DNA barcoding uncovers extensive cryptic diversity in the African long-fin tetra Bryconalestes longipinnis (Alestidae: Characiformes)

To investigate the presence of cryptic diversity in the African longfin-tetra Bryconalestes longipinnis, we employed DNA barcoding in a phylogeographic context, as well as geometric morphometrics, documenting for the first time genetic and body shape variation in the species. Analysis of cytochrome oxidase I gene (coI) sequence variation exposed extremely high levels of genetic differentiation among samples from across the geographic range of the species (up to 18%), certainly much greater than the traditionally employed c. 3% sequence divergence heuristic threshold for conspecifics. Phylogeographic analyses of coI data revealed eight clusters/clades that diverge by >4% and up to 18% (p-distance), potentially representing cryptic members of a species complex. A clear biogeographic pattern was also uncovered, in which the two main coI lineages corresponded geographically with the upper Guinea (UG) and lower Guinea (LG) ichthyofaunal provinces of continental Africa, respectively. Within each of these main lineages, however, no apparent phylogeographic structuring was found. Despite strong genetic differentiation, there is considerable overlap in body shape variation between UG and LG populations. For the most part, morphological variation does not match the strength of the molecular phylogeographic signal. Therefore, the ability to reliably utilise external body shape for regional delimitation remains elusive. Further anatomical investigation appears necessary to establish whether compelling diagnostic morphological features do exist between the divergent lineages of the B. longipinnis complex uncovered in this study.