RESUMO
The Northeastern Mata Atlântica freshwater ecoregion (NMAF) is recognized for the high degree of endemism of its ichthyofauna, whose evolutionary and biogeographic histories are still poorly understood. Oligosarcus acutirostris is a freshwater fish species endemic to the NMAF, which is distributed in coastal rivers and streams draining Bahia, Espírito Santo, and part of Minas Gerais states in eastern Brazil. Its widespread distribution in currently isolated river basins along the NMAF prompted this study, which aimed to understand what scenarios would be involved in determining its current distribution pattern, and to contribute to a better understanding of the biogeographic history of the NMAF. For this, mitochondrial and nuclear DNA sequences were analyzed based on samples from different localities along the species distribution, including its type locality. Overall, phylogeographic analyses indicate a strong genetic structure within the species evidenced mainly by the non-sharing of haplotypes between most of the basins analyzed. According to the AMOVA results, the current distribution of haplotypes is better explained by the Pleistocene coastal paleodrainages. The results are also used to test and complement a biogeographic hypothesis previously proposed for the drainages of the NMAF.(AU)
A ecorregião de água doce Mata Atlântica Nordeste (NMAF) é reconhecida pelo alto grau de endemismo da sua ictiofauna, cujas histórias evolutiva e biogeográfica ainda são pouco compreendidas. Oligosarcus acutirostris é uma espécie de peixe de água doce endêmica da NMAF, que está distribuída em rios e riachos costeiros que drenam os estados da Bahia, Espírito Santo e parte de Minas Gerais, no leste do Brasil. Sua ampla distribuição em bacias atualmente isoladas ao longo da NMAF motivou este estudo, que teve como objetivos entender quais cenários estariam envolvidos na determinação do seu padrão atual de distribuição e contribuir para uma melhor compreensão da história biogeográfica da NMAF. Para isto, foram analisadas sequências de DNA nuclear e mitocondrial, a partir de amostras de diferentes localidades ao longo da distribuição da espécie, incluindo sua localidade tipo. No geral, as análises filogeográficas indicam forte estruturação genética na espécie, evidenciada principalmente pelo não compartilhamento de haplótipos entre a maioria das bacias analisadas. De acordo com os resultados da AMOVA, a distribuição atual dos haplótipos é melhor explicada pelas paleodrenagens costeiras do Pleistoceno. Os resultados obtidos também são utilizados para testar e complementar hipótese biogeográfica previamente proposta para as drenagens da NMAF.(AU)
Assuntos
Animais , Filogeografia/métodos , Characidae/classificação , BrasilRESUMO
Killifishes are a unique and diversified fish group composed of several annual species inhabiting ephemeral pools in tropical and subtropical regions. Moreover, many genera have probably undergone fast speciation with a high number of short-ranged species of controversial taxonomy. This is the case of the "Hypsolebias flavicaudatus" complex (Aplocheiloidei, Rivulidae) that includes nine recently described taxa of remarkable morphological similarity, endemic to Brazil. Considering the potential of cytotaxonomy of killifishes, as presently revised, we performed cytogenetic analyses in two sister species within this complex (H. flagellatus and H. janaubensis), including the first mapping of ribosomal genes in Hypsolebias. Despite sharing 48 chromosomes and similar distribution of heterochromatin and 5S rDNA, their karyotype formula probably differed as a result of pericentric inversions. In addition, H. flagellatus presented a single pair bearing 18S rDNA and GC-rich regions, while multiple GC-rich and 18S signals (up to 28 chromosomes) were detected in H. janaubensis. These results reinforce the dynamism of karyotype evolution in annual killifishes favored by population isolation and small effective size. Thus, cytogenetic variation seems to be closely associated with speciation in Aplocheiloidei, representing a useful tool for identifying similar species in Hypsolebias complex, which are vulnerable to extinction.