Abstract
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.
Highlights
In the context of biodiversity loss (Kolbert, 2014; Myers, Mittermeier, Mittermeier, da Fonseca, & Kent, 2000), assessing the degree of genetic connectivity of marine populations is essential to establish effective marine protected areas
We explored the population genetic structuring and connectivity of a widely distributed hydrozoan, Macrorhynchia phoenicea α (Postaire et al, 2016a) across multiple geographic scales in the Indian and the Pacific Oceans using 15 newly developed microsatellite loci
Macrorhynchia phoenicea α is distributed on many reefs in the Western Indian Ocean and the Tropical Southwestern Pacific, but FST values underlined the high isolation of all sites, even separated by only ~1 km (e.g. MAY3 and MAY4), pointing toward extremely low gene flow at all spatial scales
Summary
In the context of biodiversity loss (Kolbert, 2014; Myers, Mittermeier, Mittermeier, da Fonseca, & Kent, 2000), assessing the degree of genetic connectivity (i.e., effective dispersal with consequences on gene flow; Carpenter et al, 2011; Jones et al, 2009; Schiavina, Marino, Zane, & Melià, 2014; Vellend & Geber, 2005) of marine populations is essential to establish effective marine protected areas. Aglaopheniids’ genus-level taxonomy is mainly based on the morphology of the reproductive structures (Bouillon et al, 2006), but as many other characters, life cycles of hydrozoans are subject to convergent or reversible evolution across their phylogeny (Collins, 2002; Leclère et al, 2007, 2009; Marques & Collins, 2004; Miglietta & Cunningham, 2012) and the diversity of Aglaopheniidae is still under assessment (Moura et al 2012; Postaire et al, 2016a, 2016b) Active dispersal in this family is thought to be limited and only achieved via spermatozoids and mature larvae (Schuchert, 2014; Winston, 2012), an assumption that was confirmed using microsatellite data for a single morpho-species, Lytocarpia brevirostris (Busk, 1852), in a recent study centered on the Western Indian Ocean (Postaire et al, 2017). The aims were to (i) investigate the structure and connectivity of M. phoenicea α populations using microsatellites (Postaire et al 2015), (ii) compare the results with the study of another Aglaopheniidae with a similar reproductive strategy (Postaire et al., 2017), and (iii) discuss the distribution ranges of Aglaopheniidae species in light of our results
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