Biologia reprodutiva e caracterização molecular de duas espécies simpátricas de lambaris e híbridos interespecíficos na cabeceira do Rio Grande, MG

Abstract

Fishes of the genus Astyanax are widely distributed in Brazilian watersheds, but they remain poorly studied. Sympatric species, which cohabit the same environment, may eventually interbreed and generate hybrids. Hybridization is important for the ecology, conservation and evolution of species, so its detection in natural environment is relevant. The aim of this work was to compare the gametogenesis and reproductive biology of A. paranae and A. fasciatus in the headwaters of Grande River and to verify by molecular analysis the occurrence of natural hybridization between these species, since an intermediate morphotype was sampled and identified as Astyanax sp. A total of 491 specimens (239 A. paranae, 213 A. fasciatus and 44 Astyanax sp.) was collected quarterly in the headwaters of Grande River between May 2014 and April 2015. The fish were sacrificed, dissected and had their biometric data and biological index obtained. Samples of gonads were collected for morphological techniques (light and electron microscopy). Caudal fins were collected and fixed in absolute ethanol for DNA extraction and amplification using primers for mitochondrial COI gene and then the PCR products were bidirectionally sequenced. For all fish collected, gonadal maturation stages were determined based on the macro and microscopic characteristics of the gonads and on the GSI values. The species A. paranae presented sexual dimorphism, with females significantly larger (9.68 ± 0.92 cm) and heavier (12.93 ± 3.89 g) than males (8.96 ± 0.66 cm, 9.50 ± 2.06 g). Specimens of Astyanax sp. presented significantly greater length and weight (10.85 ± 1.29 cm, 17.37 ± 7.01 g) than A. paranae and a trend of greater weight when compared to A. fasciatus (females: 15.95 ± 5.07 G: males: 12.86 ± 5.96 g). The highest averages of GSI were found in the August-October and November-January quarters, when a higher frequency of mature fish was observed. Astyanax sp. did not present gonadal maturation and the mean GSI was the lowest among the sampled animals (0.08 ± 0.18). The batch fecundity was statistically similar in A. paranae (5582.82 ± 1892.78 oocytes) and A. fasciatus (5668.57 ± 1816.68 oocytes), but the relative fecundity (body weight) was higher in A. fasciatus. Histological, morphometric and ultrastructural analyses showed similar characteristics of germ cells of females and males of both species. Gonads of Astyanax sp. presented several alterations such as increased interstitial tissue, vacuolated and degenerating germ cells, altered organelles, evidence of apoptosis and interrupted meiosis. The DNA Barcoding confirmed the morphological identification of A. paranae and A. fasciatus and showed the existence of haplotypes of these two species in samples of Astyanax sp. The sharing of haplotypes from two distinct species by a single morphotype, the gonadal alterations observed in these animals, as well as the evidences of reproductive biology of A. paranae and A. fasciatus strongly suggest that the intermediate morphotype Astyanax sp. is a natural infertile hybrid resulting from the crossing between these two species of lambaris in the headwaters of Grande River.