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：针对在相似选择压力下发生分化的重复种群对，可用于开展以下几方面的探究：（a）表型性状是否以相似且可预测的模式发生分化；（b）表型分化是否存在梯度变化，以此反映不同种群间自然选择强度的差异；（c）多组性状的分化程度是否存在相关性（即协同进化（concerted evolution））；（d）表型分化的梯度变化是否能够预测生殖隔离（reproductive isolation）的程度，进而揭示适应性在（生态）物种形成（ecological speciation）中的驱动作用。本研究选取胎鳉科（Poeciliidae）鱼类中的食蚊鱼属（Gambusia）与花鳉属（Poecilia）类群——这类类群已多次演化出极端嗜硫谱系，能够耐受高浓度且持续存在的毒性硫化氢（hydrogen sulfide, H₂S）——来解答上述问题。 研究结果：本研究采用多变量分析方法，综合考量生活史、体型形态与种群遗传学特征，以核微卫星（nuclear microsatellites）推断种群遗传分化，将其作为生殖隔离的替代指标，以此探究食蚊鱼属（Gambusia，次要涵盖花鳉属（Poecilia））在硫化氢胁迫下的演化分化模式。本研究发现了兼具共性与独特性的演化特征：多数极端嗜硫食蚊鱼类群可预测地演化出更大的头部与后代体型，这与适应硫化水体的先验预测相符，但成体生活史的变异则具有个体特异性。当综合分析两个属的类群时，我们发现种群间与后代相关的生活史分化与体型形态分化呈正相关，但两类性状组间的个体水平关联证据有限，这表明遗传连锁、发育相互依存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、中性遗传分化（即基因流（gene flow）的替代指标）均呈正相关。 研究结论：本研究结果表明，更高的毒性会施加更强的选择压力，且分化选择似乎会限制基因流，从而支持生态物种形成的理论场景。尽管如此，生态物种形成的进程存在差异，这部分源于分化选择强度的变异，这也凸显了即使在看似受单一强选择因子主导的自然系统中，选择调控机制的复杂性。