Conservation and genetic diversity of populations of Oryza glumaepatula Steud. in ferruginous mountaintop lakes of the Brazilian Amazonia

Abstract

Natural populations of Oryza glumaepatula, a wild relative of cultivated rice, were found in lakes at mountaintops of the Carajás Ridge, in Carajás National Forest. This species is generally found in aquatic environments of lowlands surrounded by tropical forests, and this is a rare case in which the species colonized high altitude lakes, situated amidst campo rupestre (rupicolous vegetation). This peculiarity instigated an interest on the natural history of these populations, especially on which lowland populations were the sources of the propagules that colonized the Carajás lakes. This study aimed at describing the genetic structure and divergence among four mountaintop populations in order to lay grounds for their long-term conservation. As an external comparison, four O. glumaepatula populations were used, three from Amazon Basin rivers (Solimões, Negro and Xingu), and another from the Paraguay Basin, in the Pantanal biome, in a total of 257 individuals. Eight microsatellite loci were evaluated in the eight populations. The Carajás populations showed less genetic diversity than the others, which suggests that they went through a founder effect as of their initial settling on the ridge. The fixation index was negative for the Carajás lakes populations, and this excess of heterozygotes is unexpected for a traditionally selfing species. This may be the result of selection for the ferruginous environment and/or due to the vegetative propagation of highly heterotic individuals. Two groups were detected, showing a lower divergence among the populations found in the ferruginous lakes at the mountaintops of the Carajás Ridge, when compared to the populations from riverine environments in the lowlands. For genetic conservation purposes, a large number of individuals was transplanted, based on the information generated in this work, to lakes devoid of natural populations of O. glumaepatula in a nearby ridge possessing the same rupicolous vegetation.