Invasive Toads Research Articles

Impacts of artificial light on food intake in invasive toads

Artificial light at night (ALAN) is a major form of anthropogenic disturbance. ALAN attracts nocturnal invertebrates, which are a food source for nocturnal predators, including invasive species. Few studies quantify the effects of increased food availablity by ALAN on invasive vertebrate predators, and enhancement of food intake caused by ALAN may also be influenced by various environmental factors, such as proximitity to cities, moon phase, temperature, rainfall and wind speed. Revealing the potential impacts on invasive predators of ALAN-attracted invertebrates, and the influence of other factors on these effects, could provide important insights for the management of these predators. We constructed and supplied with artificial light field enclosures for invasive toads, and placed them at locations with different levels of ambient light pollution, in northeastern Australia. In addition, we determined the effect of rainfall, temperature, wind speed, and lunar phase on food intake in toads. We found that ALAN greatly increased the mass of gut contents of invasive toads compared to controls, but that the effect was increased in dark lunar phases, and when there were low ambient light pollution levels. Effects of rainfall, temperature and wind speed on food intake were comparatively weak. To avoid providing food resources to toads, management of ALAN in rural areas, and during dark lunar phases may be advisable. On the contrary, to effectively capture toads, trapping using lights as lures at such times and places should be more successful.

Rapid Shifts in the Temperature Dependence of Locomotor Performance in an Invasive Frog, Xenopus laevis, Implications for Conservation.

Temperature is a critical abiotic factor impacting all aspects of the biology of organisms, especially in ectotherms. As such, it is an important determinant of the potential invasive ability of organisms and may limit population expansion unless organisms can physiologically respond to changes in temperature either through plasticity or by adapting to their novel environment. Here, we studied the African clawed frog, Xenopus laevis, which has become invasive on a global scale. We compared adults from an invasive population of western France with individuals from two populations in the native range in South Africa. We measured the thermal dependence of locomotor performance in adults given its relevance to dispersal, predator escape, and prey capture. Our results show significant differences in the limits of the 80% performance breadth interval for endurance with the French population showing a left shift in its limits congruent with the colder climate experienced in France. The French invasive population was introduced only about 40 years ago suggesting a rapid shift in the thermal physiology. Given that all individuals were acclimated under laboratory conditions at 23°C for 2months this suggests that the invasive frogs have adapted to their new environment. These data may allow the refinement of physiologically informed species distribution models permitting better estimates of future ranges at risk of invasion.

Relative Abundance Differences of Two Invasive Toad Species on Minami-Daito and Kita-Daito Islands, Japan

Biological invasions are major threats to global biodiversity, and island ecosystems are especially vulnerable. Many previous studies have reported the presence of invasive species on islands, but relatively few studies have quantified the population status of such species. Furthermore, multiple invasive species are often introduced to the same region or island. In such case, quantifying the relative abundance of each species would provide us with significant insight into their population dynamics and potential species interactions. Rhinella marina and Bufo gargarizans miyakonis were introduced to both Minami-daito and Kita-daito Islands before 1945. Although some studies have reported their invasion and establishment, few studies have quantified their relative abundance. To reveal their relative abundance, we set 5 km line transects and counted the number of each species from 11 to 31 July 2019. We applied generalized linear models to examine the relationship between the number of individuals observed with species and environmental factors. We also applied these models to examine the relationship between the number of individuals observed with island and environmental factors. We found the relative abundance of R. marina was significantly higher than that of B. g. miyakonis on Minami-daito Island. This is the opposite pattern of 30 years ago, suggesting the population dynamics of these invasive toads is unstable on Minami-daito Island. Although B. g. miyakonis was found on both islands, no individual of R. marina was found on Kita-daito Island. The population dynamics may depend on environmental differences between islands and ecological differences between species. Future studies are needed to reveal the potential factors determining the differences in relative abundance between islands and between species.

