Does interspecific hybridization influence evolutionary rates? An experimental study of laboratory adaptation in hybrids between Drosophila serrata and Drosophila birchii

The low initial fitness of progeny from interspecific crosses in animals an d the rarity of interspecific hybridization in natural environments have le d to a debate about the evolutionary importance of this phenomenon. Here we directly assess the effects of hybridization between Drosophila serrata an d Drosophila birchii on evolutionary rates. We looked at the effects on lab oratory adaptation over 30 generations in two laboratory environments, one of which involved nutrition and temperature stress. Laboratory adaptation o ccurred over time in both environments as reflected by a marked change in v iability. However, whilst hybrid lines at no stage performed poorly relativ e to parental lines, their rate of adaptation never exceeded that of the pa rentals. Thus, there was no evidence that hybridization increased evolution ary rates. Instead, hybrid lines converged phenotypically with one of the p arental species.