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.

种群连通性评估是构建高效海洋保护区的核心前提。该连通性除受其他参数影响外，本质上取决于物种的扩散能力。距离隔离（Isolation by Distance, IBD）是海洋物种分化的主要模式之一，在扩散能力较弱的类群中尤为突出。本研究以采自西印度洋及西南热带太平洋30个采样点的育幼型热带水螅虫Macrorhynchia phoenicea α（遵循Postaire等人2016a的分类界定）为研究对象，利用15个微卫星位点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，但该模式在大尺度范围内未被观测到。以每个克隆的一个个体作为代表开展分析时，几乎所有采样点均检测到显著的FIS值（取值范围：-0.327*** 至 0.411***）。无论空间尺度如何——无论是岛屿内部采样点间（距离<10km）还是岛屿间（距离100km至>11000km）——基因流均极低，且所有成对种群比较均得到显著的FST值（取值范围：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，各岛屿均为潜在的独立种群；而分子方差分析则表明，种群遗传分化在小尺度（岛屿内部）和中等尺度（生物地理省内岛屿间）均达到显著水平。本研究对象的育幼生活史或可解释部分近岸海洋物种的高种群分化现象：该生活史会阻碍数公里以上距离的常规扩散，进而可能催生极高的隐存多样性，每个岛屿均拥有独立的演化支系。