Gene drive-mediated population elimination for biodiversity conservation. When you come to a fork in the road, take it

Abstract

Gene drive occurs when alleles of genes, multigene cassettes, or large chromosomal regions are transmitted to fertile progeny at greater-than-Mendelian frequencies (50%). Gene drive can be used to bring about population suppression or elimination when the rate at which the drive element increases in frequency outpaces a fitness cost induced by its presence, and the population is driven to an unfit state. Much work has focused on applications involving mosquito vectors of human disease (1). Many other applications have their origin in the global problem of invasive species (2), and thinking about how to ameliorate the many harms they are associated with: food insecurity, human disease, economic loss, environmental degradation, and loss of biodiversity. Invasive species are a major driver of species extinction (3), and island endemic populations are particularly hard-hit. While islands constitute only 6.7% of land area, they host 20% of species and 50% of threatened species and account for 75% of known extinctions since the European expansion (4). Mice and rats are a common culprit (Fig. 1) The primary method for eliminating them utilizes rodenticides. This approach can succeed (5), but the economics and logistics do not scale well with island size. Toxicants can also result in off-target effects on other species, which often precludes their use on islands inhabited by humans and livestock/companion animals. Gene drive–based population suppression provides a solution that eliminates toxicant-based harms and is more humane. It is also species specific and in principle lower cost because it is self-sustaining and takes advantage of the invaders' tendency to seek out conspecifics even in complex and remote environments. Conversely, a gene drive element must also be unable to bring about suppression in nontarget areas if some individuals manage to "jump ship." The use of gene drive for population suppression thus involves a fundamental tension between the goals of robust spread and confinement of the desired outcome to the target area. Because islands are isolated, they have been a major focus of research into contexts in which gene drive for population suppression could be tested, to real conservation benefit, while limiting the possibilities for effects elsewhere. The organization GBIRd (https://www.geneticbiocontrol.org) provides an important forum for consideration of these ideas. Work by Gierus, Birand, and colleagues addresses both issues (6). It outlines a method by which island populations of mice (but not other rodents) could be eliminated through gene drive. Importantly, the designs involved contain features that ensure the drive element cannot bring about population suppression in a nontarget population.

Files

Additional details