Figure 4. Mathematical model predictions for best performing split drive.

Model predictions for releases of Ae. aegypti mosquitoes homozygous for (A) the split drive system, (B) a disease-refractory gene, or (C) a homing drive system in which the components of the split drive system are linked at the same locus. Parameters correspond to those for the best performing split drive system (w^U6b-GDe/w+; nup50-Cas9/+) (Supplementary file 7b). Releases are carried out in a population with an equilibrium size of 10,000 adults and a 1% per mosquito per generation migration rate with a neighboring population of the same equilibrium size. Model predictions were computed using 100 realizations of the stochastic implementation of the MGDrivE simulation framework (Sánchez et al., 2018). Weekly releases of 10,000 homozygous split drive males or the disease-refractory gene were simulated over a 10 week period, while a single release was simulated for the linked homing drive system. Total female population size (‘total’, dark blue), adult females with at least one copy of the disease-refractory allele (‘H*”, red), and disease-susceptible adult females without the disease-refractory allele (‘other’, purple) were plotted for each group. Notably, the split drive system is: i) largely confined to its release population, ii) reversible, and iii) present at a high frequency (>85% of adult females having at least one copy) for over three years. The split drive system outperforms inundative adult male release of the disease-refractory gene in population disease refractoriness and outperforms the confinability of a linked homing drive system. In the right column, heatmaps are shown for (D) the split drive system, (E) inundative releases of a disease-refractory gene, and (F) a linked homing drive system, and depict the window of protection in days that the proportion of mosquitoes in the release population with at least one copy of the disease-refractory allele exceeds 80%. The fitness cost (reduction in mean adult lifespan) associated with gRNA/refractory allele homozygotes is varied along the x-axis, and the number of weekly releases along the y-axis. Notably, for the split drive system, the window of protection exceeds three years following 10 or more weekly releases for gRNA/refractory allele fitness costs of 10% in homozygotes.

Figure 4—figure supplement 1. Allele frequencies for best performing split-drive construct.

Model predictions for releases of Ae. aegypti mosquitoes homozygous for the split drive system (A), a disease-refractory gene (B), or a homing drive system in which the components of the split drive system are linked at the same locus (C). Parameters correspond to those for the best performing split drive system (w^U6b-GDe/w+; nup50-Cas9/+) (Supplementary file 7b). Releases are carried out in a population with an equilibrium size of 10,000 adults that exchanges migrants with a neighboring population of the same equilibrium size at a rate of 1% per mosquito per generation. Model predictions were computed using 100 realizations of the stochastic implementation of the MGDrivE simulation framework (Sánchez et al., 2018). Weekly releases of 10,000 males homozygous for the split drive system or disease-refractory gene were carried out over a 10 week period, while a single release was carried out for the linked homing drive system. Results are plotted for female allele frequencies. Red denotes the gRNA/disease-refractory allele (H), pink denotes the wild-type allele at this locus (W), and dark blue and green represent in-frame/cost-free and out-of-frame/costly resistant alleles (R and B). Light blue represents the allele frequency of Cas9 at the second locus for the split drive system (C). Notably, the H allele reaches a frequency of ~30% in the neighboring population for the split drive releases, before being eliminated by virtue of a fitness cost. At the release site, the Cas9 allele is reduced to a population frequency of ~10% within four years of the final release, leading to a progressive decline of the gRNA/refractory allele in both populations. Reversibility can be accelerated through dilution of transgenes by releases of wild-type males.

Figure 4—figure supplement 2. Fecundity of trans-heterozygous females only slightly reduced in mathematical models.

Progeny numbers from 20 individual crosses for each parent combination crossed to wt (w+/w+) mosquitoes of the opposite sex were used to estimate fecundity. To transform progeny numbers into fecundity percentages, each progeny number was normalized to the average progeny number in the corresponding control group, heterozygous w^U6b-GDe/w+ females or males crossed to w+/w+ mosquitoes. nup50-Cas9 caused a significant reduction in fecundity, from 100.0 ± 11.6% to 88.8% ± 8.7%. Average fecundity percentages were compared to that in the corresponding control group. Bars show averages ± SD estimated from 20 data points. Statistical significance was estimated by an equal variance t-test. (p<0.02*).