The Role of the Circadian Clock in Adaptation in Seasonally Changing Environment in Drosophila montana

Kauranen, Hannele The role of the circadian clock in adaptation in seasonally changing environment in Drosophila montana Jyväskylä: University of Jyväskylä, 2012, 47 p. (Jyväskylä Studies in Biological and Environmental Science ISSN 1456-9701; 253) ISBN 978-951-39-4932-7 (nid.) ISBN 978-951-39-4933-4 (PDF) Yhteenveto: Sirkadisen kellon rooli vaihteleviin ympäristöolosuhteisiin sopeutumisessa Drosophila montana -lajilla Diss. Adaptation to daily and seasonal changes in environmental conditions is crucially important for the survival and reproduction of all organisms, especially the ones living in the northern latitudes. One of the key factors in enhancing adaptation to this kind of environment is the evolution of two time-measuring systems; the circadian clock regulating daily variation and the photoperiodic timer regulating seasonal activities. In my thesis I have studied the role of the circadian clock in adaptation in northern environment and tried to find out whether and how it is connected with the photoperiodic timer in northern Drosophila montana species. My studies showed that D. montana possesses good entraining rhythms, displays only the evening activity peak and maintains its free-running rhythm better in constant light than in constant darkness differing in all these aspects e.g. from the more southern species D. melanogaster. I also found that the species differences in fly locomotor activity rhythms can be explained by the differences at the neuronal level. The function of the photoperiodic timer in D. montana seems to be based on either a non-circadian oscillatory hourglass timer or a rapidly damping circadian oscillator. The fact that the flies of this species shift both their evening activity peak and the expression level peaks of two circadian clock genes, period and timeless, in concert with the day length suggests that D. montana uses only one circadian oscillator to measure the day length. The lack of the morning activity peak in entrained conditions, the degradation of free-running activity rhythm in constant darkness and the lack of the expression of two studied neurotransmitter and photoreceptor proteins in specific brain neurons in D. montana suggest that the circadian clock has evolved in a different direction than that of D. melanogaster. The circadian clock of D. montana shows many features important for adaptation to northern environment and has undoubtedly been one of the key factors enabling this species to distribute to the North.