Many organisms have developed an internal clock to cope with the daily and seasonal cycles in the environment. In mammals, suprachiasmatic nuclei (SCN) of the hypothalamus control circadian rhythms... Show moreMany organisms have developed an internal clock to cope with the daily and seasonal cycles in the environment. In mammals, suprachiasmatic nuclei (SCN) of the hypothalamus control circadian rhythms in behavior and physiology. Evidence links the proper function of circadian clock to mental and physical health. Aging disturbs the accurate function of the SCN and impairs many rhythms such as sleep-wake cycle. Hence improvement of clock function can aid healthy aging. In chapters 3 and 4 I show the ensemble output of the SCN neuronal network is more robust than individual cells__ output suggesting a compensatory role of the network in aging. Seasonal changes affect the physiology and reproduction success of many organisms. The SCN encodes for day-length by adjusting the pattern of its electrical activity rhythm.. In chapters 5 and 6 I reveal that plasticity in interneuronal and cell-intrinsic functions in the SCN helps the organism to adjust to yearly natural changes in photoperiod. These results imply that extensive artificial light in modern society may alter neurotransmitters action in the SCN. A better understanding of SCN network function and cellular properties facilitate alleviation of modern life-related diseases caused by circadian disturbances and aging. Show less
Temporal variation in abiotic and biotic variables such as temperature, rainfall, food availability or predation pressure profoundly affects the abilities of organisms to survive and reproduce... Show moreTemporal variation in abiotic and biotic variables such as temperature, rainfall, food availability or predation pressure profoundly affects the abilities of organisms to survive and reproduce successfully. Most organisms are remarkably flexible in the face of such heterogeneity in habitat quality, and display phenotypic plasticity in response to environmental variation, i.e. the production of alternative phenotypes from a single genotype, dependent on the experienced environment. The aftrotropical butterfly Bicyclus anynana expresses alternative adult life histories in its habitat's wet and dry seasons, including reproductive timing and lifespan. This thesis aims to increase insight into the hormonal and transcriptional patterns that underlie life history plasticity in B. anynana. The first question is how the environment experienced during development induces the two adult seasonal forms via conserved hormonal pathways. The second major question covered in this thesis is what transcriptional changes in the adult are associated with the seasonal forms, and how ageing differs between the seasons. Together, these data contribute to a better mechanistic understanding of plastic responses as adaptation to environmental variation, and provide starting points for research into mechanisms linking development and ageing in humans, and how events during early development can affect lifespan and human health. Show less
