Population dynamics in spatial suppression gene drive models and the effect of resistance, density dependence, and life history

Abstract

Due to their super-Mendelian inheritance, gene drive systems have the potential to provide revolutionary solutions to critical public health and environmental problems. For suppression drives, however, spatial structure can cause "chasing" population dynamics that may postpone target population elimination or even cause the drive to fail. In chasing, wild-type individuals elude the drive and recolonize previously suppressed areas. The drive can re-enter these recolonized areas, but often is not able to catch up to wild-type and finally eliminate it. Previous methods for chasing detection are only suitable to limited parameter ranges. In this study with expanded parameter ranges, we found that the shift from chasing dynamics to static equilibrium outcomes is continuous as drive performance is reduced. To quantify this, we defined a Weighted Average Nearest Neighbor statistic to assess the clustering degree during chasing, while also characterizing chasing by the per-generation chance of population elimination and drive loss. To detect chasing dynamics in local areas and to detect the start of chasing, we implemented Density-Based Spatial Clustering of Applications with Noise. Using these techniques, we determined the effect of arena size, resistance allele formation rate in both the germline and in the early embryo from maternally deposited Cas9, life history and reproduction strategies, and density-dependent growth curve shape on chasing outcomes. We found that larger real-world areas will be much more vulnerable to chasing and that species with overlapping generations, fecundity-based density dependence, and concave density-dependent growth curves have smaller and more clustered local chasing with a greater chance of eventual population elimination. We also found that embryo resistance and germline resistance hinder drive performance in different ways. These considerations will be important for determining the necessary drive performance parameters needed for success in different species, and whether future drives could potentially be considered as release candidates.