Across the tree of life there are numerous evolutionary transitions between different habitats (i.e., aquatic and terrestrial or marine and freshwater). Many of these dramatic evolutionary shifts parallel developmental shifts that require physiological, anatomical and behavioral changes for survival and reproduction. Diadromy (scheduled movement between marine and freshwater) has been characterized as a behavior that acts as an evolutionary intermediate state between marine and freshwater environments, implying that diadromous lineages are evolutionarily transient. This hypothesis comes with assumptions regarding the rates of evolutionary transitions in and out of diadromy as well as rates of speciation and extinction in diadromous fishes. Based on a published phylogeny of 7822 species of ray-finned fishes, state speciation and extinction models of evolutionary transition between marine, freshwater, and diadromous species suggest transition rates out of diadromy are 5–100 times higher that transition between marine and freshwater or into diadromy. Additionally, high speciation and low extinction rates separate diadromous fishes from marine and freshwater species. As a result, net diversification (net diversification = speciation – extinction) is about 7–40 times higher in diadromous fishes compared to freshwater and marine respectively. Together the transition, speciation, and extinction rates suggest diadromy is the least stable of the three states. Evolutionary transitions to diadromy are rare in fishes. However, once established, diversification rates in diadromous lineages are high compared to both marine and freshwater species. Diadromous lineages tend to be more transient than marine or freshwater lineages and are found to give rise to marine and freshwater specialists in addition to diadromous descendants. Although diadromy is not a necessary evolutionary intermediate between marine and freshwater, these results support the interpretation of diadromy as an important, occasionally intermediate state, that contributes to biodiversity in fishes in all environments. This evolutionary instability of diadromous lineages is counteracted by their relatively high diversification rates. These findings highlight the importance of integrating the dynamics of diversification and major evolutionary transitions for understanding macroevolutionary patterns.

中文翻译：

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鱼类中透湿性的进化模式：不仅是海洋和淡水之间的过渡状态

在整个生命树上，不同栖息地（即水生和陆地或海洋和淡水）之间有许多进化过渡。这些戏剧性的进化转变中有许多平行的发展转变，需要生理，解剖和行为的变化才能生存和繁殖。Diadromy（海洋和淡水之间的预定移动）已被表征为一种行为，充当海洋和淡水环境之间的进化中间状态，这暗示了adadromy世系在进化上是短暂的。该假设基于以下假设：透水鱼类的进出进化变化的速率，以及无鳍鱼类的物种形成和灭绝的速率。根据已发表的7822种鳍鳍鱼类的系统发育史，国家物种形成和灭绝模型之间的海洋，淡水和溢水物种之间的过渡过渡表明，从水产养殖的过渡速度是海洋和淡水过渡或进入水产养殖过渡的5-100倍。此外，高物种形成率和低灭绝率使海生和淡水物种中的过缺鱼类得以分离。结果，与淡水和海水相比，淡水鱼类的净多样化（净多样化=物种形成-灭绝）分别高出约7–40倍。过渡，物种形成和灭绝速度共同表明，透皮病是这三个州中最不稳定的。向鱼类的进化过渡在鱼类中很少见。但是，一旦建立，与海洋和淡水物种相比，二足谱系的多样化率很高。逆流血统比海洋或淡水血统更为短暂，并发现除了顺流后代之外，还引起了海洋和淡水专家。尽管透水气不是海洋和淡水之间必要的进化中间产物，但这些结果支持将透水子藻解释为一种重要的偶发中间状态，它有助于所有环境中鱼类的生物多样性。二元谱系的这种进化上的不稳定性被其相对较高的分散率所抵消。这些发现凸显了将多样化的动力与主要的进化转变相结合对于理解宏观进化模式的重要性。