Data from: Population differentiation or species formation across the Indian and the Pacific Oceans? An example from the brooding marine hydrozoan Macrorhynchia phoenicea

Assessing population connectivity is necessary to construct effective marine protected areas. This connectivity depends, among other parameters, inherently on species dispersal capacities. Isolation by distance (IBD) is one of the main modes of differentiation in marine species, above all in species presenting low dispersal abilities. This study reports the genetic structuring in the tropical hydrozoan Macrorhynchia phoenicea α (sensu Postaire et al. 2016a), a brooding species, from 30 sampling sites in the Western Indian Ocean and the Tropical Southwestern Pacific, using 15 microsatellite loci. At the local scale, genet dispersal relied on asexual propagation at short distance, which was not found at larger scales. Considering one representative per clone, significant positive FIS values (from -0.327*** to 0.411***) were found within almost all sites. Gene flow was extremely low at all spatial scales, among sites within islands (< 10 km distance) and among islands (100 to > 11,000 km distance), with significant pairwise FST values (from 0.035*** to 0.645***). A general pattern of IBD was found at the Indo-Pacific scale, but also within ecoregions in the Western Indian Ocean province. Clustering and network analyses identified each island as a potential independent population, while analysis of molecular variance indicated that population genetic differentiation was significant at small (within island) and intermediate (among islands within province) spatial scales. As shown by this species, a brooding life cycle might be corollary of the high population differentiation found in some coastal marine species, thwarting regular dispersal at distances more than a few kilometers and probably leading to high cryptic diversity, each island housing independent evolutionary lineages.

构建高效的海洋保护区（marine protected areas），需先开展种群连通性（population connectivity）评估。种群连通性本质上由物种的扩散能力决定，同时亦受其他多项参数的影响。距离隔离（Isolation by Distance, IBD）是海洋物种种群分化的主要模式之一，尤其在扩散能力较弱的物种中表现显著。

本研究以采自西印度洋及西南热带太平洋海域30个采样点的育幼型热带水螅虫Macrorhynchia phoenicea α（遵循Postaire等2016a的分类界定）为研究对象，利用15个微卫星位点（microsatellite loci）解析其种群遗传结构。

在局域尺度下，基株（genet）扩散依赖短距离无性繁殖，该模式在大尺度范围内未被观测到。以每个克隆选取1个代表个体进行分析，几乎所有采样点均检测到显著的FIS（种群内近交系数）正值，取值范围为-0.327***至0.411***。

所有空间尺度下的基因流均极低：无论是岛屿内部采样点间（距离<10km）还是岛屿间（距离100至>11000km），两两种群间的FST（种群分化系数）值均达到显著水平，取值范围为0.035***至0.645***。在印度-太平洋全域尺度下均检测到普遍的距离隔离模式，西印度洋生物地理省的各生态区内亦存在该模式。

聚类分析与网络分析结果显示，每个岛屿均可视为潜在的独立种群；分子方差分析则表明，种群遗传分化在小尺度（岛屿内部）及中等尺度（生物地理省内的岛屿间）均达到显著水平。

本研究物种的结果表明，育幼型生活史或许是部分近海海洋物种呈现高种群分化的内在必然结果：该生活史会阻碍物种完成数公里以上的常规扩散，进而可能催生极高的隐蔽多样性（cryptic diversity），每个岛屿均拥有独立的进化支系（evolutionary lineage）。