New resource for population genetics studies on the Australasian intertidal brown alga, Hormosira banksii: isolation and characterization of 15 polymorphic microsatellite loci through next generation DNA sequencing

The Australasian fucoid, Hormosira banksii, commonly known as ‘Neptune’s necklace’ or ‘bubbleweed’ is regarded as an autogenic ecosystem engineer with no functional equivalents. Population declines resulting from climate change and other anthropogenic disturbances pose significant threats to intertidal biodiversity. For effective conservation strategies, patterns of gene flow and population genetic structure across the species distribution need to be clearly understood. We developed a suite of 15 polymorphic microsatellite markers using next generation sequencing of 53–55 individuals from two sites (south-western Victoria and central New South Wales, Australia) and a replicated spatially hierarchical sampling design. We observed low to moderate genetic variation across most loci (mean number of alleles per locus =3.26; mean expected heterozygosity =0.38) with no evidence of individual loci deviating significantly from Hardy-Weinberg equilibrium. Marker independence was confirmed with tests for linkage disequilibrium, and analyses indicated no evidence of null alleles across loci. Independent spatial autocorrelation analyses were performed for each site using multilocus genotypes and different relatedness measures. Both analyses indicated no significant patterns between relatedness and geographic distance, complemented by non-significant Hardy-Weinberg estimates (P < 0.05), suggesting that individuals from each site represent a randomly mating, outcrossing population. A preliminary investigation of population structure indicates that gene flow among sites is limited (FST = 0.49), however more comprehensive sampling is needed to determine the extent of population structure across the species range (>10,000 km). The genetic markers described provide a valuable resource for future population genetic assessments that will help guide conservation planning for H. banksii and the associated intertidal communities.