Phylogenetics and Biogeography of the Guiana Shield Pencil Catfishes, Genus Trichomycterus

The relationships of Guiana Shield members of Trichomycterus are examined using three mitochondrial genes (Cytochrome Oxidase 1, Cytochrome b, and 16s) and one nuclear gene (RAG 2). A time-calibrated phylogeny is implemented to examine how diversification is related to the timing of major geographical events in the Guiana Shield. There was topological discordance among the gene trees; however, they overall suggest the presence of two subclades. The T. guianensis subclade consists of the strongly supported relationships of T. sp. 'Potaro, elongate' (Potaro R.) sister to T. guianensis (Potaro R.) + T. sp. 'Ireng, spotted' (Ireng R.). The T. cf. guianensis subclade consists of the strongly supported sister group relationship of T. cf. guianensis (Mazaruni, Potaro, and potentially Caroni Rivers) + T. sp. 'Mazaruni, plain' (Mazaruni R.). Weakly supported as sister to this is T. sp. 'Kusad Mountain' (Takutu R.), and sister to all other members of the subclade is T. conradi (Ireng and Potaro Rivers). The dated phylogeny suggests that the Guiana Shield clade is derived from a lowland ancestor that entered the Proto-Berbice and/or Proto-Essequibo Rivers X 17.4 Ma. The Proto-Berbice contained the lowland portions of the Ireng and Takutu Rivers, and the Proto-Essequibo contained the lowland portions of the Potaro and Mazaruni Rivers, but the histories of the upland portions of the Ireng, Potaro, and Mazaruni Rivers are less clear and have been thought to have drained northward in what we are referring to as the Grand Pakaraima River in which all members of the T. guianensis clade (except for T. sp. 'Kusad Mountain' and possibly T. conradi) were found. We interpret two geodispersal events into the Grand Pakaraima River and a potential vicariance event X 9.4 Ma between uplands and lowlands. The likely formation of the modern Guiana Shield rivers occurred 3.8-1.9 Ma, with the modern Ireng River being captured first by the Proto-Essequibo X 3.8 Ma and finally consolidated X 1.9 Ma when captured by the Rio Branco.