Deceptive Uniformity, the WWD and Amazon Connections: Phylogeographic Diversity among Intertidal Bed-Forming Mussels from South America (Brachidontes).

TROVANT, B.; ORENZANZ, J.M.; BASSO, N. G.; RUZZANTE, D.E.

Punta Arenas

Congreso; VIII Southern Connection Congress; 2016

Universidad de Magallanes

Several small mussel species (Brachidontes s.l.) dominate the physiognomy of mi-intertidial communities along the temperate coasts of South America but they are difficult to distinguis due to their high phenotypic similarity. We used two nuclear (28S and 18S) and one mitochondrial (COI) genes to reveal the existence of five species in teh region: B. solisianus, B. darwinianus, B. rodriguezii, B. granulatus and two distinct clades of Perumytilus purpuratus. The southernmost species, Perumytilus purpuratus, the only brachidontin occurring in cold-temperate waters of Chile and Argentina form a clade with Austromytilus rostratus (Australia) and Mytilisepta virgata (Japan and Hong Kong). Species of this clade are distributed along the temperate coasts of the Pacific Ocean. Austromytilus (Australia) and Perumytilus (South American) likely diverged following the breakup of Australian, Antartic and South American shelves. Perumytilus includes two genetically distinct clades confined to the Chile-Peru (North Clade) and Magellanic (South Clade) Biogeographic provinces. Brachidontes solisianus (Brazil), the northermmost species along the Atlantic coasts is phylogenetically related to the "B. exustus complex" (Gulf of Mexico and Caribbean) distributed respectively south and north of a discontinuity that includes the mouth of the Amazon and Orinoco Rivers, suggensting a role for their plumes in speciation within this complex and providing an example of an antiequatorial distribuition. Brachidontes rodriguezii (extant) is morphologically similar to a Miocene fossil form (B. lepida), indicating a regional ancestry. Our work suggests that despite their apparent uniformity, Brachidontes (s.L.) dominated communities in South America are assembled with components of herotogeneous origins.