Invasive Range Research Articles

Population genomics and genetic diversity of the invasive chrysanthemum lace bug (Corythucha marmorata) across its invasive range in Japan

The escalating global movement of alien species, facilitated by increased trade and travel, poses a pressing need to comprehend their invasive potential and the consequent ecological and economic ramifications. Despite a growing body of evidence on rapid evolutionary shifts in invasive species, comprehensive insights into the genetic variability underlying these adaptations are constrained by limited genomic resources. Understanding the role of genetic variation in the success or failure of biological invaders is thus crucial. This study focuses on the chrysanthemum lace bug, Corythucha marmorata, as a model system to investigate the interplay of genetic variation and invasion dynamics. Our analysis reveals moderate genetic structure among countries, with significant genetic differentiation observed within populations. Mitochondrial COI DNA and haplotype network analysis revealed shared haplotypes between Japan and North America, indicating recent events of introduction, while exclusive Japanese haplotypes and significant FST and GST values suggest local divergence. Phylogenetic and STRUCTURE analyses show genetic clusters unique to Japan, with populations like SAG and CER displaying higher divergence. Bottlenecks followed by divergence, as indicated by the DIYABC-RF analysis, point to a complex evolutionary history involving multiple introductions and subsequent local divergence in Japan.

An Updated Environmental Resistance Model for Predicting the Spread of Invasive Species

ABSTRACTAimPredictive models on invasive species spread can assist in identifying large‐scale invasion risk. Environmental resistance (ER) models, which predict spread based on ecological similarity to already‐invaded communities, offer one approach. However, gaps remain in understanding how different ER measurements perform across different taxa and how they can be integrated with future global change. Here, we aim to discern the primary drivers of invasion spread by comparing different ER models and then use the best models to forecast future invasion dynamics.LocationEastern US.Taxa1873 invasive plants and animals.MethodsWe developed different ER measurements, including biotic similarities among native plants in their species and phylogenetic assemblages, and functional traits, and abiotic similarities in climate, soil, and human disturbances. We obtained the best ER model for each invasive species to evaluate their potential invasion extents; and we further predicted their future range shifts under climate change.ResultsNative plant similarities provided the best proxy measure of ER for both invasive plants and animals. Invasion hotspots were identified in urban and coastal areas, and the predicted potential invasion ranges under current conditions extended from these hotspots to the neighboring areas. The invasion range for most invasives was predicted to increase under future climate change, with Arthropoda and Tracheophyta generally expanding the most among all taxa. The invasives that are predicted to expand their range in the future have already occupied larger areas than the invasives whose ranges are predicted to contract.Main ConclusionsThese results highlight the importance of maintaining diverse native communities in invasion control and raise the concern of increased invasion risk in the future. Our findings call for more efforts on invasion monitoring in areas near large cities, and increased capacity for early detection and rapid response to prevent the current invasives spreading more widely.

Optimizing survey conditions for Burmese python detection and removal using community science data

Burmese pythons (Python bivittatus) have demonstrated prolific spread and low detectability within their invasive range in Florida, USA. Consequently, programs exist which incentivize contractors to remove pythons. While surveying, contractors collect data on search effort and python captures. We examined data from South Florida Water Management District’s Python Elimination Program to determine the effect of operational and environmental covariates on two measures of survey outcome: success (i.e., probability of removing at least one python) and efficiency (i.e., the number of pythons removed per survey hour). Additionally, we assessed the spatial distribution of contractor search effort and removals. Warm temperatures (> 25 °C) improve survey outcomes, especially when surveys occur late at night and during the wet season (May–Oct). The most efficient interval for conducting surveys occurs from 20:00 to 02:00. The spatial distribution of python removals is concentrated in four regions and coincides with contractor search effort. Our results provide insights into optimizing removal efforts for invasive Burmese pythons in Florida, which may allow for increases in removal efficiency. Moreover, this study demonstrates that community science data can be used to synthesize recommendations for invasive species removal efforts.

