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Chronobiology of polar organisms: melatonin and polar lighting effects on an arctic “living fossil” (ChronoPolar)
IADC_id: 4
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Call year: 2015
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All living organisms have ‘‘biological clocks’’ that regulate physiological and behavioural functions by means of rhythms similar to the geophysical rhythms of the earth; these rhythms have an evident adaptive value to enable organisms to anticipate and, hence, to prepare for predictable changes in their environment (King & Takahashi 2000). This occurs as interaction between the clocks and exogenous time cues, the most prominent of which is the 24-h light–dark cycle. However, in polar environments, the strength of this time cues is greatly reduced around the summer and winter solstices when the sun never sets or never rises.rnThe presence of circadian clocks is independent of the environmental conditions. There are recent evidences that, when daily transitions of dusk and dawn are not present, reindeer and ptarmigan that live in the high Arctic do not exhibit circadian rhythms in their behaviour and physiology. Free-ranging reindeer do not exhibit 24-h locomotor activity rhythms in summer and winter, under continuous light and continuous darkness photoperiod. Differently, during the equinoxes, animals express a circadian regulation of locomotor activity (van Oort et al. 2005, 2007). Seasonal absence of circadian rhythmicity has been recorded also in the daily activity of the Svalbard ptarmigan (Stokkan et al. 1986; Reierth & Stokkan 1998). In addition to the behavioural data, new hormonal and molecular evidences suggesting that reindeer living at high Arctic lack the underlying biological clock, circadian rhythms were not present neither in melatonin secretion nor in the expression of the clock genes (Stokkan et al. 2007; Lu et al. 2010).rnThe diversity of behavioural responses, even within the limited number of species tested, is surprising and suggests that several factors may be involved in regulating circadian variability. It has been proposed that circadian clocks can be adaptively modified to enable species-specific time-keeping under polar conditions (Bloch et al. 2013; Lu et al. 2010; van Oort et al. 2007). Thereby, clocks would be ‘fitted’ to specific aspects of the ecology and behaviour of an organism.rnAnimals everywhere are confronted by environments that demand specialized behavioural and metabolic responses; for those of us intent on understanding the adaptive significance of clocks and rhythms, arctic organisms represent an excellent model in chronobiological studies.rnThe aim of the study was to collect behavioural and physiological data on biological rhythms of high arctic invertebrate Lepidurus arcticus (Branchiopoda, Nostostraca) to provide bases for further genetic investigations on the function of the biological clock on arctic invertebrate.
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David Hazlerigg - University of Tromso
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