Microsatellite markers in an invasive strain of Asparagopsis taxiformis (Bonnemaisoniales, Rhodophyta): insights in ploidy level and sexual reproduction

Eight polymorphic nuclear microsatellite loci were identified from the invasive Indo-Pacific Mediterranean strain of Asparagopsis taxiformis. Microsatellite markers were tested against a panel of specimens collected along the Italian (Elba, Naples) and Californian (Catalina Island) coasts, all belonging to the same mitochondrial lineage. In addition, we used Hawaiian specimens, belonging to a closely related mitochondrial lineage. The markers amplified in all of the specimens but failed consistently in thalli of two more distantly related mitochondrial lineages of A. taxiformis as well as in specimens belonging to the sister species Asparagopsis armata. Since haploid female individuals among the Mediterranean specimens contained cystocarps, genotyping was performed on supposedly haploid female specimens and supposedly diploid cystocarps separately. As expected, external allelic contribution was detected in the cystocarps. However, even after removal of these reproductive structures, gametophyte thalli exhibited patterns consisting of up to three alleles in all of the tested populations indicating polyploidy. An elevated number of distinct genotypes (up to 85%) were found per population, suggesting high intra-population variation. Results showed high genetic similarity between the two Mediterranean populations screened and lower similarity between these two and the Californian one within the same mitochondrial lineage. Lowest similarity was found between these three and the Hawaiian population belonging to the other related mitochondrial lineage 1.