Unraveling the Role of Ubiquitin-Conjugating Enzyme UBE2T in Tumorigenesis: A Comprehensive Review

Ubiquitin-conjugating enzyme E2 T (UBE2T) is a crucial E2 enzyme in the ubiquitin-proteasome system (UPS), playing a significant role in the ubiquitination of proteins and influencing a wide range of cellular processes, including proliferation, differentiation, apoptosis, invasion, and metabolism. Its overexpression has been implicated in various malignancies, such as lung adenocarcinoma, gastric cancer, pancreatic cancer, liver cancer, and ovarian cancer, where it correlates strongly with disease progression. UBE2T facilitates tumorigenesis and malignant behaviors by mediating essential functions such as DNA repair, apoptosis, cell cycle regulation, and the activation of oncogenic signaling pathways. High levels of UBE2T expression are associated with poor survival outcomes, highlighting its potential as a molecular biomarker for cancer prognosis. Increasing evidence suggests that UBE2T acts as an oncogene and could serve as a promising therapeutic target in cancer treatment. This review aims to provide a detailed overview of UBE2T’s structure, functions, and molecular mechanisms involved in cancer progression as well as recent developments in UBE2T-targeted inhibitors. Such insights may pave the way for novel strategies in cancer diagnosis and treatment, enhancing our understanding of UBE2T’s role in cancer biology and supporting the development of innovative therapeutic approaches.

Life-history traits of the invasive and biggest European freshwater fish, the wels catfish (Silurus glanis) show high potential for colonisation in Southern Europe

Context The invasive wels catfish is spreading to many European waterbodies and is the subject of controversy concerning its environmental impact. Aims The objective was to investigate its life-history traits (growth and reproduction) for the first time in southern France. Methods A culling action was used to assess the key life-history traits, using sections of pectoral spines for age and growth estimations, and gonad macroscopic examination for the reproduction parameters. Key results The biggest individual was a 227-cm male. The age was accurately estimated from clear translucent marks on spines, with a maximum of 13 years for both sexes. The growth appeared to be extremely rapid and was the highest at old ages recorded from both the native and the invasive distribution range. The length and age at first sexual maturity, 70.1 cm for 4–5-year-old females, and 54.1 cm for 2–3-year-old males, were the lowest recorded in Europe, indicating an early maturity. Conclusions The life-history parameters (rapid growth, early maturation, high fecundity) showed a very high potential for adaptation and colonisation. Implications The cost and management required to regulate the species appear not easily feasible, particularly when combined with its high growth rate.

Antennal sensory array in the Argentine ant, Linepithema humile, and two carpenter ants, Camponotus mus and Camponotus aethiops

Ants play a crucial role in both natural settings, impacting ecosystem functions, and in human-altered environments, where they can potentially cause harm. The Argentine ant, Linepithema humile, is recognized globally as an important invasive species, known for its ability to colonize diverse habitats and causing significant ecological and economic damage. In contrast, species of the Camponotus genus, while sharing similar food habits, typically have more restricted ranges and are also highly adapted to human-modified environments. This study serves as a foundational investigation into the antennal morphology of L. humile and two Camponotus species—one native and one from the invasive range of L. humile. We employed a systematic sampling method to analyse the distribution and relative abundance of chaetic, basiconic, and trichoidea sensilla along the last antennomere. Our results indicate that Camponotus and L. humile have similar proportions of the sensilla analysed, with chaetic and basiconic sensilla increasing towards the tip, while trichoidea sensilla tended to decrease. Notably, both native species of Argentina, L. humile and Camponotus mus, exhibited significantly higher abundances of chaetic and trichoidea curvata sensilla compared to C. aethiops from France. This study establishes a framework for future research aimed at exploring the chemosensory responses associated with these sensilla, paving the way for deeper insights into how these ants interact with their environment.

Live Fast, Die Young: Life History Traits of an Apex Predator Exacerbate the Ecological Impact of a Toxic Invader.

We studied a population of large varanid lizards (yellow-spotted monitors Varanus panoptes) on a floodplain in tropical Australia. Growth records from radio-tracked lizards show that despite their large adult body sizes (to > 7 kg in males), these lizards attained sexual maturity at less than 1 year of age and rarely lived for more than 2 years (females) or 4 years (males), even before mortality increased due to the arrival of toxic cane toads (Rhinella marina). This is a "faster" life history than has been reported for other species of large monitors. Growth was especially rapid in males during the wet season. The low survivorship prior to toad invasion was due to predation by pythons; communal nesting by female varanids may render them especially vulnerable. The life history of yellow-spotted monitors requires high feeding rates, favouring the evolution of "risky" tactics such as consuming novel prey items (such as cane toads); and the combination of high abundance (> 20 adult lizards per square kilometre) and high feeding rates (> 9.9 kg of prey per lizard per annum) means that these giant lizards play a critical role in energy and nutrient flow within the floodplain ecosystem. As a result, foodwebs with the yellow-spotted monitor as an apex predator are more vulnerable to disruption by cane toads than is the case in other parts of the toad's invasive range, where the varanid species affected by toads have "slower" life histories.

