Apparent signal of competition limits diversification after ecological transitions from marine to freshwater habitats

Adaptive radiations are typically triggered when a lineage encounters a significant range of open niche space (ecological opportunity), stemming from i) colonization of new areas, ii) extinction of competitors, or iii) key innovations. The most well-known of these is the colonization of new areas, either through geographic dispersal or the invasion of a novel ecological habitats. One aspect of ecological opportunity that has rarely been studied, however, is whether the existence of potential competitors may act to limit evolutionary diversification in newly colonized adaptive zones. Here, we show that in multiple geographically independent reinvasions of freshwaters by marine Sea Catfishes (Ariidae), rates of diversification (estimated as a function of morphological disparity and cladogenesis) have been constrained by pre-existing high diversity freshwater lineages. Only one region (Australia-New Guinea), characterized by an otherwise-depauperate freshwater fauna, has an ariid invasion ...适应辐射（Adaptive radiation）通常在某一演化支（lineage）遭遇大面积开放生态位空间（即生态机遇，ecological opportunity）时触发，其成因可分为三类：i）开拓新区域，ii）竞争者灭绝，iii）关键创新（key innovations）。其中最广为人知的成因类型是通过地理扩散或入侵全新生态栖息地来实现新区域定殖。然而，生态机遇中极少被关注的一个方面是，潜在竞争者的存在是否会限制新近定殖适应带内的演化分化。本研究表明，在海洋海鲶科（Ariidae）类群多次地理独立的淡水生境再次定殖事件中，多样化速率（以形态分异度与分支成种（cladogenesis）为估算依据）受到了预先存在的高多样性淡水演化支的约束。仅有一个区域——澳大利亚-新几内亚区域，其本地淡水动物群物种贫乏，出现了海鲶科类群的成功定殖……