Molecular basis of photoperiodic adaptation in Daphnia

• Applicant: Dr. Anke Schwarzenberger
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 401831661

In pathenogenetic arthropods, photoperiodism is responsible for the spectacular switch from asexual reproduction in spring and summer to sexual reproduction and resting egg production in winter. The production of resting eggs is ecologically highly relevant for thetransfer of haplotypes to the next generation, in seasons when asexual descendants cannot survive. The molecular basis for such a response to photoperiod is largely unknown, especially in crustaceans. The crustacean Daphnia is of high ecological impactsince i) it is a keystone species in the transfer of carbon from phytoplankton to a higher trophic level, and ii) influences the seasonal dynamic of whole aquatic food webs. The objective of this project is to elucidate molecular mechanisms underlying seasonal and local adaptation of Daphnia to changes in photoperiod. By combining a field study with controlled laboratory experiments, and by making use of state-of-the-art genetic methodology (e.g. droplet digital PCR), I will investigate several targets which are expected to be involved in photoperiodic response: i) Enzymes of the melatonin synthesispathway and ii) genes of the circadian clock. If seasonal and/or local adaptation to changes in photoperiod can be observed, I expect either phenotypic plasticity or clonal differences of Daphnia (concerning melatonin synthesis and gene expression changes) to be responsible. I assume that Daphnia clones differ in melatonin synthesis regardlessof absence or presence of adaptation to photoperiod. Expected differences in endogenous melatonin concentration should result in clonal differences in response to exogenous stress, i.e. predation and crowding. Daphnia have been shown to possess an extraordinary high rate of duplicated genes. Therefore, it is most likely that differences in melatonin production of Daphnia clones result from copy number variation of melatonin synthesis genes. The difference in copy numbers - measured via droplet digital PCR - is expected to be the main cause for adaptation to changes in photoperiod and susceptibility to exogenous stress.

• DFG Programme: Research Grants