Comparative morphology, phylogenetic relationships, and taxonomic revision of South American killifishes of the Melanorivulus zygonectes species group (Cyprinodontiformes: Rivulidae)

摘要

This study includes the first phylogenetic analysis for the M. zygonectes species group, a Glade of small rivulid killifishes, endemic to an area comprising the transitional zone between the Amazon rain forest and the Cerrado savannah, in central and northeastern Brazil. The phylogenetic analysis integrating 59 morphological characters and DNA sequences highly supports monophyly of the group. Fourteen species are considered valid, including eleven previously described, of which most had their distribution areas and diagnoses revised on the basis of recent new collections, and three new species: M. kayabi from the Rio Tapajos and middle Rio Xingu drainages; M. rubroreticulatus from the lower Rio Xingu drainage; M. modestus from the upper Rio Tapajos drainage; M. megaroni from the upper and middle Rio Xingu drainage; M. sahnonicaudus, M. spixi, new species, M. rubromarginatus, M. crixas, M. javaeh, M. karaja, and M. zygonectes, M. petrisecundi, new species, and M. wallacei, new species, from the Araguaia-Tocantins drainage system; and M. parnaibensis from the Rio Parnaiba basin. All clades contained in the M. zygonectes group have at least part of their members occurring in the Araguaia-Tocantins drainage system, a distribution pattern that is interpreted as evidence of a possible past distribution restricted to that area. This study once again supports the importance of using colour pattern characters of live specimens in systematics of aplocheiloid killifishes, since they were useful to diagnose species and sub-clades of the M. zygonectes group, besides increasing Glade support when added to molecular data.