Selection on a Modified Genetic Network with a Novel Artificial Link in Drosophila Melanogaster

It is clear that the genetic networks that control the shape and patterning of important phenotypic traits are much more important to trait evolution than was previously thought. This study addresses the ability of the Drosophila melanogaster wing development network to adapt to a topology change. I manipulated the wing development network of Drosophila melanogaster by engineering new links between key genes. These links produce a range of perturbations to the normal wing phenotype; some have no visible effect, some are lethal, some have a mildly penetrant effect present in a small proportion of individuals, and others are strongly penetrant, affecting all individuals carrying the new link. One novel link produced altered wing venation phenotypes in all individuals. I created a large experimental population that carried this new link in a variable genetic background. This population was split into four equal replicate lines. I selected for a wild-type phenotype in two replicate populations for 8 generations while also selecting to retain the new link. Two replicates that served as controls experienced selection to retain the new link, but no selection for a less severe phenotype. Two metrics that quantify different aspects of wing perturbation were analyzed, index and type. Index describes the total size of perturbations to an individual wing, but treats all changes as parts of a single phenotype; type quantifies the number of separate perturbations in an individual wing, but not their size. Analysis of the distributions of type show that selected replicates have moved toward lower type scores in the selected populations, and that the distribution of perturbation type in selected flies is lower than that of control flies in the final generation of selection. Index scores also show a reduction over time in selected lines; however, control flies and selected flies are not significantly different in the final generation. Interestingly, when index scores are analyzed separately within types, the most severe types experience a reduction in index over time, while the least severe types show a slight increase of index scores. Together, these results suggest that while artificial selection may play some role in the observed decline in perturbation to normal phenotype, natural selection is likely to be the stronger force causing these changes.