High genetic variability is preserved in relict populations of Cattleya lobata (Orchidaceae) in the Atlantic Rainforests inselbergs

Abstract

Inselberg formations rise from the eastern Brazilian landscape like islands interspersed within a matrix of tropical vegetation. As this environment is highly threatened by recent urban expansion and the indiscriminate exploitation of natural resources, the orchid species endemic to these inselbergs have suffered drastic reductions in the sizes of their populations. To verify whether this process has been accompanied by the loss of total genetic variability and stochastic changes of the genetic structure of the remaining populations, the genetic variability and structure of all known relict Cattleya lobata populations were assessed using dominant molecular markers (ISSRs), and their genetic conservation status was defined. High genetic variability was detected (H e = 0.262; I = 0.463), with most of the variation occurring within the populations (93%), along with a weak but significant genetic structure (ΦST = 0.074; P < 0.001). Pollination by deception and long-distance seed dispersal may explain the higher variability values than those expected for impacted species with small populations. Historical factors, such as a more continuous distribution in the recent past with interconnected populations and perennial habit with long-lived individuals, can contribute to the maintenance of ancestral genotypes and a highly variable and homogeneous gene pool. These factors can reduce the possible effects of genetic drift, even in the most heavily impacted C. lobata populations in the tourist areas of Rio de Janeiro.