Urbanization and environmental variation drive phenological changes in the spotted lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae)

Abstract The spotted lanternfly (Lycorma delicatula) invaded the USA in 2014. The population has grown into the millions and spread across multiple states, primarily in the north-east but extending into the midwest. We analysed nearly 20 000 records of spotted lanternflies from the citizen-science platform iNaturalist across all reported locations in the USA to explore spatiotemporal patterns of activity and abundance as the invasion progresses. Observations on iNaturalist are consistent with reports of rapid exponential growth in the early years of the invasion. However, in the oldest parts of the invasive range, abundance exhibits logarithmic growth suggestive of reaching carrying capacity in these regions. Since 2015, observed activity has shifted earlier each year and life-cycle stages have lengthened concurrent with a general northern expansion. Activity patterns were correlated with urbanization generally, and earlier activity was associated with higher temperatures in both urban and non-urban locations. Together, these findings suggest that urbanization, and the urban heat island in particular, could facilitate invasion into colder climates and beyond predictions based on current occupancy. Understanding how life-cycle timing is shifting as the invasion progresses, in addition to the environmental factors shaping these changes, underscores the importance of integrating evolutionary ecology into invasion forecasts.

Population Genetics and Invasion History of the European Starling Across Aotearoa New Zealand.

The expansion of human settlements over the past few centuries is responsible for an unprecedented number of invasive species introductions globally. An important component of biological invasion management is understanding how introduction history and postintroduction processes have jointly shaped present-day distributions and patterns of population structure, diversity and adaptation. One example of a successful invader is the European starling (Sturnus vulgaris), which was intentionally introduced to numerous countries in the 19th century, including Aotearoa New Zealand, where it has become firmly established. We used reduced representation sequencing to characterise the genetic population structure of the European starling in New Zealand, comparing it to that present in sampling locations in the native range and invasive Australian range. The population structure and genetic diversity patterns we found suggested restricted gene flow from the majority of New Zealand to the northmost sampling location (Auckland). We also profiled genetic bottlenecks and shared outlier genomic regions, which supported historical accounts of translocations between both Australian subpopulations and New Zealand, and provided evidence of which documented translocation events were more likely to have been successful. Using these results as well as historic demographic patterns, we demonstrate how genomic analysis complements even well-documented invasion histories to better understand invasion processes, with direct implications for understanding contemporary gene flow and informing invasion management.

Threshold Concentrations of Ions in the Environment Determining the Borders of the Invasive Species Dreissena polymorpha Range in Fresh Waterbodies

Threshold Concentrations of Ions in the Environment Determining the Borders of the Invasive Species Dreissena polymorpha Range in Fresh Waterbodies

Global invasion history with climate-related allele frequency shifts in the invasive Mediterranean fruit fly (Diptera, Tephritidae: Ceratitis capitata)

The Mediterranean fruit fly (Ceratitis capitata) is a globally invasive species and an economically significant pest of fruit crops. Understanding the evolutionary history and local climatic adaptation of this species is crucial for developing effective pest management strategies. We conducted a comprehensive investigation using whole genome sequencing to explore (i) the invasion history of C. capitata with an emphasis on historical admixture and (ii) local climatic adaptation across African, European, Central, and South American populations of C. capitata. Our results suggest a stepwise colonization of C. capitata in Europe and Latin America in which Mediterranean and Central American populations share an ancestral lineage. Conversely, South American invasion history is more complex, and our results partly suggest an old secondary invasion into South America from Europe or a colonization of South America directly from Africa, followed by admixture with an European lineage. Throughout its invasive range, C. capitata is challenged with diverse climatic regimes. A genome wide association study identified a relationship between allele frequency changes and specific bioclimatic variables. Notably, we observed a significant allele frequency shift related to adaptation to cold stress (BIO6), highlighting the species’ ability to rapidly adapt to seasonal variations in colder climates.

