On the Role of Natural Selection in the Genetic Divergence of Migration-Coupled Populations. Frequency-Dependent Selection

The present study continues the investigation of the mechanisms of primary genetic divergence of migration-coupled populations. The modeling is based on the experiment performed by Yu.P. Altukhov et al. with box populations of Drosophila melanogaster. In this experiment, primary divergence of the subpopulation genetic structures was demonstrated at the two genetic diversity marker loci (α-GDH and esterase-6). Earlier we showed that at the α-GDH locus in the experimental system, there was a high probability of disruptive selection, which provided the maintenance of the observed primary genetic divergence. The objective of the study was to identify the mechanisms that contributed to the primary genetic divergence at the esterase-6 locus. The discrete-time mathematical models for the allele frequency dynamics in large panmictic population and in a system of 30 local migration-coupled populations were analyzed. Comparison of the simulation results with the experimental results led to the conclusion that, with the high probability, in the artificial population system under consideration, frequency-dependent selection at the esterase-6 locus acted against the background of density-dependent selection. It was demonstrated that, with identical selection in subpopulations connected by small migrations, this type of selection promoted divergence, and the genetic differences in neighboring populations were found to be considerably more pronounced than they could be under the conditions of genetic drift.