Direct Typing of Polymorphic Microsatellites in the Colonial Tunicate Botryllus schlosseri (Ascidiacea)

Abstract Five microsatellite loci of the marine protochordate Botryllus schlosseri were cloned: four of uninterrupted (AG) n repeats and one of bath (AG) n and (TG) n repeats. By means of an innovative procedure small colony fragments were minimally treated to serve as templates for PCR with microsatellite-specific primers. Four of the loci were polymorphic: 7-8 discrete alleles were scored in nine colonies, heterozygosity ranging between 44-80%. At locus number 811 spacing of the alleles and gel-resolution were highest, therefore, ten additional colonies were typed and in total nine alleles were scored with maximal allelic interval of 120 base pair and 53% heterozygous colonies. The high levels of microsatellite-polymorphism provide a new tool as individual markers for studies on aspects of the botryllid polymorphic allorecognition system.