南极鱼类多样性和适应性进化研究进展

Biodiversity and adaptive evolution of Antarctic notothenioid fishes

南极地区是地球上唯一未被人类活动大量影响的地区,其极端寒冷的环境为南极生物的进化提供了"温床"。过去三千万年间,南极鱼亚目鱼类在南极海洋逐渐变冷的过程中快速进化,从一个温暖海域的底栖祖先分化成南极海域最为多样化的鱼类类群。由于其在南极圈内和南极圈外的各种温度区间都有分布,因而成为研究鱼类适应性进化和耐寒机制的良好生物模型。本文综述了有关南极海域鱼类区系组成与物种多样性现状,南极鱼亚目鱼类适应低温的一系列特化的生物学性状及其关键的遗传进化机制。现有研究表明:南极鱼类在几千万年零度以下低温环境的进化中发生了大量基因的大规模扩增和基因表达的改变,如铁调素、卵壳蛋白和逆转座子等118个基因发生了显著的扩增。另外,有些从南极鱼中获得的抗寒基因已经用于提高动植物低温抗性的研究并取得了良好的效果。在今后的几年中,将会有多个南极鱼物种的全基因组得到破译,在低温适应相关基因的功能和进化方面的研究也会更加深入,这些研究将深入揭示低温压力下基因组的进化规律以及鱼类低温适应的分子机制。

The sea surrounding the Antarctic continent is one of the coldest regions in the world. It provides an environmentally unique and isolated ＂hotbed＂ for evolution to take place. In the past 30 million years, species of Pereiform suborder Notothenioidei evolved and diversified from a benthic and temperate-water ancestor, and now dominate the fish fauna of the coldest ocean. Because of their distribution across temperature zones both inside and outside the Antarctic Polar Front, notothenioid fishes are regarded as excellent model organisms for exploring mechanisms of adaptive evolution, particularly cold adaptation. We first summarize research progress on the biodiversity of Antarctic fish and then review current findings on the peculiar biological characteristics of Antarctic notothenioids that evolved in response to a freezing environment. Research has revealed that extensive gene duplication and transcriptomic changes occurred during the adaptive radiation of notothenioid fish. Examples of highly duplicated genes in the Antarctic lineages include genes encoding hepcidin, and zona pellucida proteins, in addition to various retrotransposable elements. A few genes from Antarctic notothenioid fishes have been used as transgenes and demonstrated to be effective in making transgenic plants cold-hardy. In the coming years, the genomes of some Antarctic notothenioid species will be fully sequenced and the adaptive functions of duplicated genes will be further elucidated. Such studies will deepen our understanding of how genomes evolve in freezing environments, and provide an improved knowledge of molecular mechanisms of cold adaptation.