Invasive Alien Species themed issue

One of the first things that often springs to mind when thinking about invasive alien species is the infamous Eastern Grey Squirrel (Sciurus carolinensis). Under the UK’s Wildlife and Countryside Act 1981, it is an offence to release grey squirrels into the wild without a licence. According to the Forestry Commission England, grey squirrels outnumber native red squirrels by a whopping 15,000 red to over 2 million greys. They are also responsible for damaging broadleaved and coniferous woodlands, estimated to cost the UK £6–10 million pounds (~$8–13 million) each year. These little critters are such pests that there exists a 2019 ‘Grey Squirrels and England’s Woodland’ action plan. So, what solutions are on the horizon to bring these populations into a more sustainable equilibrium? Some argue that gene drive technology is the answer. A 2021 study, “Novel Combination of CRISPR-Based Gene Drives Eliminates Resistance and Localizes Spread,” published in Scientific Reports, asserts that existing gene drive technologies could be combined to help control the invasive grey squirrel population in the UK with little risk to other populations. Furthermore, the findings suggest that this is a humane, efficient and costeffective method of control. Clustered regularly interspaced short palindromic repeats (CRISPR) is an RNA-guided gene-editing platform that makes use of a bacterially derived protein (Cas9) and a synthetic guide RNA to introduce a doublestrand break at a specific location within the genome. The 2021 case study revealed that the combined gene drive (HD-ClvR) – a novel combination of CRISPR-based gene drives – effectively suppressed a targeted grey squirrel population. It appeared to pose minimal risk to other populations by combining the advantages of its individual components: homing, cleave-and-rescue and daisyfield. If you are unfamiliar with squirrel primogeniture, you are not alone. Homing ensures that the altered gene is passed on to future generations by inserting it into the germline: the cells that pass on genetic information to offspring. Cleave-and-rescue ensures that offspring with resistant gene variants do not develop. Daisyfield limits the number of altered genes that can be passed on from one individual to the next, thus limiting their spread outside the target population. Described by some as ‘molecular scissors’, CRISPR is used to make targeted, precise changes to the DNA of plants and animals – which, as one might expect, raises its fair share of ethical concerns. In a fascinating – verging on alarming – TED talk in 2015, ‘How CRISPR Lets Us Edit Our DNA’, geneticist Jennifer Doudna asks the scientific community to pause and discuss the ethics of this new tool, including the possibility of creating ‘designer babies’. An April 2021 episode of the BBC’s Costing the Earth radio series also explores these moral conundrums, asking the important question: Should we use this power to interfere with Nature, and if so, how should it be controlled? It’s well worth a listen: https:// www.bbc.co.uk/programmes/m000tsl4