Résumé
The fine-scale genetic structure and how it varies between generations
depends on the spatial scale of gene dispersal and other fundamental
aspects of species’ biology, such as the mating system. Such knowledge is
crucial for the design of genetic conservation strategies. This is
particularly relevant for species that are increasingly fragmented such as
Boswellia papyrifera. This species occurs in dry tropical forests from
Ethiopia, Eritrea and Sudan and is an important source of frankincense, a
highly valued aromatic resin obtained from the bark of the tree. This
study assessed the genetic diversity and fine-scale spatial genetic
structure (FSGS) of two cohorts (adults and seedlings) from two
populations (Guba-Arenja and Kurmuk) in Western Ethiopia and inferred
intra-population gene dispersal in the species, using microsatellite
markers. The expected heterozygosity (HE) was 0.664–0.724. The spatial
analyses based on kinship coefficient (Fij) revealed a significant
positive genetic correlation up to a distance of 130 m. Spatial genetic
structure was relatively weak (Sp = 0.002–0.014) indicating that gene
dispersal is extensive within the populations. Based on the FSGS patterns
found, we estimate indirectly gene dispersal distances of 103 and 124 m
for the two populations studied. The high heterozygosity, the low fixation
index and the low Sp values found in this study are consistent with
outcrossing as the (predominant) mating system in B. papyrifera. We
suggest that seed collection for ex situ conservation and reforestation
programmes of B. papyrifera should use trees separated by distances of at
least 100 m but preferably 150 m to limit genetic relatedness among seeds
from different trees.