Leveraging a natural murine meiotic drive to suppress invasive populations.

Invasive rodents are a major cause of environmental damage and biodiversity loss, particularly on islands. Unlike insects, genetic biocontrol strategies including population-suppressing gene drives with biased inheritance have not been developed in mice. Here, we demonstrate a gene drive strategy (tCRISPR) that leverages super-Mendelian transmission of the t haplotype to spread inactivating mutations in a haplosufficient female fertility gene (Prl). Using spatially explicit individual-based in silico modeling, we show that tCRISPR can eradicate island populations under a range of realistic field-based parameter values. We also engineer transgenic tCRISPR mice that, crucially, exhibit biased transmission of the modified t haplotype and Prl mutations at levels our modeling predicts would be sufficient for eradication. This is an example of a feasible gene drive system for invasive alien rodent population control.

Concurrent invasions of European starlings in Australia and North America reveal population-specific differentiation in shared genomic regions.

A species' success during the invasion of new areas hinges on an interplay between the demographic processes common to invasions and the specific ecological context of the novel environment. Evolutionary genetic studies of invasive species can investigate how genetic bottlenecks and ecological conditions shape genetic variation in invasions, and our study pairs two invasive populations that are hypothesized to be from the same source population to compare how each population evolved during and after introduction. Invasive European starlings (Sturnus vulgaris) established populations in both Australia and North America in the 19th century. Here, we compare whole-genome sequences among native and independently introduced European starling populations to determine how demographic processes interact with rapid evolution to generate similar genetic patterns in these recent and replicated invasions. Demographic models indicate that both invasive populations experienced genetic bottlenecks as expected based on invasion history, and we find that specific genomic regions have differentiated even on this short evolutionary timescale. Despite genetic bottlenecks, we suggest that genetic drift alone cannot explain differentiation in at least two of these regions. The demographic boom intrinsic to many invasions as well as potential inversions may have led to high population-specific differentiation, although the patterns of genetic variation are also consistent with the hypothesis that this infamous and highly mobile invader adapted to novel selection (e.g., extrinsic factors). We use targeted sampling of replicated invasions to identify and evaluate support for multiple, interacting evolutionary mechanisms that lead to differentiation during the invasion process.

Environment and shipping drive environmental DNA beta-diversity among commercial ports.

The spread of nonindigenous species by shipping is a large and growing global problem that harms coastal ecosystems and economies and may blur coastal biogeographical patterns. This study coupled eukaryotic environmental DNA (eDNA) metabarcoding with dissimilarity regression to test the hypothesis that ship-borne species spread homogenizes port communities. We first collected and metabarcoded water samples from ports in Europe, Asia, Australia and the Americas. We then calculated community dissimilarities between port pairs and tested for effects of environmental dissimilarity, biogeographical region and four alternative measures of ship-borne species transport risk. We predicted that higher shipping between ports would decrease community dissimilarity, that the effect of shipping would be small compared to that of environment dissimilarity and shared biogeography, and that more complex shipping risk metrics (which account for ballast water and stepping-stone spread) would perform better. Consistent with our hypotheses, community dissimilarities increased significantly with environmental dissimilarity and, to a lesser extent, decreased with ship-borne species transport risks, particularly if the ports had similar environments and stepping-stone risks were considered. Unexpectedly, we found no clear effect of shared biogeography, and that risk metrics incorporating estimates of ballast discharge did not offer more explanatory power than simpler traffic-based risks. Overall, we found that shipping homogenizes eukaryotic communities between ports in predictable ways, which could inform improvements in invasive species policy and management. We demonstrated the usefulness of eDNA metabarcoding and dissimilarity regression for disentangling the drivers of large-scale biodiversity patterns. We conclude by outlining logistical considerations and recommendations for future studies using this approach.

Gene drives for vertebrate pest control: Realistic spatial modelling of eradication probabilities and times for island mouse populations.

