Diversidade da fauna de peixes do rio Tocantins com uso do DNA barcoding e percepção dos pescadores sobre os impactos das barragens

Abstract

The ichthyofauna of the Tocantins River has many endemic species; however, it has been little studied in molecular terms, which could provide more robustness to the process of specimen identification and, consequently, reveal and assist in solving problems in taxonomic identification by indicating high levels of cryptic diversity, possible identification errors or new species. In addition, this river is heavily impacted by hydroelectric power plants (HPPs) that cause several socio-environmental damages such as reduced fish diversity, population displacement and health problems. Fishermen have extensive local ecological knowledge that can be used to improve the understanding of the impacts of HPPs. In this sense, the objective of the present study was to identify fish specimens from the Tocantins River using DNA barcoding and classical fish taxonomy and to evaluate fishermen's perception of the impacts of hydroelectric power plants in the middle and lower Tocantins River. Collections were carried out at five points, resulting in the capture of 725 individuals with the partial sequence of the cytochrome oxidase subunit I (COI) gene obtained (620 bp). In this way, the specimens were analyzed using both morphological criteria and four molecular approaches to species delimitation. Twenty-five fishermen in three municipalities were also interviewed using a questionnaire with 22 questions. Data analysis was performed considering the descriptive analysis of the responses. A total of 443 haplotypes were recovered with an average intraspecific K2P genetic distance of 1.82%. A total of 138 species were identified based on morphological criteria, much lower than that indicated by the four molecular methods (Assemble Species by Automatic Partitioning [ASAP], Barcode Index Number [BIN], Generalized Mixed Yule Coalescentant [GMYC] and Bayesian Poisson Tree Processes [bPTP]) through which 152–157 molecular entities were identified. A total of 41 unique BINs were obtained based on data generated by the BOLDSystems platform. According to the results indicated by ASAP (considered the most appropriate molecular approach in this study), there was an increase of 17 molecular entities (12.32%) when compared to the number of species identified through morphological criteria, which may indicate cryptic diversity, candidates for new species, and incorrect identifications. Twenty-one inconsistencies were indicated between the different species identification approaches. Regarding the fishermen's perception, there was convergence in the responses towards the perception of a decrease in fish diversity after the construction of the HPPs, including fish of commercial interest, which is linked to the decrease in income and increased food insecurity of these families. In addition, the fishermen noted an increase in symptoms that may be a consequence of mercury contamination and diarrhea as a possible consequence of the decrease in water quality. Despite all these socio-environmental losses, fishermen report a lack of prior consultation, representation and transparency in the decision-making process that preceded the construction of hydroelectric plants. We therefore conclude that by using the integration of classical taxonomy and DNA barcoding, it was possible to identify identification problems and reveal hidden diversity. It is suggested that these taxonomic problems be carefully evaluated and resolved by specialists. Furthermore, fishermen perceive themselves as being strongly affected from a socio-environmental point of view and do not mention any benefits, other than energy production, offered to the community by these projects. The state apparatus at the time was indifferent to the traditional knowledge of these fishermen and negligent in elucidating the different impacts that the hydroelectric plants would cause.