Direct typing of polymorphic microsatellites in the colonial tunicate Botryllus schlosseri (Ascidiacea)

Five microsatellite loci of the marine protochordate Botryllus schlosseri were cloned: four of uninterrupted (AG)(n) repeats and one of both (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.