A molecular phylogenetic approach to the phylum Cycliophora provides further evidence for cryptic speciation in Symbion americanus

摘要

Cryptic speciation is a phenomenon that has been reported in a wide range of marine invertebrates, including the American cycliophoran Symbion americanus. Although cryptic speciation is often proposed based on phylogeographical analyses, here we demonstrate the utility of multilocus molecular phylogenetic approaches in identifying cryptic lineages within the phylum Cycliophora. Thirteen individuals from three putative cryptic lineages of S. americanus, as well as two individuals each from the European species S. pandora and a new species of Symbion living on Homarus gammarus, were sequenced for up to 4.8 kb of genomic DNA over four loci (COI, 16S rRNA, 18S rRNA and 28S rRNA). Phylogenetic analyses of individual loci as well as combined data clearly support a division between American and European cycliophorans. Moreover, the American cycliophorans consistently form three well-supported clades, which is congruent with the presence of three putative reproductively isolated lineages in a species complex. Further studies are necessary to more precisely describe the evolution of reproductive isolation within S. americanus.