A quantitative and systematic analysis of Anopheles stephensi bionomics and control approaches

Anopheles stephensi is a mosquito endemic to South Asia and the Arabian Peninsula that has recently been detected in eight African countries, posing a significant threat to global malaria control efforts. A challenge with An. stephensi is that it requires unique surveillance and control tools when compared to other malaria vectors. Through a systematic literature review, we investigated the efficacy of trapping methods and controls for An. stephensi mosquitoes, with a focus on studies of its behavior and biology. Data from 83 articles (native range: Afghanistan, India, Iran, Iraq, Pakistan, and Qatar; invasive range: Djibouti, Ethiopia, Sri Lanka, Saudi Arabia, and Sudan) met our study inclusion criteria. Data from these studies revealed that using host-seeking animal baited traps increased the number of mosquitoes collected per trap per day in the native range when compared to host-seeking human baited traps. However, these differences were not present in data collection rate assessments from the invasive range. We also found that An. stephensi equally used a large variety of breeding habitats in the native range, but that it tended to prefer water reservoirs and wastewater in the invasive range. Finally, we found that temephos, fenthion, Bacillus thuringiensis israelensis, and Beauveri bassiana were more effective at reducing larvae in their native range compared to the approaches found in our systematic literature search, but the relative effectiveness of these approaches in the invasive range was less clear. Understanding proven historical surveillance and control approaches is essential to the advancement of invasive An. stephensi mitigation efforts, but continued investigations in the invasive range are critical to reducing the impacts of malaria morbidity and mortality.

Rising temperatures may increase fungal epizootics in northern populations of the invasive spongy moth in North America

Insect pest species are generally expected to become more destructive with climate change because of factors such as weakened host tree defences during droughts and increased voltinism under rising temperatures; however, responses will vary by species due to a variety of factors, including altered interactions with their natural enemies. Entomopathogens are a substantial source of mortality in insects, but the likelihood of epizootics can depend strongly on climatic conditions. Previous research indicates that rates of infection of the spongy moth (Lymantria dispar) by its host-specific fungal pathogen, Entomophaga maimaiga, increase with environmental moisture and decrease as temperatures rise. High temperatures may have direct and indirect (due to the associated drying) effects on the fungus, but the interactive effects between temperature and moisture level on larval infection are unclear. Here, we test the hypothesis that warmer, drier conditions will decrease rates of infection of spongy moth larvae by E. maimaiga. We evaluated the effects of precipitation and temperature on larval mortality caused by E. maimaiga with a manipulative field experiment, conducted in one of the northernmost and coldest parts of the spongy moth’s non-native range in North America. We caged laboratory-reared spongy moth larvae in experimentally warmed open-air forest plots, exposing the larvae to soil inoculated with E. maimaiga resting spores during two consecutive trials. Caged larvae were exposed to three temperature treatments — ambient, 1.7 °C above ambient and 3.4 °C above ambient — and either supplemental precipitation (+173 mm per trial) or ambient precipitation. Opposite to our hypothesis, there was no significant effect of supplemental precipitation, nor an interaction between precipitation and temperature. There was, however, a significant positive effect of increasing temperature on the number of larvae infected. On average, in each respective trial, larval infection increased by 44% and 50% under the elevated temperature treatments compared to ambient temperature. Experimental warming may have increased infections because ambient temperatures at the field site were suboptimal for fungal germination. The results from this experiment suggest that, in colder portions of the spongy moth’s invasive range, increasing temperatures due to climate change may enhance the ability of E. maimaiga to help control populations of the spongy moth.

Intra-species quantification reveals differences in activity and sleep levels in the yellow fever mosquito, Aedes aegypti.

Aedes aegypti is an important mosquito vector of human disease with a wide distribution across the globe. Climatic conditions and ecological pressure drive differences in the biology of several populations of this mosquito species, including blood-feeding behaviour and vector competence. However, no study has compared activity and/or sleep among different populations/lineages of Ae. aegypti. Having recently established sleep-like states in three mosquito species with observable differences in timing and amount of sleep among species, we investigated differences in activity and sleep levels among 17 Ae. aegypti lines drawn from both its native range in Africa and its invasive range across the global tropics. Activity monitoring indicates that all the lines show consistent diurnal activity, but significant differences in activity level, sleep amount, number of sleep bouts and bout duration were observed among the lines. The variation in day activity was associated with differences in host preference and ancestry for the lineages collected in Africa. This study provides evidence that the diurnal sleep and activity profiles for Ae. aegypti are consistent, but there are significant population differences for Ae. aegypti sleep and activity levels and interactions with host species may significantly impact mosquito activity.

