Polymorphic dinucleotide microsatellite loci in the clonal ascidian Diplosoma listerianum: predominance of compound and highly interrupted imperfect repeats.

We report the isolation of the first dinucleotide microsatellite loci from the clonal ascidian, Diplosoma listerianum. Most repeats were compound and highly interrupted, with flanking sequences containing many small interspersed repetitive regions. Consequently, most primers detected polymerase chain reaction products outside the expected size range, and only five out of 15 primers detected polymorphic single-locus markers. Characterization of five variable loci from two UK populations revealed three to seven alleles per locus, with observed heterozygosity of 0.00-0.86 and expected heterozygosity of 0.10-0.66. Three loci showed significant heterozygote deficits either because of inbreeding, population substructure or the presence of null alleles.