Molecular phylogeny of thoracican barnacles based on the mitochondrial 12S and 16S rRNA genes

Abstract

Partial sequences of 12S and 16S rRNA genes were collected from four thoracican barnacle genera, Capitulum, Chthamalus, Megabalanus, and Tetraclita, to investigate their phylogenetic relationships. Both neighbor joining and maximum parsimony analyses and combined data showed monophyly of the four genera with high bootstrap values, congruent with classification of barnacles based on morphology. The three genera, Chthamalus, Megabalanus and Tetraclita, formed a monophylic group, and the pedunculate genus, Capitulum, formed a paraphylic group with them. The phylogenetic relationships among the three sessile barnacles based on the 12S rRNA gene differed from those based on the 16S rRNA gene or a combination of the 12S and 16S rRNA genes. Based on the 12S rRNA gene the two sessile barnacle genera, Megabalanus and Chthamalus, formed one group, whereas Tetraclita formed another group. However, based on the 16S rRNA gene and combined data of the 12S and 16S rRNA genes, Megabalanus and Tetraclita were the closest relatives among the three sessile barnacles. This was congruent with the results based on larval characters and the nuclear 18S rRNA gene reported previously, but differed from morphological classification. Thus, the 16S rRNA gene appears to be more reliable than the 12S rRNA gene in elucidating the phylogenetic relationships of these four genera within the thoracican barnacles.