Development of repressible sterility to prevent the establishment of feral populations of exotic and genetically modified animals

Proposals to farm non-native and genetically modified species are often highly contentious because there is no reliable method of ensuring that they do not escape, reproduce and become environmental problems. Suggested approaches to prevent breeding outside hatcheries are unable to guarantee sterility in both sexes or cannot easily be applied to animals. We developed and tested on two contentious groups — fish and oysters — genetic constructs that render the animals functionally sterile outside of hatchery conditions, but allow normal development in captivity following brief provision of a repressor compound at a particular life history stage. “Sterile Feral” constructs consist of a stage-specific promoter, a blocker for a critical developmental gene and a repressible element. In transient assays, prototype constructs worked as expected, causing high mortality under non-repressed conditions in both fish and molluscs, and lower mortality, often equal to controls, in the presence of the repressible element (doxycycline). Sterile feral technology can potentially be applied to a wide range of species and be designed to use multiple, independent sterilizing constructs, minimizing the risk of establishing feral populations. Full tests of efficiency, however, require trials in integrated lines, currently in progress, and the usefulness of the technology could depend on the development of an improved repressible element.