海鞘与文昌鱼谁更接近脊椎动物的始祖

ASCIDIAN OR AMPHIOXUS? WHO IS THE CLOSEST LIVING RELATIVE OF VERTEBRATES?

脊椎动物的起源是进化生物学研究的核心问题之一,目前人们普遍认为脊椎动物与无脊椎动物中的脊索动物起源于同一个原始祖先。头索动物文昌鱼和尾索动物海鞘是现存的无脊椎动物中和脊椎动物亲缘关系最近的类群,是研究胚胎发育机制和脊索动物统进化的典型材料。长期以来,文昌鱼一直被认为是脊椎动物的姊妹类群,比尾索动物海鞘更接近于脊椎动物。但最近的研究却有了相反的观点,这导致了脊索动物进化历程之争,引起人们广泛的兴趣和关注。本文介绍这两类原索动物的研究现状,并对它们的进化地位以及作为研究脊椎动物起源的模型进行了探讨。

The origin of vertebrates has always been a core question in evolutionary biology.It is well accepted that vertebrates and invertebrate chordate derived from a common ancestor.The invertebrate chordates comprise cephalochordates amphioxus and urochordata ascidian,which are the extant closest living relatives of the vertebrate.Both of them are classical materials to study the developmental mechanisms and chordate phylogeny.The long-standing consensus places amphioxus as sister to vertebrates,with tunicates as the earliest diverging chordate subphylum.However,recent studies suggested that the evolutionary positions of tunicates and cephalochordates should be reversed,which lead to the conflicting chordate phylogenies and has sparked interest in restudying the phylogenetic relationships within chordates.The features of these two organisms are described and compared in this review,their evolutionary status and the application as model systems for vertebrates origin and evolution are also discussed.