Study of the effects of different base populations on the size and variability of short-term responses to selection in Drosophila : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
In the last decade or so the importance of the choice of a base population for selection experiments has gained recognition. Concurrent with this, there has been a surge of research activity in selection utilising heterogeneous hybrid foundation stocks for both laboratory animals and larger domestic species. The growing popularity of selection within crossbred base population is based on the premise that by crossing together different populations or strains to form a foundation stock, greater genetic variability is made available thus allowing a greater genetic response. There is also the additional advantage of greater viability of hybrid individuals. Yet, comparatively few experiments have been carried out specifically to evaluate the importance of base populations and particularly the relative merits of selection within "purebred" populations and "crossbred" populations in terms of size, trend and variability of response. James (1966) stressed the vital role of choosing the right base population for animal breeding schemes. Results from his theoretical considerations point in favour of selection from hybrid stocks derived from two or more populations as opposed to selection from a single but genetically superior population. There is definite need for reliable and more conclusive evidence on this important aspect of selection and it is primarily for this purpose that the present investigation is undertaken. The selection experiment is designed to provide data amenable to detailed analysis of the variability of responses within and between populations and the relationship of the response to the genetic nature of the foundation stocks. The present experimental design consists of concurrent and identical two-directional mass selection for abdominal bristles in two laboratory strains of Drosophila melanogaster of diverse origins and in the hybrid population formed by crossing them. Within each selection line a number of replicates are carried in order to assess the variability of response.