Invasive alien species continue to threaten global biodiversity. CRISPR-based gene drives, which can theoretically spread through populations despite imparting a fitness cost, could be used to suppress or eradicate pest populations. We develop an individual-based, spatially explicit, stochastic model to simulate the ability of CRISPR-based homing and X chromosome shredding drives to eradicate populations of invasive house mice (Mus muculus) from islands. Using the model, we explore the interactive effect of the efficiency of the drive constructs and the spatial ecology of the target population on the outcome of a gene-drive release. We also consider the impact of polyandrous mating and sperm competition, which could compromise the efficacy of some gene-drive strategies. Our results show that both drive strategies could be used to eradicate large populations of mice. Whereas parameters related to drive efficiency and demography strongly influence drive performance, we find that sperm competition following polyandrous mating is unlikely to impact the outcome of an eradication effort substantially. Assumptions regarding the spatial ecology of mice influenced the probability of and time required for eradication, with short-range dispersal capacities and limited mate-search areas producing 'chase' dynamics across the island characterized by cycles of local extinction and recolonization by mice. We also show that highly efficient drives are not always optimal, when dispersal and mate-search capabilities are low. Rapid local population suppression around the introduction sites can cause loss of the gene drive before it can spread to the entire island. We conclude that, although the design of efficient gene drives is undoubtedly critical, accurate data on the spatial ecology of target species are critical for predicting the result of a gene-drive release.

The U.S. market for imported wildlife not listed in the CITES multilateral treaty.

The international wildlife trade presents severe conservation and environmental security risks, yet no international regulatory framework exists to monitor the trade of species not listed in the appendices of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). We explored the composition and dynamics of internationally regulated versus nonregulated trade, with a focus on importations of wild-caught terrestrial vertebrates entering the United States from 2009 to 2018. We used 10 years of species-level trade records of the numbers of live, wild-caught animals imported to the United States and data on International Union for the Conservation of Nature (IUCN) estimates of extinction risk to determine whether there were differences in the diversity, abundance, and risk to extinction among imports of CITES-listed versus unlisted species. We found 3.6 times the number of unlisted species in U.S. imports compared with CITES-listed species (1366 vs. 378 species). The CITES-listed species were more likely to face reported conservation threats relative to unlisted species (71.7% vs. 27.5%). However, 376 unlisted species faced conversation threats, 297 species had unknown population trends, and 139 species were without an evaluation by the IUCN. Unlisted species appearing for the first time in records were imported 5.5 times more often relative to CITES-listed species. Unlisted reptiles had the largest rate of entry, averaging 53 unique species appearing in imports for the first time per year. Overall trade quantities were approximately 11 times larger for imports of unlisted species relative to imports of CITES-listed species. Countries that were top exporters of CITES-listed species were mostly different from exporters of unlisted species. Because of the vulnerabilities of unlisted, traded species entering the United States and increasing global demand, we strongly recommend governments adapt their policies to monitor and report on the trade of all wildlife.

