TRANSPOSABLE ELEMENTS AS POPULATION DRIVE MECHANISMS - SPECIFICATION OF CRITICAL PARAMETER VALUES

With a view to the possible use of transposable elements (TEs) as a mechanism to drive genes into insect vector populations, we used a three-parameter density dependent growth equation to examine the critical parameter values that determine whether or not a mobile element will spread and become fixed in a finite diploid vector population. Populations were simulated with parameter values affecting size, reproductive rate, density-dependence, and transposition efficiency of the mobile element. Simulations indicated that an equilibrium was reached quickly, typically in <50 generations. Even when initially present at less-than-or-equal-to 1% of a large population, the mobile element spread quickly and became fixed if transposition efficiency was equal to unity and infertility caused by the element decreased reproductive capacity by as much as 45%. These results were insensitive to the values of basic wild type reproductive rates and density dependence, but population size, transposition efficiency of the element, reproductive mte individuals bearing TEs and initial ratio of TE-bearing to wild individuals modified the outcome. As population size and transposition efficiency decreased in value, TEs became fixed less easily. However, even in populations as small as n = 100, an element with a transposition efficiency >0.75 that reduces fertility <25% will become fixed when introduced at a frequency as low as 1% of the total population. These results are consistent with previously reported population genetics models. They suggest that engineered transposons with a wide range of properties may be used to drive genes, such as those for parasite resistance, into wild vector populations.