Data from: Glacial cycles as an allopatric speciation pump in North Eastern American freshwater fishes

Allopatric speciation may be the principal mechanism generating new species. Yet, it remains difficult to judge the generality of this process because few studies have provided evidence that geographic isolation has triggered the development of reproductive isolation over multiple species of a regional fauna. Here, we first combine results from new empirical data sets (7 taxa) and published literature (9 taxa) to show that the eastern Great Lakes drainage represents a multispecies suture zone for glacial lineages of freshwater fishes with variable levels of genetic divergence. Second, we performed amplified fragment length polymorphism analyses among four pairs of lineages. Results indicate that lineages with relatively deep levels of mtDNA 5′ COI (barcode) sequence divergence (>2%) developed strong reproductive barriers, while lineages with lower levels of divergence show weaker reproductive isolation when found in sympatry. This suggests that a threshold of 2% sequence divergence at mtDNA could be used as a first step to flag cryptic species in North American freshwater fishes. By describing different levels of divergence and reproductive isolation in different co-occurring fishes, we offer strong evidence that allopatric speciation has contributed significantly to the diversification of north-eastern American freshwater fishes and confirm that Pleistocene glacial cycles can be viewed as a ‘speciation pump’ that played a predominant role in generating biodiversity.

地理成种（allopatric speciation）或许是新物种形成的核心机制。然而，该过程的普遍性仍难以判定，因鲜有研究能证实地理隔离可触发区域动物类群内多个物种的生殖隔离演化。在此研究中，我们首先整合全新实测数据集（涵盖7个分类单元）与已发表文献数据（涵盖9个分类单元）的结果，证实五大湖东部流域是遗传分化水平各异的淡水鱼类冰川支系的多物种缝合带。其次，我们对四组支系开展了扩增片段长度多态性（amplified fragment length polymorphism, AFLP）分析。结果显示：线粒体DNA 5'端COI（条形码序列）序列分化水平较高（>2%）的支系已形成较强的生殖隔离屏障；而分化水平较低的支系若同域分布，则仅表现出较弱的生殖隔离。这表明，线粒体DNA序列2%的分化阈值可作为初步筛选北美淡水鱼类隐存物种（cryptic species）的标准。通过刻画不同同域分布鱼类类群的分化水平与生殖隔离程度，我们为地理成种显著推动北美东北部淡水鱼类的物种多样化提供了坚实证据，并证实更新世冰期循环可被视为‘成种泵’，其在生物多样性形成过程中发挥了主导作用。