Likewise, C. audax and C. lateralis are very similar in morphology, with limited diagnostic traits that differentiate both species ( Smith & Miller, 1986). This led to C. garmani being considered synonymous with C. lateralis until Smith & Miller (1986) resurrected it as a valid taxon. Characodon lateralis and C. garmani were described in 18 respectively, based on a brief description of morphological characters with limited diagnostic value. Taxonomy and classification of the genus had been historically uncertain and unstable, mainly due to limitations in the original descriptions. Previous studies found that the distribution areas of C. audax and C. lateralis are separated by the waterfall known as El Salto, locating C. audax north (above) of waterfall and C. lateralis south (below) of it ( Domínguez-Domínguez et al., 2010). Characodon lateralis was described from an uncertain locality in “Central America”, but this is likely to be an error considering that no specific locality was given for the type material. The genus has a disjunct distribution pattern: C. garmani occurs in the northeast of Mexico within the Nazas River basin ( Miller, Minckley & Norris, 2005), whereas C. audax and C. lateralis occur in the northwest of Mexico at the headwaters of the Mezquital River basin ( Domínguez-Domínguez et al., 2010). The genus is represented by three recognized species: Characodon lateralis ( Günther, 1866), C. garmani ( Jordan & Evermann, 1898) and C. audax ( Smith & Miller, 1986), all of which are restricted to isolated springs and streams in the northern arid highlands of the states of Durango and Coahuila, Northern Mexico ( Domínguez-Domínguez, Doadrio & Perez-Ponce De Leon, 2006). The genus Characodon is the earliest diverging lineage of the Goodeinae subfamily, sharing a common ancestor with the rest of Goodeinae around 15.5 Mya ( Domínguez-Domínguez et al., 2010). Goodeids are notable for their unusual reproductive biology among fishes, typified by internal fertilization, viviparity and matrotrophy (the continuous extra-vitelline supply of nutrients from the parent to the progeny during gestation) ( Miller, Minckley & Norris, 2005 see details of these goodeid traits in ( Uribe et al., 2018)). The members of the subfamily Goodeinae are small-bodied freshwater fishes widespread throughout the Mexican highlands and adjacent areas, encompassing approximately 40 species. The possible processes identified as contributing to the formation of differentiated genetic groups are isolation, low population size, recurrent bottlenecks, and the strong sexual selection exhibited by the genus. Significant genetic structure was found within each haplogroup and suggests the existence of at least four Evolutionary Significant Units (ESUs) within the examined populations. The results with both markers show the presence of two highly differentiated haplogroups one distributed north and the other distributed south of the waterfall, with genetic distances of 1.7 and 13.1% with cytb and d-loop respectively, and divergence calculated to have occurred 1.41 Mya. We perform a phylogeographic study using the mitochondrial cytb gene and d-loop region to elucidate the evolutionary history of C. audax are classed as endangered, and have been the subject of taxonomic controversy since their description: previous studies have recognized a genetic differentiation in two groups separated by the El Salto waterfall, but morphological analyses contradict these genetic results. garmani, with the latter, considered extinct. Within this subfamily, the genus Characodon is the earliest diverging lineage of which three species have been described: C. Most of the species are restricted to small and isolated streams or springs. The subfamily Goodeinae is a group of fishes endemic to the Mexican highlands. Genetic differentiation in the genus Characodon: implications for conservation and taxonomy. Cite this article Beltrán-López RG, Pérez-Rodríguez R, Montañez-García OC, Artigas-Azas JM, Köck M, Mar-Silva AF, Domínguez-Domínguez O. For attribution, the original author(s), title, publication source (PeerJ) and either DOI or URL of the article must be cited. Licence This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. 5 Haus des Meeres Aqua-Terra Zoo, Vienna, Austria DOI 10.7717/peerj.11492 Published Accepted Received Academic Editor Nicholas Jeffery Subject Areas Biogeography, Conservation Biology, Evolutionary Studies, Taxonomy, Freshwater Biology Keywords Goodeidae, Endemic, ESU, Evolutionary history, Taxonomy, Conservation Copyright © 2021 Beltrán-López et al.
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