Historical gene flow within and among populations of Luehea divaricata in the Brazilian Pampa

Abstract

Within and among population gene flow is a central aspect of the evolutionary history of ecosystems and essential for the potential for adaptive evolution of populations. We employed nuclear microsatellite markers to assess inter- and intra-population gene flow in five natural populations of Luehea divaricata growing in the Pampa biome, in southern Brazil. This species occurs in practically all secondary forests of the Pampa and has recognized ecological significance for these formations. The genetic structuring of the studied populations suggests limited gene dispersal among forest fragments, despite a homogeneous level of migration among populations. Notwithstanding the gene flow among populations, significant SGS is still found in some fragments. Significant spatial genetic structure within population was also found likely as result of limited seed and/or pollen dispersal. The scattered distribution of the populations and their relatively high density seem to limit pollen dispersal. Also seed dispersal by wind is not efficient due to large distances among forest formations. As conservationist actions towards preserving the genetic resources of L. divaricata and the Brazilian Pampa, we suggest the protection of the existing forest formations and the maintenance of the natural expansion of the forests over the grasslands in the biome.

Simulating the selfing and migration of Luehea divaricata populations in the Pampa biome to investigate the conservation potential of their genetic resources

“…The estimated number of L. divaricata individuals per fragment was based on a phytosociological survey performed in 2013 (Stefenon VM, unpublished results). Furthermore, the data to verify the genetic simulations were obtained from Nagel et al (2015). L. divaricata was used as a model for this simulation study, because of its ecological importance and the possibility of local threat by the expansion of agriculture, livestock, and urban growth in the Pampa biome.…”

“…The computer program EASYPOP version 2.0.1 (Balloux, 2001) was used to determine the rates of selfing and migration that would result in parameters similar to those determined by Nagel et al (2015). Generally, EASYPOP is used to simulate population genetic datasets, and it includes various mutation and migration models.…”

“…For the mutation settings, we simulated 5 and 10 loci that evolved according to the single-step mutation (SSM), with a proportion of 0.1 K-allele model (KAM) events, under 45 possible allelic states, according to the data obtained by Ruas et al (2009), Conson (2012, and Nagel et al (2015). A mutation rate of 0.0004 mutations per locus per generation was assumed.…”

“…Gene flow is a critical factor for the distribution of genetic variation, because a high gene flow tends to homogenize genetic structures, whereas a low gene flow allows for the non-random distribution of alleles and genotypes. Therefore, understanding the connectivity of individuals within and among populations is a primary aspect of population ecology, evolution, and conservation (Nagel et al, 2015).…”

“…The trees originated from five different forest fragments in the Brazilian Pampa biome. Such a biome is characterized by the fragmented distribution of formations (Nagel et al, 2015), affecting the genetic, ecological, and reproductive patterns of its species with a risk of extinction. Our objective was to study the genetic, ecological, and reproductive patterns that best explain the genetic structure, to gain a better understanding of the evolutionary history and provide input for conservation planning.…”