Identification of the factors that lead to dispersal and inbreeding

Abstract

Individual-based simulation modelling is an excellent method for testing hypotheses, while including realistic and stochastic population parameters. This thesis considers the evolution of dispersal or inbreeding through individual-based simulation modelling. The occurrence of exclusive inbreeding and exclusive outbreeding is found in a number of organisms and are referred to as mixed mating. Mixed mating is suggested to be in response to low levels of inbreeding depression as well as simultaneous inbreeding- and outbreeding depression while intermediately related mating partners are not available. The results of this thesis show that stable mixed mating strategies evolve in the presence of both inbreeding and outbreeding depression, as well as, under conditions where low levels of inbreeding depression are present. Also, inclusive fitness allows higher levels of inbreeding in genetic systems where the mating partners are more related to each other. Dispersal evidently evolves in response to inbreeding depression. A number of other factors, such as local mate competition and the cost of dispersal also influence the rate of dispersal. In addition to these factors, it is shown in this thesis that male dispersal evolves when there is variation in patch sex ratios. Simulation data also supports parent offspring conflict models, as males have reduced dispersal rates when they, rather than their parents, determine the dispersal rate. Population structure is affected by dispersal rates. Using individual-based simulation modelling and various sampling strategies, reveals that few molecular markers, for a few individuals, are sufficient to accurately detect population subdivision, especially when the sub-populations are large. It is, however, indicated that planning prior to sampling are important for proper assessment of population structure. Lastly, molecular data from the pollinating fig wasp Platyscapa awekei reveals that this species suffers from low levels of inbreeding depression. However, when this data are simulated, stable mixed mating did not evolve although it is observed in P. awekei. Sex ratio variation, high local mate competitions and male only broods are therefore suggested to drive male dispersal. It is consequently advantageous to use various techniques to unravel the evolution of a trait and gain insight into the system.