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

With a view to the possible use of transposable elements (TEs) as a me chanism to drive genes into insect vector populations, we used a three -parameter density dependent growth equation to examine the critical p arameter values that determine whether or not a mobile element will sp read and become fixed in a finite diploid vector population. Populatio ns were simulated with parameter values affecting size, reproductive r ate, density-dependence, and transposition efficiency of the mobile el ement. 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 quick ly 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 si ze, transposition efficiency of the element, reproductive mte individu als bearing TEs and initial ratio of TE-bearing to wild individuals mo dified the outcome. As population size and transposition efficiency de creased in value, TEs became fixed less easily. However, even in popul ations as small as n = 100, an element with a transposition efficiency >0.75 that reduces fertility <25% will become fixed when introduced a t a frequency as low as 1% of the total population. These results are consistent with previously reported population genetics models. They s uggest that engineered transposons with a wide range of properties may be used to drive genes, such as those for parasite resistance, into w ild vector populations.