Illumina next generation ddRAD sequencing SNP data from: Contrasting genetic diversity and structure between endemic and widespread damselfishes are related to differing adaptive strategies

Aim: Discerning when, where, and how processes of isolation lead to differing biogeography is especially complex for marine species with similar ecological niches and within the same geographic location. We assessed population genetics of congeneric and ecologically similar damselfishes within their overlapping distributions and across potential barriers to geneflow. Taxon: Dascyllus marginatus (endemic) and Dascyllus abudafur (widespread). Location: Coral reefs from the Red Sea, Djibouti, Yemen, Oman, and Madagascar. Methods: We used RADseq derived SNPs to investigate key differences in population genetics between both species and discuss barriers shaping genetic differentiation (neutral vs. selective) and biogeography. Results: Dascyllus marginatus inhabited the Red Sea, the coasts of Yemen (including Socotra), and the Gulf of Oman. Dascyllus abudafur species was present from the Red Sea to Madagascar but was absent from Yemen and Oman. Populations of D. marginatus had an order of magnitude higher genetic differentiation compared to D. abudafur, as well as several outlier loci (suggesting selective pressure), which were absent in D. abudafur despite equal sampling locations. In both species, specimens from the Red Sea and Djibouti formed one genetic cluster separated from all other locations. Main conclusions: The stronger genetic structure at smaller geographic scale of the endemic species seems associated to faster adaptation to environmental differences; whereas the widespread species only experienced reduced geneflow and neutral differentiation at much larger geographic scales. Restrictive transitions (between the Gulf of Aqaba and the Red Sea or the Red Sea and the Gulf of Aden) did not affect the genetic architecture of either species, while the environmental shift within the Red Sea (at 22°N/20°N) affected the endemic but not the widespread species. Samples from continental Yemen revealed that a genetic break in the Gulf of Aden likely reflects historical colonization processes and not contemporary environmental regimes.