El Mercado Estadunidense de Fauna Importada No Enlistada en el Tratado Multilateral CITES Resumen Aunque el mercado internacional de fauna representa un riesgo severo para la conservación y la seguridad ambiental, no existe un marco internacional de regulación para monitorear el mercado de especies que no están en los apéndices de la Convención sobre el Comercio Internacional de Especies Amenazadas de Fauna y Flora Silvestres (CITES). Exploramos la composición y las dinámicas del mercado regulado internacionalmente frente al que no lo está, enfocados en la importación de vertebrados terrestres capturados en vida silvestre que entraron a Estados Unidos entre 2009 y 2018. Usamos el registro de comercio a nivel de especie del número de animales vivos capturados en vida silvestre e importados a Estados Unidos durante diez años y datos de los estimados de extinción de la Unión Internacional para la Conservación de la Naturaleza (UICN) para determinar si hay diferencias en la diversidad, abundancia y el riesgo de extinción entre las especies importadas enlistadas o no en CITES. Encontramos 3.6 veces más el número de especies no enlistadas en las importaciones a Estados Unidos en comparación con las especies enlistadas en CITES (1,366 versus 378 especies). Fue más probable que las especies de CITES enfrentaran amenazas de conservación reportadas en relación con las especies no enlistadas (71.7% vs. 27.5%). Sin embargo, 376 especies no enlistadas enfrentaron amenazas de conservación, 297 especies no cuentan con tendencias poblacionales conocidas y 139 especies no estaban evaluadas por la UICN. Las especies no enlistadas que aparecieron por primera vez en los registros fueron importadas 5.5 más veces en relación con las especies en CITES. La mayor tasa de entrada la tuvieron los reptiles no enlistados, con un promedio de 53 especies únicas al año registradas por primera vez en las importaciones. La cantidad generalizada de intercambios fue once veces mayor para la importación de especies no enlistadas en relación con la importación de especies CITES. La mayoría de los principales países exportadores de especies CITES fue diferente a la de los exportadores de especies no enlistadas. Debido a la vulnerabilidad de las especies comerciales no enlistadas que entran a los Estados Unidos y al incremento de la demanda global, recomendamos firmemente que los gobiernos adapten sus políticas para monitorear y reportar el mercado de toda la fauna.

Signatures of selection in a recent invasion reveal adaptive divergence in a highly vagile invasive species.

A detailed understanding of population genetics in invasive populations helps us to identify drivers of successful alien introductions. Here, we investigate putative signals of selection in Australian populations of invasive common starlings, Sturnus vulgaris, and seek to understand how these have been influenced by introduction history. We used reduced representation sequencing to determine population structure, and identify Single Nucleotide Polymorphisms (SNPs) that are putatively under selection. We found that since their introduction into Australia, starling populations have become genetically differentiated despite the potential for high levels of dispersal, and that starlings have responded to selective pressures imposed by a wide range of environmental conditions across their geographic range. Isolation by distance appears to have played a strong role in determining genetic substructure across the starling's Australian range. Analyses of candidate SNPs that are putatively under selection indicated that aridity, precipitation and temperature may be important factors driving adaptive variation across the starling's invasive range in Australia. However, we also noted that the historic introduction regime may leave footprints on sites flagged as being under adaptive selection, and encourage critical interpretation of selection analyses in non-native populations.

Dissecting the null model for biological invasions: A meta-analysis of the propagule pressure effect.

A consistent determinant of the establishment success of alien species appears to be the number of individuals that are introduced to found a population (propagule pressure), yet variation in the form of this relationship has been largely unexplored. Here, we present the first quantitative systematic review of this form, using Bayesian meta-analytical methods. The relationship between propagule pressure and establishment success has been evaluated for a broad range of taxa and life histories, including invertebrates, herbaceous plants and long-lived trees, and terrestrial and aquatic vertebrates. We found a positive mean effect of propagule pressure on establishment success to be a feature of every hypothesis we tested. However, establishment success most critically depended on propagule pressures in the range of 10-100 individuals. Heterogeneity in effect size was associated primarily with different analytical approaches, with some evidence of larger effect sizes in animal rather than plant introductions. Conversely, no variation was accounted for in any analysis by the scale of study (field to global) or methodology (observational, experimental, or proxy) used. Our analyses reveal remarkable consistency in the form of the relationship between propagule pressure and alien population establishment success.

A guide to using the internet to monitor and quantify the wildlife trade.

