Polymorphic microsatellite loci from Dacryodes edulis (Burseraceae), a Central African rainforest and fruit-tree species.

PREMISE OF THE STUDY: Microsatellite markers were isolated and characterized from Dacryodes edulis (Burseraceae), a tropical rainforests fruit tree of central Africa. METHODS AND RESULTS: Using an enrichment protocol, six microsatellites loci were developed from Dacryodes edulis. We investigated polymorphism using 45 trees from three widely separated populations in Cameroon. All loci were polymorphic, with the number of alleles ranging from 2 to 15. Polymorphism was widely variable among loci and expected heterozygosities ranged from 0.06 to 0.84 with a mean value of 0.49. CONCLUSIONS: These loci will be useful for the in-depth analysis of population structure and phylogeographic variation throughout the distribution range of Dacryodes edulis and other related taxa, Dacryodes buettneri and D. normandii, in which all loci were also amplified. Furthermore, they will offer the opportunity to study early domestication processes acting on the genetic diversity of Dacryodes edulis.

Characterization of 15 microsatellite loci in the pulmonate snail Pseudosuccinea columella (Mollusca, Gastropoda).

We characterized 15 new variable microsatellites in the freshwater snail Pseudosuccinea (Lymnaea) columella, as well as conditions for multiplexing and simultaneously genotyping sets of loci. Two to six alleles were detected per locus over the six populations studied. Gene diversity ranged from 0.000 to 0.498, but essentially no heterozygous individuals were observed. This resulted in extremely high F(IS) estimates, and therefore high selfing rates. The F(ST) estimates ranged from 0.18 to 1 among populations, but was generally high. These markers will constitute efficient tools for investigating the population structure of this invasive species. Cross-species amplification was on the whole unsuccessful.

Natural hybridization between a clonally propagated crop, cassava (Manihot esculenta Crantz) and a wild relative in French Guiana.

Because domestication rarely leads to speciation, domesticated populations often hybridize with wild relatives when they occur in close proximity. Little work has focused on this question in clonally propagated crops. If selection on the capacity for sexual reproduction has been relaxed, these crops would not be expected to hybridize with their wild relatives as frequently as seed-propagated crops. Cassava is one of the most important clonally propagated plants in tropical agriculture. Gene flow between cassava and wild relatives has often been postulated, but never demonstrated in nature. We studied a population of a wild Manihot sp. in French Guiana, which was recently in contact with domesticated cassava, and characterized phenotypes (10 morphological traits) and genotypes (six microsatellite loci) of individuals in a transect parallel to the direction of hypothesized gene flow. Wild and domesticated populations were strongly differentiated at microsatellite loci. We identified many hybrids forming a continuum between these two populations, and phenotypic variation was strongly correlated with the degree of hybridization as determined by molecular markers. Analysis of linkage disequilibrium and of the diversity of hybrid pedigrees showed that hybridization has gone on for at least three generations and that no strong barrier prevents admixture of the populations. Hybrids were more heterozygous than either wild or domesticated individuals, and phenotypic comparisons suggested heterosis in vegetative traits. Our results also suggest that this situation is not uncommon, at least in French Guiana, and demonstrate the need for integrated management of wild and domesticated populations even in clonally propagated crops.