Variabilidade genética e distribuição geográfica da piramutaba Brachyplatystoma vaillantii (Valenciennes, 1840) (siluriformes:pimelodidae) na amazônia brasileira e peruana

Abstract

The piramutaba (Brachyplatystoma vaillantii) (Siluriformes: Pimelodidae) is a migrating catfish of high commercial value in the Amazon. Environmental DNA (DNAa) offers an innovative approach to overcome challenges associated with species detection in freshwater ecosystems. Currently, the Purus River is not considered part of the piramutaba migration area. However, fishery landing data indicate catches of this species in previous years. Taking into account the need to obtain information for a better management of fishery resources, a Specific Molecular Detection System (SMDS) by qPCR with hydrolysis probe was developed to investigate the presence of B. vaillantii in DNAa in Purus River. The primers and probe were designed from sequences of the mitochondrial DNA control region, being then submitted to in silico, in vitro and in situ validation tests, besides the limit of detection (LOD) determined at 10-8ng/µL in qPCR assays. Water samples from 24 sites (1L/site) were collected between the municipality of Lábrea (middle Purus River) and the mouth of Purus River, which were vacuum filtered with cellulose membranes, then fragmented and the DNAa extracted. A DNAa sample from the piramutaba nursery was used as positive control. The concentration of DNAa varied between 2.9 and 70.4 ng/µL. B. vaillantii was detected in six locations in Purus River. With the SMDS developed it is possible to detect B. vaillantii in studies, enabling better strategies for conservation and management of the species. To know its genetic status, we sequenced the mitochondrial DNA control region of 150 individuals, collected at five sites, covering the entire length of the Solimões-Amazonas River in Brazil. Analysis of molecular variance indicated that almost all the variability was contained within localities (99.86%), and estimates of gene flow for this species were high (FST = 0.0014), indicating that B. vaillantii forms a single population along the Solimões-Amazonas River with larger genetic variability than other species of the genus Brachyplatystoma currently available. In order to evaluate the genetics of B. vaillantii, analyses were performed from the control region (CR) of mitochondrial DNA and 10 microsatellite loci (SSR) using samples from 10 locations, six in the Amazon/Solimões River channel and four of its tributaries. Among 492 individuals sequenced, 409 haplotypes were verified. The genotype of 333 individuals indicated 172 alleles. Demography tests indicated population expansion in the species. Bayesian analyses indicated homogeneous genetic distribution among localities. Analysis of molecular variance of the two markers, indicated most variation within sampled localities and low FST fixation index (CR=0.0063; SSR=0.0158), and were also agreeable indicating high level of gene flow. Thus, the genetic homogeneity for B. vaillantii in the Amazon basin is explicit. We propose an update of the geographical distribution of piramutaba in the Amazon, delimiting its occurrence from all available information, including the rivers Javari, Tapajós, Japurá and Içá as an area of occurrence/migration of piramutaba. The reproduction of B. vaillantii has not been confirmed in these tributaries, but the occurrence in these rivers, which reinforces not only the need for further studies addressing the life cycle of the species but also the importance of the conservation of tributaries for the sustainable management, not only of this, but also of other species of migratory fish.