The unrivaled growth in e-commerce of animals and plants presents an unprecedented opportunity to monitor wildlife trade to inform conservation, biosecurity, and law enforcement. Using the internet to quantify the scale of the wildlife trade (volume and frequency) is a relatively recent and rapidly developing approach that lacks an accessible framework for locating relevant websites and collecting data. We produced an accessible guide for internet-based wildlife trade surveillance. We detailed a repeatable method involving a systematic internet search, with search engines, to locate relevant websites and content. For data collection, we highlight web-scraping technology as an efficient way to collect data in an automated fashion at regularly timed intervals. Our guide is applicable to the multitude of trade-based contexts because researchers can tailor search keywords for specific taxa or derived products and locations of interest. We provide information for working with the diversity of websites used in wildlife trade. For example, to locate relevant content on social media (e.g., posts or groups), each social media platform should be examined individually via the site's internal search engine. A key advantage of using the internet to study wildlife trade is the relative ease of access to an increasing amount of trade-related data. However, not all wildlife trade occurs online and it may occur on unobservable sections of the internet.

Resumen Una Guía para Usar el Internet para Monitorear y Cuantificar el Mercado de Fauna El crecimiento incomparable del comercio en línea de animales y plantas representa una oportunidad sin precedentes para monitorear el mercado de fauna y así orientar a la conservación, la bioseguridad y la aplicación de la ley. El uso del internet para cuantificar la escala del mercado de fauna (volumen y frecuencia) es una estrategia relativamente reciente y de rápido desarrollo que carece de un marco de trabajo accesible para la localización de sitios web relevantes y para la recolección de datos. Realizamos una guía accesible para la vigilancia del mercado de fauna en internet. Detallamos un método repetible que involucra una búsqueda sistemática por internet, por medio de buscadores, para localizar sitios web y contenidos relevantes. Para la recolección de datos, resaltamos la tecnología de web scraping como una manera eficiente de obtener datos de manera automatizada a intervalos regulares de tiempo. Nuestra guía puede aplicarse a la multitud de contextos basados en el mercado porque los investigadores pueden adaptar las palabras de búsqueda a taxones específicos o productos derivados y a localidades de interés. Proporcionamos información para poder trabajar con la diversidad de sitios web que se usan para el mercado de fauna. Por ejemplo, para localizar contenido relevante en las redes sociales (p. ej.: publicaciones o grupos), cada plataforma social debería ser examinada individualmente por medio del buscador interno del sitio. Una ventaja importante de usar el internet para estudiar el mercado de fauna es el acceso relativamente sencillo a una creciente cantidad de datos relacionados con el mercado. Sin embargo, no todo el mercado de fauna ocurre en línea y puede que suceda en secciones inobservables del internet.

Remoteness promotes biological invasions on islands worldwide.

One of the best-known general patterns in island biogeography is the species-isolation relationship (SIR), a decrease in the number of native species with increasing island isolation that is linked to lower rates of natural dispersal and colonization on remote oceanic islands. However, during recent centuries, the anthropogenic introduction of alien species has increasingly gained importance and altered the composition and richness of island species pools. We analyzed a large dataset for alien and native plants, ants, reptiles, mammals, and birds on 257 (sub) tropical islands, and showed that, except for birds, the number of naturalized alien species increases with isolation for all taxa, a pattern that is opposite to the negative SIR of native species. We argue that the reversal of the SIR for alien species is driven by an increase in island invasibility due to reduced diversity and increased ecological naiveté of native biota on the more remote islands.

Adaptive changes in the genomes of wild rabbits after 16 years of viral epidemics.

Since its introduction to control overabundant invasive European rabbits (Oryctolagus cuniculus), the highly virulent rabbit haemorrhagic disease virus (RHDV) has caused regular annual disease outbreaks in Australian rabbit populations. Although initially reducing rabbit abundance by 60%, continent-wide, experimental evidence has since indicated increased genetic resistance in wild rabbits that have experienced RHDV-driven selection. To identify genetic adaptations, which explain the increased resistance to this biocontrol virus, we investigated genome-wide SNP (single nucleotide polymorphism) allele frequency changes in a South Australian rabbit population that was sampled in 1996 (pre-RHD genomes) and after 16 years of RHDV outbreaks. We identified several SNPs with changed allele frequencies within or close to genes potentially important for increased RHD resistance. The identified genes are known to be involved in virus infections and immune reactions or had previously been identified as being differentially expressed in healthy versus acutely RHDV-infected rabbits. Furthermore, we show in a simulation study that the allele/genotype frequency changes cannot be explained by drift alone and that several candidate genes had also been identified as being associated with surviving RHD in a different Australian rabbit population. Our unique data set allowed us to identify candidate genes for RHDV resistance that have evolved under natural conditions, and over a time span that would not have been feasible in an experimental setting. Moreover, it provides a rare example of host genetic adaptations to virus-driven selection in response to a suddenly emerging infectious disease.

