Genetic basis of local adaptation in the crustacean Daphnia magna
During my Post-doc at the University of Basel, I focused on the genetic basis of sexual reproduction induction in the crustacean D. magna. D. magna is a perthenogenetic organism: female can switch from asexual reproduction to to the production of sexual resting eggs (so called ephippia) when environmental conditions deteriorate. In this organism, resting egg is the sole way of surviving hars condition and their production is therefore a major fitness related life-history trait (left: asexual female; right: sexual female with ephippia)
In Europe, D. magna occur in 4 different type of habitat (1) where water freezes in winter but is permanent in summer (Estern Europe) (2) where wahter dessicate in summer but stay permanent in winter (Southern Europe) (3) where water does not dessicate nor freeze (the lucky ones, Altalntic cost) (4) where water freeze in winter and desiccate in spring and summer (Scandinavian population).
Using individuals from different region of Europe, I could show that ephippia production is induced when the photoperiod indicate the imminence of habitat deterioration and is therefore locally adapted. For instance, population from Eastern Europe (blue lines) produce more ephippia in short-day (winter conditions, frost) than in long-day conditions. On the contrary, population from Southern Europe or midle East (red lines) produce more ephippia in long-day (summer conditions, dessiccation) than in short-day conditions. Roulin_Mol_Ecol_2013.pdf
Using a F2 cross, we could find a QTL for ephippia production. In a suite of follow-up experiments, I could identify a candidate gene responsible for the variation of resting egg production in natural populations…more soon!