Abstract
Gene flow studies provide information on gene exchange between populations, which is essential for developing genetic conservation strategies. Such analyses enable a better understanding of the life history and seed and pollen dispersal mechanisms of plant species. In this study, we investigate pollen and seed flow in a regenerant population of the pioneer species Astronium fraxinifolium in an area degraded during the construction of a hydroelectric dam. We mapped, sampled, sexed, and genotyped 386 individuals in the regenerant population (RP), as well as 128 adult trees located along two highways adjacent to the degraded area; one in Mato Grosso do Sul State (MS) and other in São Paulo State (SP). Parentage analyses was carried out for 370 individuals of the RP population, using as putative parents 348 individuals from RP and all 128 individuals sampled in MS and SP. Based on parentage analysis and eight microsatellite loci, our analyses revealed that for individuals of the RP with an identified father (pollen donor), 1.1% of the pollen was dispersed up to 532 m, while for those with an identified mother (seed donor), 0.5% of seeds were dispersed up to 4,782 m. However, a large proportion of pollen (76.5%) and seeds (57%) immigrated from trees outside the sampled populations. Pollen and seeds were dispersed through a pattern of isolation by distance. Genetic diversity was significantly similar between adults of both highway populations and individuals from RP, with significant levels of inbreeding detected only in RP. Our results demonstrate that the nearest trees contributed pollen and seeds for the recovery of the degraded area, indicating reproductive spatial isolation among the sampled populations due to the damming of the river. Such results help to understand the process of regeneration for A. fraxinifolium in regenerant populations to inform strategies for conservation and environmental recovery with this species.
Highlights
Human interference in environments can trigger changes in biodiversity and disrupt ecosystem processes in tropical forests [1], especially in the savannah biome, one of the richest and possibly most threatened tropical savannas in the world [2]
The outcome for a species that remains isolated will depend on its ability to persist, despite the size of the remaining reproductive population, restrictions in gene flow, genetic drift, and increases in self-fertilization and mating between relatives, which generally result in a decrease in genetic diversity [8,9,10] and accentuate inbreeding in descendant populations, where the inbreeding can result in inbreeding depression [11,12,13,14,15,16]
Our results show that A. fraxinifolium can reach a height of 19.8 m (S1 Table)
Summary
Human interference in environments can trigger changes in biodiversity and disrupt ecosystem processes in tropical forests [1], especially in the savannah biome, one of the richest and possibly most threatened tropical savannas in the world [2]. Reductions in natural population size and tree density can lead to increases in levels of inbreeding and genetic differentiation among isolated forest remnants [3] These factors can augment the risk of extinction for species and populations due to restrictions in gene flow dynamics and changes in mating patterns that can continue for several generations [3,4,5,6,7]. Gene flow if limited can lead to increase in genetic drift and inbreeding and reduced levels of genetic diversity, defining the patterns of spatial genetic structure (SGS) of the population In this context, the gene flow affects the effective population size, which is determined by the number and spatial distribution of the different pollen and seed donors (non-relatives and non-inbreeding) that contribute to the effective dispersion [20] and formation of the generations
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