New evidence for habitat specific selection in Wadden Sea Zostera marina populations revealed by genome scanning using SNP and microsatellite markers

Eelgrass Zostera marina is an ecosystem-engineering species of outstanding importance for coastal soft sediment habitats that lives in widely diverging habitats. Our first goal was to detect divergent selection and habitat adaptation at the molecular genetic level; hence, we compared three pairs of permanently submerged versus intertidal populations using genome scans, a genetic marker-based approach. Three different statistical approaches for outlier identification revealed divergent selection at 6 loci among 46 markers (6 SNPs, 29 EST microsatellites and 11 anonymous microsatellites). These outlier loci were repeatedly detected in parallel habitat comparisons, suggesting the influence of habitat-specific selection. A second goal was to test the consistency of the general genome scan approach by doubling the number of gene-linked microsatellites and adding single nucleotide polymorphism (SNP) loci, a novel marker type for seagrasses, compared to a previous study. Reassuringly, results with respect to selection were consistent among most marker loci. Functionally interesting marker loci were linked to genes involved in osmoregulation and water balance, suggesting different osmotic stress, and reproductive processes (seed maturation), pointing to different life history strategies. The identified outlier loci are valuable candidates for further investigation into the genetic basis of natural selection

Identification and characterization of 14 polymorphic EST-derived microsatellites in eelgrass (Zostera marina)

Zostera marina, the dominant seagrass on the Northern Hemisphere, forms the basis of important but threatened marine ecosystems. Here, we report 14 microsatellite DNA markers derived from an expressed sequence tag library corresponding to a wide range of genes. All loci were moderately to highly polymorphic, with allele numbers ranging from three to eight in a single Wadden Sea population of 48 individuals. Observed heterozygosities ranged from 0.082 to 0.837. Reaction conditions for five pooled polymerase chain reactions are given. The markers will advance the population genetics of seagrasses because they allow indirect tests of selection on closely linked genes