Comparative analysis of Japanese three-spined stickleback clades reveals the Pacific Ocean lineage has adapted to freshwater environments while the Japan Sea has not

Divergent selection and adaptive divergence can increase phenotypic diversification amongst populations and lineages. Yet adaptive divergence between different environments, habitats or niches does not occur in all lineages. For example, the colonization of freshwater environments by ancestral marine species has triggered adaptive radiation and phenotypic diversification in some taxa but not in others. Studying closely related lineages differing in their ability to diversify is an excellent means of understanding the factors promoting and constraining adaptive evolution. A well-known example of the evolution of increased phenotypic diversification following freshwater colonization is the three-spined stickleback. Two closely related stickleback lineages, the Pacific Ocean and the Japan Sea occur in Japan. However, Japanese freshwater stickleback populations are derived from the Pacific Ocean lineage only, suggesting the Japan Sea lineage is unable to colonize freshwater. Using stable is...

歧化选择（divergent selection）与适应性分化（adaptive divergence）可提升种群与支系间的表型多样化（phenotypic diversification）水平。然而，并非所有支系都会在不同环境、生境或生态位间发生适应性分化。例如，祖先海洋物种对淡水环境的定殖，曾在部分类群中引发适应辐射（adaptive radiation）与表型多样化，但在另一些类群中并未出现此类现象。研究在多样化能力上存在差异的近缘支系，是解析驱动与限制适应性进化的各类因素的极佳研究路径。淡水定殖后表型多样化提升的经典案例之一为三刺棘鱼（three-spined stickleback）。在日本海域分布有两支近缘的棘鱼支系，分别为太平洋支系与日本海支系。然而，日本的淡水棘鱼种群仅起源于太平洋支系，这表明日本海支系无法完成淡水定殖。本研究采用稳定（原文内容未完整呈现）。