The Global Distribution and Drivers of Alien Bird Species Richness.

Alien species are a major component of human-induced environmental change. Variation in the numbers of alien species found in different areas is likely to depend on a combination of anthropogenic and environmental factors, with anthropogenic factors affecting the number of species introduced to new locations, and when, and environmental factors influencing how many species are able to persist there. However, global spatial and temporal variation in the drivers of alien introduction and species richness remain poorly understood. Here, we analyse an extensive new database of alien birds to explore what determines the global distribution of alien species richness for an entire taxonomic class. We demonstrate that the locations of origin and introduction of alien birds, and their identities, were initially driven largely by European (mainly British) colonialism. However, recent introductions are a wider phenomenon, involving more species and countries, and driven in part by increasing economic activity. We find that, globally, alien bird species richness is currently highest at midlatitudes and is strongly determined by anthropogenic effects, most notably the number of species introduced (i.e., "colonisation pressure"). Nevertheless, environmental drivers are also important, with native and alien species richness being strongly and consistently positively associated. Our results demonstrate that colonisation pressure is key to understanding alien species richness, show that areas of high native species richness are not resistant to colonisation by alien species at the global scale, and emphasise the likely ongoing threats to global environments from introductions of species.

Predicting the Risk of Biological Invasions Using Environmental Similarity and Transport Network Connectedness.

Understanding the risk of biological invasions associated with particular transport pathways and source regions is critical for implementing effective biosecurity management. This may require both a model for physical connectedness between regions, and a measure of environmental similarity, so as to quantify the potential for a species to be transported from a given region and to survive at a destination region. We present an analysis of integrated biosecurity risk into Australia, based on flights and shipping data from each global geopolitical region, and an adaptation of the "range bagging" method to determine environmental matching between regions. Here, we describe global patterns of environmental matching and highlight those regions with many physical connections. We classify patterns of global invasion risk (high to low) into Australian states and territories. We validate our analysis by comparison with global presence data for 844 phytophagous insect pest species, and produce a list of high-risk species not previously known to be present in Australia. We determined that, of the insect pest species used for validation, the species most likely to be present in Australia were those also present in geopolitical regions with high transport connectivity to Australia, and those regions that were geographically close, and had similar environments.

High accuracy at low frequency: detailed behavioural classification from accelerometer data.

Accelerometers are a valuable tool for studying animal behaviour and physiology where direct observation is unfeasible. However, giving biological meaning to multivariate acceleration data is challenging. Here, we describe a method that reliably classifies a large number of behaviours using tri-axial accelerometer data collected at the low sampling frequency of 1 Hz, using the dingo (Canis dingo) as an example. We used out-of-sample validation to compare the predictive performance of four commonly used classification models (random forest, k-nearest neighbour, support vector machine, and naïve Bayes). We tested the importance of predictor variable selection and moving window size for the classification of each behaviour and overall model performance. Random forests produced the highest out-of-sample classification accuracy, with our best-performing model predicting 14 behaviours with a mean accuracy of 87%. We also investigated the relationship between overall dynamic body acceleration (ODBA) and the activity level of each behaviour, given the increasing use of ODBA in ecophysiology as a proxy for energy expenditure. ODBA values for our four 'high activity' behaviours were significantly greater than all other behaviours, with an overall positive trend between ODBA and intensity of movement. We show that a random forest model of relatively low complexity can mitigate some major challenges associated with establishing meaningful ecological conclusions from acceleration data. Our approach has broad applicability to free-ranging terrestrial quadrupeds of comparable size. Our use of a low sampling frequency shows potential for deploying accelerometers over extended time periods, enabling the capture of invaluable behavioural and physiological data across different ontogenies.

