Relações filogenéticas em Xenurobrycon Myers & Miranda-Ribeiro e discussão sobre miniaturização no gênero (Characiformes: Characidae: Stevardiinae)

Abstract

Species of Xenurobrycon hold remarkable evolutionary novelties related to secondary sexual characters and important paedomorphic features resultant of the miniaturization process. Four equally parsimonious hypotheses on the phylogenetic relationships of Xenurobrycon species are presented based on the analysis of 128 morphological characters obtained through the study of all valid species of the genus and 3 additional morphotypes, possibly new species. The outgroup is composed of 9 taxa, mostly members of Xenurobryconini and all members of the Stevardiinae.Xenurobrycon is recovered as a monophyletic group, supported by 23 synapomorphies, of which 18 are exclusive and five are homoplastic. The monophyly of the tribe Xenurobryconini, where Scopaeocharax appears as a sister group of (Xenurobrycon + Tyttocharax). Of the 128 characters used, 45 are related to the ontogenetic truncation process, evaluated by a comparative study between the miniature species and the developmental sequence of closely related species (Moenkhausia pittieri and Salminus brasiliensis). Two main ontogenetic truncation events were observed in the evolution of Xenurobryconini, one in the base of the clade composed by Xenurobrycon and Tyttocharax, another in Xenurobrycon coracoralinae. Tyttocharax as revealed as the genus having the most truncated species in the tribe. Phylogenetic analysis indicated that the clade that includes Xenurobrycon macropus and Xenurobrycon sp. C is the sister group of the remaining species of the genus, exhibiting a unique pattern of hypertrophied caudal scale in the tribe. Xenurobrycon pteropus, Xenurobrycon sp. A and Xenurobrycon sp. B form a monophyletic group. Xenurobrycon coracoralinae is the sister specie of this clade in all trees. The position of Xenurobrycon varii, Xenurobrycon polyancistrus, and, mainly, of Xenurobrycon heterodon vary among the cladograms, possibly due to missing entries of X. heterodon. According to this analysis, it is evident that the evolution of Xenurobrycon is intimately related to evolutionary novelties associated to secondary sexual characters.

Revisão taxonômica e osteologia do complexo de espécies Hemigrammus geisleri Zarske & Géry (Characiformes: Characidae)

“…Para a comparação e compreensão de aspectos osteológicos do "complexo" Hemigrammus geisleri, foi utilizado o estudo do desenvolvimento ósseo de Salminus brasiliensis (Mattox et al, 2014) e estudos recentes com peixes miniaturas ou de pequeno porte que apresentam truncamentos ontogenéticos (e.g. Mattox et al, 2013, Mattox et al, 2016, Marinho, 2017, Mattox & Conway, 2021, Marinho, 2022, Gentile, 2022, Mansani, 2022.…”

“…O estudo da osteologia de peixes têm-se mostrado uma importante ferramenta na compreensão e diagnose das espécies (Mattox et al, 2013, Mattox et al, 2016, Marinho, 2022, Gentile, 2022, Mansani, 2022, além do auxílio no conhecimento do desenvolvimento e evolução dos peixes. Embora Hemigrammus geisleri, Hemigrammus sp.…”