Abstract
Schizolecis is a monotypic genus of Siluriformes widely distributed throughout isolated coastal drainages of southeastern Brazil. Previous studies have shown that fish groups found in isolated river basins tend to differentiate over time in the absence of gene flow, resulting in allopatric speciation. In this study, we used partial sequences of the mitochondrial gene COI with the analysis of the General Mixed Yule Coalescent model (GMYC) and the Automatic Barcode Gap Discovery (ABGD) for single locus species delimitation, and a Principal Component Analysis (PCA) of external morphology to test the hypothesis that Schizolecis guntheri is a complex of species. We analyzed 94 samples of S. guntheri for GMYC and ABGD, and 82 samples for PCA from 22 coastal rivers draining to the Atlantic in southeastern Brazil from the Paraná State to the north of the Rio de Janeiro State. As a result, the GMYC model and the ABGD delimited five operational taxonomy units (OTUs – a nomenclature referred to in the present study of the possible new species delimited for the genetic analysis), a much higher number compared to the traditional alfa taxonomy that only recognizes S. guntheri across the isolated coastal rivers of Brazil. Furthermore, the PCA analysis suggests that S. guntheri is highly variable in aspects of external body proportions, including dorsal-fin spine length, pectoral-fin spine length, pelvic-fin spine length, lower caudal-fin spine length, caudal peduncle depth, anal width and mandibular ramus length. However, no exclusive character was found among the isolated populations that could be used to describe a new species of Schizolecis. Therefore, we can conclude, based on our results of PCA contrasting with the results of GMYC and ABGD, that S. guntheri represents a complex of species.
Highlights
The distribution pattern of single fish species throughout independent hydrographic systems is unusual among fishes of the Atlantic rainforest rivers (Menezes et al, 2007) as well as among members of Otothyrinae (Reis et al, 2003)
The variation is partly distributed within populations and partly between populations, and apparently, it represents a continuous distribution of external morphology, as we can observe in the Principal Component Analysis (PCA) scatter plot (Figure 1)
Our results showed that the measures with greater variations were, respectively: dorsal-fin spine length, pectoral-fin spine length, pelvic-fin spine length, lower caudal-fin spine length, caudal peduncle depth, anal width and mandibular ramus length, as we can observe in the PCA loading values (Table 1)
Summary
The distribution pattern of single fish species throughout independent hydrographic systems (i.e., current not connected rivers) is unusual among fishes of the Atlantic rainforest rivers (Menezes et al, 2007) as well as among members of Otothyrinae (Reis et al, 2003). Genetic and Morphological Analyses of Schizolecis guntheri (Melo et al, 2016), Piabina (Pereira et al, 2011), and Astyanax (Ornelas-Garcia et al, 2008), have shown that species of these groups may present large discontinuities in their distribution patterns with high genetic divergences, but with low morphological variability among geographically isolated populations. These results suggest that these groups may represent a complex of species –, i.e., they are constituted by two or more morphological variable species that are erroneously classified (and hidden) under one species name (Brown et al, 1995). The GMYC method is based on a likelihood method that seeks to determine the threshold between speciation and coalescent events from an ultrametric gene tree, whereas ABGD methods use the gap among organisms belonging to the same species and organisms from different species as a limit to species delimitation
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