Variabilidade genética em populações de Mimosa acutistipula Mart. (Benth.) var. ferrea Barneby (Leguminosae) em vegetação de Canga na Amazônia

Abstract

The iron-rich canga areas that are present in the Carajás National Forest, PA – Brazil, have very different characteristics and are considered rare environments. In Oriental Amazon, the iron-rich cangas are located in rocky summits of residual reliefs, surrounded by a forest matrix. The high content of iron present in the soil favors the development of an adapted vegetation, called metal-tolerant savannahs or simply canga vegetation, which often lodge harbours endemic species. Mimosa acutistipula var. ferrea is a shrubby-arborescent species of natural and abundant occurrence in the study area, being representative of the rocky vegetation that covers the canga sites. This study investigated the distribution patterns of genetic variability in populations of this species through the analysis of microsatellite DNA loci from the chloroplast (cpSSR) genome. In total, 119 individuals from nine populations distributed in canga areas located in the Serra de Carajás, PA, were sampled. Parameters of genetic diversity and structure were estimated, and the relationship between haplotypes found in nine populations of M. acutitispula var. ferrea in the study area was determined. A total of nine alleles (2 to 5 alleles/locus) at three cpSSR loci investigated in nine populations were found. The average index of genetic diversity in populations was HE = 0,33, ranging from 0,215 to 0,485. An analysis o molecular variance (AMOVA) showed that most of genetic variation is contained within populations (78 to 95%), indicating low to moderate genetic structuring (differentiation) of populations, based on the stepwise mutation model (RST = 0,052) and the infinite alleles model (FST = 0,215). The combination analysis of different alleles found in the three polymorphic cpSSR loci enabled the identification of 13 haplotypes, most of them shared between sampled populations of M. acutistipula, corroborating the low genetic structuring found in AMOVA. The occurrence of several common cpDNA haplotypes in most populations of the species suggests that historical events, related to climatic alternations during the Pleistocene, and gene flow possibly influenced the current pattern of distribution of genetic variability in populations of the species in the region. However, it was also detected recently derived haplotypes exclusive to some populations, which differentiation probably happened after the isolation of the canga areas within the forest matrix after the Late Glacial Maximum (LGM).