| Summary: | When an organism migrates from one area to another it comes into contact with many boundaries to its survival and fitness. The fruitfly Drosophila melanogaster has migrated from Africa, into Europe and colonised much of the rest of the world. The subject of this thesis is to better understand how Drosophila has adapted to survive the temperate climates in Europe. The variability of temperature and light from one season to the next makes adaptation of the circadian clock and life history strategy all the more important. Drosophila appear to have adjusted to the new conditions by exhibiting diapause in low temperatures when the nights are long and by altering several other characteristics of its circadian clock that may be related to diapause. One of these is a novel European single nucleotide polymorphism in the timeless gene that allows flies to maintain a more robust diapause than flies carrying the ancestral allele. This variant exists in all European populations and winter simulation experiments reveal that it maintains its diapause for longer than the ancestral variant. These experiments also supported the possibility that Drosophila diapause can be maintained for much longer periods than previous studies have indicated. Experiments with ancestral African D. melanogaster lines alongside several closely related species indicates that diapause may not be a recent adaptation, but an ancient response to stressful conditions that has adapted in Europe to be more sensitive to low temperatures and short photoperiods. I also discover that a splice variant of the period gene has a dramatic, further cementing the controversial relationship between clock genes and diapause. In addition I have performed a study of putative functional polymorphisms in this untranslated region around this splice site from European populations. Finally, a study of putative clock genes reported in Chapter 3 provides a cautionary tale as to the dangers of using RNAi.
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