New Zealand stunned the world in 2016 announcing a goal to eradicate mammalian predators by 2050. The key targets are possums, rats and stoats; species that cause enormous damage to our flora and fauna and in some cases are an economic burden to our productive sectors.
As all of these species were introduced to New Zealand from elsewhere there is little sympathy nationally for any of them and their control and eradication has been a key component of conservation and animal health management in this country for decades. Thanks to the work of many we can control and even eradicate many of these species at increasingly large scales. The success of these programs has seen a variety of “pest-free” offshore sanctuaries formed, such as Kapiti Island and the Orokonui mainland sanctuary where many native species, including kiwi, kokako, and kaka now have a realistic chance for population persistence and recovery.
Pest control with current technologies over significant spatial scales is definitely possible, but its time-consuming and expensive. Thus if we want to reach a goal of a pest free New Zealand by 2050 we either have to make this a priority and open up the national cheque book, or we need to come up with much smarter (read cheaper) ways to control our pest problem. One promising new approach to pest eradication now emerging are so called “gene drives” that promote the inheritance of a particular gene to increase its frequency in a population. Most of us will recall that for the most part we receive half of the copies of our genes from each parent. However, a gene drive distorts that rule promoting the inheritance of a particular copy of a gene to an individual’s offspring. That distortion in and of itself is relatively harmless, but if you can couple that distortion in inheritance to a genetic trait that effects an individuals survival or ability to reproduce you have the beginnings of a powerful tool that can be used to elicit control of population growth and persistence i.e. you have a tool that could be used for population regulation or even eradication.
The idea of gene drives has been around for about 20 years. However in the last few years it has catapulted into reality with the discovery of a new gene editing system CRISPR/Cas9 than can be used to drive itself and a particular trait through populations with startling speed —from generation to generation up to 90% of offspring will inherit the gene drive. So far, ‘gene drives’ have been developed in yeast, the fruit fly, and two mosquito species. One of the mosquito gene drives, causes a malaria-resistance gene to be passed on to the mosquitoes' offspring, meaning they are unable to transmit malaria in mice. The other mosquito gene drive propagates a gene that sterilizes all female mosquitoes (which could suppress specific mosquito populations to levels that will not support malaria transmission). Work aimed at developing a new strategy for mammalian pest control is already underway overseas.
Here the idea is to produce mice that carry the sry gene, the key sex-determining gene in most mammals, linked to gene-drive that ensures that 9 out of 10 offspring will be male. The idea has promise, but there are many unknowns as to whether this will work in mice, whether the idea can transfer to other species, and whether society is ready to accept a tool that involves genetic modifications that are predicted to race through populations.
Many of these issues are now the focus of new work in our lab funded through the Biological Heritage National Science. There are multiple barriers to the uptake and application of this technology that we are currently focusing on. The first, and most important, is the social acceptability of this technology, which will undoubtedly be governed by multiple things including the perceived benefits versus threats. We will need to do a lot of work over coming years to quantify the risks and benefits of such strategies to inform the discussions we must have before this work develops much further. I have discussed some concerns about this technology here.
A further barrier is technological. Genetic engineering of mice is well established, but we are much less able to genetically engineer rats. Genetic manipulations of possums, stoats and other pests will likely be more of a challenge than many people anticipate. While we have new gene editing technologies that speed this process up the task of genetically manipulating some of the species we will target will require a great deal of specialist expertise and knowledge of the biology of these pest species. It is exceeding unlikely that gene drives developed for mouse will work in these other species so each will require a boutique solution.
The persistence of these gene drives in the wild is a further area of uncertainty. If the gene drives affect an individual’s health or ability to attract and obtain mates they may struggle to persist. Further, in the large populations common to the pests we seek to control, mutations in the gene drive are almost inevitable. If such mutations in activate either the gene drive or the gene linked to it (e.g. in mice the gene drive and sry gene become inactivated so that offspring will drop back to 50:50 male and female) then obviously the population suppression will be rapidly removed. We are currently modelling the efficacy of a variety of gene drive options, including the possibility of linking gene drives to mutations harmful to males via maternally inherited mitochondrial DNA, and we hope these data will be helpful in informing discussions prior to investment in the development of any systems here in New Zealand.
The last issue is one of logistics and funding. If we are serious about this endeavour we need to get organised and start planning out what the work flow for this project would look like over the next decade plus. The first target of eradicating a pest species by 2025 is only 7 years away, and where we now stand this is likely going to be hard to achieve. If we start today we need months to plan, several years in the lab, and years for controlled field trials, before eventual deployment at landscape scales. It will take massive effort and years to achieve eradication of possums, rats and stoats. This is the NZ version of the space-race and we need commitment and resource aplenty if we are to achieve it. It can be done, but whether we have the resolve to resource this appropriately and see this through to completion remains uncertain.
Kevin Esvelt (MIT)
Dan Tompkins (Predator Free 2050)
James Russell (Auckland)