Data from: Lineage diversification in a widespread species: roles for niche divergence and conservatism in the Common Kingsnake, Lampropeltis getula

Niche conservatism and niche divergence are both important ecological mechanisms associated with promoting allopatric speciation across geographic barriers. However, the potential for variable responses in widely distributed organisms has not been fully investigated. For allopatric sister lineages, three patterns for the interaction of ecological niche preference and geographic barriers are possible: i) niche conservatism at a physical barrier, ii) niche divergence at a physical barrier, and iii) niche divergence in the absence of a physical barrier. We test for the presence of these patterns in a transcontinentally distributed snake species, the Common Kingsnake (Lampropeltis getula), to determine the relative frequency of niche conservatism or divergence in a single species complex inhabiting multiple distinct niches. We infer the phylogeographic structure of the kingsnake using a rangewide dataset sampled for the mitochondrial gene cyt-b. We use coalescent simulation methods to test for the presence of structured lineage formation versus fragmentation of a widespread ancestor. Finally, we use statistical techniques for creating and evaluating ecological niche models to test for conservatism of ecological niche preferences. Significant geographic structure is present in the kingsnake, for which coalescent tests indicate structured population division. Surprisingly, we find evidence for all three patterns of conservatism and divergence. This suggests that ecological niche preferences may be labile on recent phylogenetic time scales, and that lineage formation in widespread species results from an interaction between inertial tendencies of niche conservatism and natural selection on populations in ecologically divergent habitats.

生态位保守性（niche conservatism）与生态位分化（niche divergence）均为推动地理屏障介导异地物种形成（allopatric speciation）的核心生态机制。然而，广布生物的响应差异尚未得到充分探究。针对异地姐妹支系（sister lineages），生态位偏好与地理屏障的相互作用存在三种可能模式：i）物理屏障下的生态位保守性；ii）物理屏障下的生态位分化；iii）无物理屏障场景下的生态位分化。我们以跨大陆分布的普通王蛇（Lampropeltis getula）为研究类群，检验上述模式是否存在，以明确栖息于多种迥异生境的单一物种类群中，生态位保守性与分化的相对发生频率。本研究依托覆盖全分布范围的线粒体基因cyt-b采样数据集，推断王蛇的系统地理种群结构；采用溯祖模拟（coalescent simulation）方法，检验究竟存在结构化支系形成过程，还是广布祖先种群发生了碎片化分化；最后通过构建与评估生态位模型（ecological niche models）的统计手段，验证生态位偏好的保守性。研究结果表明，王蛇种群存在显著的地理结构，溯祖模拟结果也证实了种群存在结构化分化。令人意外的是，我们获取了支持全部三种模式的实验证据。该结果暗示，生态位偏好可能在近期系统发育时间尺度上具有不稳定性，而广布物种种支的形成，是生态位保守性的惯性倾向与生态分化生境中种群所受自然选择共同作用的产物。