Marcadores genéticos e sua contribuição para a caracterização das espécies e reconstrução da história evolutiva do gênero Euryoryzomys (Rodentia: sigmodontinae)

Abstract

Morphological similarities among rodents hinders the taxonomy of the group. Previously, the genus Oryzomys had its species allocated in species complexes. Cytogenetics and molecular information pointed out to the existence of cryptic entities among those species complexes. Accordingly, Oryzomys was later split in ten new genera, being Euryoryzomys one of them. Six species and another one not formally described are recognized for the genus. These species are morphologically similar, and have a broad distribution through different phytophysiognomies. Cytogenetic represents an important tool to identify some species, and the karyotype for E. legatus is still missing. Furthermore, systematic studies are also extremely relevant to recover the phylogenetic relationships of the species of the genus and their diversification evolutionary hypotheses. The aim of this study was to describe the karyotype of E. legatus, and to perform phylogenetic analyses on Euryoryzomys species. Chromosomal preparation of E. legatus were analyzed based on conventional Giemsa staining, C and G-banding patterns, and fluorescence in situ hybridization (FISH) using telomeric probes. The karyotype of E. legatus showed 2n=80, NF=86, and FISH analyses showed signals in the telomeric regions. The phylogenetic analyses using all the recognized Euryoryzomys species were based on 83 partial sequences of the mitochondrial gene cytochrome b (cyt-b) - 11 produced in this study - and 17 partial sequences of the nuclear gene interphotoreceptor retinoid binding protein (IRBP) - four obtained in this study -, besides 11 taxa that composed the outgroup. Phylogenetic analyses - applying Bayesian inference and Maximum-Likelihood methods – using concatenated dataset recovered the monophyly of the genus with low support, and the following topology: ((E. macconnelli A, ((E. macconnelli B, E. macconnelli C), E. macconnelli D)), ((E. emmonsae A, E. emmonsae B), (E. russatus, ((E. lamia, Euryoryzomys sp.), (E. nitidus B, (E. nitidus A, (E. nitidus MSB70697, E. legatus))))))). The diploid number, chromosomes morphology and banding patterns of E. legatus were similar to those of E. emmonsae, E. nitidus, and E. russatus described in the literature. Cytogenetic data are informative to distinguish E. legatus from three other species: E. lamia, E. macconnelli, and Euryoryzomys sp. The phylogenetic analyses indicated the hypothesis that E. emmonsae, E. macconnelli, and E. nitidus - and according to the literature, E. lamia - may represent species complexes (cryptic species previously revealed by the cytogenetics data or morphology and corroborated by the phylogenetic reconstruction). Three subclades (northeast, southeast and south-southeast) were recovered for E. russatus, which demonstrates that phylogeographic analyses are needed, based on the sample size. E. nitidus was recovered as polyphyletic, and its phylogenetic relationships with E. legatus must be further investigated. The phylogenetic analyses indicates that species of Euryoryzomys from humid areas should have diverged earlier than species from open and refugia areas. This study increases the knowledge of Euryoryzomys and shows that the difficulty on species delimitation and their diversification processes are still strongly related to sample gaps, given the wide distribution of the genus. Fieldwork expeditions are still required to resolve this basic deficiency. Subsequently, taxonomic revisions are also required, especially under an integrative taxonomy approach.