Résumé
Selection processes are believed to be an important evolutionary driver
behind the successful establishment of non-indigenous species, however
evidence is still scarce. Genome-scans have often identified loci with
atypical patterns of genetic differentiation (i.e. outliers) indicative of
selection processes. Using microsatellite- and AFLP-based genome-scans, we
looked for evidence of post-introduction selection in the mollusk
Crepidula fornicata, native from the northwestern Atlantic and introduced
in the northeastern Atlantic and northeastern Pacific during the 19th and
20th centuries. We examined 683 individuals from 7 native and 15
introduced populations spanning the latitudinal introduction and native
ranges of the species. Our results showed the high genetic diversity in
all populations with little genetic structure between the two ranges, a
pattern typical of marine invaders. Analyzing 344 loci, no outliers were
detected between introduced and native populations or within introduced
populations. The genomic sampling may have been insufficient to reveal
selection especially if it acts on traits determined by a few genes. Eight
outliers were however identified within the native range, underlining a
genetic singularity congruent with a well-known biogeographic break along
the Florida. Our results call into question the relevance of AFLP
genome-scans in detecting adaptation on the time-scale of biological
invasions: genome-scans often reveal long-term adaptation involving
numerous genes throughout the genome but seem less effective in detecting
recent adaptation from pre-existing variation on polygenic traits. This
study advocates other methods to detect selection effects during
biological invasions – on phenotypic traits, although genome-scans may
remain useful for elucidating introduction histories.