Competition Among Genotypes in Tribolium castaneum at Varying Densities and Gene Frequencies (The Sooty Locus)

1. Mixtures of three genotypes (+/+, +/s, s/s) for the autosomal mutant sooty were reared at five initial gene frequencies and four densities. Replication of the experiments resulted in a total of 59,280 beetles being employed in the experiment. The heterozygote is distinguishable in adults. The frequency and dry weight of emerging adults was recorded by genotypes. A rough measure of total developmental time was also obtained. The wild type strain was found to be contaminated with sooty at a gene frequency of 0.02 for most replicates. 2. Adult survivorship is measured as the percentage of egg input for a given genotype. Figure 1 illustrates the results. The lower three densities did not have any pronounced effects; at density 100/g overall survivorship was markedly reduced. The homozygous wild type has the highest survivorship in the study; the heterozygote is intermediate through the lower densities but lowest in survivorship at the highest density. The relative survivorships of the three genotypes depend on the gene frequency of sooty: at 0.25qsrelations may be summarized by +/+ > s/s > +/s, at 0.5qsby +/+ > +/s > s/s and at 0.75qsby +/s > +/+ > s/s. Relationships at 0.5qsare more consistent while those of the other two gene frequencies showed some heterogeneity among replicates. From the results it is clear that the performance of the heterozygote improves with an increase in the gene frequency of sooty. 3. Dry weights of adults were highest at 20/g. The three genotypes weighed as follows when in mixed culture: s/s >> +/+ > +/s. Gene frequency in the cultures has a marked effect on weights of +/+ and +/s individuals. These responses are illustrated in figure 2. Approximation to straight line functions are obtained when weight of +/+ and +/s individuals is graphed as a function of the proportion of +/s plus s/s individuals in the population. Thus, weight is not simply a function of the gene frequency of sooty in a culture, but of the frequencies of the two genotypes carrying the s allele. 4. Heterozygotes are intolerant to crowding, especially with their own genotype. Weight relations among genotypes depend on whether the beetles were reared in pure or mixed culture. Thus, the performance of genotypes when interacting with other genotypes cannot be predicted from their performance in pure culture. 5. At the higher gene frequencies heterozygotes predominate among the early emerging adults, while s/s individuals are largely late emerging ones. 6. The facil