Molecular and morphometric analysis of nominal Brachidontes exustus (Mollusca, Mytilidae) in Brazilian waters

Abstract

Brachidontes exustus (Mollusca, Mytilidae) is mainly distributed in Central America, where it has been recognized as a complex of species. This study aimed to determine whether B. exustus extends beyond the Amazon Barrier and southward along the Brazilian West Atlantic coast. Mitochondrial genes coding for cytochrome-c oxidase, subunit I (COI) and 16S subunit of ribosomal ribonucleic acid (16S rRNA) were analyzed with shell parameters on Brazilian populations (Salvador, Arraial do Cabo and Fernando de Noronha) of scorched mussels previously recorded as B. exustus. Multivariate morphometric analysis showed partial discrimination of species. Molecular analysis confirmed B. exustus at Salvador, a population highly similar to Cartagena (Colombia), both belonging to the Atlantic Clade of the B. exustus complex. This fact adds evidence to the idea of the Amazon outflow as a semipermeable barrier. In the southeast of Brazil, B. exustus was not found; instead, B. darwinianus is the species represented at Arraial do Cabo (state of Rio de Janeiro), associated with brackish waters. Scorched mussels from Fernando de Noronha are most closely related to B. puniceus from Cape Verde with 4.4% differentiation. Demonstrating an independent evolutionary history since at least the beginning of the Pleistocene, its proposed new name is B. noronhensis.