Department of Biological Sciences, Western Michigan University, 1903 W Michigan Ave, Kalamazoo, MI 49008-5410, USA.
Department of Biology, University of Oklahoma, 730 Van Vleet Oval, Room 314, Norman, OK 73019, USA.
Integr Comp Biol. 2022 Aug 25;62(2):406-423. doi: 10.1093/icb/icac085.
Evolutionary transitions between marine and freshwater ecosystems have occurred repeatedly throughout the phylogenetic history of fishes. The theory of ecological opportunity predicts that lineages that colonize species-poor regions will have greater potential for phenotypic diversification than lineages invading species-rich regions. Thus, transitions between marine and freshwaters may promote phenotypic diversification in trans-marine/freshwater fish clades. We used phylogenetic comparative methods to analyze body size data in nine major fish clades that have crossed the marine/freshwater boundary. We explored how habitat transitions, ecological opportunity, and community interactions influenced patterns of phenotypic diversity. Our analyses indicated that transitions between marine and freshwater habitats did not drive body size evolution, and there are few differences in body size between marine and freshwater lineages. We found that body size disparity in freshwater lineages is not correlated with the number of independent transitions to freshwaters. We found a positive correlation between body size disparity and overall species richness of a given area, and a negative correlation between body size disparity and diversity of closely related species. Our results indicate that the diversity of incumbent freshwater species does not restrict phenotypic diversification, but the diversity of closely related taxa can limit body size diversification. Ecological opportunity arising from colonization of novel habitats does not seem to have a major effect in the trajectory of body size evolution in trans-marine/freshwater clades. Moreover, competition with closely related taxa in freshwaters has a greater effect than competition with distantly related incumbent species.
鱼类的进化历史中，海洋和淡水生态系统之间的转变曾多次发生。生态机会理论预测，那些在物种贫乏地区殖民的谱系比那些在物种丰富地区入侵的谱系更有潜力进行表型多样化。因此，海洋和淡水之间的过渡可能会促进跨海洋/淡水鱼类进化枝的表型多样化。我们使用系统发育比较方法分析了跨越海洋/淡水边界的九个主要鱼类进化枝的体型数据。我们探讨了栖息地转变、生态机会和群落相互作用如何影响表型多样性模式。我们的分析表明，海洋和淡水生境之间的转变并没有驱动体型进化，而且海洋和淡水谱系之间的体型差异很小。我们发现，淡水谱系的体型差异与独立过渡到淡水的次数无关。我们发现，特定区域的体型差异与物种丰富度呈正相关，与亲缘关系密切的物种多样性呈负相关。我们的研究结果表明，固有种群的多样性不会限制表型多样化，而是亲缘关系密切的分类群的多样性会限制体型多样化。由于新栖息地的殖民而产生的生态机会似乎对跨海洋/淡水进化枝的体型进化轨迹没有重大影响。此外，与淡水亲缘关系密切的分类群的竞争比与距离较远的现存物种的竞争更有影响。
