Comparative population genetics of red alga occupying different salinity conditions

Abstract

Osmotic stress is one of the major abiotic stresses in seaweeds, which may physiologically acclimate to changing osmolarity by altering their transcriptome under hyper- or hypo-osmotic conditions. Also local adaptations leading to genetic differentiation between populations may develop. DNA-based genetic markers and sequencing provide the essential tools to investigate genetic diversity and differentiation and signs of selection. Whole-genome or transcriptome sequencing facilitates marker development and allows in-depth investigations on the population genetic structures of organisms. In this chapter, a special attention is paid on a set of genetic studies conducted on the marine red alga Furcellaria lumbricalis, including populations in the Atlantic Ocean (35 psu) and the brackish Baltic Sea (3.8-8 psu). The amount of genetic variation did not differ between ocean and brackish populations, but differences were observed between marker types. The expressed sequence tag (EST)-derived microsatellites possessed less variation and showed greater differentiation than the putatively neutral microsatellites, whereas the EST-derived SNP markers contained even less variation and showed even more differentiation. Yet, the most distinct result was that F. lumbricalis showed definite differentiation between the ocean and brackish populations in expressed genomic regions, while such differentiation was not detected by presumably neutral loci. Thus, suboptimal salinity is a stress factor that affects population genetic structures. However, such differentiation would have been missed if the investigations on F. lumbricalis had relied on the analysis of only neutral markers.