Community phylogeographic patterns reveal how a barrier filters and structures taxa in North American warm deserts

Aim: The study of biogeographic barriers has been instrumental in understanding the evolution and distribution of taxa. With the increasing availability of empirical datasets, emergent patterns can be inferred from communities by synthesizing how barriers filter and structure populations across species. We assemble phylogeographic data across a barrier and perform spatially-explicit simulations to quantify spatiotemporal patterns of divergence, the influence of species traits on these patterns, and the statistical power needed to differentiate alternative diversification modes. Location: North America Methods: We incorporate published datasets to examine taxa around the Cochise Filter Barrier, separating the Sonoran and Chihuahuan Deserts of North America, to synthesize phylogeographic structuring across the community with respect to organismal functional traits. We then use simulation and machine learning to assess the power of phylogeographic model selection. Results: Taxa distributed across the Cochise Filter Barrier show heterogeneous responses to the barrier in levels of gene flow, phylogeographic structure, divergence timing, barrier width, and divergence mechanism. These responses correlate with locomotor and thermoregulatory traits. Many taxa show a Pleistocene population genetic break, often with introgression after divergence. Allopatric isolation and isolation-by-environment are the primary mechanisms structuring genetic divergence within taxa. Simulations reveal that in spatially-explicit isolation-with-migration models across the barrier, age of divergence, presence of gene flow, and presence of isolation-by-distance can confound the interpretation of evolutionary history and model selection by producing easily-confusable results. We re-analyze five empirical genetic datasets to illustrate the utility of these simulations despite these constraints. Main Conclusions: By synthesizing phylogeographic data for the Cochise Filter Barrier we show that barriers interact with species traits to differentiate taxa in communities over millions of years. Identifying diversification modes across the barrier for these taxa remains challenging because commonly invoked demographic models may not be identifiable across a range of likely parameter space.

研究目标：生物地理屏障（biogeographic barriers）的研究对于理解类群（taxa）的演化与分布具有重要意义。随着实证数据集的可获取性不断提升，我们可以通过综合分析屏障如何过滤并构建跨物种种群的结构，从群落中推断出新兴格局。本研究整合了某一屏障两侧的系统生物地理学（phylogeography）数据，并开展空间显式模拟，以量化分化的时空格局、物种性状对这些格局的影响，以及区分不同分化模式所需的统计效力。
研究区域：北美洲
研究方法：我们整合已发表的数据集，对分隔北美洲索诺兰沙漠与奇瓦瓦沙漠的科奇斯过滤屏障（Cochise Filter Barrier）周边的类群进行分析，以综合解析群落内基于生物功能性状的系统生物地理学结构。随后我们借助模拟与机器学习方法，评估系统生物地理学模型选择的效力。
研究结果：分布于科奇斯过滤屏障两侧的类群对该屏障的响应存在异质性，具体体现在基因流水平、系统生物地理学结构、分化时间、屏障宽度以及分化机制等方面。这些响应与类群的运动和体温调节性状显著相关。多数类群表现出更新世（Pleistocene）种群遗传断裂，且常伴随分化后的基因渐渗（introgression）现象。异域隔离（allopatric isolation）与环境隔离（isolation-by-environment）是塑造类群内遗传分化的主要机制。模拟结果显示，在该屏障两侧的空间显式迁移-隔离（isolation-with-migration）模型中，分化年代、基因流的存在以及距离隔离效应均会通过产生易混淆的结果，干扰演化历史的解读与模型选择。我们重新分析了5组实证遗传数据集，以说明尽管存在上述限制，本研究的模拟方法仍具有应用价值。
主要结论：通过整合科奇斯过滤屏障的系统生物地理学数据，本研究表明生物地理屏障会与物种性状相互作用，在数百万年的尺度上塑造群落内类群的分化差异。然而，要识别这些类群跨越该屏障的分化模式仍颇具挑战，因为常用的种群统计模型在一系列合理的参数空间内可能无法被有效区分。