Evolutionary aspects of hybrid dysgenesis in Drosophila

Abstract

Hybrid dysgenesis results from the movement of specific transposable elements following hybridization between populations having different element complements. The phenotypic and molecular properties of P, I, and hobo elements in Drosophila are briefly described to provide a background for discussion of the evolutionary significance of the phenomenon of hybrid dysgenesis. It is argued that most mobile element systems are apt to produce dysgenic traits, but that other properties of the P–M and I–R systems of hybrid dysgenesis, such as nonreciprocity and tissue specificity, will be more restricted in their occurrence. There is good evidence that mobile elements may move between both closely and distantly related species in the genus Drosophila, but it is not known whether this type of event is frequent enough to have evolutionary consequences. It appears to be unlikely on theoretical grounds that hybrid dysgenesis acts directly as a postmating reproductive isolating mechanism. The ubiquity of mobile elements and the observed high frequency of insertional mutations induced by them suggest that these elements could contribute to increased population genetic variability, which may differ from that produced by other natural mutagens. However, there is no direct evidence that this variability has long-term evolutionary significance. Although there is currently little clear evidence for hybrid dysgenesis in other insect genera, it is premature to conclude that this phenomenon is restricted to a few mobile element families in Drosophila.