Phylogenomics, evolution of trophic traits and divergence times of hemiodontid fishes (Ostariophysi: Characiformes).

The South American characiform family Hemiodontidae comprises five genera and 34 species. The family lacks comprehensive phylogenetic hypotheses resolving its species relationships. The studies that addressed these questions exhibited a narrow taxon sampling or used single-locus markers. Herein we surveyed hundreds of ultraconserved elements (UCEs) loci to provide the first molecular phylogenetic hypothesis and divergence time estimates for hemiodontids encompassing all its genera and most species (27 of the 34 valid species). We also tracked the history of the protractile upper jaw in the genera Argonectes and Bivibranchia across the recovered phylogenies through ancestral state reconstruction. Our results corroborate the monophyly of Hemiodontidae and the genera Argonectes and Bivibranchia in all phylogenetic methods with maximum clade support. The genera Anodus and Hemiodus were not monophyletic because Anodus elongatus was sister to the monotypic Micromischodus instead of A. orinocensis, and H. immaculatus did not form a clade with its other congeners, but instead was sister to the clade including Anodus and Micromischodus. All remaining species of Hemiodus were placed together into a monophyletic group, where they were arranged into four major subclades. The relationship in the family is summarised as: (Bivibranchia, (Argonectes, ((H. immaculatus, (Anodus, Micromischodus)), Hemiodus clade))), in discordance with the morphological phylogeny that placed all genera monophyletic and resolved the family as: ((Anodus, Micromischodus), (Hemiodus, (Argonectes, Bivibranchia))). The origin of Hemiodontidae was estimated from the Late Cretaceous to the Middle Paleogene, with the mean age in the Paleocene, while the origin of most hemiodontid genera except Bivibranchia occurred in the Miocene. Unordered parsimony and likelihood reconstruction indicates that Argonectes and Bivibranchia developed their protractile upper jaw independently.

Molecular species delimitation of the genera Anodus, Argonectes, Bivibranchia and Micromischodus (Ostariophysi: Characiformes)

ABSTRACT A good taxonomic assessment of specimens is an essential task to many biological studies and DNA data have provided additional sources of information to assist in the disentanglement of taxonomic problems among living organisms, as has been the case of some taxa of the megadiverse Neotropical ichthyofauna. Here we assessed all valid species in the Neotropical freshwater fish genera Anodus, Argonectes, Bivibranchia and Micromischodus of the family Hemiodontidae to establish molecular species boundaries among them. All species delimitation methods defined exactly only one MOTU for Anodus elongatus, Argonectes longiceps, A. robertsi, Bivibranchia bimaculata, B. notata, B. velox, and Micromischodus sugillatus, resulting in total congruence between nominal species and MOTUs for these seven taxa. The three species having discordant results across analyses: Anodus orinocensis, Bivibranchia fowleri, and Bivibranchia simulata, matched more than one MOTU per species in some methods, meaning that cryptic diversity may exist within these taxa. Overall, this great correspondence among morphological and molecular boundaries for thae species analysed seem to be indicative of a reasonably stable taxonomy within these Hemiodontidae genera.

RESUMO Uma avaliação taxonômica adequada dos espécimes é uma tarefa essencial para muitos estudos biológicos, e os dados de DNA têm fornecido fontes adicionais de informações para auxiliar no desemaranhamento de muitos grupos taxonômicos, como tem sido o caso de alguns táxons da megadiversa ictiofauna Neotropical. Aqui examinamos todas as espécies válidas dos gêneros de peixes Neotropicais de água doce Anodus, Argonectes, Bivibranchia e Micromischodus (família Hemiodontidae) para estabelecer limites moleculares entre elas. Todos os métodos de delimitação definiram exatamente apenas uma MOTU para Anodus elongatus, Argonectes longiceps, A. robertsi, Bivibranchia bimaculata, B. notata, B. velox e Micromischodus sugillatus, resultando em congruência total entre espécies nominais e MOTUs para estes sete táxons. As três espécies com resultados divergentes entre as análises, a saber, Anodus orinocensis, Bivibranchia fowleri e Bivibranchia simulata, corresponderam a mais de um MOTU por espécie em alguns métodos, mostrando que pode existir uma diversidade críptica dentro desses taxa. No geral, esta grande correspondência entre os limites morfológicos e moleculares para as espécies analisadas parece indicar uma taxonomia relativamente estável para esses gêneros de Hemiodontidae.

A new species of Hemiodus Müller (Characiformes: Hemiodontidae) from the lower Rio Xingu, Brazil.

A new species of Hemiodus is described from the Rio Xingu basin, Pará, Brazil. It is distinguished from congeners by the combination of presence of a dark longitudinal stripe extending from head to tip of lower caudal-fin lobe, an oblique blotch on dorsal-fin, 9-11 scale rows above lateral line, 58-66 perforated lateral line scales, and 17-20 circumpeduncular scales. Comments on the conservation status of the new species, as well as its relationships among Hemiodus species, are made.