A new species from subtropical Brazil and evidence of multiple pelvic fin losses in catfishes of the genus Cambeva (Siluriformes, Trichomycteridae)

Abstract

A third pelvic-less species of Cambeva from river basins draining the Geral mountain range in southern Brazil is described. It is distinguished from other congeners lacking pelvic fin and girdle, C. pascuali and C. tropeiro, by having six pectoral-fin rays, 20–23 dorsal procurrent caudal-fin rays, 15–20 opercular and 25–30 interopercular odontodes and a different colour pattern consisting of flank dark brownish-grey with two irregular horizontal rows of small pale yellow grey marks. Whereas available molecular evidence indicates that C. pascuali is more closely related to C. zonata, a species with well-developed pelvic fin, and C. tropeiro is more closely related to C. balios, another species also with well-developed pelvic fin; osteological data strongly suggest that the new species herein described is more closely related to C. diatropoporos than to other congeners. Therefore, this study indicates that the pelvic fin and pelvic-fin support have been lost independently in each of these three species of Cambeva, which corresponds to 11% of all describe species. This result highly contrasts with the closely-related trichomycterine genera Trichomycterus, in which only one in 50 species lost pelvic fin and girdle (0.2%) and Scleronema with all the nine included species having well-developed pelvic fin. These data suggest a stronger tendency to losing pelvic fin in Cambeva, but factors favouring this evolutionary event are still unknown.

Filling distribution gaps: Two new species of the catfish genus Cambeva from southern Brazilian Atlantic Forest (Siluriformes, Trichomycteridae)

“…Cambeva is a morphologically homogeneous genus, with relatively little external morphological variation when compared to the closely related genus Trichomycterus (sensu Katz et al 2018). However, as here and elsewhere observed (Costa et al 2020d), osteological characters may be useful to distinguish closely species and to tentatively support relationship hypotheses. Unfortunately, due to the absence of osteological data in descriptions of species that are rare in ichthyological collections, present diagnoses are still directed to combinations of character states of the external morphology that may be checked in original descriptions (see diagnoses above).…”

“…Molecular phylogenies including species of Cambeva have been directed to more inclusive trichomycterid groups (Ochoa et al 2017(Ochoa et al , 2020Katz et al, 2018;Costa et al, 2020c), consequently comprising a limited sample of taxa belonging to this genus. Therefore, phylogenetic relationships among species of Cambeva are still poorly known (Costa et al, 2020d). However, the available molecular analyses, including a recent unilocus analysis (Donin et al 2020), have corroborated similar intrageneric clades, including a clade named as the C. balios group by Costa et al (2020d), comprising all species from the Lagoa dos Patos system and part of the species from the Paraná-Uruguay system, and another clade, here named as C. davisi group, including species from the Rio Paraná basin and smaller coastal basins.…”

“…Therefore, phylogenetic relationships among species of Cambeva are still poorly known (Costa et al, 2020d). However, the available molecular analyses, including a recent unilocus analysis (Donin et al 2020), have corroborated similar intrageneric clades, including a clade named as the C. balios group by Costa et al (2020d), comprising all species from the Lagoa dos Patos system and part of the species from the Paraná-Uruguay system, and another clade, here named as C. davisi group, including species from the Rio Paraná basin and smaller coastal basins. Costa et al (2020d) described some osteological character states presumably supporting the C. balios group and a subclade, but no morphological feature supporting the C. davisi group or its subclades has been described.…”

“…Costa 2009;Costa et al 2020b). Among these specialised freshwater biotopes are mountain streams, with numerous endemic fishes being first sampled and described in recent years, mainly belonging to the Trichomycterinae (Costa et al 2020c(Costa et al , 2020dDonin et al 2020;dos Reis et al 2020;Vilardo et al 2020), a catfish subfamily (Siluriformes: Trichomycteridae) occurring between southern Central America and Patagonia, in southern South America (Katz et al 2018).…”

“…pectoral fin lacking a filament at the tip of the first ray and hypertrophied cheek muscles), but equivocally omitted in Katz et al (2018). Among the species not occurring in the Rio Paraná basin, two occur in the São Francisco basin (Costa 1992), five in the Lagoa dos Patos system Malabarba 2011, 2013), two in the Rio Uruguai basin (Datovo et al 2012;Costa et al 2020d), and three in the Rio Ribeira de Iguape and smaller coastal basins (Eigenmann 1918;Bizerril 1994;Wosiacki and Oyakawa 2005). However, no species was described from the wide area, about 250 km long, between the coastal river basins of northern Santa Catarina state (Bizerril 1994;Katz and Barbosa 2014) and the southern end of the Atlantic Forest, in the Lagoa dos Patos system.…”