Short Communication |
Corresponding author: Aysegul Birand ( aysegul.birand@adelaide.edu.au ) Academic editor: Ingolf Kühn
© 2022 Aysegul Birand, Phillip Cassey, Joshua V. Ross, Paul Q. Thomas, Thomas A. A. Prowse.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Birand A, Cassey P, Ross JV, Thomas PQ, Prowse TAA (2022) Scalability of genetic biocontrols for eradicating invasive alien mammals. NeoBiota 74: 93-103. https://doi.org/10.3897/neobiota.74.82394
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CRISPR-based gene drives offer novel solutions for controlling invasive alien species, which could ultimately extend eradication efforts to continental scales. Gene drives for suppressing invasive alien vertebrates are now under development. Using a landscape-scale individual-based model, we present the first estimates of times to eradication for long-lived alien mammals. We show that demography and life-history traits interact to determine the scalability of gene drives for vertebrate pest eradication. Notably, optimism around eradicating smaller-bodied pests (rodents and rabbits) with gene-drive technologies does not easily translate into eradication of larger-bodied alien species (cats and foxes).
Cat, fox, gene drive, invasive mammals, mice, rabbit, rat, spatial model
Alien vertebrates are some of the costliest invasive alien species worldwide (
CRISPR-based gene-drive approaches promise ground-breaking tools for the eradication or suppression of invasive alien species (
Here, we investigated how differences in the life-history traits of five invasive mammals (mice, rats, rabbits, feral cats, and red foxes) interact and influence the feasibility of deploying gene-drive technologies for population suppression at large spatial scales. We used an individual-based, spatially explicit, stochastic model that provides realistic estimates of eradication probabilities and expected times to eradication, due to its ability to model large population sizes at a landscape level (see Suppl. material
Times to eradication with various release strategies in mice and other invasive mammals using Y-drive. A the X-chromosome shredding Y-drive is located on the Y chromosome, and cuts the X chromosome at multiple locations during spermatogenesis (with probability px = 0.96). The X-bearing sperm are destroyed and eggs are predominantly fertilized by Y-bearing sperm, causing disproportionately more male offspring B interquartile ranges for the time to eradication of mice with various spatial release strategies when the number of individuals released per patch, Ni, is varied and the maximum dispersal distance D = 3 patches, and C when Ni = 1 and D is varied (100 simulations for each combination) D violin plots showing the distributions of simulated times to eradication (1000 simulations for each species) and circles representing areas that each species with roughly 200,000 individuals would occupy. The colors of violin plots and circles represent probabilities of eradication and density estimates, respectively.
Based on density estimates in Australia (d in Table
Parameters that are related to the demography and life-history traits for each species, along with the areas that the species are assumed to occupy with roughly 200,000 individuals, based on density estimates obtained from literature. We note that these density estimates are used for area (A) calculation only, and due to the stochastic nature of the simulations, densities change through time and also across simulations.
Species | b | n c | age m | ω | p m | d | A | ∆i | D |
---|---|---|---|---|---|---|---|---|---|
Mouse | 6 | 6 | 2 | [0.48, 0.58] | [0.41, 0.51] | 5000 | 40 | 0.4 | [2, 4] |
Black rat | 4 | 6 | 2 | [0.62, 0.67] | [0.63, 0.73] | 1000 | 200 | 2 | [7, 9] |
Rabbit | 4 | 4 | 3 | [0.82, 0.87] | [0.15, 0.25] | 25 | 8000 | 12.5 | [7, 9] |
Cat | 4 | 2 | 5 | [0.85, 0.90] | [0.20,0.30] | 2 | 100000 | 25 | [3, 5] |
Fox | 4 | 2 | 5 | [0.88, 0.93] | [0.71, 0.81] | 2 | 100000 | 45 | [7, 9] |
We initially simulated various spatial gene-drive release strategies and compared the simulated times to eradication for mice (Fig.
In order to capture the uncertainty in some of the demographic and dispersal parameters in our simulations, we generated uniform distributions based on the parameter ranges of the probabilities of survival (ω) and polyandry (pm), and for dispersal distances (D) (Table
The probability of eradication for small-bodied species (0.97, 1.0, 1.0, respectively for mice, rats, and rabbits) was higher than for large-bodied species (0.50, and 0.89 respectively for cats and foxes, Fig.
Median eradication times of roughly 200,000 individuals with the X-chromosome shredding drive were 17.7 years for mice, 18.5 years for rats, 48.0 years for rabbits, 142.3 years for cats, and 169.0 years for foxes, with nearly 90% population suppression achieved at half that time (Suppl. material
Our results are in agreement with theoretical models suggesting that gene drives could eradicate large populations of short-lived mammals successfully, within reasonable time periods, and could be an attractive alternative to current lethal control methods (
The authors acknowledge the Kaurna people as the Traditional Owners of the land where we live and work. We acknowledge the Kaurna people as the custodians of the Adelaide region and we respect and value their past, present and ongoing connection to the land and cultural beliefs.
This study was supported by the following grants and institutions: Australian Research Council Linkage Grant LP180100748 awarded to P.T., J.V.R., P.C. and T.A.A.P.; NSW Government for ‘Genetic Biocontrol Technology for Pest Mammal Control’ awarded to P.T. and P.C.; and SA Government Research, Commercialisation and Startup Fund for ‘Establishment of the SA genetic biocontrol technology hub for invasive mammalian pests’ awarded to P.T., P.C. and J.V.R. This work was also supported with supercomputing resources provided by the Phoenix HPC service at the University of Adelaide.
Tables S1, S2
Data type: Pdf file
Explanation note: Methods.