The colonization of freshwater habitats by marine-adapted organisms represents a major transition that has only occurred a few times in the evolution of animals. Only around half of the extant animal phyla have representatives in both marine and freshwater environments and even within those phyla some major clades are restricted to marine environments. Moving from marine to freshwater environments can create severe osmotic and ionic stresses and the mechanisms that animals have used to adapt to those stresses are still not well understood. In this study, we downloaded amino acid sequence data from 11 spiralian animal genomes (four freshwater taxa representing four different phyla as well as 7 marine taxa) and identified a number of gene family expansions that have occurred exclusively in the freshwater lineages. Further investigation of these gene families and the timing and nature of their expansions will illuminate one of the major evolutionary transitions in the history of life on Earth.

适应海洋的生物对淡水栖息地的殖民代表了动物进化过程中仅发生过几次的重大转变。只有大约一半的现存动物门在海洋和淡水环境中都有代表，即使在这些门内，一些主要的进化枝也仅限于海洋环境。从海洋环境转移到淡水环境会产生严重的渗透和离子压力，而动物用来适应这些压力的机制仍不清楚。在这项研究中，我们从 11 个螺旋动物基因组（代表四种不同门的四种淡水分类群以及 7 种海洋分类群）中下载了氨基酸序列数据，并确定了一些仅发生在淡水谱系中的基因家族扩展。