Invasive anuran driven trophic cascade: An alternative hypothesis for recent critical weight range mammal collapses across northern Australia

Predators are fundamentally important in regulating many global ecosystems, and perturbations of predator populations through impacts by invasive species are frequently implicated in the degradation of these ecosystems. In considering recent declines of native critical weight range (35–5500 g) mammals in northern Australia, most attention has focused on predator–prey interactions between a mammalian invader, the feral cat (Felis catus), and these mammals. Little consideration has been given to the possible implications of changed reptilian predator assemblages resulting from invasion by another vertebrate, the toxic cane toad (Rhinella marina). We used reptile removal records from licenced reptile catchers in three widely spaced towns in the savannas of northern Australia to explore potential impacts of toads on apex and meso-predatory snakes and large lizards. In addition, simultaneous fauna survey data from one town with reptile removal records were used to identify cascading faunal impacts associated with toad invasion. Intervention analyses revealed empirical linkages between toad invasion, apex predator declines, meso-predator increases and declines of critical weight range mammals and other prey groups. Based on the timing and strength of intervention we postulate a novel hypothesis and supporting conceptual model linking recent mammal declines with trophic cascades following toad invasion. The conceptual model is discussed in relation to the prevailing feral cat focussed hypotheses regarding northern Australia’s dramatic small mammal declines. Future studies will need to test putative interactions and their importance so that appropriate management can be implemented to stem ongoing mammal losses.

Paradoxical population resilience of a keystone predator to a toxic invasive species

Abstract ContextThe invasive cane toad (Rhinella marina) has decimated populations of a keystone predator, the yellow-spotted monitor (Varanus panoptes), causing trophic cascades in Australian animal communities. Paradoxically, some V. panoptes populations coexist with toads. Demonstrating patterns in heterogeneous population-level impacts could reveal mechanisms that mediate individual effects, and provide managers with the ability to predict future impacts and assist in population recovery. AimsThe aim of the present study was to search for spatial patterns of population resilience of V. panoptes to invasive cane toads. MethodsPublished literature, unpublished data, reports and anecdotal information from trained herpetologists were used to test the emerging hypothesis that resilient predator populations are mainly coastal, whereas non-resilient populations are mostly inland. Key resultsPost-toad invasion data from 23 V. panoptes populations supported the idea that toad impacts on V. panoptes were heterogeneous; roughly half the populations could be designated as resilient (n=13) and half as non-resilient (n=10). Resilient populations had longer times since toad invasion than did non-resilient populations (39 versus 9 years respectively), supporting the idea that some recovery can occur. Non-resilient populations were exclusively inland (n=10), whereas resilient populations were split between inland (n=5) and coastal (n=8) populations. Resilient inland populations, however, were mainly confined to areas in which decades had passed since toad invasion. ConclusionsThe findings suggest that coastal V. panoptes populations fare much better than inland populations when it comes to surviving invading cane toads. ImplicationsUnambiguous recovery of monitor populations remains undemonstrated and will require long-term population monitoring before and after toad invasion.

Invasive toads are close to but absent from Komodo National Park

The islands of Komodo National Park in the Wallacea region are the habitats of Komodo dragon (Varanus komodoensis). Although the Wallacea islands have lower species richness compared to the other large islands in Indonesia, they are rich in endemics, and the occurrence of invasive species would therefore threatened the ecological, economic and social balance of the regions. Several papers have hinted at the possibility of the invasion of Komodo National Parks by Asian toads, a situation which would potentially affect the survival of the Komodo dragon. To detect the presence of the invansive toad Duttaphrynus melanostictus in Komodo National Park and its surroundings areas we carried out an amphibian survey using a Visual Encounter Survey method during February to April 2018. The surveyed location consisted of two main islands within Komodo National Park (Rinca island and Komodo island), Flores island (Labuan Bajo and Cumbi village) and Sumbawa island (Sape). Two species of amphibians were found in Komodo National Park (Rinca island and Komodo island), while seven species of amphibians were found across all four locations. No D. melanostictus toads were found in Flores (including in Komodo National Park), however the toad was found to be abundant in Sape (Sumbawa island).

