Reduced gene flow and high population structure in four species of Chresta (Compositae, Vernonieae) from the Brazilian Caatinga represent challenges for their conservation

Measures of genetic diversity and population structure are fundamental when studying evolutionary processes in different species. In the present study, we use nuclear SSR markers to investigate the population genetics of four rock-dwelling species of Chresta Vell. ex DC. that occur in the Brazilian Caatinga and present fragmentary populations. Eleven SSR markers previously developed for species of Chresta were used, and a total of 156 individuals from 13 populations were genotyped. Chresta harleyi H.Rob. showed medium levels of inbreeding, while C. subverticillata Siniscalchi & Loeuille showed excess of heterozygotes. The four species present a high number of genetic clusters, showing strong population structuring, and low number of migrants between populations of a same species and among different species. Our results reveal a scenario expected for naturally isolated populations, with strong genetic structuring, high levels of inbreeding and reduced gene flow, affected by geographical distance. We discuss possible effects on the evolution of the group and also impacts on the conservation of these species.