Data from: Molecular phylogeny and phylogeography of the Australian freshwater fish genus Galaxiella, with an emphasis on dwarf Galaxias (G. pusilla)

The freshwater fauna of Southern Australia is primarily restricted to the southwestern and southeastern corners of the continent, and is separated by a large, arid region that is inhospitable to this biota. This geographic phenomenon has attracted considerable interest from biogeographers looking to explain evolutionary diversification in this region. Here, we employed phylogenetic and phylogeographic approaches to evaluate the effect of this barrier on a group of four galaxiid fish species (Galaxiella) endemic to temperate Southern Australia. We also tested if continental shelf width has influenced connectivity among populations during low sea levels when rivers, now isolated, could have been connected. We addressed these questions by sampling each species across its range using multiple molecular markers (mitochondrial cytochrome b sequences, nuclear S7 intron sequences, and 49 allozyme loci). These data also allowed us to assess species boundaries, to refine phylogenetic affinities, and to estimate species ages. Interestingly, we found compelling evidence for cryptic species in G. pusilla, manifesting as allopatric eastern and western taxa. Our combined phylogeny and dating analysis point to an origin for the genus dating to the early Cenozoic, with three of the four species originating during the Oligocene-Miocene. Each Galaxiella species showed high levels of genetic divergences between all but the most proximate populations. Despite extensive drainage connections during recent low sea levels in southeastern Australia, populations of both species within G. pusilla maintained high levels of genetic structure. All populations experienced Late Pleistocene-Holocene population growth, possibly in response to the relaxation of arid conditions after the last glacial maximum. High levels of genetic divergence and the discovery of new cryptic species have important implications for the conservation of this already threatened group of freshwater species.

澳大利亚南部的淡水动物群主要局限于该大陆的西南与东南角，被一片广阔的干旱区域与该区域隔开，这片干旱区域对这类生物群而言不适宜居。这一地理现象引发了生物地理学家的广泛关注，他们致力于解释该区域的进化分化机制。本研究采用系统发育与系统地理学方法，评估了这一隔离屏障对4种特有分布于澳大利亚南部温带区域的南乳鱼属（Galaxiella）鱼类的影响。此外，本研究还检验了：在低海平面时期——彼时如今被隔离的河流本可相互连通——大陆架宽度是否会影响种群间的连通性。我们通过在每个物种的分布范围内开展采样，结合多种分子标记（线粒体细胞色素b基因序列、核S7内含子序列以及49个同工酶位点）解答上述研究问题。这些数据同时也使我们得以评估物种边界、厘清系统发育亲缘关系，并估算物种分化时间。有趣的是，我们在巴氏南乳鱼（G. pusilla）中发现了隐存物种的有力证据，该隐存物种表现为异域分布的东部与西部支系类群。联合系统发育与年代分析结果显示，南乳鱼属的起源可追溯至早新生代，4个物种中的3个形成于渐新世-中新世时期。除最邻近的种群外，各南乳鱼属物种的种群间均存在高水平的遗传分化。尽管澳大利亚东南部在近期低海平面时期存在广泛的水系连通，巴氏南乳鱼的两个支系种群仍维持着高水平的遗传结构。所有种群均经历了晚更新世-全新世的种群扩张，这可能是对末次冰盛期后干旱环境缓解的响应。高水平的遗传分化以及新发现的隐存物种，对于这一已处于受威胁状态的淡水鱼类类群的保护具有重要意义。