title: Scorched mussels (Brachidontes spp., Bivalvia: Mytilidae) from the tropical and warm-temperate southwestern Atlantic: the role of the Amazon River in their speciation.
abstract: Antitropicality is a distribution pattern where closely related taxa are separated by an intertropical latitudinal gap. Two potential examples include Brachidontes darwinianus (south eastern Brazil to Uruguay), considered by some authors as a synonym of B. exustus (Gulf of Mexico and the Caribbean), and B. solisianus, distributed along the Brazilian coast with dubious records north of the intertropical zone. Using two nuclear (18S and 28S rDNA) and one mitochondrial gene (mtDNA COI), we aimed to elucidate the phylogeographic and phylogenetic relationships among the scorched mussels present in the warm-temperate region of the southwest Atlantic. We evaluated a divergence process mediated by the tropical zone over alternative phylogeographic hypotheses. Brachidontes solisianus was closely related to B. exustus I, a species with which it exhibits an antitropical distribution. Their divergence time was approximately 2.6 Ma, consistent with the intensification of Amazon River flow. Brachidontes darwinianus, an estuarine species is shown here not to be related to this B. exustus complex. We suspect ancestral forms may have dispersed from the Caribbean to the Atlantic coast via the Trans-Amazonian seaway (Miocene). The third species, B rodriguezii is presumed to have a long history in the region with related fossil forms going back to the Miocene. Although scorched mussels are very similar in appearance, their evolutionary histories are very different, involving major historical contingencies as the formation of the Amazon River, the Panama Isthmus, and the last marine transgression.
authors.affiliation: Instituto de Diversidad y Evolución (IDEAus-CONICET) Boulevard Brown 2915 U9120ACF Puerto Madryn Chubut Argentina.
authors.forename: Berenice
authors.initials: B
authors.lastname: Trovant
authors.affiliation: Instituto de Diversidad y Evolución (IDEAus-CONICET) Boulevard Brown 2915 U9120ACF Puerto Madryn Chubut Argentina.
authors.forename: Néstor G
authors.initials: NG
authors.lastname: Basso
authors.affiliation: Instituto de Diversidad y Evolución (IDEAus-CONICET) Boulevard Brown 2915 U9120ACF Puerto Madryn Chubut Argentina.
authors.forename: José María
authors.initials: JM
authors.lastname: Orensanz
authors.affiliation: Departamento de Ecología y Evolución Facultad de Ciencias Universidad de la República Iguá 4225 C.P. 11400 Montevideo Uruguay.
authors.forename: Enrique P
authors.initials: EP
authors.lastname: Lessa
authors.affiliation: Universidade Federal do Rio Grande - FURG Av. Itália km 8 Bairro Carreiros 96203-900 Rio Grande Brazil.
authors.forename: Fernando
authors.initials: F
authors.lastname: Dincao
authors.affiliation: Department of Biology Dalhousie University 1355 Oxford St. Halifax Nova Scotia B3H 4R2 Canada.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Ruzzante
keywords: Amazon River; mussels; southwestern Atlantic ocean; speciation