A critical deliberation of the ‘species complex’ status of the globally spread colonial ascidian <i>Botryllus schlosseri</i>

Abstract The accurate taxonomic identity for the worldwide-distributed invasive ascidian Botryllus schlosseri has not been resolved. Employing molecular tools, primarily mtDNA, previous studies unveiled five divergent clades (A–E), suggesting a complex of cryptic species. A recent study allocated and E to different Here, worldwide B. 's COI distribution map drawn, based on 2927 specimens, elucidating 160 haplotypes (100 singletons). Clade emerged as most abundant globally widespread, while other had more limited distributions (primarily B, C). Inter-clade intra-clade divergences were similar, with no clear barcoding gaps between clades, illuminating than two putative OTUs. Network analyses genetic similarities among clades' identified groups, depending threshold values away from suggested boundaries. Three additional markers (H3, 18S, 28S) disclosed clade A, segregating D strongly integrating. Allorecognition assays resulted in indifference rejection outcomes, characteristics within-species allorecognition repertoire. question whether is single species or further discussed, leading assertion that it widely variable species, there enough evidence its designation complex.