Abstract: Neotropical catfishes of the genus Rhamdia are divided into cis- and trans-Andean/Middle American reciprocally monophyletic components, the latter notable for its considerable cave-dwelling diversity. Despite previous research, uncertainties remain regarding the systematics and historical biogeography of the Middle American clade. To test previous phylogenetic hypotheses and improve our understanding of the evolutionary history of this group of Middle American freshwater fishes, we generated and analyzed comparative mitogenome-wide data from most valid species and known cave-dwelling forms. Our results corroborate this clade as divided into two reciprocally monophyletic groups (split dated at ~9 Ma): a clade representing the species Rhamdia guatemalensis (crown group dated at ~2.8 Ma) and a clade consisting of the remaining Middle American species (i.e., the Rhamdia laticauda species group; crown group dated at ~4 Ma). Our results also confirm the notion that R. laticauda is deeply paraphyletic and that phylogenetically scattered geographic lineages of this taxon could represent different species. Our divergence time estimates coupled with present-day distribution patterns support the biogeographic scenario in which northward dispersal and colonization of Central America and southern North America by Rhamdia was catalyzed by the emergence of the Panamanian Isthmus land bridge and stream captures across Lower Central America. Cave colonization in Middle American Rhamdia is widespread, convergent, relatively recent (dating from the Pleistocene), and most likely opportunistic, with established cave-dwelling populations possibly representing “evolutionary dead ends”.

Key words: catfishes, heptapterids, hypogean, karst caves, troglomorphic, mitochondrial genomes