The role of photoperiod in the entrainment of endogenous clocks and rhythms in Antarctic krill (Euphausia superba)

• Main Author: Piccolin, Fabio
• Format: Thesis
• Language: unknown
• Published: 2018
• Subjects: Antarc*; Antarctic; Antarctic Krill; Antarctica; Euphausia superba; Southern Ocean
• Online Access: https://epic.awi.de/id/eprint/49560/; https://epic.awi.de/id/eprint/49560/1/PiccolinPhD.pdf; https://hdl.handle.net/10013/epic.8d07e0dd-d055-4bea-8f0f-cae69bff2fdf

Antarctic krill (Euphausia superba), hereafter krill, are key players in the ecosystem of the Southern Ocean. They are distributed all around Antarctica, and they are exceptionally abundant, representing the main link between primary producers and the higher trophic levels in the Antarctic marine food web. Due to their high ecological relevance, krill have been extensively studied in the field and in the laboratory, and it is known that their life-cycle is shaped by fundamental daily and seasonal rhythmic events. Actual knowledge about the external and internal factors involved in the regulation of rhythmic functions in krill is still quite limited but pivotal, especially in the context of future environmental changes driven by climate change. One hypothesis is that the daily and seasonal rhythmic functions in krill might be regulated through the activity of so-called “endogenous” clocks. Endogenous clocks are molecular function units, which promote rhythmic oscillations in transcription, physiology and behavior at the daily and seasonal levels. Endogenous clocks can be entrained (i.e. synchronized) by rhythmic environmental cues, like the day/night cycle (i.e. photoperiod = day length) at the daily level, and the seasonal photoperiodic cycle at the seasonal level. The implications of endogenous rhythmicity (i.e. rhythmicity promoted by endogenous clocks) in the regulation of rhythmic biological functions are well documented among terrestrial species, but studies dealing with marine organisms are very scarce. At the daily level, the best studied endogenous clock is the circadian clock, which is based on molecular feedback loops generating a rhythm with a period of approximately 24 h. Specific light-sensitive proteins promote the entrainment of the circadian clock with the day/night cycle, ensuring effective synchronization of rhythmic output functions according to daily recurring environmental changes. In krill, a circadian clock has been recently identified and characterized, and its influence on daily rhythms ...