Recent expansion of Daphnia across Beringia, 2001-2011

Daphnia pulex is quickly becoming an attractive model species in the field of ecological genomics due to the recent release of its complete genome sequence, a wide variety of new genomic resources, and a rich history of ecological data. Sequences of the mitochondrial NADH dehydrogenase subunit 5 and cytochrome c oxidase subunit 1 genes were used to assess the global phylogeography of this species, and to further elucidate its phylogenetic relationship to other members of the Daphnia pulex species complex. Using both newly acquired and previously published data, we analyzed 398 individuals from collections spanning five continents. Eleven strongly supported lineages were found within the D. pulex complex, and one lineage in particular, panarctic D. pulex, has very little phylogeographical structure and a near worldwide distribution. Mismatch distribution, haplotype network, and population genetic analyses are compatible with a North American origin for this lineage and subsequent spatial expansion in the Late Pleistocene. In addition, our analyses suggest that dispersal between North and South America of this and other species in the D. pulex complex has occurred multiple times, and is predominantly from north to south. Our results provide additional support for the evolutionary relationships of the eleven main mitochondrial lineages of the D. pulex complex. We found that the well-studied panarctic D. pulex is present on every continent except Australia and Antarctica. Despite being geographically very widespread, there is a lack of strong regionalism in the mitochondrial genomes of panarctic D. pulex ‐ a pattern that differs from that of most studied cladocerans. Moreover, our analyses suggest recent expansion of the panarctic D. pulex lineage across continents with some continents sharing identical haplotypes. The hypothesis that hybrid asexuality has contributed to the recent and unusual geographic expansion of the panarctic D. pulex lineage warrants further study.

蚤状溞（Daphnia pulex）近年来随着其完整基因组序列的发布、各类新型基因组学资源的涌现，以及丰富的生态学研究数据积累，正快速成为生态基因组学领域极具吸引力的模式物种。本研究利用线粒体烟酰胺腺嘌呤二核苷酸脱氢酶亚基5（mitochondrial NADH dehydrogenase subunit 5）与细胞色素c氧化酶亚基1（cytochrome c oxidase subunit 1）基因序列，对该物种的全球系统地理学（phylogeography）进行评估，并进一步阐明其与蚤状溞复合群其他类群的系统发育关系。研究整合了新获取与已发表的样本数据，对横跨五大洲的398份个体样本开展了分析。在蚤状溞复合群中，共鉴定出11个得到强力支持的演化支；其中泛北极蚤状溞（panarctic D. pulex）支系几乎无系统地理学结构，且分布近乎遍及全球。错配分布（mismatch distribution）分析、单倍型网络（haplotype network）分析与群体遗传学分析结果均支持该支系起源于北美，并在晚更新世发生了空间扩张。此外，分析表明，蚤状溞复合群内该支系与其他物种在南北美洲间的跨大陆扩散事件多次发生，且扩散方向以北向南为主。本研究结果进一步支撑了蚤状溞复合群11个主要线粒体演化支的演化关系。研究发现，被广泛研究的泛北极蚤状溞支系分布于除澳洲与南极洲外的所有大陆。尽管其地理分布极为广泛，但泛北极蚤状溞的线粒体基因组未呈现显著的区域分化——这一模式与多数已研究的枝角类（cladocerans）截然不同。此外，分析提示泛北极蚤状溞支系近期发生了跨大陆扩张，部分大陆间共享完全一致的单倍型。关于杂交无性生殖是否促成了泛北极蚤状溞支系近期且异常的地理扩张这一假说，仍有待进一步研究验证。