Genetic structure and historical gene flow in Araucaria angustifolia populations across two Brazilian regions.

Abstract

Araucaria angustifolia (araucaria) is a conifer tree of high ecological and social values in the Brazilian subtropical region. However, the species is threatened with extinction. We examined the genetic variability and gene flow between populations of araucaria through a coalescent approach. DNA samples were collected from 185 trees in a provenance and progeny established with seeds collected in 15 natural populations. The genotyping was performed using a 3 K Axiom SNPs array to verify the intensity and direction of the migratory flow between neighboring populations. All models were run with MIGRATE-N software. The migration rate, the effective number of migrants per generation ( $x{N}_i{m}_{\mathrm{ij}}$ ), and the effective population size (N_e) were estimated. The mean N_e observed for the southernmost populations (729 ± 293) was found higher than that of the northernmost ones (390 ± 176). We identified neighboring populations that stand out as the main sources of migrant individuals and the ones that receive a high migration flow. By correlating the migration parameters with climatic variables, we observed that the minimum average temperature in the coldest month, and the amount of rain in the driest month show a high and significant correlation with $x{N}_i{m}_{\mathrm{ij}}$ values. In general, the observed gene flow suggests a connection between the remnant populations of araucaria, which constitute the greatest sources of genetic diversity of the species found in the southernmost region of Brazil.