Invasive alien mammals can have a catastrophic impact on local flora and fauna, causing species extinction and profound environmental change. Classical control methods such as baiting with poison, trapping or hunting are currently not possible on a large scale, so researchers are looking for alternatives.
CRISPR-based genome engineering is often seen as a “silver bullet” for pest control. Despite growing interest in developing this technology for invasive mammals such as mice, rats, rabbits, feral cats and foxes, research so far has focused only on mice.
Scientists have wondered whether genome-editing technologies could help wipe out larger mammals, and if so, how long it would take.
To address these questions, a team of researchers from the University of Adelaide developed a mathematical model capable of simulating the effects of gene drives on mammal populations at a landscape scale. Posted in public domain NeobiotaTheir study is the first to estimate the time it would take to eradicate long-lived alien mammals.
Using CRISPR-Cas9 technology, the simulated gene drive relies on “molecular scissors” inserted into the Y chromosome that target and cut the X chromosome at the right time during meiosis, so that only sperm carrying the Y chromosome are viable and can successfully fertilize an egg. Therefore, males who carry the drive should only produce sons who also carry the molecular scissors on their Y chromosome. Over several generations, females will be rarer and produce fewer offspring; as a result, the population will decrease.
This “X-shredder” drive has been successfully developed and demonstrated to suppress the population cells of malaria-carrying mosquitoes, but has not yet been developed in mammals. The model shows that the X-shredder drive can potentially achieve landscape eradication of mice, rats, rabbits, feral cats and red foxes, but the probability of success and the time it will take to destroy them varies greatly.
The researchers tested the X-shredder’s ability to destroy a population of 200,000 individuals of each species. “CRISPR-based gene drives offer novel solutions for the control of invasive alien species that could eventually expand eradication efforts to continental scales,” they concluded.
The method can be effective against small pests such as rodents and rabbits. The expected extirpation time is 18 years for mice, 19 years for rats, and 48 years for rabbits, with 90% population suppression achieved in about half that time.
However, the results suggest that gene drives are not a one-size-fits-all solution: they may not be as useful for larger species such as cats and foxes.
“The probability of extermination of wild cats with gene drives is equal to a coin toss, 50/50; and assuming the coin lands on the right side, it will take about 140 years to get rid of them,” says Dr. Aysegul Birand. , part of the research team. “The probability of eliminating foxes is higher, but the wait is even longer.”