Patterns of genetic diversity and structure of a threatened palm species (Euterpe edulis Arecaceae) from the Brazilian Atlantic Forest

Abstract

The detection of distribution patterns of genetic diversity of plant and animal species has contributed to the understanding of biodiversity and evolutionary history of the Atlantic Forest. We used microsatellite markers to access the genetic diversity and structure of 26 populations and 527 adult individuals of Euterpe edulis, a native palm which is an important food resource for fauna and is intensively exploited due to economic reasons. We found high genetic diversity and inbreeding in all populations analyzed. We report highest rates of inbreeding for this species, which could reflect the anthropic impacts of selective cutting, fragmentation, and change in foraging behavior from pollinators and less availability and mobility of large dispersers. We detected by STRUCTURE, two genetic groups, Northern and Southern, which divide the Brazilian Atlantic Forest geographically. These groups have low genetic admixtures, but we found a region of lineage hybridization in the contact zone with low recent gene flow. Distribution pattern of this species corroborates results from previous studies reporting the Last Glacial Maximum (LGM) have shaped the structuring of the species through movements of forests' expansion and contraction. The STRUCTURE analysis of each group revealed the presence of genetic subgroups with low rates of recurrent gene flow. Southern subgroups have higher rates of admixtures than the Northern subgroups, revealing greater historical connectivity of forests in this region.

Fig. 1. Clustering analysis and geographical distribution of two geographic clusters in Euterpe edulis.

A Geographic distribution in the Brazilian Atlantic Forest (light greenish-gray) and lineage assignments of populations to Northern group (dark purple) and Southern group (dark green). The diagram represents the average of each proportion of assignment (Q) of the genetic groups for the population contemporary gene pool. In light gray the map of Brazil, highlighting the region sampled in dark gray. B ΔK statistic, based on the likelihood function, identified K = 2 as the most appropriate number of genetic groups. C Graph of cluster analysis in STRUCTURE. Each horizontal bar represents an individual. The colors represent the coefficient of association for each genetic group (see Table 1 for population codes). AL Alagoas, BA Bahia, DF Distrito Federal, ES Espírito Santo, MG Minas Gerais, SP São Paulo, PR Paraná, SC Santa Catarina, and RS Rio Grande do Sul.

Fig. 2. Clustering analysis and geographical distribution of four geographic subgroups in Euterpe edulis.

A Geographic distribution in the Brazilian Atlantic Forest (light greenish-gray) and lineage assignments of populations to Northeast subgroup (light purple), Central-North subgroup (purple), Southeast subgroup (green) and Sub-South subgroup (light green). The diagram represents the average of each proportion of assignment (Q) of the genetic groups for the population contemporary gene pool. In light gray the map of Brazil, highlighting the region sampled in dark gray. ΔK statistic, based on likelihood function, identified K = 2 for the Northern (B) and Southern (C) genetic group as the most appropriate number of genetic groups. The colors in purple tones represent the North group, and the colors in green tones represent the South group. D Graph of the cluster analysis in STRUCTURE. Each horizontal bar represents an individual. The colors indicate an association coefficient for each genetic subgroup (see Table 1 for population codes). The rivers Paraná and Paranapanema favor the maintenance of remnants of the Brazilian Atlantic Forest along its course and are possible limits for the distribution of contemporary plant lineages (Martins 2011). AL Alagoas, BA Bahia, DF Distrito Federal, ES Espírito Santo, MG Minas Gerais, SP São Paulo, PR Paraná, SC Santa Catarina, and RS Rio Grande do Sul.

Fig. 3. Recurrent gene flow rates estimated by BayesAss analysis.

A Rate of gene flow between the Northern (dark purple) and Southern (dark green) genetic groups. B Rate of gene flow between the Northeast (lilac) and Central-North (purple) genetic subgroups. C Rate of gene flow between the Southeast (green) and Sub-South (light green) genetic subgroups. The groups and subgroups analyzed were detected by population structure analysis using the STRUCTURE software. The circles correspond to each genetic group and subgroup and the size of the circles indicates the sample size (North groups with 230 individuals and south with 297 individuals; Northeast subgroups with 110 individuals, Central-North with 120 individuals, Southeast with 118 individuals and Sub-South with 179 individuals). The arrows inside the circle indicate the gene flow within the population and the horizontal arrows indicate the direction of gene flow between genetic groups and subgroups and their thickness varying with intensity.