Mutation rates in hybrids between sibling species of Drosophila

It has recently been suggested that sterility or inviability in species hybrids might result from the movement of transposable elements. Because such movement is often detectable by an increased mutation rate, I studied the effect of interspecific hybridization in the Drosophila melanogaster group on the mutation rate of X-linked visibles. This rate did not differ between hybrids and intraspecific controls. This was also true for the germ-line excision rate of a transposable element, although the rate of somatic excision was two to sixfold higher in hybrids than in pure species. Combined with previous work, these results do not support a role for transposable elements in speciation.