Proteínas plasmáticas na estimativa da variabilidade genético-populacional da tartaruga da Amazônia (Podocnemis expansa Schweigger, 1812)

Abstract

This study aimed to test the potential of plasma proteins in the identification of the Amazon turtle stocks (Podocnemis expansa Schweigger, 1812). Through the starch gel electrophoresis technique three protein systems: transferrin (Tf), albumin (Alb) and general protein (GP), and four enzymes: esterase (EST - EC 3.1.1.1), phosphoglucomutase (PGM - EC 2.7.5.1), malate dehydrogenase (MDH - EC 1.1.1.37) and superoxide dismutase (SOD - EC 3.15.1.1), extracted from blood plasma from three population samples: Uatumã-AM, Trombetas-PA and Tapajós-PA, were tested. The zones of electroforetic activity in the gels were presumably coded by 11 loci, of which seven were monomorphic (PG-1, PG-2, EST-1, EST-2, PGM-1, SOD-1 and SOD-2) and four polymorphic (Tf, Alb, MDH and PGM-2). Comparing the genotypic and allelic distribution of the four polymorphic loci detected, the MDH locus was the only one that did not show good genetic balance according to Hardy-Weinberg expectations. The chi-square (x2) analyses to test the hypothesis of independent segregation between the pairs of polymorphic loci examined, revealed no statistically significant differences. Contingency tables for calculating the chi-square (x2) applied to examine the distribution of alleles of the Tf locus, revealed no statistically significant temporal variation (x2 5= 3.05, 0.70 > P > 0.50) in the areas sampled. Despite all existing pressures due especially to the high human consumption of the Amazon turtle in the region, programs for the conservation of its natural populations are ensuring the maintenance of the genetic variability of this species over time, at least for the Tf locus. Estimates of genetic variation showed the highest values of polymorphism (36.36%), average number of alleles per locus (1.36) and mean expected heterozygosity (He) (0.1211), in the Tapajós sample. From the analysis of population genetic structure using F statistics (FIS, FIT and FST) of Wright the average values detected for FIS and FIT of 0.1347 and 0.1912, are considered moderate and moderately high, respectively. The average value of FST was 0.0652, indicating a moderate genetic differentiation between population samples examined, where the loci that contributed most to this difference were the MDH and PGM-2. The estimated gene flow expressed as number of migrants per generation (Nm) between population samples was 3.58. The dendrogram based on UPGMA method illustrates the smallest genetic distance between population samples of Trombetas and Uatumã, where such samples are presumably part of a large panmitic population i.e. the same stock, and the largest genetic distance of these samples in relation to the Tapajós sample. Exact test for population differentiation of pairwise comparisons between the population samples, revealed highly significant statistical differences among all comparisons made with the sample of Tapajós. The data presented herein point to a possible existence of distinct subpopulations stocks of P. expansa in the area sampled. It is especially recommended that the region of the Tapajós must be a further researched and programs for the preservation and management of the P. expansa more intensified in the whole Amazon region in order to maintain the genetic variability of its populations. Futhermore the data were tentatively interpreted in the light of the refuge hypothesis.