Disentangling synergistic disease dynamics: Implications for the viral biocontrol of rabbits.

European rabbits (Oryctolagus cuniculus) have been exposed to rabbit haemorrhagic disease virus (RHDV) and myxoma virus (MYXV) in their native and invasive ranges for decades. Yet, the long-term effects of these viruses on rabbit population dynamics remain poorly understood. In this context, we analysed 17 years of detailed capture-mark-recapture data (2000-2016) from Turretfield, South Australia, using a probabilistic state-space hierarchical modelling framework to estimate rabbit survival and epidemiological dynamics. While RHDV infection and disease-induced death were most prominent during annual epidemics in winter and spring, we found evidence for continuous infection of susceptible individuals with RHDV throughout the year. RHDV-susceptible rabbits had, on average, 25% lower monthly survival rates compared to immune individuals, while the average monthly force of infection in winter and spring was ~38%. These combined to result in an average infection-induced mortality rate of 69% in winter and spring. Individuals susceptible to MYXV and immune to RHDV had similar survival probabilities to those having survived infections from both viruses, whereas individuals susceptible to both RHDV and MYXV had higher survival probabilities than those susceptible to RHDV and immune to MYXV. This suggests that MYXV may reduce the future survival rates of individuals that endure initial MYXV infection. There was no evidence for long-term changes in disease-induced mortality and infection rates for either RHDV or MYXV. We conclude that continuous, year-round virus perpetuation (and perhaps heterogeneity in modes of transmission and infectious doses during and after epidemics) acts to reduce the efficiency of RHDV and MYXV as biocontrol agents of rabbits in their invasive range. However, if virulence can be maintained as relatively constant through time, RHDV and MYXV will likely continue realizing strong benefits as biocontrol agents.

Dodging silver bullets: good CRISPR gene-drive design is critical for eradicating exotic vertebrates.

Self-replicating gene drives that can spread deleterious alleles through animal populations have been promoted as a much needed but controversial 'silver bullet' for controlling invasive alien species. Homing-based drives comprise an endonuclease and a guide RNA (gRNA) that are replicated during meiosis via homologous recombination. However, their efficacy for controlling wild populations is threatened by inherent polymorphic resistance and the creation of resistance alleles via non-homologous end-joining (NHEJ)-mediated DNA repair. We used stochastic individual-based models to identify realistic gene-drive strategies capable of eradicating vertebrate pest populations (mice, rats and rabbits) on islands. One popular strategy, a sex-reversing drive that converts heterozygous females into sterile males, failed to spread and required the ongoing deployment of gene-drive carriers to achieve eradication. Under alternative strategies, multiplexed gRNAs could overcome inherent polymorphic resistance and were required for eradication success even when the probability of NHEJ was low. Strategies causing homozygotic embryonic non-viability or homozygotic female sterility produced high probabilities of eradication and were robust to NHEJ-mediated deletion of the DNA sequence between multiplexed endonuclease recognition sites. The latter two strategies also purged the gene drive when eradication failed, therefore posing lower long-term risk should animals escape beyond target islands. Multiplexing gRNAs will be necessary if this technology is to be useful for insular extirpation attempts; however, precise knowledge of homing rates will be required to design low-risk gene drives with high probabilities of eradication success.

Alien species as a driver of recent extinctions.

We assessed the prevalence of alien species as a driver of recent extinctions in five major taxa (plants, amphibians, reptiles, birds and mammals), using data from the IUCN Red List. Our results show that alien species are the second most common threat associated with species that have gone completely extinct from these taxa since AD 1500. Aliens are the most common threat associated with extinctions in three of the five taxa analysed, and for vertebrate extinctions overall.

