Perturbation of a gene pool I. Dynamics ofAdh system and five metric traits in differently introgressed populations ofDrosophila melanogaster

Abstract

This paper discusses the possibilities of restoring in a perturbed genome the genetic situation existing before the perturbation. For this reason we allowed a continuous flow of genes of the original genome (Oregon strain) into the perturbed one. The initial perturbation of the Oregon strain consisted of a cross with the unrelated Canton strain.

We further set up an experiment which aimed at checking the evolutionary dynamics of theAdh locus, of five metric traits and of fitness in the different synthetic gene pools obtained by decreasing the percentage of the Canton genes compared to the introgressed Oregon ones.

As the two strains are differently monomorphic at theAdh locus, initially we used theAdh genotype frequency as marker of the genetic substitution. We then considered the resulting gene pools before and after two years of cage culture where no factors other than meiosis and natural selection affected the results. Finally we performed breeding experiments between these cage populations and the two original strains which attempt to check whether there is genetic evidence of the different level of introgressive hybridization.

The results indicate that during the two years of cage culture the populations experienced a convergence phenomenon which produced average genotypes unexpectedly similar to one another. These similarities pertain toAdh allele frequency, metric traits, reproductive fitness, and, most of all, the behaviour exhibited in the crosses with the two strains. We conclude that the introgressive hybridization failed to restore an Oregon-like genome. Our findings are discussed in terms of two explanatory hypotheses: that heterozygosity was the only driving force of the evolutionary pathways of the examined populations; alternatively that Canton and Oregon genes combined non-additively giving rise to a new hybrid coadaptive system.