Ecosystem size predicts the probability of speciation in migratory freshwater fish

Predicting speciation is a fundamental goal of research in evolutionary ecology. The probability of speciation is often positively correlated with ecosystem size. Although the mechanisms driving this correlation are generally difficult to identify, a shared geographic and ecological context provides a suitable condition to study the mechanisms that promote speciation in large ecosystems by reducing the number of factors to be considered. Here, we determined the correlation between speciation and ecosystem size, and discussed the underlying mechanisms of this relationship, using a probable parallel ecotype formation for freshwater fish. Our population genetic analysis revealed that speciation of the landlocked goby, Rhinogobius sp. YB, of the Ryukyu Archipelago, Japan, from its migratory ancestor, R. brunneus, occurred in parallel across five islands. Logistic regression analysis showed that speciation probability could be predicted using island size. The results suggest that ecosystem size predicts the occurrence of adaptation and reproductive isolation, likely through its association with three possible factors: divergent selection strength, population persistence, and occurrence probability of habitat separation.

预测物种形成（speciation）是进化生态学研究的核心目标之一。物种形成概率通常与生态系统规模呈正相关。尽管阐明这一相关性背后的作用机制通常颇具挑战，但共享的地理与生态背景能够减少需考量的变量数量，为探究大型生态系统中促进物种形成的机制提供了适宜条件。本研究以淡水鱼类一例疑似平行生态型形成事件为研究对象，明确了物种形成与生态系统规模之间的相关性，并探讨了该关联的潜在机制。本研究的群体遗传学分析（population genetic analysis）结果显示：产自日本琉球群岛的陆封型虾虎鱼（landlocked goby）Rhinogobius sp. YB，从其洄游型祖先R. brunneus分化形成的物种形成事件，在五个岛屿上平行发生。逻辑回归分析（logistic regression analysis）结果表明，可通过岛屿规模预测物种形成概率。研究结果提示，生态系统规模可预测适应性演化与生殖隔离（reproductive isolation）的发生，这一关联大概率与三类潜在因素相关：歧化选择强度（divergent selection strength）、种群存续（population persistence）以及生境分离（habitat separation）的发生概率。