explore the evolution of reproductive barriers in the absence of geographic isolation. Dark and light morphs are ecologically partitioned into basaltic and coral microhabitats a few meters apart. To test whether ecological barriers have reduced gene flow among dark and light phenotypes, we evaluated genetic variation at 30 microsatellite loci and a nuclear exon (Mc1r) associated with melanistic coloration. We report low, but significant microsatellite differentiation among color morphs and stronger divergence in the coding region of Mc1r indicating signatures of selection. Critically, we observed greater genetic divergence between color morphs on the same reefs than between the same morphs in different geographic locations. We hypothesize that adaptation to the contrasting microhabitats is overriding gene flow and is responsible for the partial reproductive isolation observed between sympatric color morphs. Combined with complementary studies of hawkfish ecology and behavior, these genetic results indicate an ecological barrier to gene flow initiated by habitat selection and enhanced by assortative mating. Hence the arc-eye hawkfish fulfill theoretical expectations for the earliest phase of speciation-with-gene-flow.进化生物学研究的核心挑战之一，在于探明能够促进生殖隔离形成的生态因子。因此，对处于部分生殖隔离的类群开展研究，有望为进化分化的内在机制提供全新视角。本研究以弧眼鹰䱵（Paracirrhites arcatus）的适应性体色多态性为研究对象，探究无地理隔离条件下生殖隔离的演化进程。深色与浅色体色型在生态位上发生分化，分别占据玄武岩与珊瑚微生境，二者空间间隔仅数米。为验证生态屏障是否已降低深色与浅色表型间的基因流，我们对30个微卫星（microsatellite）位点以及与黑化体色相关的核外显子Mc1r进行了遗传变异分析。研究结果显示，不同体色型间的微卫星分化程度较低但具有统计学显著性，而Mc1r编码区的分化程度更为显著，这指示了选择作用的分子信号。尤为关键的是，我们观测到同一生礁上不同体色型间的遗传分化程度，高于不同地理区域内同体色型的遗传分化水平。我们据此提出假说：对差异化微生境的适应性演化抵消了基因流，这正是同域分布体色型间所观测到的部分生殖隔离的成因。结合鹰䱵生态学与行为学的相关补充研究，本研究的遗传学结果表明，由生境选择所引发、并通过选型交配（assortative mating）强化的生态屏障，阻碍了基因流的传递。因此，弧眼鹰䱵符合伴基因流物种形成早期阶段的理论预期。