Résumé
In the marine environment, differential gene exchange between partially
reproductively isolated taxa can result in introgression that extends over
long distances due to high larval dispersal potential. However, the degree
to which this process contributes to inter-locus variance of genetic
differentiation within introgressed populations remains unclear. Using a
genome-scan approach in the Indo-Pacific eel Anguilla marmorata, we
investigated the degree of interpopulation genetic differentiation, the
rate of introgression, and within-population genetic patterns at 858 AFLP
markers genotyped in 1117 individuals. Three divergent populations were
identified based on clustering analysis. Genetic assignments of
individuals revealed the existence of different types of hybrids that
tended to co-occur with parental genotypes in three population contact
zones. Highly variable levels of genetic differentiation were found
between populations across the AFLP markers, and reduced rates of
introgression were shown at some highly differentiated loci. Gene flow
across semipermeable genetic barriers was shown to generate spatial
introgression patterns at some loci which define within-population
structure over long distances. These results suggest that differential
introgression in subdivided populations may be relevant when interpreting
spatial variation patterns displayed by outlying loci in other marine fish
populations.