Rapid buildup of sympatric species diversity in Alpine whitefish

Adaptive radiations in postglacial fish offer excellent settings to study the evolutionary mechanisms involved in the rapid buildup of sympatric species diversity from a single lineage. Here, we address this by exploring the genetic and ecological structure of the largest Alpine whitefish radiation known, that of Lakes Brienz and Thun, using microsatellite data of more than 2000 whitefish caught during extensive species‐targeted and habitat‐randomized fishing campaigns. We find six strongly genetically and ecologically differentiated species, four of which occur in both lakes, and one of which was previously unknown. These four exhibit clines of genetic differentiation that are paralleled in clines of eco‐morphological and reproductive niche differentiation, consistent with models of sympatric ecological speciation along environmental gradients. In Lake Thun, we find two additional species, a profundal specialist and a species introduced in the 1930s from another Alpine whitefish radiation. Strong genetic differentiation between this introduced species and all native species of Lake Thun suggests that reproductive isolation can evolve among allopatric whitefish species within 15,000 years and persist in secondary sympatry. Consistent with speciation theory, we find stronger correlations between genetic and ecological differentiation for sympatrically than for allopatrically evolved species.

冰期后鱼类的适应辐射（Adaptive radiations）为探究单一支系快速形成同域物种多样性（sympatric species diversity）的演化机制提供了绝佳的研究体系。本研究以目前已知规模最大的阿尔卑斯白鱼适应辐射群——布里恩茨湖与图恩湖白鱼类群为研究对象，借助针对物种且生境随机化的大规模捕捞作业所采集的2000余尾白鱼的微卫星（microsatellite）数据，解析其遗传与生态结构。研究共发现6个遗传与生态分化显著的物种，其中4种同时分布于两个湖泊，另有1个为此前未被记录的新物种。这4个物种呈现出清晰的遗传分化梯度，且该梯度与生态形态及繁殖生态位分化梯度高度契合，符合沿环境梯度发生同域生态物种形成（sympatric ecological speciation）的理论模型。在图恩湖中，我们还发现了另外2个物种：一种为深湖栖特化种（profundal specialist），另一种是1930年代从另一阿尔卑斯白鱼适应辐射群引入的物种。该引入物种与图恩湖所有本土物种间均存在强烈的遗传分化，这表明异域白鱼种群（allopatric whitefish species）间可在15000年内演化出生殖隔离（reproductive isolation），并在次级同域分布（secondary sympatry）状态下得以维持。本研究结果与物种形成理论（speciation theory）一致：相较于异域演化物种（allopatrically evolved species），同域演化物种（sympatrically evolved species）的遗传分化与生态分化间存在更强的相关性。