Invasive toads adopt marked capital breeding when introduced to a cooler, more seasonal environment

Abstract Amphibians from cold and seasonal environments show marked capital breeding and sustained resource allocation to growth when compared with conspecifics from warmer, less seasonal environments. Capital breeding fuels reproduction by using only stored energy, and larger sizes and masses confer higher fecundity, starvation resistance and heat and water retention. Invasive populations act as experiments to explore how resources are allocated in novel environments. We investigated resource allocation of the southern African toad Sclerophrys gutturalis in a native source population (Durban) and in an invasive population recently (< 20 years) established in a cooler, more seasonal climate (Cape Town). After dissection, lean structural mass (bones and muscles), gonadal mass, liver mass and body fat percentage were measured in 161 native and invasive animals sampled at the beginning and the end of the breeding season. As expected, female gonadal mass decreased throughout the breeding season only in the invaded range. Thus, invasive female toads adopt a more marked capital breeding strategy than native conspecifics. Conversely, males from both populations appear to be income breeders. Also, male and female toads from the invaded range allocate more resources to growth than their native counterparts. Such a novel allocation strategy might be a response to the low temperatures, reduced rainfall and heightened seasonality encountered by the invasive population.

Feeding Habits of the Japanese Rice Frog, Fejervarya kawamurai, as an Invasive Species

Fejervarya kawamurai (Dicroglossidae) is an invasive species occurring in several populations in the Kanto region, including Fujisawa City, Kanagawa Prefecture, Japan. To estimate the ecological impacts of this frog, we investigated the food habits of invasive populations. We collected 119 individuals of F. kawamurai. Of these, 108 (90.8%) had stomach contents that included various small animals. Therefore, this invasive frog might influence the ecosystem via predation pressure on small native animals.

May the (selective) force be with you: Spatial sorting and natural selection exert opposing forces on limb length in an invasive amphibian.

Spatial sorting on invasion fronts drives the evolution of dispersive phenotypes, and in doing so can push phenotypes in the opposite direction to natural selection. The invasion of cane toads (Rhinella marina) through tropical Australia has accelerated over recent decades because of the accumulation of dispersal-enhancing traits at the invasion front, driven by spatial sorting. One such trait is the length of the forelimbs: invasion-front toads have longer arms (relative to body length) in comparison with populations 10-20years after invasion. Such a shift likely has fitness consequences: an increase of forearm length would decrease the strength with which a male could cling to a female during amplexus and so render such a male less competitive in competition for mates, compared to short-armed conspecifics. Our laboratory trials of attachment strength confirmed that males with relatively longer arms were easier to displace, and competition trials show higher duration of amplexus for males with shorter arms. Together with the sharp cline in limb length observed behind the invasion front, these results imply an opposition of selective forces: spatial sorting optimizes dispersal, but as this force wanes behind the invasion front, we see the primacy of natural selection reassert itself.

Pathogen Dynamics in an Invasive Frog Compared to Native Species.

Emerging infectious diseases threaten the survival of wildlife populations and species around the world. In particular, amphibians are experiencing population declines and species extinctions primarily in response to two pathogens, the fungus Batrachochytrium dendrobatidis (Bd) and the iridovirus Ranavirus (Rv). Here, we use field surveys and quantitative (q)PCR to compare infection intensity and prevalence of Bd and Rv across species and seasons on Jekyll Island, a barrier island off the coast of Georgia, USA. We collected oral and skin swabs for 1year from four anuran species and three families, including two native hylids (Hyla cinerea and Hyla squirella), a native ranid (Rana sphenocephala), and the invasive rain frog Eleutherodactylus planirostris. Bd infection dynamics did not vary significantly over sampling months, but Rv prevalence and intensity were significantly higher in fall 2014 compared to spring 2015. Additionally, Rv prevalence and intensity were significantly higher in E. planirostris than in the other three species. Our study highlights the potential role of invasive amphibians as drivers of disease dynamics and demonstrates the importance of pathogen surveillance across multiple time periods and species to accurately capture the infectious disease landscape.

