Adaptation from standing genetic variation and from mutation

Dissertation presented to obtain the Ph.D degree in Evolutionary Biology ; Understanding the genetic basis of adaptation is crucial to explain the emergence and maintenance of the multitude of life forms we find on Earth today. Perhaps even more importantly, gaining knowledge about how fast organisms can cope with environmental changes may prove crucial in a world being altered at increasing speed due to the human actions. The study of adaptive evolution may therefore have major implications (and applications) in Agriculture, Conservation of endangered species and even Human Health. Natural selection has long been appreciated as one of the predominant evolutionary mechanisms and it enjoys a solid theoretical framework regarding its requirements, its effects and its limitations. Empirically, however, it has proved quite challenging to study. In wild populations natural selection is particularly difficult to characterize and measure since in these settings other evolutionary mechanisms (such as genetic drift or gene flow) often occur simultaneously. In addition to this, the different evolutionary mechanisms may vary greatly in time and in space with respect to their relative influences on the evolutionary dynamics of populations.(.)