Data from: Origins and functional diversification of salinity-responsive Na+, K+ ATPase α1 paralogs in salmonids

The Salmoniform whole-genome duplication is hypothesized to have facilitated the evolution of anadromy, but little is known about the contribution of paralogs from this event to the physiological performance traits required for anadromy, such as salinity tolerance. Here, we determined when two candidate salinity-responsive paralogs of the Na+, K+ ATPase α subunit (α1a and α1b) evolved and studied their evolutionary trajectories and tissue-specific expression patterns. We found that these paralogs arose during a small scale duplication event prior to the Salmoniform, but after the teleost, whole-genome duplication. The ‘freshwater paralog’ (α1a) is primarily expressed in the gills of Salmoniformes and an unduplicated freshwater sister-species (Esox lucius), and experienced positive selection in the fresh-water ancestor of Salmoniformes and Esociformes. Contrary to our predictions, the ‘saltwater paralog’ (α1b), which is more widely expressed than α1a, did not experience positive selection during the evolution of anadromy in the Coregoninae and Salmonine. To determine if parallel mutations in Na+, K+ ATPase α1 may contribute to salinity tolerance in other fishes, we studied independently evolved salinity-responsive Na+, K+ ATPase α1 paralogs in Anabas testudineus and Oreochromis mossambicus. We found that a quarter of the mutations occurring between salmonid α1a and α1b in functionally important sites also evolved in parallel in at least one of these species. Together, these data argue that paralogs contributing to salinity tolerance evolved prior to the Salmoniform whole-genome duplication and that strong selection and/or functional constraints have led to parallel evolution in salinity-responsive Na+, K+ ATPase α1 paralogs in fishes.鲑形目（Salmoniformes）全基因组复制事件被推测推动了溯河洄游习性的演化，但学界对该事件产生的旁系同源基因（paralogs）在溯河洄游所需生理性能性状（如盐度耐受性）中的贡献仍不甚明晰。本研究明确了两个候选盐度响应型钠钾ATP酶（Na+, K+ ATPase）α亚基旁系同源基因（α1a与α1b）的演化起源，并探究了二者的演化轨迹与组织特异性表达模式。研究发现，这两个旁系同源基因起源于鲑形目分化前、硬骨鱼（teleost）全基因组复制事件之后发生的一次小规模复制事件。该‘淡水旁系同源基因’（α1a）主要在鲑形目与一种未发生全基因组复制的淡水姊妹物种白斑狗鱼（Esox lucius）的鳃组织中表达，并在鲑形目与狗鱼目（Esociformes）的淡水祖先类群中经历了正选择作用。与本研究的预设相悖，表达范围较α1a更广的‘海水旁系同源基因’（α1b），在白鲑亚科（Coregoninae）与鲑亚科（Salmoninae）的溯河洄游习性演化过程中并未经历正选择作用。为探明钠钾ATP酶α1上的平行突变是否会对其他鱼类的盐度耐受性产生影响，我们对攀鲈（Anabas testudineus）与莫桑比克罗非鱼（Oreochromis mossambicus）中独立演化出的盐度响应型钠钾ATP酶α1旁系同源基因开展了研究。结果显示，鲑科α1a与α1b功能重要位点间的突变中，有四分之一在上述至少一个物种中发生了平行演化。综上，本研究数据表明，参与盐度耐受性调控的旁系同源基因起源早于鲑形目全基因组复制事件，且强烈的选择压力与/或功能约束共同促成了鱼类盐度响应型钠钾ATP酶α1旁系同源基因的平行演化。