No survival of native larval frogs in the presence of invasive Indian bullfrog Hoplobatrachus tigerinus tadpoles

Invasive amphibians have considerable negative impacts on recipient ecosystems, however, impact has been assessed for only a few species, limiting risk assessments. In particular, the impact of invasive anurans with carnivorous tadpoles have not been examined thoroughly. The Indian bullfrog (Hoplobatrachus tigerinus), native to the Indian sub-continent, is rapidly invading the Andaman archipelago, Bay of Bengal after its recent introduction. We aimed to evaluate the effect of carnivorous H. tigerinus tadpoles on two species of endemic anuran tadpoles Microhyla chakrapanii and Kaloula ghoshi, in a mesocosm experiment. Rapid predation by larval H. tigerinus resulted in no survival of endemic frog tadpoles. Survival of H. tigerinus was density-dependent. The study is timely in elucidating the impact of invasive larval H. tigerinus on native anurans and substantiates the need to manage invasive populations (or potential incursions) of the species on the Andaman archipelago and elsewhere.

Mild segregation in the breeding preferences of an invasive anuran (Discoglossus pictus) and its main native competitor (Epidalea calamita) in ephemeral ponds

Abstract The choice of breeding sites by pond-breeding anurans has notable consequences for the fitness of larvae. Hence, beyond pond typology and phenology, adults can also discriminate according to several other features, for instance to favour allotopy with potential competitors. However, the lack of shared evolutionary history might impede proper ecological differentiation with alien species during the first stages of invasions. Here, we studied several possible sources of ecological segregation between the invasive Discoglossus pictus and the native Epidalea calamita in ephemeral ponds, where the native toad hardly had competition before the arrival of the invasive frog. During spring of 2016, we periodically surveyed 69 ephemeral ponds in three areas with different invasion histories to detect the presence/absence of eggs and tadpoles of these species. Invasive D. pictus started breeding earlier than E. calamita, but differences were not significant. Similarly, there were not clear differences among areas with different invasion histories. However, we found for both species a mutual tendency to directly avoid larval syntopy at the end of the reproductive season. We also found interspecific differences in the features that both species use for pond choice, preferring the native species shallower and less vegetated ephemeral ponds. Globally however, co-occurrence was high, pointing at other processes as key to the coexistence between both species in these habitats.

Influence of a mortality trade-off on the spreading rate of cane toads fronts

We study the influence of a mortality trade-off in a nonlocal reaction-diffusion-mutation equation that we introduce to model the invasion of cane toads in Australia. This model is built off of one that has attracted attention recently, in which the population of toads is structured by a phenotypical trait that governs the spatial diffusion. We are concerned with the case when the diffusivity can take unbounded values and the mortality trade-off depends only on the trait variable. Depending on the rate of increase of the penalization term, we obtain the rate of spreading of the population. We identify two regimes, an acceleration regime when the penalization is weak and a linear spreading regime when the penalization is strong. While the development of the model comes from biological principles, the bulk of the article is dedicated to the mathematical analysis of the model, which is very technical. The upper and lower bounds are proved via the Li-Yau estimates of the fundamental solution of the heat equation with potential on Riemannian manifolds and a moving ball technique, respectively, and the traveling waves by a Leray-Schauder fixed point argument. We also present a simple method for a priori bounds.