Tests of ecogeographical relationships in a non-native species: what rules avian morphology?

The capacity of non-native species to undergo rapid adaptive change provides opportunities to research contemporary evolution through natural experiments. This capacity is particularly true when considering ecogeographical rules, to which non-native species have been shown to conform within relatively short periods of time. Ecogeographical rules explain predictable spatial patterns of morphology, physiology, life history and behaviour. We tested whether Australian populations of non-native starling, Sturnus vulgaris, introduced to the country approximately 150 years ago, exhibited predicted environmental clines in body size, appendage size and heart size (Bergmann's, Allen's and Hesse's rules, respectively). Adult starlings (n = 411) were collected from 28 localities from across eastern Australia from 2011 to 2012. Linear models were constructed to examine the relationships between morphology and local environment. Patterns of variation in body mass and bill surface area were consistent with Bergmann's and Allen's rules, respectively (small body size and larger bill size in warmer climates), with maximum summer temperature being a strongly weighted predictor of both variables. In the only intraspecific test of Hesse's rule in birds to date, we found no evidence to support the idea that relative heart size will be larger in individuals which live in colder climates. Our study does provide evidence that maximum temperature is a strong driver of morphological adaptation for starlings in Australia. The changes in morphology presented here demonstrate the potential for avian species to make rapid adaptive changes in relation to a changing climate to ameliorate the effects of heat stress.

The influence of numbers on invasion success.

The process by which a species becomes a biological invader, at a location where it does not naturally occur, can be divided into a series of sequential stages (transport, introduction, establishment and spread). A species' success at passing through each of these stages depends, in a large part, on the number of individuals available to assist making each transition. Here, we review the evidence that numbers determine success at each stage of the invasion process and then discuss the likely mechanisms by which numbers affect success. We conclude that numbers of individuals affect transport and introduction by moderating the likelihood that abundant (and widespread) species are deliberately or accidentally translocated; affect establishment success by moderating the stochastic processes (demographic, environmental, genetic or Allee) to which small, introduced populations will be vulnerable; and affect invasive spread most likely because of persistent genetic effects determined by the numbers of individuals involved in the establishment phase. We finish by suggesting some further steps to advance our understanding of the influence of numbers on invasion success, particularly as they relate to the genetics of the process.

Understanding the biological invasion risk posed by the global wildlife trade: propagule pressure drives the introduction and establishment of Nearctic turtles.

Biological invasions are a key component of human-induced global change. The continuing increase in global wildlife trade has raised concerns about the parallel increase in the number of new invasive species. However, the factors that link the wildlife trade to the biological invasion process are still poorly understood. Moreover, there are analytical challenges in researching the role of global wildlife trade in biological invasions, particularly issues related to the under-reporting of introduced and established populations in areas with reduced sampling effort. In this work, we use high-quality data on the international trade in Nearctic turtles (1999-2009) coupled with a statistical modelling framework, which explicitly accounts for detection, to investigate the factors that influence the introduction (release, or escape into the wild) of globally traded Nearctic turtles and the establishment success (self-sustaining exotic populations) of slider turtles (Trachemys scripta), the most frequently traded turtle species. We found that the introduction of a species was influenced by the total number of turtles exported to a jurisdiction and the age at maturity of the species, while the establishment success of slider turtles was best associated with the propagule number (number of release events), and the number of native turtles in the jurisdiction of introduction. These results indicate both a direct and indirect association between the wildlife trade and the introduction of turtles and establishment success of slider turtles, respectively. Our results highlight the existence of gaps in the number of globally recorded introduction events and established populations of slider turtles, although the expected bias is low. We emphasize the importance of researching independently the factors that affect the different stages of the invasion pathway. Critically, we observe that the number of traded individuals might not always be an adequate proxy for propagule pressure and establishment success.