Comparative study on the population genetics of the red algae Furcellaria lumbricalis occupying different salinity conditions

Furcellaria lumbricalis is a red algae occurring in low salinity to fully marine conditions. Here, both putatively neutral and EST-derived microsatellite markers were developed and used to examine the genetic structure of northern European populations inhabiting different salinity conditions ranging from 35 to 3.6 psu. The amount of genetic variation did not differ between ocean and brackish populations, but differences were observed between marker types; EST-derived markers possessed less variation and showed greater differentiation than the putatively neutral microsatellites. No multicopy multilocus genotypes were detected despite expected asexuality in brackish populations. The Bayesian STRUCTURE analysis, when conducted for expressed marker data, indicated the presence of two main clusters, the Atlantic Ocean and Baltic Sea, while no clear structuring was observed based on putatively neutral microsatellites. The moderate level of genetic differentiation at neutral loci is probably due to genetic drift, a feasible explanation considering long distances between many populations, while the high level of differentiation in EST-linked markers reflects selection pressures.