Natural selection of synthetic gene drives for population suppression can favour an intermediate strength of drive

Synthetic gene drives are being investigated as tools to suppress pest populations, and it is important to understand how natural selection will act on variant drivers that may either arise by de novo mutation or are intentionally released. In this study we extend previous spatially implicit stochastic models to examine the evolutionary dynamics of synthetic driving Y chromosomes in patchy environments when population size is responding dynamically to the spread of the driver, and derive conditions for the existence of an evolutionarily stable strategy (ESS) for drive strength. Under broad conditions an intermediate drive strength emerges as the ESS, capable of outcompeting both stronger and weaker variants. Additionally, we show how the intentional release of two drivers straddling the ESS can help stabilise population dynamics. Finally, inbreeding depression has the effect of expanding the range of conditions under which no intermediate ESS exists, with ever stronger drive being selected until the population is eliminated. These results provide insights into the expected evolutionary trajectories of gene drive systems, with important implications for the design and release of gene drives for pest and vector control.