Evolutionary origin and early biogeography of otophysan fishes (Ostariophysi: Teleostei)

Biogeography of the mega-diverse, freshwater and globally-distributed Otophysi has received considerable attention. The attraction largely stems from assumptions as its ancient origin, and by being almost exclusively freshwater, their suitability as to explanations of trans-oceanic distributions. Despite multiple hypotheses explaining present-day distributions, problems remain, precluding more parsimonious explanations. Underlying previous hypotheses involve alternative phylogenies for Otophysi, uncertainties as to temporal diversification and assumptions integral to various explanations. We reexamine the origin and early diversification of this clade based on a comprehensive time-calibrated, molecular-based phylogenetic analysis and event-based approaches for ancestral range inference of lineages. Our results do not corroborate current phylogenetic classifications of otophysans. We demonstrate Siluriformes are never sister to Gymnotiformes and Characiformes are most likely non-monophyletic. Divergence-time estimates specify a split between Cypriniformes and Characiphysi as a result of fragmentation of Pangea. The early diversification of characiphysans either predated, or was contemporary with, the separation of Africa and South America, and involved a combination of within- and between-continental divergence events for these lineages. The inter-continental diversification of siluroids and characoids postdated major inter-continental tectonic fragmentations (<90Mya). Post-tectonic drift dispersals are hypothesized to account for current patterns of distribution of these latter two clades.

高度多样、淡水栖息且全球分布的骨鳔总目（Otophysi）的生物地理学研究已受到广泛关注。该研究热度主要源于两项核心假设：其一，该类群拥有古老的起源；其二，由于几乎完全局限于淡水生境，它们非常适合用于解释跨洋分布格局。尽管已有多项假说试图解释其现生分布格局，但仍存在诸多问题，难以得到更简约的解释。既往各类假说的核心局限包括：骨鳔总目系统发育关系存在多种分歧假说、类群分化时间的不确定性，以及各类解释所依赖的固有假设缺陷。本研究基于一套全面的时间校准分子系统发育分析，结合谱系祖先分布区推断的事件型方法，重新审视了该演化支的起源与早期分化过程。本研究结果并不支持当前针对骨鳔类的系统发育分类框架：研究表明，鲇形目（Siluriformes）从未与电鳗目（Gymnotiformes）构成姊妹群，且脂鲤形目（Characiformes）大概率并非单系群。分化时间估算结果显示，鲤形目（Cypriniformes）与脂鲤总类（Characiphysi）的分化源自盘古大陆（Pangea）的裂解。脂鲤总类的早期分化要么早于非洲与南美洲的分离时间，要么与之同步，该类群的分化事件同时包含了大陆内部与大陆之间的谱系分化过程。鲇类与脂鲤类的跨大陆分化发生在主要的跨大陆构造裂解事件（早于9000万年前）之后。研究假设，构造事件后的漂流扩散可解释这两个演化支当前的分布格局。