Scorched Mussels (Brachidontes spp.) from the Southwestern Atlantic: the role of the Isthmus of Panama and the Amazon River in their Speciation

TROVANT, B.; BASSO, N. G.; ORENZANZ, J.M.; LESSA, E. P.; DINCAO, F.; RUZZANTE, D.E.

Guarujá

Congreso; Evolution 2015; 2015

Society for the Study of Evolution

The biogeography of South American marine biota is known to have been influenced by major historical contingencies; such is the changed of the river flow towards the Atlantic Ocean at the beginning of late Miocene. This large freshwater discharge into the Atlantic isolated marine populations on both sides of the river resulting in a distribution pattern known as "anti-equatorial". This type of distribution is included in a broader pattern called antitropicality, defined as latitudinal distribution with a disruption of variable length centered in the tropical zone. Brachidontes darwinianus (SE Brazil to Uruguay) constitute a potential pattern of this type of distribution as it was considered by some authors as a synonym of B. exustus (Gulf of Mexico and the Caribbean). The second potential case is B. solisianus, distributed along the Brazilian coast although has also been cited for localities north of the tropics but the status of these records requires more scrutiny. Our goal is to elucidate phylogeographic and phylogenetic relationships of the scorched mussels present on the warm temperate region of South West Atlantic -B. solisianus and B. darwinianus - evaluating antitropicality over alternative phylogeographic hypotheses. To achieve this, sequences of two nuclear (18S and 28S rDNA) and one mitochondrial (mtDNA COI) genes were used and the phylogenetic relationships of the Brachidontinae were reconstructed. In the phylogeny inferred from COI sequences, Brachidontes solisianus (Brazil) and B. "exustus I" sensu Lee and Ó Foighil (2005) (Gulf of Mexico and the Caribbean) appear as members of a pair distributed north and south of the mouth of the Amazon River, with a divergence time of approximately 2.6 Ma. This time is consistent with an increase in the flow of the Amazon River during the Pleistocene. Brachidontes darwinianus was not related to the B. "exustus" cryptic species complex, so in this case the antitropicality hypothesis is refuted. The hypothesis that the seaway that connected the Southwestern Atlantic Ocean to the Caribbean region during the Miocene may have been the scene of connections between these two regions is discussed.