Geographic variation of Moenkhausia bonita (Characiformes: Characidae) in the rio de la Plata basin, with distributional comments on M. intermedia

Abstract

Moenkhausia bonita occurs in numerous additional localities from the Bermejo, Paraná, Paraguay, and Uruguay river basins. Given that this finding greatly expands the distributional range of M. bonita, we carried out an intraspecific comparison, using multivariate methods for 18 morphometric and eight meristic characters taken from a comprehensive sample of 536 specimens. All localities were distributed in four major geographic groups as follows: Bermejo, Paraná, Paraguay, and Uruguay. Results of the morphometric comparisons showed significant differences among the studied groups except between the Paraguay and Uruguay groups. Statistical differences in meristic values were found for most between-group comparisons, especially in those resulting from discriminant canonical analyses (DCA). Specimens from the Bermejo basin were the most distinct group in most morphological comparisons. However, the overall subtle differences found in body morphology likely reflect intraspecific variation within M. bonita and seem to be mainly influenced by spatial and environmental features of drainages. As M. bonita was previously identified as M. intermedia in the río de La Plata basin, distributional comments on the latter species in that basin are provided.

Gymnotus paraguensis, a Good Example of Phenotypic Plasticity in the Pantanal Biome, Brazil

“…It would nevertheless appear to be most parsimonious to believe that these karyotypically diverse units represent distinct species, and that the variation in coloration patterns observed in G. paraguensis reflects the phenotypic plasticity of this species, a common phenomenon in fish. 55,72,73 What is clear is that the subspecies proposed by Craig et al 29 are not supported by the data, and Fricke et al, 8 for example, do not apply the subspecies category to G. carapo in their catalog of fishes (www.researcharchive.calacademy.org/research/ ichthyology/catalog/fishcatmain.asp).…”

Hidden or unnoticed? Multiple lines of evidence support the recognition of a new species of Pseudocorynopoma (Characidae: Corynopomini)

“…For example, Vanegas‐Ríos et al . (2019) recently reviewed samples of Moenkhausia bonita Benine, Castro and Sabino, 2004, from a wide geographical range and considered the distinctiveness in the colour patter ( e.g ., rio Bermejo population) as evidence of high phenotypic variability within this widespread species – given the subtle morphological differences among the studied populations in terms of morphometric and meristic data. In an opposite decision, Bertaco and Malabarba (2013) hypothesized Hollandichthys taramandahy Bertaco & Malabarba, 2013 as a new species mostly based on colour pattern and notwithstanding the subtle morphological differences in counts and measurements to Hollandichthy multifasciatus (Eigenmann and Norris 1900).…”

“…This strong structure challenges the differentiation of populations from species. For example, in Characidae – the most diverse family of freshwater fishes in the Neotropical region (Fricke et al ., 2020) – species recognition has been traditionally based on counts of scales or fin rays, with geographically distinct morphotypes often considered a priori variants in the lack of discrete differences in these counts ( e.g ., Lucena & Soares, 2016; Malabarba & Weitzman, 1999; Vanegas‐Ríos et al ., 2019). Nonetheless, when geographically isolated variants are considered species based on non‐discrete characteristics such as morphometrics, colour pattern or molecular evidence ( e.g ., Melo et al ., 2016; Reis, 2017; Weitzman & Malabarba, 1999), the recognition of these groups as species may be subjective or fall within the “grey zone of speciation” (Roux et al ., 2016).…”

Ichthyofauna of the ribeirão Sucuri, tributary of rio Tietê, upper rio Paraná basin, southeastern Brazil

“…The specimens did not present a complete lateral line, as observed in the original description(Benine et al 2004). However,Vanegas-Ríos et al (2019) analyzed populations of M. bonita from the Bermejo, Paraná, Paraguay, and Uruguay basins and determined that observed differences in body shape and completeness of lateral line are intraspecific variations. Hemigrammus marginatus Ellis, 1911 was the name used for the specimens from upper rio Paraná; however,Ota et al (2015) restricted this species to the basin of the rio São Francisco and rivers of northeastern Brazil.…”