Dissecting the invasion history of Spotted-Wing Drosophila (Drosophila suzukii) in Portugal using genomic data

BackgroundThe invasive pest Spotted-Wing Drosophila, Drosophila suzukii (Matsumura), causes extensive damage and production losses of soft-skinned fruits. Native to Asia, the species has now spread worldwide, with first reports in Portugal in 2012. In this study, we focus on the genomic signatures of the recent Portuguese invasion, in the context of worldwide patterns established in previous works. We analyzed whole genome pool sequencing data from three Portuguese populations (N = 240) sampled in 2019 and 2021.ResultsThe correlation of allele frequencies suggested that Portuguese populations are related to South European ones, indicating a Mediterranean invasion route. While two populations exhibited levels of genetic variation comparable to others in the invasive range, a third showed low levels of genetic diversity, which may result from a recent colonization of the region. Genome-wide analyses of natural selection identified ten genes previously associated with D. suzukii’s invasive capacity, which may have contributed to the species’ success in Portugal. Additionally, we pinpointed six genes evolving under positive selection across Portuguese populations but not in European ones, which is indicative of local adaptation. One of these genes, nAChRalpha7, encodes a nicotinic acetylcholine receptor, which are known targets for insecticides widely used for D. suzukii control, such as neonicotinoids and spinosyns. Although spinosyn resistance has been associated with mutations in the nAChRalpha6 in other Drosophila species, the putative role of nAChRalpha7 in insecticide resistance and local adaptation in Portuguese D. suzukii populations encourages future investigation.ConclusionsOur results highlight the complex nature of rapid species invasions and the role of rapid local adaptation in determining the invasive capacity of these species.

Germination ecology of Phytolacca americana L. in its invasive range

AbstractInvasive species are a worldwide problem, and the germination process is useful to understand the characteristics that allow alien species to be invasive and their projected response to global climate change. Phytolacca americana is one of the most invasive plants in Italy, and we tested, for different populations (from different altitudes) how light, temperature, and cold stratification affect seed germination. According to our analyses, P. americana produces an exceptionally high number of seeds that may potentially survive in soil for extended periods. Seeds subjected to cold stratification and exposed to warmer temperatures, both in light and darkness, exhibited faster germination, with a higher germination rate and a shorter T50. Seeds collected at the highest elevation (337 m a.s.l.) have germinated in all tested thermal conditions, albeit with a lower germination percentage and a longer T50 compared with seeds collected at lower elevations (5 and 50 m a.s.l.) and tested under warm and moderate temperatures. In general, P. americana seems to adapt to moderate‐warm temperatures (at low elevations) and moderate‐cool temperatures (at highest elevations) and appears to increase germination with seeds exposed to cold stratification. These results, in a scenario of climate change, show that the invasiveness of P. americana may increase in the future.

Stable isotope analysis reveals fish juveniles as a temporal main resource consumed by invasive pumpkinseed (Lepomis gibbosus)

AbstractThe pumpkinseed Lepomis gibbosus (Linnaeus, 1758) is a small centrarchid fish species from North America that has invaded most European basins, with pronounced expected impacts. Analyses of pumpkinseed diet in its invasive range using gut content analysis (GCA) show macrozoobenthos as the most common dietary item, suggesting a competitive effect on native fish communities. Our study uses a combination of GCA and stable isotope analysis (SIA) to document pumpkinseed diet at two sites in its invaded range and relates pumpkinseed diet preferences with parasitic load. SIA revealed juvenile fish as a major prey item at one of the sites (63 and 50% of the diet of small and the large fish), while GCA showed pumpkinseed preying mostly on macroinvertebrates (chironomids, gastropods, Ephemeroptera, and Zygoptera larvae) at both sites. While infrequent infection by trophically transmitted parasitic nematodes could be related to low consumption of zooplankton, substantial infection by metacercariae of Posthodiplostomum centrarchi Hoffman1958 appears to reflect relatively high consumption rates of its intermediate host, physid snails. Using SIA allowed to demonstrate that pumpkinseed feeding in its non-native range can be based on piscivory, emphasising the need for combining multiple methods when studying the impact of non-native species on food webs.

