The methods of population genetics will be applied to two main levels of the species. The investigators will concentrate on making models that can lead to realistic predictions and explanations. One part of the work will compare the fitness (survival and fertility) of individuals produced by inbreeding with the fitness of those produced by outcrossing to unrelated individuals. Such comparisons allow estimates of "inbreeding depression", the fitness deficit of inbred progeny relative to the fitness of outbred progeny. Inbreeding depression is very important in plant and animal breeding, and may also be important in determining the evolution of breeding systems. The genetic causes of inbreeding depression are not fully understood at present. So studying populations which display both outcrossing and self-fertilization (as in most plant populations) should help to distinguish between the different possible mechanisms. To do this, the investigators will study a model in which many genetic loci affect fitness because the loci are subject to mutations having deleterious effects on fitness. The investigators will make predictions about the relationship of inbreeding depression and level of self-fertilization. Then they will compare these theoretical results with data from natural and domesticated plant populations. Studies of how new species are formed will use models in which population randomly shifts from one equilibrium state to another. Populations founded by a small number of colonists will be used. The process may be important in generating new species, and has been much discussed recently under the name of "peak shifting". Few studies of genetic models of the process have been carried out, but these studies must be done before it is known how likely peak shift is.
