The ascidian Asterocarpa humilis (Heller, 1878) in the South Western Atlantic: a native or introduced species?

TATIÁN M; MAGGIONI T; TURÓN X; DE ARANZAMENDI MC; ALURRALDE G; TAVERNA A

Puerto Madryn

Congreso; X International Conference on Marine Bioinvations; 2018

Taxonomic problems when dealing with morphologicallysimilar marine taxa can hinder the correct assignment of the status of aspecies as native or introduced. This is the case of Asterocarpa humilis (Heller, 1878) considered native for theSouthern Hemisphere. The species was originally described for New Zealand andlater cited for Tasmania and South Africa. However, for Chile A. humilis was considered introduced, aswell as for the Northern Hemisphere in Great Britain and France. For the SWAtlantic, another species with a similar morphology, Cnemidocarpa robinsoni Hartmeyer, 1918 has been reported as acryptogenic species. The aim of this work was to define the entity and statusof these species: Asterocarpa humilisand Cnemidocarpa robinsoni throughmolecular analyses. We sequenced a partial fragment of COI gene of sevensamples of C. robinsoni collected atthe Argentine Sea. A median joining haplotype network was constructed includingthe seven new sequences and four sequences of A. humilis from Chile, New Zealand and France mined from publisheddatabases. Four haplotypes with eight variable sites were obtained. Thehaplotype network shows a more frequent haplotype present in South America andFrance, suggesting that the Argentine specimens described as C. robinsoni and those from Chile andFrance as A. humilis, correspond tothe same taxonomic entity. Phylogenetic trees reconstructed by BayesianInference, Maximum Likelihood and Maximum Parsimony, grouped A. humilis and C. robinsoni into one well-supported monophyletic clade. The scarcegenetic difference among individuals from distant populations proves theexistence of a unique specific identity. Thus, the name Asterocarpa humilis takes precedence over Cnemidocarpa robinsoni; the latter must be considered a juniorsynonym of the former. The presence of this species in natural habitats inaddition to its register in old collections (1920) in the SW Atlantic, suggeststhat the species is native for this area.