Résumé
Dormancy is a common adaptation in invertebrates to survive harsh
conditions. Triggered by environmental cues, populations produce resting
eggs that allow them to survive temporally unsuitable conditions. Daphnia
magna is a crustacean that reproduces by cyclical parthenogenesis,
alternating between the production of asexual offspring and the sexual
reproduction of diapausing eggs (ephippia). Prior to ephippia production,
males (necessary to ensure ephippia fertilization) are produced
parthenogenetically. Both the production of ephippia and the
parthenogenetic production of males are induced by environmental factors.
Here, we test the hypothesis that the induction of Daphnia magna resting
egg production shows a signature of local adaptation. We postulated that
Daphnia from permanent ponds would produce fewer ephippia and males than
Daphnia from intermittent ponds, and that the frequency and season of
habitat deterioration would correlate with the timing and amount of male
and ephippia production. To test this, we quantified the production of
males and ephippia in clonal D. magna populations in several different
controlled environments. We found that the production of both ephippia and
males varies strongly among populations in a way that suggests local
adaptation. By performing QTL mapping with parent clones from contrasting
pond environments, we identified non-overlapping genomic regions
associated with male and ephippia production. Since the traits are
influenced by two different genomic regions and both are necessary for
successful resting egg production, we suggest that the genes for their
induction co-evolve.