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.

异域成种（Allopatric speciation）或许是新物种产生的核心机制。然而，目前仍难以评估该过程的普遍性，因为鲜有研究能够证实地理隔离可引发区域动物类群内多个物种逐步形成生殖隔离。本研究首先整合全新实证数据集（涵盖7个类群）与已发表文献数据（涵盖9个类群）的结果，证明大湖东部流域是遗传分化水平各异的淡水鱼类冰期谱系的多物种缝合带。其次，我们对4对谱系开展了扩增片段长度多态性（amplified fragment length polymorphism）分析。结果显示，线粒体DNA 5′端细胞色素C氧化酶亚基I（mtDNA 5′ COI，即DNA条形码）序列分化程度较高（>2%）的谱系已形成较强的生殖隔离障碍；而在同域分布时，分化程度较低的谱系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查北美淡水鱼类隐存物种的标准。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，我们为异域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作“成种泵”，其在生物多样性形成过程中发挥了主导作用。