RESUMO
An integrative approach based on morphological and multilocus genetic data was used to describe a new species of Nematocharax from the headwaters of the upper Contas River on the Diamantina Plateau, north-eastern Brazil and to infer the relationships among evolutionary lineages within this fish genus. Multispecies coalescent inference using three mitochondrial and five nuclear loci strongly supports a basal split between Nematocharax venustus and the new species, whose distinctive morphological characters include absence of filamentous rays on pelvic fins of maturing and mature males, reduced anal-fin lobe length and lower body depth. The unique morphological and genetic traits of the population from the upper Contas River were supported by previous reports based on cytogenetics, DNA barcode and geometric morphometrics, reinforcing the validation of the new species. The conservation status of this new species is discussed.
Assuntos
Characidae/classificação , Variação Genética , Animais , Evolução Biológica , Brasil , Characidae/anatomia & histologia , Characidae/genética , Classificação/métodos , Masculino , Filogenia , Rios , Análise de Sequência de DNA , Especificidade da EspécieRESUMO
Cytogenetic studies in Neotropical electric knifefish of genus Gymnotus have shown a remarkable interspecific variability, including distinct sex chromosome systems. In this study, we present the first chromosomal data in Gymnotus bahianus from Contas River basin, northeastern South America. Based on extensive analyses, the modal diploid values were 2n = 36 (30m/sm + 6st) for females and 2n = 37 (32m/sm + 5st) for males. Therefore, a novel XX/XY1Y2 sex chromosome system is described for the genus. Single nucleolar organizer regions (NORs) interspersed to GC-rich sites were detected on a subtelocentric pair (7th) for both sexes and confirmed by ï¬uorescent in situ hybridization with 18S rDNA probes. Heterochromatin was detected at pericentromeric regions of all chromosomes and interspersed to NORs on pair 7 and 5S rDNA cistrons on pair 9. The highly differentiated karyotype of Gymnoytus bahianus, with low diploid numbers and a unique XX/XY1Y2 system, reinforces the independent origin of sex chromosomes in Gymnotiformes and seems to reflect the particular evolutionary history of this species in a small and isolated drainage system. Moreover, in spite of morphological similarities, the present results indicate a remarkable chromosomal divergence in relation to closely related species such as G. sylvius and G. carapo.
Assuntos
Evolução Biológica , Gimnotiformes/genética , Cromossomos Sexuais/genética , Animais , Feminino , Heterocromatina , Cariótipo , Masculino , Região Organizadora do Nucléolo/genética , RNA Ribossômico 18S/genética , América do SulRESUMO
Little is known on genetics of Brazilian coral reef fish and most of this information is limited to chromosome characterization of major representative species. The diploid chromosome number in marine fish varies from 2n= 22-26 to 2n = 240-260. Despite of this apparent diversity, most studied marine species have a diploid complement with 48 acrocentric chromosomes. This latter trend is mostly observed among Perciformes, an important major taxon of coral reef fishes. Studies in the families Pomacentridae, Pomacanthidae and Chaetodontidae, for example, have shown a common karyotype pattern entirely formed by 48 uniarmed chromosomes. However, rare numerical and structural chromosome polymorphisms and cryptic chromosome rearrangements involving heterochromatin segments and/or nucleolar organizing sites have been reported among such fishes. Although new chromosome forms can contribute to the establishment of genetically isolated populations, their role in reef fish speciation at marine realm still is an open question. More recently, genomic DNA analyses using RAPD and microsatellites, and sequencing and RFLP of mitochondrial DNA have increasingly been used in Atlantic reef fish species. Genetic homogeneity over wide geographical ranges has been reported for different fish groups, in contrast to several cases of population substructuring related to environmental constraints or evolutionary history. Amazonas outflow and upwelling on the Southeastern coast of Brazil are believed to be strong barriers to dispersal of some reef species. Moreover, it is suggested that the pattern of speciation and population structure at South Atlantic is quite distinctive from Pacific Ocean, even when comparing closely related taxa. Further genetic studies are strongly encouraged in Brazilian reef fishes in order to provide a reliable scenario of the genetic structure in this important and diverse fish group.