Diversidade genética e padrões populacionais da Pirapitinga Piaractus brachypomus (Cuvier, 1818) characiformes: um critério para seu manejo

Abstract

In the neotropics, Piaractus brachypomus is one of the largest Characiforme species, widely dispersed throughout the Orinoco and Amazon Basins. It is a migratory fish that carries out its lifecycle in fluvial and lacustrine environments. Its omnivorous feeding habits focus on seeds, making it, along other species, an seed disperser very important to the tropical forest. In aquiculture it is a pioneer species in the development of this activity in South America. mostly in countries like Colombia. Peru and Venezuela. As a fishing resource the species is very important for local and regional consumption, what drives over-exploration of natural populations. Management strategies for conservation and use, although in pracfice, do not show positive effects for its recovery in the natural environment. The lack of biological information in a populatin level does pose a limit on the correct management of this natural resource under the concepts of basin and trans-border management. The development of molecular techniques in the last years have delivered appropriate tools for the understanding of a population, its dynamics and conservation status. In this study, an genetic-populational approach of Piaractus brachypomus within its natural range was carried out. This work was based upon the premisse that the population is panmictic by its migratory behavior, reproductive strategy and wide distribution. A total of 398 specimens, from different sites in the Amazon and Orinoco basins, were collected and then analyzed with 7 microsatellites in total, by the transferability of microsatellites developed for phylogenetically near species. Also used were mitochondria' Dloop and CO! to support large scale population analysis and morphological considerations. Orinoco and Amazon basins populations were found to be highly structured. with restricted gene flow within them, and also genetical and morphological diagnostic features that differentiate between them, what makes possible to delimit each as a Significant Evolutionary Unit — SEU. Orinoco basin population has showed panmictic within all its range (RsT=0.044), with moderate genetic diversity (He=0,66) when compared to other neotropical fish. Gene flow was bi-directional and asymmetric (Nm=2,03 to 7,21 effective immigrant per generation), being the floodplain known as the Internal delta", that which receives the greater number of immigrants. The average effective population size was Ne=1675. the largest population located in the Guaviare basin. It was detected a populational decline 690 years ago. what has been associated to then current environmental variations such as climatic changes and strong El Nino events. The Amazon basin population showed high genetic diversity (He=0,72) when compared to other amazonian fish. It is moderately structured in two biological structures (Fsr=3,057: K=2), a product of past geomorphological barriers during the region formation. The west biological unit is associated with the Amazon sedimentary basin. the east biological unit is associated with the crystalline shields and a contact zone in the main Solimoes-Amazonas river and its adjacent areas. Gene flow showed complex and asymmetrical interactions, and was low (Nm= 0.85 a 4,75 effective immigrants per generation) when compared to other migratory Amazonian fish, but sufficient to maintain population connectivity. Effective population size was Ne=1139. slightly lower than the Orinoco population, despite the its wide range. It was detected a populational decline dated by 2507 years ago, what is associated to strong variations in the environment then. As the two SEU were defined and characterized it is suggested that management be separated for each Piaractus brachypomus population. It is suggested that the Amazon basin population must have a differentiated management according to the biological units and contact zones, to be established according to the national territories that they occupy. The Orinoco basin. otherwise, may have a integrated management between the two countries that make up the region, based upon the fact that the population is panmictic.