Turner Leslie M, Hoekstra Hopi E
Division of Biological Sciences, University of California, San Diego, USA.
Mol Biol Evol. 2006 Sep;23(9):1656-69. doi: 10.1093/molbev/msl035. Epub 2006 Jun 14.
Rapid evolution of reproductive proteins has been documented in a wide variety of taxa. In internally fertilized species, knowledge about the evolutionary dynamics of these proteins between closely related taxa is primarily limited to accessory gland proteins in the semen of Drosophila. Investigation of additional taxa and functional classes of proteins is necessary in order to determine if there is a general pattern of adaptive evolution of reproductive proteins between recently diverged species. We performed an evolutionary analysis of 2 egg coat proteins, ZP2 and ZP3, in 15 species of deer mice (genus Peromyscus). Both of these proteins are involved in egg-sperm binding, a critical step in maintaining species-specific fertilization. Here, we show that Zp2 and Zp3 gene trees are not consistent with trees based on nonreproductive genes, Mc1r and Lcat, where species formed monophyletic clades. In fact, for both of the reproductive genes, intraspecific amino acid variation was extensive and alleles were sometimes shared across species. We document positive selection acting on ZP2 and ZP3 and identify specific amino acid sites that are likely targets of selection using both maximum likelihood approaches and patterns of parallel amino acid change. In ZP3, positively selected sites are clustered in and around the region implicated in sperm binding in Mus, suggesting changes may impact egg-sperm binding and fertilization potential. Finally, we identify lineages with significantly elevated rates of amino acid substitution using a Bayesian mapping approach. These findings demonstrate that the pattern of adaptive reproductive protein evolution found at higher taxonomic levels can be documented between closely related mammalian species, where reproductive isolation has evolved recently.
生殖蛋白的快速进化在多种分类群中都有记载。在体内受精的物种中，关于这些蛋白在近缘分类群之间的进化动态的知识主要局限于果蝇精液中的附属腺蛋白。为了确定在最近分化的物种之间是否存在生殖蛋白适应性进化的一般模式，有必要对其他分类群和蛋白功能类别进行研究。我们对15种鹿鼠（白足鼠属）中的两种卵壳蛋白ZP2和ZP3进行了进化分析。这两种蛋白都参与精卵结合，这是维持物种特异性受精的关键步骤。在这里，我们表明Zp2和Zp3基因树与基于非生殖基因Mc1r和Lcat构建的树不一致，在基于非生殖基因构建的树中，物种形成单系类群。事实上，对于这两种生殖基因，种内氨基酸变异广泛，等位基因有时在物种间共享。我们记录了作用于ZP2和ZP3的正选择，并使用最大似然法和平行氨基酸变化模式确定了可能是选择目标的特定氨基酸位点。在ZP3中，正选择位点聚集在小家鼠中与精子结合相关的区域及其周围，这表明这些变化可能会影响精卵结合和受精潜力。最后，我们使用贝叶斯绘图方法识别出氨基酸替代率显著升高的谱系。这些发现表明，在分类级别较高时发现的适应性生殖蛋白进化模式，在生殖隔离最近才进化出来的近缘哺乳动物物种之间也可以被记录到。
