Photoperiodic time measurement in Antarctic krill Euphausia superba
The Southern Ocean ecosystem is characterized by seasonal features such as varying daylight duration, food availability and sea ice coverage. Antarctic krill, Euphausia superba, are one of the most abundant species in the world and play a key role in this ecosystem. Krill have evolved seasonal rhythms to adapt to their seasonal environment, but how the synchronization process with environmental cues functions mechanistically is not fully understood. Within the scope of this thesis the effect of the photoperiod on the seasonal course of metabolic activity of Antarctic krill should be investigated. Krill were exposed to three different photoperiodic simulations each over a period of one year (half a year respectively). All other experimental conditions like food availability and water quality/temperature were constant. The (photoperiodic) simulations were 1) a natural photoperiodic course corresponding to light conditions at 66° S (LD), 2) constant darkness (DD) and 3) the natural course of the photoperiod shortened to half a year (LD 1/2). Under the simulation of the natural course of the photoperiod it could be shown that the activity and mRNA levels of metabolic key enzymes involved in the carbohydrate metabolism and the respiratory chain followed the simulated photoperiodic course, irrespective of the constant food availability. These observations are similar to the previous ones made in the field, where activities were high in summer months and low during winter months. Activities and mRNA of levels of HOAD (beta oxidation of fatty acids) showed a different pattern with increasing values (with a hold-up in winter) and a peak in spring. These observations are also reasonable in context with lipid dynamics observed in the field. Similar seasonal patterns for all enzymes were observed for animals kept under total darkness, suggesting that the metabolic activity is regulated endogenously. In this context the results from the shortened photoperiod LD 1/2 demonstrated an adaptation of the course of metabolic activity to the photoperiodic cycle. This leads to the conclusion that the photoperiod is a very important environmental zeitgeber for the regulation of the seasonal cycle of krill’s metabolic activity. The courses of the metabolic activity observed in DD point to circannual rhythmicity and a putative circannual clock, which governs these rhythms. However, the involvement of krill’s circadian clock in seasonal time-keeping cannot be excluded yet and further investigations need to focus on the role of the circadian clock in seasonal time-keeping.
Cloning and characterization of the circadian clock genes in the Antarctic Krill Euphausia superba
The Antarctic krill Euphausia superba is a key species in the Southern Ocean ecosystem, an environment subjected to extreme seasonal variations throughout the year. Understanding krill’s adaptability to this environment is becoming urgent because of the ongoing rapid environmental changes. In this perspective, investigating the mechanisms that govern endogenous biological rhythms in this organism would give important insights in understanding krill’s biology. At present, very scarce information is available about the endogenous molecular clock of crustaceans and of krill in particular, due to the inaccessibility of the extremely large genome of this polar pelagic organism.
Herein, a first characterization of the principal circadian clock genes in Antarctic krill is reported. Full-length sequences of core clock and clock-associated genes have been identified and cloned. Phylogenetic analyses and a first characterization of functional domains have been performed for E. superba clock, cycle, period, timeless and its paralog timeout. These analyses revealed that these genes actually are homologs of the circadian clock genes of crustaceans, insects and vertebrates. Moreover, a preliminary circadian expression profile of clock genes was determined by quantitative real-time PCR. No significant circadian rhythms were observed for these genes during 24 hours cycles.
These first evidences on the existence of a molecular clock in E. superba pave the way for unravelling the circadian clock molecular mechanism in this polar pelagic organism, and suggest a first picture of the core clock in crustaceans.
Time to (dia)pause – clock gene expression patterns in the calanoid copepod Calanus finmarchicus during early and late diapause (started February 2015)
In the ocean many organisms show a pronounced rhythmic behavior with physiological and behavioral patterns oscillating with a period of approximately 24 hours. Diel vertical migration (DVM) and seasonal diapause are critical life history events for the calanoid copepod Calanus finmarchicus, the biomass dominant zooplankton species of most of the North Atlantic Ocean. We assume that daily and seasonal rhythms of zooplankton are controlled by an endogenous circadian clock ensuring optimal adaption of physiological, biochemical and behavioral processes to prevailing local environmental conditions. Thus, a small timing mismatch between biological processes and the environment such as timing shifts of the onset of phytoplankton blooms caused by climate change could potentially have significant consequences for the entire Calanus-based ecosystem. The study is planned to detect potential clock genes and compare diurnal gene expression patterns in C. finmarchicus being in early and late diapause. Copepods have been collected by 24h in situ sampling from Kongsfjorden, Svalbard (79°N). Primers will be designed by the aid of recently described potential clock genes in C. finmarchicus and data available at the NCBI database to investigate potential clock genes and to identify housekeeping genes for verification. Gene sequence analysis will be conducted with RNA extraction, cDNA synthesis and real-time quantitative PCR. A comparison between diurnal gene expression patterns of copepods being in their early and late diapauses shall give an inside of the involvement of potential circadian clock genes in seasonal rhythmicity.