Species-specific factors affecting the population dynamics of P transposable elements in Drosophila melanogaster and Drosophila simulans.

Abstract

In order to compare the population dynamics of P elements in the sibling species D. melanogaster and D. simulans, three sets of studies were performed. In a series of comparative mixed population experiments, P-M mixed populations of D. melanogaster evolved into P or Q populations, depending on the strength of the P strains used as the original parental strains. However, no mixed populations of D. simulans evolved into P populations; even when the strongest P strains of D. simulans were used, all mixed populations evolved into Q or M' populations. Using an excision assay system, excision frequencies in a variety of strains of D. melanogaster and D. simulans were measured. On average, excision frequencies of P elements from plasmids were significantly lower in D. simulans than in D. melanogaster. In addition, there were no statistically significant correlations between GD sterility and excision frequencies. Using single neomycin -marked P elements, transposition frequencies of P elements were compared in D. melanogaster and D. simulans. As with excision frequencies, transposition frequencies were lower in D. simulans than in D. melanogaster. In addition, the position of the original insertion site had a strong effect on transposition frequency. All of these three experiments showed significantly lower average activity of P elements in D. simulans than in D. melanogaster. This consistency suggests that the three sets of results were influenced either directly and/or indirectly by common factors, such as host-encoded factors. Therefore, differences in the activity of P elements in these two species may be influenced by different host-encoded factors. The absence of P elements in natural populations of D. simulans may also be explained by the presence of different host factors.