Investigating the history of natural selection among closely related species can elucidate how genomes diverge in response to disparate environmental pressures. Molecular evolutionary approaches can be integrated with knowledge of gene functions to examine how evolutionary divergence may affect ecologically relevant traits such as temperature tolerance and species distribution limits. Here, we integrate transcriptome-wide analyses of molecular evolution with knowledge from physiological studies to develop hypotheses regarding the functional classes of genes under positive selection in one of the world's most widespread invasive species, the warm-tolerant marine mussel Mytilus galloprovincialis. Based on existing physiological information, we test the hypothesis that genomic functions previously linked to divergent temperature adaptation at the whole-organism level show accelerated molecular divergence between warm-adapted M. galloprovincialis and cold-adapted congeners. Combined results from codon model tests and analyses of polymorphism and divergence reveal that divergent selection has affected genomic functions previously associated with species-specific expression responses to heat stress, namely oxidative stress defence and cytoskeletal stabilization. Examining specific loci implicated in thermal tolerance among Mytilus species (based on interspecific biochemical or expression patterns), we find close functional similarities between known thermotolerance candidate genes under positive selection and positively selected loci under predicted genomic functions (those associated with divergent expression responses). Taken together, our findings suggest a contribution of temperature-dependent selection in the molecular divergence between warm- and cold-adapted Mytilus species that is largely consistent with results from physiological studies. More broadly, this study provides an example of how independent experimental evidence from ecophysiological investigations can inform evolutionary hypotheses about molecular adaptation in closely related nonmodel species.

中文翻译：

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比较基因组学揭示了在耐温和耐寒的海洋贻贝中不同的热选择。

研究密切相关物种之间的自然选择历史可以阐明基因组如何响应不同的环境压力而发散。分子进化方法可以与基因功能知识整合在一起，以检验进化差异如何影响与生态相关的特征，例如温度耐受性和物种分布极限。在这里，我们将分子进化的全转录组分析与来自生理学研究的知识相结合，以发展关于在世界上最广泛的入侵物种之一-耐温贻贝贻贝Mytilus galloprovincialis中正选择作用下基因功能类别的假设。根据现有的生理信息，我们检验了以下假设：先前与全生物水平的温度适应差异相关的基因组功能显示，温暖适应的M. galloprovincialis和寒冷适应的同类细胞之间的分子分化加速。密码子模型测试以及多态性和发散性分析的综合结果表明，发散选择影响了基因组功能，该功能先前与对热应激的物种特异性表达反应有关，即氧化应激防御和细胞骨架稳定。检查与Mytilus物种有关的耐热性的特定基因座（基于种间生化或表达模式），我们发现在正向选择下的已知耐热候选基因与正向选择的基因座在预测的基因组功能（与不同表达反应相关的基因）下的功能相似。两者合计，我们的发现表明温度依赖的选择在适应温育和低温适应的Mytilus物种之间的分子差异中的贡献，这在很大程度上与生理研究的结果一致。更广泛地讲，该研究提供了一个示例，说明了来自生态生理学研究的独立实验证据如何能够为与紧密相关的非模型物种的分子适应性有关的进化假说提供信息。我们的研究结果表明温度依赖性选择对适应温育和低温适应的Mytilus物种之间的分子差异的贡献，这在很大程度上与生理研究的结果一致。更广泛地讲，该研究提供了一个示例，说明了来自生态生理学研究的独立实验证据如何能够为与紧密相关的非模型物种的分子适应性有关的进化假说提供信息。我们的研究结果表明温度依赖性选择对适应温育和低温适应的Mytilus物种之间的分子差异的贡献，这在很大程度上与生理研究的结果一致。更广泛地讲，该研究提供了一个示例，说明了来自生态生理学研究的独立实验证据如何能够为与紧密相关的非模型物种的分子适应性有关的进化假说提供信息。