Genética populacional do peixe-boi da Amazônia, trichechus inunguis natterer, 1883 (mammalia, sirenia) na Amazônia brasileira: implicações para sua conservação

Abstract

The Amazonian manatee, Trichechus inunguis, the only exclusively fresh water sirenian, is distributed thought out the whole in the Amazonian region where it is found from the Marajó Bay (Brazil) up to Colombia, Peru, and Equator. The indiscriminate large scale capture for commercial use was the main reason of its population reduction, which associated with the low reproductive rate limits a potential of a quick recovery of the species. The Aquatic Mammals Laboratory (LMA-INPA, Manaus-AM) and the Preservation and Research Center of Aquatic Mammals of Eletronorte (CPPMA-Balbina-AM) undertake "ex situ" conservation programs which focus on the rescue and rehabilitation of animals seized from poachers, research activities, and environmental education, reproduction in captivity, and also reintroductions of Amazonian manatees into the wild. Conservation genetics aim to minimize extinction risk caused by genetic factors. Thus the knowledge of the levels and distribution of the genetic variability is essential for the planning of in situ and ex situ management and conservation strategies for the Amazonian manatee. Using microssatélites markers, the goal of the present project is to analyse paternity of animals born and raised in captivity at LMA-INPA and CPPMA-Balbina, as well as to verify the level and the distribution of the genetic variability of the Amazonian manatee, to confirm if hybridization events exists between the two manatee species that occur in Brazil, evaluating the genetic contribution of each species and to find in which direction the hybridization events occur; and with this information provide subsidies of fundamental importance for the establishment of efficient conservation strategies and management of this species. With this goal in mind, 20 microssatellite loci originally developed for Trichechus manatus were utilized in T. inunguis. All of the loci were in Hardy-Weinberg equilibrium and the tests of linkage disequilibrium were not significant for any pair of loci within each population. The levels of genetic diversity found for the Amazonian manatee was relatively larger when compared with the other sirenians. The high level of polymorphism of the loci used in this study allowed for the successful paternity identification of the Amazonian manatee born in captivity. The probability of success were 99,83% for the calf Erê; 81,38% for Tuã, 90,21% for a stillborn calf, 90,21% for Kinjá, and 97,84% for Inaê. At CPPMA/Balbina, the probability of success was 94,98% to a premature calf of Miri, 98,38% for Morena and 97,09% for Uatumã. In the population analyses it was observed that no genetic structure exist among the regions sampled (FST - 0,00205, p = 1,0). The values of M (absolute number of migrants) varied from 21,902 to infinite, confirming the high level of gene flow among the regions and that these populations do not present signs of the effects of a recent population bottleneck. It seems obvious that the Amazonian manatee has suffered a population reduction due to great commercial exploration during the 1930 s to 1950 s, however most likely since these animals have a long life span and generation time, the effects of that reduction were not detected genetically. With the results obtained with the program STRUCTURE, it was possible to observe two very different "populations", representing the species T. inunguis and T. manatus. However, the individuals Para_100, Para_b13 and Para_domn reject the hypothesis of belonging to their corresponding species. In other words, they are hybrid individuals. Those individuals are from of the Amazonian estuary, an area of sympatry of the two species, and where had already suggested the existence of a possible hybridization area for the species. The program BayesAss+ uses a Bayesian population assignment approach to estimate rates of recent immigration events between populations from individual multilocus genotypes. Similar to the program STRUCTURE, the program BayesAss+ indicated that certain individuals do not belong to their supposed species. Further analyses in the programs IMa and MIGRATE also confirm the existence of ongoing gene flow between T. manatus and T. inunguis indicating that this would be the main direction of the introgression. The MIGRATE analyses confirmed the presence of gene flow between T. inunguis and T. manatus, with the Pará population of T. inunguis receiving high number of migrants of the marine manatee (Nm=5,0045), while gene flow in the direction from T. manatus to T. inunguis was lower (Nm=2,3395). Analyses in the isolation with migration program IMa confirmed the presence of gene flow significantly different from zero between T. inunguis and T. manatus and the existence of clear difference in the direction of gene flow with Nm=7,4779 from T. manatus to T. inunguis vs. Nm=1,7188 from T. inunguis to T. manatus. These analyses indicated ongoing but unequal gene flow between T. manatus and T. inunguis suggesting the main direction of introgression.