The opposing forces of gene flow and isolation are two major processes shaping genetic diversity. Understanding how these vary across space and time is necessary to identify the environmental features that promote diversification. The detection of considerable geographic structure in taxa from the arid Nearctic has prompted research into the drivers of isolation in the region. Several geographic features have been proposed as barriers to gene flow, including the Colorado River, Western Continental Divide (WCD), and a hypothetical Mid-Peninsular Seaway in Baja California. However, recent studies suggest that the role of barriers in genetic differentiation may have been overestimated when compared to other mechanisms of divergence. In this study, we infer historical and spatial patterns of connectivity and isolation in Desert Spiny Lizards (Sceloporus magister) and Baja Spiny Lizards (Sceloporus zosteromus), which together form a species complex composed of parapatric lineages with wide distributions in arid western North America. Our analyses incorporate mitochondrial sequences, genomic-scale data, and past and present climatic data to evaluate the nature and strength of barriers to gene flow in the region. Our approach relies on estimates of migration under the multispecies coalescent to understand the history of lineage divergence in the face of gene flow. Results show that the S. magister complex is geographically structured, but we also detect instances of gene flow. The WCD is a strong barrier to gene flow, while the Colorado River is more permeable. Analyses yield conflicting results for the catalyst of differentiation of peninsular lineages in S. zosteromus. Our study shows how large-scale genomic data for thoroughly sampled species can shed new light on biogeography. Furthermore, our approach highlights the need for the combined analysis of multiple sources of evidence to adequately characterize the drivers of divergence.

中文翻译：

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通过对沙漠多刺蜥蜴的基因组分析揭示干旱新北极的基因流动和分离


基因流动和分离的对立力量是塑造遗传多样性的两个主要过程。了解这些如何随空间和时间变化对于确定促进多元化的环境特征是必要的。在干旱的 Nearctic 分类群中检测到相当大的地理结构，这促使对该地区孤立的驱动因素进行研究。已经提出了几个地理特征作为基因流动的障碍，包括科罗拉多河、西部大陆分水岭 （WCD） 和下加利福尼亚州假设的中半岛航道。然而，最近的研究表明，与其他分化机制相比，障碍在遗传分化中的作用可能被高估了。在这项研究中，我们推断了沙漠多刺蜥蜴 （Sceloporus magister） 和巴哈多刺蜥蜴 （Sceloporus zosteromus） 的历史和空间连通性和孤立模式，它们共同形成了一个由广泛分布于干旱的北美西部的旁系谱系组成的物种复合体。我们的分析结合了线粒体序列、基因组尺度数据以及过去和现在的气候数据，以评估该地区基因流动障碍的性质和强度。我们的方法依赖于对多物种合并下迁移的估计，以了解面对基因流动的谱系分化的历史。结果表明，S. magister 复合体在地理上是结构化的，但我们也检测到基因流动的实例。WCD 是基因流动的强大屏障，而科罗拉多河的渗透性更强。分析得出了 S. zosteromus 半岛谱系分化催化剂的相互矛盾的结果。 我们的研究表明，彻底采样物种的大规模基因组数据如何为生物地理学提供新的见解。此外，我们的方法强调了对多个证据来源进行综合分析的必要性，以充分描述分歧的驱动因素。