Estudo de estrutura genética da espécie de Cactácea colunar Pilosocereus machrisii utilizando DNA microssatélite

Abstract

Pilosocereus machrisii is a columnar cacti with natural fragmented distribution; restrict to campos rupestres vegetation patches or rocky outcrops on the Cerrado domain; in Central and eastern Brazil. These features makes P. machrisii an appropriate biological model for population genetic studies aiming to gather information on population structure; since small and isolated populations are often vulnerable to genetic drift and high levels of inbreeding. Genetic diversity and population structure were assessed for ten microsatellite loci in 12 P. machrisii populations; covering the majority of the species distribution. Genetic diversity levels were relatively similar on sampled populations; except for Brotas-SP samples; that showed lower levels than those observed for other locations. Significant Hardy Weinberg Equilibrium departures were detected in eight different populations; for one or two loci. High levels of genetic differentiation and private alleles with elevated frequencies were detected; with total FST value of 0.357. The genetic structure of P. machrisii was analyzed with STRUCTURE and SAMOVA softwares; and populations were grouped in four main clusters; with secondary structure on two of these clusters. Significative levels of correlation between genetic and geographic distances were observed for the whole dataset; however; when the genetic groups were analyzed separately; no correlation was verified. Furthermore; the genetic relationship between the populations was observed with a principal coordinate analysis (PCA) and an UPGMA dendrogram. The genetic structure observed in P. machrisii suggests that historical factors caused populations fragmentation; with subsequent geographic isolation and high genetic differentiation between them.