The genetical response to natural selection by varied environments. II. Observations on replicate populations in spatially varied laboratory environments.

From each of two populations of Drosophila melanogaster, collected two months previously, from Chateau Tahbilk, S. Australia and Groningen, The Netherlands, duplicate populations were initiated in each of four environments which differed in their degree of environmental heterogeneity. Differing combinations of three food media based on oatmeal/treacle, potato or fig were used to simulate levels of environmental heterogeneity within the populations. The polymorphic loci, Adh, Est-6, G-6pdh, alpha-Gpdh, Pgm, Lap-D and Aph in both the Chateau Tahbilk and Groningen derived populations and 6Pgdh, which was only polymorphic in the populations which came from Chateau Tahbilk, were monitored in the experiment. The populations maintained a size of about 2500 adults and were sampled after 16 and 32 generations. Large changes of phenotype frequency were shown by all loci. Despite a frequent divergence of phenotype frequencies between duplicate cages, systematic effects of occasion and environment were present and allele frequencies at many loci were shown to be changing at a faster rate than could be due to random genetic drift. Genetic heterozygosity differed between environments but was not positively correlated with degree of environmental heterogeneity.