Three new species of the killifish genus Melanorivulus from the Rio Paraná Basin, central Brazilian Cerrado (Cyprinodontiformes, Aplocheilidae)

Abstract

Three new species of Melanorivulus are described from the upper and middle Rio Paraná Basin, central Brazilian Cerrado. These species are members of the M. pictus species group, endemic to central Brazilian plateaus and adjacent areas, and are easily diagnosed by colour pattern characters, but their relationships with other congeners of the group are still uncertain. Melanorivulus proximus sp. n., from the middle Rio Aporé drainage, and M. nigromarginatus sp. n., from the Rio Corrente drainage, are possibly more closely related to other species endemic to streams draining the slopes of the Caiapó range, whereas M. linearis sp. n., from the upper Rio Pardo drainage, middle Rio Paraná Basin, is considered more closely related to M. egens, a species also endemic to this part of the Basin. This study corroborates the high diversity of species of Melanorivulus in the central Brazilian Cerrado plateaus repeatedly reported in previous studies, indicating once more that different species are often found restricted to short segments of the same river drainage. The intense habitat loss recorded in recent years combined to the high species diversity limited to specific Cerrado freshwater ecosystems, the veredas, indicates that species of Melanorivulus endemic to this part of the Brazilian Cerrado are highly threatened with extinction.

Unrecognized biodiversity in a world’s hotspot: three new species of Melanorivulus (Cyprinodontiformes: Rivulidae) from tributaries of the right bank of the Rio Paraná basin, Brazilian Cerrado

“…According to Costa (2016Costa ( , 2017 patterns involving the caudal fin contain a high concentration of phylogenetically informative characters, useful to delimit most species of the M. zygonectes, M. pinima and M. dapazi group. The same is also valid to distinguish species of the M. pictus group (Costa, 2018).…”

“…11). The relatively low variability of character states among species of the M. pictus group makes colour pattern characters an essential source to diagnose species and to es- timate their relationships, since molecular data are still not available for most species (Costa, 2018). The only molecular study corroborates species and groups delimitations according to colour patterns ).…”

“…However, most of the species are found in Brazil and occur in the Cerrado biome along several river basins drained mainly by the upper tributaries of the Rio Araguaia, Tocantins, Paraná and Paraguay basins and the adjacent Cerrado-Amazon ecotone . Recent killifish inventories of the Brazilian Cerrado have revealed a high diversity of Melanorivulus species (e.g., Costa 2012, 2018, Volcan et al 2017, indicating that species inhabiting the region have small geographical ranges, often restricted to short segments of a single river drainage (Costa 2017, Volcan et al 2017. Despite the wide geographical distribution and high diversity, little is known about the conservation, distribution, biology and ecology of most Melanorivulus species (Severo-Neto and Volcan 2018).…”

“…The Melanorivulus pictus species group currently comprises 18 species (Volcan et al 2017, Costa 2018, with 16 species occurring in the Rio Paraná basin: M. apiamici (Costa, 1989) in the Rio Paraná, M. egens (Costa, 2005), in the Rio São Domingos, M. formosensis (Costa, 2008) and M. nigromarginatus Costa, 2018 for the Rio Corrente, M. giarettai (Costa, 2008) for the Rio Araguari basin, M. leali Costa, 2013 for the Rio Grande basin, M. nigropunctatus Volcan, Klotzel & Lanés, 2017 and M. ofaie Volcan, Klotzel & Lanés, 2017 for the Rio Verde basin, M. faucireticulatus (Costa, 2008), M. pictus (Costa, 1989) and M. vittatus (Costa, 1989) for the Rio Claro basin, M. polychromus Nielsen, 2016 for the Rio São José dos Dourados basin, M. rutilicaudus (Costa, 2005) for the Rio Verde basin, M. scalaris (Costa, 2005) for the Rio Sucuruí basin, M. proximus Costa, 2018 for Rio Aporé and M. linearis Costa, 2018 for the upper Rio Pardo basin. Two other species occur exclusively in the upper Rio Tocantins and Araguaia basin: M. planaltinus (Costa & Brasil, 2008) for the Rio Cocal and M. litteratus (Costa, 2005) for the Salto stream, respectively.…”

“…Most species of the M. pictus group are reported for highlands, mainly in the headwaters of the main tributary drainage on the right bank of the Rio Paraná (Costa 2012, 2018, Volcan et al 2017. On the other hand, perhaps caused by insufficient sampling, there is a large gap of records in lower areas, downstream the headwaters (Figure 3).…”