Hydric Balance and Locomotor Performance of Native and Invasive Frogs

An animal’s physiology should be closely adapted to its environment to optimize organismal function, so physiological traits may be mismatched when animals are introduced to new locations. For introduced amphibians, mismatched traits involving hydric balance or performance across hydric states could have profound impacts on their abundance and distribution, and thus their invasion success. We examined susceptibility to dehydration in invasive Cuban treefrogs (Osteopilus septentrionalis) and two sympatric native treefrogs (Hyla spp.) in Florida, USA, by measuring rates of evaporative water loss, rates of water uptake, and sensitivity of locomotor performance to dehydration. Of the three species, Cuban treefrogs were the most susceptible to dehydration by experiencing the highest rate of evaporative water loss and lowest rate of water uptake. Green treefrogs (H. cinerea) were the most resistant to dehydration by losing water the slowest and gaining water the fastest, and squirrel treefrogs (H. squirella) were intermediate in rates of water loss and uptake. Dehydrating frogs by 20% of their fully hydrated body masses affected the locomotor performance of all species by decreasing maximum jump lengths, decreasing speed, and increasing successive jump lengths. The maximum jump lengths of Cuban treefrogs and green treefrogs were more sensitive to dehydration than those of squirrel treefrogs. Despite this sensitivity, Cuban treefrogs still outperformed both native species in maximum jump length and speed, even when controlling for body size. Consequently, the performance of dehydrated Cuban treefrogs was similar to that of fully hydrated native treefrogs. Our results suggest that Cuban treefrogs are more susceptible to dehydration and its effects than several native competitors; however, they may be able to at least partly compensate for these effects with their large body size, superior locomotor performance, and strong affinity for refugia. Our findings highlight different strategies used by frogs to maintain water balance and suggest that Cuban treefrog densities may be higher in areas with greater moisture availability and habitat complexity, including urban and densely forested areas. Native treefrogs may experience stronger competition and predation from Cuban treefrogs in these areas, which supports anecdotal reports of native frog declines.

Changes in the aquatic macroinvertebrate communities throughout the expanding range of an invasive anuran

Invasive species are among the most significant threats to biodiversity. They have direct and indirect effects on the colonized environments including the alteration of food webs structure by predation. Thus, the diet of invasive animal populations, and its effects on trophic networks, is a crucial factor that must be considered in the context of global change. In this study, we focused on the invasive population of the African clawed frog, Xenopus laevis in France, and compared the composition of the aquatic macroinvertebrate communities in colonized ponds of the core and the edge of the population range, as well as in surrounding areas. While previous studies recorded a broad diet of invertebrate and a low selectivity of prey items, they failed to identify the prey categories the most strongly affected. Here, we report a significant decrease in the proportion of nektonic macroinvertebrates in ponds occupied by X. laevis. Interestingly, this effect is not significant when evaluating the density of each taxonomic category of nektonic invertebrate separately. This result, combined with the existing literature, suggests that X. laevis preferably consumes large nektonic items first when it arrives at a new site and subsequently focuses on smaller planktonic or benthic prey after the proportion of nekton has been reduced.

