Department of Evolution, Ecology & Organismal Biology, The Ohio State University, Columbus, Ohio, USA.
Department of Botany and Rocky Mountain Herbarium, University of Wyoming, Laramie, Wyoming, USA.
Mol Ecol. 2022 Aug;31(16):4402-4416. doi: 10.1111/mec.16595. Epub 2022 Jul 17.
Pleistocene glacial cycles drastically changed the distributions of taxa endemic to temperate rainforests in the Pacific Northwest, with many experiencing reduced habitat suitability during glacial periods. In this study, we investigate whether glacial cycles promoted intraspecific divergence and whether subsequent range changes led to secondary contact and gene flow. For seven invertebrate species endemic to the PNW, we estimated species distribution models (SDMs) and projected them onto current and historical climate conditions to assess how habitat suitability changed during glacial cycles. Using single nucleotide polymorphism (SNP) data from these species, we assessed population genetic structure and used a machine-learning approach to compare models with and without gene flow between populations upon secondary contact after the last glacial maximum (LGM). Finally, we estimated divergence times and rates of gene flow between populations. SDMs suggest that there was less suitable habitat in the North Cascades and Northern Rocky Mountains during glacial compared to interglacial periods, resulting in reduced habitat suitability and increased habitat fragmentation during the LGM. Our genomic data identify population structure in all taxa, and support gene flow upon secondary contact in five of the seven taxa. Parameter estimates suggest that population divergences date to the later Pleistocene for most populations. Our results support a role of refugial dynamics in driving intraspecific divergence in the Cascades Range. In these invertebrates, population structure often does not correspond to current biogeographic or environmental barriers. Rather, population structure may reflect refugial lineages that have since expanded their ranges, often leading to secondary contact between once isolated lineages.
更新世冰川周期极大地改变了太平洋西北地区温带雨林特有种的分布，许多物种在冰川期经历了适宜栖息地减少的情况。在这项研究中，我们调查了冰川周期是否促进了种内分化，以及随后的范围变化是否导致了次生接触和基因流。对于七种太平洋西北地区特有的无脊椎动物物种，我们估计了物种分布模型（SDM），并将其投影到当前和历史气候条件下，以评估在冰川周期中栖息地适宜性如何变化。利用来自这些物种的单核苷酸多态性（SNP）数据，我们评估了种群遗传结构，并使用机器学习方法比较了在末次冰盛期（LGM）后发生次生接触时种群之间有无基因流的模型。最后，我们估计了种群之间的分歧时间和基因流速率。SDM 表明，与间冰期相比，冰川期北喀斯喀特山脉和落基山脉北部的适宜栖息地较少，导致 LGM 期间适宜栖息地减少和栖息地破碎化增加。我们的基因组数据确定了所有分类群的种群结构，并支持在七个分类群中的五个分类群中发生次生接触时的基因流。参数估计表明，大多数种群的种群分歧发生在更新世晚期。我们的研究结果支持避难所动态在驱动喀斯喀特山脉种内分化中的作用。在这些无脊椎动物中，种群结构通常与当前的生物地理或环境障碍不一致。相反，种群结构可能反映了避难所谱系，这些谱系后来扩大了它们的范围，通常导致曾经隔离的谱系之间发生次生接触。
