Data from: Extremophile Poeciliidae: multivariate insights into the complexity of speciation along replicated ecological gradients

Background: Replicate population pairs that diverge in response to similar selective regimes allow for an investigation of (a) whether phenotypic traits diverge in a similar and predictable fashion, (b) whether there is gradual variation in phenotypic divergence reflecting variation in the strength of natural selection among populations, (c) whether the extent of this divergence is correlated between multiple character suites (i.e., concerted evolution), and (d) whether gradual variation in phenotypic divergence predicts the degree of reproductive isolation, pointing towards a role for adaptation as a driver of (ecological) speciation. Here, we use poeciliid fishes of the genera Gambusia and Poecilia that have repeatedly evolved extremophile lineages able to tolerate high and sustained levels of toxic hydrogen sulfide (H2S) to answer these questions. Results: We investigated evolutionary divergence in response to H2S in Gambusia spp. (and to a lesser extent Poecilia spp.) using a multivariate approach considering the interplay of life history, body shape, and population genetics (nuclear miscrosatellites to infer population genetic differentiation as a proxy for reproductive isolation). We uncovered both shared and unique patterns of evolution: most extremophile Gambusia predictably evolved larger heads and offspring size, matching a priori predictions for adaptation to sulfidic waters, while variation in adult life histories was idiosyncratic. When investigating patterns for both genera (Gambusia and Poecilia), we found that divergence in offspring-related life histories and body shape were positively correlated across populations, but evidence for individual-level associations between the two character suites was limited, suggesting that genetic linkage, developmental interdependencies, or pleiotropic effects do not explain patterns of concerted evolution. We further found that phenotypic divergence was positively correlated with both environmental H2S-concentration and neutral genetic differentiation (a proxy for gene flow). Conclusions: Our results suggest that higher toxicity exerts stronger selection, and that divergent selection appears to constrain gene flow, supporting a scenario of ecological speciation. Nonetheless, progress toward ecological speciation was variable, partially reflecting variation in the strength of divergent selection, highlighting the complexity of selective regimes even in natural systems that are seemingly governed by a single, strong selective agent.研究背景：在相似选择压力下发生分化的重复种群对，可用于探究以下科学问题：(a) 表型性状是否以相似且可预测的方式发生分化；(b) 表型分化是否存在梯度变异，且该变异能够反映种群间自然选择强度的差异；(c) 多个性状组合（即协同进化）间的分化程度是否存在相关性；(d) 表型分化的梯度变异是否可预测生殖隔离程度，从而提示适应作用可作为（生态）物种形成的驱动因素。 本研究以食蚊鱼属（Gambusia）和花鳉属（Poecilia）的花鳉科鱼类为研究对象，这些类群已多次演化出能够耐受高浓度且持续暴露的有毒硫化氢（H₂S）的极端适应性类群，以此解答上述科学问题。 研究结果：本研究采用多变量分析方法，结合生活史特征、体型形态与群体遗传学的相互关系（以核微卫星标记推断种群遗传分化，以此作为生殖隔离的替代指标），探究了食蚊鱼属（Gambusia spp.，次要研究对象为花鳉属Poecilia spp.）在应对硫化氢（H₂S）时的演化分化模式。 本研究揭示了既有共有也有独特的演化模式：多数极端适应性食蚊鱼类群可预测地演化出更大的头部与子代体型，这与适应硫化物水体的先验预测相符，而成体生活史特征的变异则呈现特异化特征。在对两个属（食蚊鱼属与花鳉属）的模式进行综合分析时，我们发现与子代相关的生活史特征分化与体型形态分化在种群间呈正相关，但两类性状组合在个体水平上的关联证据有限，这提示遗传连锁、发育互作或多效性效应无法解释协同进化的模式。此外，我们还发现表型分化与环境硫化氢浓度以及中性遗传分化（基因流的替代指标）均呈正相关。 研究结论：本研究结果表明，毒性水平越高，施加的选择压力越强，且歧化选择似乎会限制基因流，这支持了生态物种形成的理论情境。尽管如此，生态物种形成的进展程度存在差异，这部分反映了歧化选择强度的变异，同时也凸显了即使在看似由单一强选择因子主导的自然系统中，选择压力体系依然具有复杂性。