Résumé
Background: The two North Atlantic eel species, the European and the
American eel, represent an ideal system in which to study parallel
selection patterns due to their sister species status and the presence of
ongoing gene flow. A panel of 80 coding-gene SNPs previously analyzed in
American eel was used to genotype European eel individuals (glass eels)
from 8 sampling locations across the species distribution. We tested for
single-generation signatures of spatially varying selection in European
eel by searching for elevated genetic differentiation using FST-based
outlier tests and by testing for significant associations between allele
frequencies and environmental variables. Results: We found signatures of
possible selection at a total of 11 coding-gene SNPs. Candidate genes for
local selection constituted mainly genes with a major role in metabolism
as well as defense genes. Contrary to what has been found for American
eel, only 2 SNPs in our study correlated with differences in temperature,
which suggests that other explanatory variables may play a role. None of
the genes found to be associated with explanatory variables in European
eel showed any correlations with environmental factors in the previous
study in American eel. Conclusions: The different signatures of selection
between species could be due to distinct selective pressures associated
with the much longer larval migration for European eel relative to
American eel. The lack of parallel selection in North Atlantic eels could
also be due to most phenotypic traits being polygenic, thus reducing the
likelihood of selection acting on the same genes in both species.