“More than meets the eye”: phylogeographic inferences and remarkable cryptic diversity and in endemic catfish Parotocinclus (Loricariidae: Hypoptopomatinae) from neglected and impacted basins in South America

The restricted range, taxonomic uncertainties and the apparent phylopatric behavior of Parotocinclus (dwarf plecos) make this fish group an excellent model to infer diversification patterns in Neotropical rivers. Thus, the aim of this study was to investigate the spatial–temporal relationships and the presence of cryptic forms in Parotocinclus cristatus from poorly known and human-impacted drainages in northeastern Brazil based on mitochondrial COI (589 bp) and Cyt-b (835 bp) and nuclear (Rhodopsin, 473 bp) markers. The phylogenetic reconstruction, haplotype network and species delimitation algorithms revealed three conspicuous and restricted molecular operational units (MOTUs) within P. cristatus. The samples from Cachoeira and Una basins represent a single MOTU dating back to the Early Pliocene, resulting in deep genetic divergence when compared to the other lineages. The MOTUs from Contas and Almada river basins diverged around 2.1 Ma, while the latter encompassed highly structured populations between upper and lower watersheds (0.6 Ma, Pleistocene). The closest relationship between more distant basins than nearby drainages indicates an intricate scenario of headwater captures that challenge traditional studies based on current geographic reliefs and ichthyofauna inventories. Therefore, caution when biogeographic inferences are carried out without further understanding about the genetic diversity and the geomorphological history, as commonly reported in fishes from eastern basins in Brazil. Finally, the conspicuous Linnean and Wallacean shortfalls in dwarf plecos, including unique lineages from unprotected and highly degraded areas, justifies a thorough review of their taxonomic status since valid species are the major source of information for defining conservation policies.