Slow and steady wins the race: spatial and stochastic processes and the
failure of suppression gene drives
Abstract
Gene drives that skew sex ratios offer a new management tool to suppress
or eradicate pest populations. Early models and empirical work suggest
that these suppression drives can completely eradicate well-mixed
populations, but models that incorporate stochasticity and space (i.e.,
drift, and founder events) often result in loss or failure of the drive.
We developed a stochastic model to examine these processes in a simple
1-dimensional space. This simple space allows us to map the events and
outcomes that emerged and examine how properties of the drive’s wave of
invasion affect outcomes. Our simulations, across a
biologically-realistic section of parameter space, suggest that drive
failure might be a common outcome in spatially explicit, stochastic
systems, and that properties of the drive wave appear to mediate
outcomes. Surprisingly, the drives that would be considered fittest in
an aspatial model were strongly associated with failure in the spatial
setting. The fittest drives cause fast moving, narrow drive waves that
have a high chance of being penetrated by founder events, leading to
failure. Our results also show that high rates of dispersal reduce the
chance of failure because drive waves get disproportionately wider as
dispersal rates increase. Overall, wide, slow-moving drive waves were
much less prone to failure. Our results point to the complexity inherent
in using a genetic system to effect demographic outcomes and speak to a
clear need for ecological and evolutionary modelling to inform the drive
design process.