Genetic diversity and phylogeography of the smooth cordgrass Spartina alterniflora and its invasion into Korean coasts

The smooth cordgrass, Spartina alterniflora Loisel, is an aggressive invasive species that significantly impacts coastal ecosystems worldwide. Native to the eastern United States, it has rapidly spread along East Asian coasts and was unintentionally introduced into Korea, leading to the devastation of native ecosystems. This study examines the population genetic structure and invasion pathway of S. alterniflora along Korean coasts using chloroplast DNA (cpDNA) fragments and nuclear ITS. Our results revealed that the S. alterniflora population in Korea primarily consists of two geographically isolated haplotypes (C1 and C4). Furthermore, two individuals were found to have haplotype N, potentially a newly discovered haplotype in this study. The haplotypes C1 and C4 are widely distributed in both the native population and the introduced population in East Asia. Thus, the presence of these two haplotypes in different localities in Korea suggests multiple invasion events. The phylogenetic tree from the nuclear ITS showed no significant genetic variation between regions. Comparisons of the cpDNA data of this study with the available GenBank data from the native range in the U.S. and the invasive range in East Asia (China and Japan) revealed that the East Asian population (China, Japan, and Korea) is nearly homogeneous (AMOVA; Fst = 0.06871, p = 0.5). Our findings suggest that the C1 and C4 haplotypes might have been introduced into Korea at least two times, possibly via natural dispersal and/or transport vectors. This emphasizes the importance of strengthening coastal management to prevent further spread.

Predicting the Invasion Range of the Common Myna, Acridotheres tristis Linnaeus, 1766 in Egypt under Climate Change

The common myna bird (Acridotheres tristis Linnaeus, 1766) is widely recognized as one of the most formidable invasive avian species globally. The bird poses significant challenges due to its ability to outcompete a variety of native cavity-nesting birds. Additionally, the common myna is a notable agricultural pest and a substantial threat to indigenous biodiversity. The current study is focused on understanding the distribution pattern of the common myna (Acridotheres tristis Linnaeus, 1766) in Egypt and the significant favorable conditions to predict the invasion scale of the bird to the Egyptian fauna. To determine the environmental variables influencing the invasion range of the common myna in Egypt, a Species Distribution Model (SDM) was employed. The current work documented 117 invasion sites of the species from February to December 2023. The predicted habitats are mainly concentrated close to the Nile Delta of Egypt, the Suez Canal region, North and South Sinai, in addition to scattered areas on the Red Sea coast, along the riverbanks of Upper Egypt, in addition to a few northwestern areas of the Western Desert. The most significant environmental factors affecting the establishment were the Minimum Temperature of the Coldest Month, the Mean Temperature of the Coldest Quarter, and Elevation. The current invaded areas comprise about 0.8% of Egypt (8240 km2 out of roughly one million km2). We found that this is significant and of concern due to the expectation of increasingly favourable conditions due to global warming; this will turn this invasive species into a real threat to Egyptian ecosystems due to its aggressive competition with native cavity-nesting birds, its impact as an agricultural pest, and its potential to disrupt local biodiversity.

Tracking the invasive and euryhaline pikeperch Sander lucioperca in the lower River Thames using acoustic telemetry indicates no movements into areas of relatively high salinity.

Native to Central and Eastern Europe, the euryhaline pikeperch Sander lucioperca can acclimatize to elevated salinity levels (e.g., up to 30‰), but it remains unknown whether their invasive populations use this ability to inhabit and/or disperse through brackish waters, such as estuaries and inshore areas. To test whether invasive pikeperch show a propensity to move into areas of relatively high salinity, their spatial use and movement patterns (e.g., home range, distances moved, and movement rates) were assessed using acoustic telemetry in the upper River Thames estuary, southeast England. Analyses revealed that individual pikeperch were capable of moving relatively long distances in a short time (e.g., speeds up to 70 m min-1), with movement patterns associated more with tidal state and elevation at the water surface (both assumed to relate to changes in salinity) than diurnal changes. There were no recorded movements of any pikeperch into the more saline, downstream waters of the estuary where salinity levels were recorded to over 40‰, with the mean salinity in the most downstream area where pikeperch were detected being 1.39‰ (range of logger: 1.22-1.71). The results suggest that these pikeperch did not use high salinity waters when less saline waters were available, and thus the risk that they will use to move through high salinity areas to expand their invasive range appears low. Accordingly, efforts to minimize risks of the further dispersal of invasive pikeperch populations can focus on control and containment programmes within fresh waters.