INVESTIGATION OF PHENOTYPIC AND GENOTYPIC STRUCTURE OF A NATURAL DROSOPHILA POPULATION WITH REGARD TO INDIVIDUAL-RESPONSE TO AN INCREASE AND SEASONAL CHANGE OF POPULATION-DENSITY

In spring and summer, the natural population of Drosophila studied exh ibited a high level of phenotypic and genotypic heterogeneity with reg ard to change of individual fertility with an increase of density of a dult flies. From spring to autumn, the level of genotypic variation de creased. In autumn, all phenotypic variation resulted from environment al factors. In spring, individuals sensitive to overcrowding, adapted to low density, and highly fertile in low-density conditions prevailed in the population. In summer and autumn, the population was mostly co mposed of individuals with opposite characteristics. On the basis of t he obtained results, a conclusion on operation of cyclic density-depen dent selection in the population examined was made. Selection's functi onal role in control of seasonal population size dynamics is discussed .