THE RELATION BETWEEN FITNESS COMPONENTS AND POPULATION PREDICTION IN DROSOPHILA. I: THE ESTIMATION OF FITNESS COMPONENTS

Abstract

An experimental system is described for estimating the components of fitness operating in the adult phase of the life cycle of Drosophila. The system entails the mating together of contrived genotypic mixtures. The progeny from such crosses allow for the estimation of adult components of fitness for the sexes sepa- rately.- The application of the experimental system is illustrated by experi- ments on Drosophila melanogaster fourth chromosome recessive mutants, eyeless( e ) and shaven ( s ) . These were studied in repulsion linkage phase in order to have a genetic system mimicking two alleles with a distinguishable heterozygote (e/s wild type).- The female adult components indicate that ee and e/s have the same fitness which is considerably greater than ss. The male adult compon- ents show a strong superiority of e/s over both homozygotes, and the depressed fitness values of the latter two vary with the female genotype to which the males are mated, indicating mating interactions. The larval component (viability) is also estimated for each genotype, and it is found that these viability effects aresmall compared to the adult components.- The adult fitness components esti- mated are interpreted in terms of a collision model of mating behavior involving a conditional probability of mating, aij, upon each male-female encounter. and a conditional expectation of eggs, kij, given that a mating occurs.- Stress is placed on the general approach of defining a small number of net fitness components which encompass the entire life cycle and which are accessible for experimental evaluation.