Padrões genético-populacionais de “tracajá” Podocnemis unifilis nos rios Madeira, Mamoré e Guaporé

Abstract

The species Podocnemis unifilis, popularly known as ‘‘tracajá’’, belongs to the Podocnemididae family, whose geographic distribution extends throughout the Amazon and Orinoco basins. The species is capable of moving through large areas of flooded forest when Amazon rivers flood, and is known to spawn in different types of habitat. However, recent studies have shown that environmental factors can affect their dispersal and consequently the genetic structure of their populations. Furthermore, the species has suffered a long history of illegal hunting and unrestrained consumption of its eggs, which may have affected its genetic diversity. Some rivers in the Amazon basin have rapids and waterfalls that can act as geographic barriers and thus limit population groups, making them more susceptible to stochastic and anthropic factors. This is the case of the tracajás that occur along the Madeira River, a river that had waterfalls and rapids in its upper course. In the last 15 years, this river has undergone drastic changes caused by the construction of two hydroelectric plants, Jirau and Santo Antônio, which caused serious changes in the aquatic environment and consequently directly affected the aquatic and semi-aquatic fauna of that region. Therefore, understanding the effects of the construction of these HPPs over time is of fundamental importance to implement conservation and management measures for the affected species. This work aimed to evaluate genetic diversity, population structure and the influence of natural barriers on populations of Podocnemis unifilis from the Madeira, Mamoré and Guaporé rivers collected before the construction of these HPPs. To do this, we used markers for the control region of mitochondrial DNA, 6 microsatellite loci and genomic SNPs. Individuals were collected from two locations below the waterfalls, Manicoré and Urupiara, and three locations above the waterfalls, Guajará-Mirim, Pimenteiras, and Costa Marques. 52 individuals were sequenced for the control region of mitochondrial DNA, 42 individuals were genotyped for 6 microsatellite loci and 40 individuals were sequenced via Next Generation Sequencing, to obtain SNPs with the ddRADseq methodology. For each marker, genetic diversity indicators were calculated. Genetic structure was inferred through AMOVA analysis, pairwise comparisons of Fst, Bayesian analysis of population structure and DAPC analysis. The results showed different patterns of genetic diversity for the 3 markers: for mitochondrial DNA, high levels of genetic diversity were observed followed by microsatellites, and lower values were observed for SNPs. The results suggest that the rapids of the Madeira/Guaporé River acted as a barrier restricting gene flow between populations above and below these geomorphological structures. Therefore, two large management units for P. unifilis are suggested, one above and one below the HPP development. Genetic monitoring of populations is suggested since the sampling in this work was carried out before the construction of the Jirau and Santo Antônio hydroelectric plants. In other words, it is of fundamental importance to obtain data on current populations, as it is almost 15 years after the closure of the hydroelectric plants.