Invasion of the guttural toads

The Western Cape region of South Africa is a modern Garden of Eden packed with indigenous species spread across two globally recognised biodiversity hotspots. So, when the snore-like call of invasive guttural toads (Sclerophrys gutturalis) threatening to displace native populations was first heard in Cape Town in 2000, alarm bells began ringing. Giovanni Vimercati from Stellenbosch University, South Africa, says, ‘The ability of this species to invade Cape Town is surprising’, as guttural toads are usually better suited to the more humid and warmer environments of subtropical southern Africa than the cooler, dry Mediterranean climate of the Western Cape. Yet, despite the mismatch, the population flourished. ‘As the invading population expanded, individuals would need to cope with the new climate by rapidly adapting to their drier cooler surroundings’, says Vimercati; and they have done so remarkably quickly. Concerned by the toads’ success, Vimercati and his PhD supervisors, John Measey and Sarah Davies, decided to investigate how the invaders’ ability to withstand dehydration had altered during the two decades following the occupation.Explaining that it is relatively easy to find the toads by torchlight as they congregate after dark around ponds during the breading season, Vimercati says that the main problem was the reluctance of homeowners in Cape Town and Durban to allow the scientists into their gardens. ‘They and their dogs were not always enthusiastic’, chuckles Vimercati. As soon as the toads were captured, the trio measured how dehydrated the animals were by popping them into a shallow tub of water and weighing them until they absorbed no more. Not surprisingly, the Cape Town toads were more dehydrated (∼90% hydrated) than the toads from Durban (∼95% hydrated), and when the team blew a gentle breeze over the fully hydrated animals in the lab, the two groups lost water at roughly the same rates, so the invaders had not improved their waterproofing. However, the team noticed that the Cape Town toads hunkered down more, tucking their legs in beneath their body and pulling their head down close to the ground in a bid to conserve water. The invaders were also better at reabsorbing water that had been lost; they were better equipped to cope with water losses. But how did the dehydration affect their performance?‘I spent hours running round in small circles after reluctant toads’, laughs Vimercati, as he describes chasing the dehydrated animals (90% and 80% hydration) around a small racetrack in the dead of night to find out how well the Cape Town invaders and their Durban cousins coped when they were low on water. Impressively, the invaders were more robust than their indigenous cousins, with five of the 90% hydrated animals covering distances of over 500 m, in contrast to the Durban toads, which only managed an average distance of 250 m. And when the team checked how well the animals coped with colder conditions by gently chilling them until they could no longer right themselves after toppling over, the toads from cooler Cape Town were able to return to a squatting position at temperatures down to 7.1°C, while the Durban animals were only able to recover at temperatures above 8.2°C.‘Although they've only been there for 20 years, invading toads in Cape Town are better suited than their native cousins to survive and reproduce in the new surroundings’, says Vimercati and he warns ‘These kinds of rapid adaptations may allow guttural toads to invade climates quite unlike their native conditions, making it hard to predict their potential success in new areas’.

Gut Check: Predatory Ecology of the Invasive Wrinkled Frog (Glandirana rugosa) in Hawai‘i

Invertebrates constitute the most diverse Pacific island animal lineages and have correspondingly suffered the most devastating extinction rates. Losses of native invertebrate lineages have been driven largely by ecosystem changes brought about by loss of habitat and direct predation by introduced species. Although Hawai‘i notably lacks native terrestrial reptiles and amphibians, both intentional and unintentional anthropogenic releases of herpetofauna have resulted in establishment of more than two dozen species of frogs, toads, turtles, lizards, and a snake. Despite well-known presence of nonnative predatory species in Hawai‘i, ecological impacts remain unstudied for a majority of these species. In this study, we evaluated diet of the Japanese wrinkled frog, Glandirana rugosa, an intentional biocontrol release in the Hawaiian Islands in the late nineteenth century. We collected live frogs on O‘ahu and used museum collections from both O‘ahu and Maui to determine exploited diet composition. These data were then compared with a published dietary analysis from the native range in Japan. We compiled and summarized field and museum distribution data from O‘ahu, Maui, and Kaua‘i to document current range of this species. Gut content analyses suggest that diet composition in the Hawaiian Islands is significantly different from that in its native Japan. In the native range, dominant taxonomic groups by volume were Coleoptera (beetles), Lepidoptera (moths, butterflies), and Formicidae (ants). Invasive frogs in Hawai‘i exploited mostly Dermaptera (earwigs), Amphipoda (landhoppers), and Hemiptera (true bugs). In Hawai‘i this species also exploited endemic insects (∼4% total volume, 7 genera) and snails (14 snails in three endemic genera). Our results suggest the need for more indepth assessment of ecological impacts of G. rugosa and other established herpetofauna in Hawai‘i to improve our ability to prevent and manage ecological damage and ultimately restore diverse island ecosystems.

