PhD student : Victoria LOUIS

Supervisor (HDR): Franck Lartaud (LECOB)
Co-supervisor: Laurence Besseau (BIOM)

• General information:
• The general aim of this thesis is to study the role of biological clocks on synchronization processes of biomineralization of the shell in the mussel M. galloprovincialis. The objective is to determine if the environment acts directly on the shell biomineralization process or if a biological clock allows the bivalve to anticipate the environmental circadian variation thus regulating the shell growth. We hypothesized that photoperiod (day/night alternation over a 24h cycle), temperature and/or trophic resources would synchronize the biological clock, alone or in combination, leading to control the rhythmic activity of shell biomineralization process in the Mediterranean mussel Mytilus galloprovincialis.

In order to achieve these objectives, different cruises in the Bay of Banyuls will be done at circadian scales, and in vitro experiments at the OOB will test the role of the main drivers (photoperiod, temperature, feeding). Part of the work will be dedicated to the analysis of the growth patterns of the shell of M. galloprovincialis, obtained after chemical labelling technique (calcein) and recapture. Sclerochronological analysis of thin sections of the shells will be reached by fluorescence microscopy and scanning electron microscopy (SEM). A transcriptome analysis of the main molecular players involved in biological clocks (clock genes such as Clock, Bmal, Cry, Per and Rorb) and genes for metabolic activity and biomineralization (carbonic anhydrase, , nacrein, chitinase et Ca²⁺ ATPase), will be developed at different sampling points of the 24h cycle by a broadband approach (NanoString technology). The analysis of the amount of tissue biomarkers (lipids, proteins, carbohydrates) accessed by colorimetry will give a first indication of the assimilation of energy reserves, which will be complemented by the characterization of the variability of the food intake, approached by metabarcoding analysis of the stomach contents, achieved by high-throughput sequencing (Illumina MiSeq) of 16S and 18S rRNA genes.

Finally, the study will benefit from data of the Prime|80 project -TEMPO- dealing with the dynamic conditions and the potential variation of trophic resources in the mussel habitat, to carry out a comparative study of the different ecological compartments likely to initiate a rhythmic response of activity in this species.