AGGREGATION AND THE MAINTENANCE OF GENETIC DIVERSITY - AN INDIVIDUAL-BASED CELLULAR-MODEL

A cellular model, where each individual is explicitly defined, is used to describe a population of a mycophagous species of Drosophila. Patc hes represent single fungal fruiting bodies which are only available a s oviposition sites for a single fly generation. Standard competition equations are used to describe the interaction between larval genotype s at each patch. Dispersal of adults is obligatory and uses a simple m odel of patch choice to produce aggregated arrivals of adults at fresh patches. The degree to which aggregation of adults and eggs can promo te coexistence of genotypes in a one-locus, two-allele system with dom inance is explored. When both phenotypes (A- and aa) are aggregated, a polymorphism can be maintained for over 1000 generations even when th e selective disadvantage of one phenotype (aa) is great. This model en hances the degree of polymorphism in a population, using aggregation. It does not preclude the operation of other methods which enhance the coexistence of genotypes. Therefore, it is acting to augment the degre e of polymorphism maintained in species which exploit patchy and ephem eral habitats, including all Drosophila and a wide range of other orga nisms.