Miocene and Pliocene colonization of the Central American Isthmus by the weakly electric fish B rachyhypopomus occidentalis (Hypopomidae, Gymnotiformes)

Aim We present a molecular phylogenetic and biogeographical analysis of B rachyhypopomus occidentalis , one of the few gymnotiform electric fish in Central America, to further understand the colonization and diversification processes of primary freshwater fishes over the Central American Isthmus. Location Lower Central America. Methods We used Bayesian and maximum‐likelihood phylogenetic reconstructions using mitochondrial [cytochrome c oxidase subunit I ( COI ) and ATP synthase 6 and 8 ( ATPase 8 / 6 )] and nuclear ( RAG1 and rhodopsin) genes and extensive geographical sampling, together with molecular clock analyses and tests of biogeographical scenarios to assess the timing and mode of dispersal and diversification. Results We identified high levels of phylogeographical structure, with a highly divergent lineage composed of individuals from western Atlantic Panama (Bocas), sister to all trans‐Andean South American and Central American lineages. The Pacific slope of Panama showed surprisingly little genetic structure compared with the Atlantic slope. Molecular‐clock and biogeographical analyses support two waves of colonization originating from South America: a first dispersal event in the late Miocene with the Bocas lineage as the only relict, and a second major colonization in the late Pliocene leading to the establishment of B. occidentalis in all central and eastern Panama drainages. Main conclusions The genetic structure of B. occidentalis over the Isthmian landscape reflects the progressive, complex and dynamic geological evolution of the region. Our results support multiple colonization events, with an ancient Miocene dispersal event followed by a recent rapid expansion in the late Pliocene, probably facilitated by the final closure of the Isthmus, which provided an important corridor.