Behavioural responses of an Australian colubrid snake (Dendrelaphis punctulatus) to a novel toxic prey item (the Cane Toad Rhinella marina)

The invasion of a toxic prey type can differentially affect closely related predator species. In Australia, the invasive Cane Toad (Rhinella marina) kills native anurophagous predators that cannot tolerate the toad’s toxins; but predators that are physiologically resistant (i.e., belong to lineages that entered Australia recently from Asia, where toads of other species are common) have been more resilient. In the current study, we examine the case of an Asian-derived predator lineage that relies on behavioural not physiological adaptations to deal with toads. Despite their Asian origins, Common Tree Snakes (Dendrelaphis punctulatus) are highly sensitive to toad toxins; yet this snake has not declined in abundance due to toads. We exposed captive (field-collected) snakes to toads of different sizes and ontogenetic stages, to quantify feeding responses and outcomes. Tree Snakes were less likely to attack toads than to attack native frogs, and rarely retained their hold on large toads. Tree Snakes ingested frogs of a wide range of body sizes but only ingested very small toads (< 1 g vs. up to 30 g for frogs). Behavioural responses were virtually identical between Tree Snakes from invaded versus yet-to-be-invaded areas, suggesting that preadaptation (from Asia) rather than adaptation (within Australia) is the key to successful utilisation of this novel but potentially toxic prey resource. Nonetheless, a previously-documented shift in relative head sizes of Tree Snakes coincident with toad invasion suggests that the ancestral behavioural tactic may have been reinforced by a recent morphological shift that further reduces maximal prey size, and hence the risk of fatal poisoning.

Not such silly sausages: Evidence suggests northern quolls exhibit aversion to toads after training with toad sausages

AbstractThe invasion of toxic cane toads (Rhinella marina) is a major threat to northern quolls (Dasyurus hallucatus) which are poisoned when they attack this novel prey item. Quolls are now endangered as a consequence of the toad invasion. Conditioned taste aversion can be used to train individual quolls to avoid toads, but we currently lack a training technique that can be used at a landscape scale to buffer entire populations from toad impact. Broad‐scale deployment requires a bait that can be used for training, but there is no guarantee that such a bait will ultimately elicit aversion to toads. Here, we test a manufactured bait – a ‘toad sausage’ – in a small captive trial, for its ability to elicit aversion to toads in northern quolls. To do this, we exposed one group of quolls to a toad sausage and another to a control sausage and compared the quolls' predatory responses when presented with a dead adult toad. Captive quolls that consumed a single toad sausage showed a reduced interest in cane toads, interacting with them for less than half the time of their untrained counterparts and showing reduced Attack behaviour. We also quantified bait uptake in the field, by both quolls and non‐target species. These field trials showed that wild quolls were the most frequent species attracted to the baits, and that approx. 61% of quolls consumed toad‐aversion baits when first encountered. Between 40% and 68% of these animals developed aversion to further bait consumption. Our results suggest that toad‐aversion sausages may be used to train wild quolls to avoid cane toads. This opens the possibility for broad‐scale quoll training with toad aversion sausages: a technique that may allow wildlife managers to prevent quoll extinctions at a landscape scale.

Invasion history alters the behavioural consequences of immune system activation in cane toads.

Acute activation of the immune system often initiates a suite of behavioural changes. These "sickness behaviours"-involving lethargy and decreased activity-may be particularly costly on invasion fronts, where evolutionary pressures on dispersal favour individuals that move large distances. We used a combination of field and laboratory studies to compare sickness behaviours of cane toads from populations differing in invasion history. To do this we stimulated immune system activation by injecting lipopolysaccharide (LPS) to mimic bacterial infection. We predicted that LPS would result in less severe sickness behaviour in toads from range-edge populations because they had undergone selection for rapid and sustained dispersal (activities in conflict with lethargy and decreased activity). Contrary to our prediction, LPS injection caused a greater reduction in dispersal-relevant traits in invasion-front individuals than in conspecifics from the range-core. Our data suggest that the rapid invasion of cane toads through tropical Australia has seen an evolutionary shift in the magnitude of sickness behaviour elicited by pathogen infection. The increased sickness behaviour among range-edge toads suggests a shift away from pathogen tolerance (seen in range-core populations) towards resistance to pathogen attack. But as a consequence, when pathogens do become successfully established, toads from invasion-front populations may have less capacity to tolerate their ill-effects.