Since it is not known how the selection for divergent phenotypic traits may indirectly affect genome size, the current study selected drosophila melanogaster for small and large body size for up to 220 generations, and cochliomyia macellaria were selected for 32 generations for fast and slow development.
Genome size varies widely across organisms yet has not been found to be related to organismal complexity in eukaryotes. Although there is no evidence for a relationship with complexity, there is evidence to suggest that other phenotypic characteristics, such as nucleus size and cell-cycle time, are associated with genome size, body size, and development rate. The current study found that size in D. melanogaster significantly changed in terms of both cell-count and genome size in isolines, but only the cell-count changed in lines which were maintained at larger effective population sizes. Larger genome sizes only occurred in a subset of D. melanogaster isolines originated from flies selected for their large body size. Selection for development time did not change average genome size yet decreased the within-population variation in genome size with increasing generations of selection. This decrease in variation and convergence on a similar mean genome size was not in correspondence with phenotypic variation and suggests stabilizing selection on genome size in laboratory conditions. (publisher abstract modified)