Temporal synchronization of other key polar pelagic organisms
Alfred Wegener Institute for Polar and Marine Research (AWI), Australian Antarctic Division (AAD), University of Padova (UP), Charité Universitätsmedizin Berlin (CUB), Carl von Ossietzky University Oldenburg (UO), Helmholtz Centre for Environmental Research (UFZ)
In this work package we will start to utilize the knowledge that we derived from our investigations on krill regarding the mechanisms of photoperiodic time measurement and the putative role of clock genes in this process on other key polar pelagic invertebrates. The focus will be in the first place on the calanoid copepod species Calanus finmarchicus, a key species of the North Atlantic polar biome. This species plays an important trophic role in northern sub polar and polar ecosystems as a grazer of phytoplankton and as a prey for higher trophic levels such as the larval stages of commercially important fish species such as cod. C. finmarchicus has evolved specific daily and seasonal patterns in depth distribution, feeding activity, reproduction and metabolic activity to adapt to their environment that is very similar to that described above for krill. Most pronounced is an ontogenetic seasonal migration associated with a diapause – a dormant state of reduced metabolism and arrested development – during winter to escape from temporally unfavorable environmental condition. There is ample evidence that several copepod functions manifest a pattern of rhythmicity that is synchronized to the cycle of day and night and that the pattern of the rhythm and manifestation of the function may change with a seasonal changing light- dark cycle (e.g., appearance of a dormant phase or a cessation of vertical migration) . However, a molecular understanding of the principles of these interactions is still lacking.
The first step in this work package will be to prove the existence of a circadian clock and of clock- controlled physiological processes. After that, the circadian adaptation of C. finmarchicus to its environment will be investigated. The main experimental platform for this work will be the Research Vessel Polarstern. In different seasons, freshly caught copepods will be maintained in cooling containers under different light-dark cycles and time series will be sampled. Physiological activities will be measured on organismic (respiration, feeding growth), cellular (enzyme activity) and genetic level. For the analyses of genetic expression pattern of circadian genes and putative clock controlled target genes C. finmarchicus will be sampled and shock frozen for molecular analyses at the AWI in close cooperation with the Costa and the Kramer lab. As a prerequisite, low-throughput Expressed Sequence Tag (EST) projects already result in the publication of high quality sequence fragments of canonical clock genes for C. finmarchicus (e.g. period, GenBank: FK868108.1; timeless, GenBank: ES237746.1; cry1, GenBank: GR410803.1; cry2, GenBank: EL966083.1). Therefore, the identification of clock genes will be carried out using a degenerate PCR strategy exploiting homolog sequences available for many animal species. To test for circadian adaptation to the polar environment, comparison of circadian characteristics (e.g. amplitude, period, phase relation) between clock genes at different seasons will give us the possibility to identify critical changes with photoperiod. Considering patterns of differential expression of target genes will potentially demonstrate a link between the effect of photoperiod on clock gene expression and downstream transcriptional effects, and hence an involvement of the circadian system in photoperiodic time measurement. The results derived from the investigations on C. finmarchicus will be used as basis for the investigations on further key calanoid copepods mentioned previously.
25. Marcus NH (1986) Population dynamics of marine copepods: The importance of photoperiodism. Amer Zool 26: 469-477