No abstract

The genus Psalidodon Eigenmann, 1911 (Characiformes Characidae) is a fish group with great diversity, expressed at the chromosomal, genetic and taxonomic level. The genus is markedby events of allopatric and vicariant evolution, by the formation of complexes of species andby wide geographical distribution. Both in these fish and other organisms, the association ofstudies with molecular markers and geometric morphometric techniques are useful in delimitingsignificantly evolutionary units (ESU). In this work, we performed maximum likelihood esti-mates (MLE) from mitochondrial Cyt b gene sequences and canonical variables (CVA) from13 landmarks in eight populations of P. aff. paranae Eigenmann, 1914. The analysis of Max-imum likelihood resulted in the structuring of populations in two different clades, one of whichwas composed only of individuals from a small population inhabiting a stream with approxi-mately two km of length, demonstrating their clear distinction from the other populations. Theanalysis of canonical variation demonstrated the complete structuring of this population, andthe position of each clade in the morpho-space was congruent with the topography observedin the MLE. Based on the results found, the existence of a new endemic species of the genusPsalidodon is evident.

Deuterodon is a genus of the subfamily Stethaprioninae, a group of Neotropical fish known as tetras. Deuterodon hastatus represents a species complex, which is supported by cytogenetic and molecular data. In this study, we show the results of comparative evolutionary analyses of the ATP synthase subunit 6 gene in four Deuterodon species, in addition to ribosomal markers ( 18S rDNA and 5S rDNA ), of a new population of the D. hastatus species complex from the Angra dos Reis/RJ region. The study population comprised a new cytotype, which we refer to as cytotype D, in D. hastatus , with 2n = 50 = 6M+8SM+8ST+28A. We obtained three different clades of D. hastatus in our phylogeny, one of them composed only by specimens of cytotype D. By using molecular clock dating, we observed that the radiation of Deuterodon from southeastern Brazil seemed to be associated with neotectonic events that occurred during the Miocene-Pliocene and Pliocene-Pleistocene transitions, marked by the capture of headwater streams and marine transgressions. The results obtained reinforce the idea that D. hastatus is a species complex, and at least three evolutionary significant units were identified in this group.

The genus Psalidodon, in turn, has shown great potential in studies involving the variation of form associated with genetic characteristics (Alves et al., 2020;Rocha et al., 2019). Rocha et al. (2019) demonstrated the correspondence between molecular data and body shape variation in different mitochondrial lineages of P. rivularis and P. paranae Eigenmann, 1914. The study also reinforced the taxonomic validity between the two species, both through molecular and morphometric data.Approaches involving cytogenetic markers together with geometric morphometry were used by Castro et al.