Résumé
Because parasitism is thought to play a major role in shaping host
genomes, it has been predicted that genomic regions associated with
resistance to parasites should stand out in genome scans, revealing
signals of selection above the genomic background. To test whether
parasitism is indeed such a major factor in host evolution and to better
understand host-parasite interaction at the molecular level, we studied
genome-wide polymorphisms in 97 genotypes of the planktonic crustacean
Daphnia magna originating from three localities across Europe. Daphnia
magna is known to coevolve with the bacterial pathogen Pasteuria ramosa
for which host genotypes (clonal lines) are either resistant or
susceptible. Using association mapping, we identified two genomic regions
involved in resistance to P. ramosa, one of which was already known from a
previous QTL analysis. We then performed a naïve genome scan to test for
signatures of positive selection and found that the two regions identified
with the association mapping further stood out as outliers. Several other
regions with evidence for selection were also found, but no link between
these regions and phenotypic variation could be established. Our results
are consistent with the hypothesis that parasitism is driving host genome
evolution.