Aspectos limnológicos e genéticos da Nymphaea rudgeana G. Mey. em ambientes aquáticos na savana de Roraima

Abstract

The study of genetic diversity has helped researchers to define, and understand, the biology structure of the population, as well as revealing possible biological variations due to changes in environmental conditions, thus being possible to draw up plans for long-term preservation. In Roraima state, one of the most frequent species in the water bodies is the Nymphaea rudgeana G.Mey., which by the ecological point of view is considered to be a bioindicator of little impacted or de-polluted environments. Therefore, the present study aims to establish possible relationships between limnological factors and genetic variability of N. rudgeana in lakes and streams in savanna areas of the state. The samples were collected in four lakes and four streams distributed in a radius of 50km around the city of Boa Vista. The abiotic samples (limnological variables) were collected from July 2013 to April 2014, being determined the following parameters: pH, dissolved oxygen, nitrate, nitrite, ammonia, alkalinity, orthophosphate, electrical conductivity and depth. In November 2013, young leaves were collected for genetic analysis by ISSR markers in 24 individuals distributed in eight populations. The analysis of Student's t-test indicated significant differences (p <0.05), for the pH, electrical conductivity, ammonia, orthophosphate and depth ratings between the streams and lakes analyzed. In genetic analysis, three ISSR indicators were used, which generated a total of 45 fragments amplified with 94.8% polymorphism. The AMOVA showed that there was a similar percentage of the genetic variability within and among populations, but most of the variation is found within populations (52.09%), while 47.91% is due to interpopulation variability. The Mantel test showed that there was no significant correlation between geographical distances and estimated genetic distances (r =0.53,p=0.085) nor with the estimated environmental distances (r =-0.23, p = 0.682) between limnological parameters. Cluster analysis (UPGMA) showed the formation of two groups that united most of the individuals in the North, West and East sides separating them from the South side. By linking these data with the limnological composition it is noticed that there was this same separation occurring due to the associated environmental gradient with decreasing alkalinity and nitrate in the water samples and an increase in the concentrations of nitrite and phosphate. From the observed results, we can infer that the separation of these two groups occurred because of environmental factors and human impacts that may favor the differentiation of genotypes found along the gradient, since the increase or decrease of these elements can act as a limiting factor in primary production plants and are essential in the formation of molecules. More detailed studies are needed to confirm this relationship.