Phylogeography of Oligosarcus acutirostris (Characiformes: Characidae): testing biogeographic hypotheses in the Northeastern Mata Atlântica freshwater ecoregion

Abstract The Northeastern Mata Atlântica freshwater ecoregion (NMAF) is recognized for the high degree of endemism of its ichthyofauna, whose evolutionary and biogeographic histories are still poorly understood. Oligosarcus acutirostris is a freshwater fish species endemic to the NMAF, which is distributed in coastal rivers and streams draining Bahia, Espírito Santo, and part of Minas Gerais states in eastern Brazil. Its widespread distribution in currently isolated river basins along the NMAF prompted this study, which aimed to understand what scenarios would be involved in determining its current distribution pattern, and to contribute to a better understanding of the biogeographic history of the NMAF. For this, mitochondrial and nuclear DNA sequences were analyzed based on samples from different localities along the species distribution, including its type locality. Overall, phylogeographic analyses indicate a strong genetic structure within the species evidenced mainly by the non-sharing of haplotypes between most of the basins analyzed. According to the AMOVA results, the current distribution of haplotypes is better explained by the Pleistocene coastal paleodrainages. The results are also used to test and complement a biogeographic hypothesis previously proposed for the drainages of the NMAF.

摘要：大西洋森林东北部淡水生态区（Northeastern Mata Atlântica freshwater ecoregion, NMAF）以其鱼类区系（ichthyofauna）的高度特有性而闻名，该区域鱼类的演化与生物地理历史迄今仍鲜有深入研究。尖吻寡脂鲤（Oligosarcus acutirostris）是该生态区特有的淡水鱼类，分布于巴西东部巴伊亚州、圣埃斯皮里图州及米纳斯吉拉斯州部分区域的沿海河流与溪流中。该物种在大西洋森林东北部淡水生态区内多个相互隔离的流域中广泛分布，这一特征促使本研究展开，旨在解析塑造其当前分布格局的潜在演化情景，并为深化对该生态区生物地理历史的认知提供支撑。为此，研究采集了该物种分布范围内不同采样点（包括其模式产地）的样本，对线粒体与核DNA序列开展分析。整体系统地理学分析（phylogeographic analyses）结果显示，该物种内部存在显著的遗传结构，主要体现为多数分析流域间无共享单倍型（haplotype）。根据分子方差分析（Analysis of Molecular Variance, AMOVA）的结果，当前单倍型的分布格局更符合更新世沿海古水系假说。本研究结果还被用于检验并补充此前针对大西洋森林东北部淡水生态区流域提出的生物地理假说。