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Richard Shine - One of the best experts on this subject based on the ideXlab platform.
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evolutionary shifts in anti predator responses of invasive cane Toads rhinella marina
Behavioral Ecology and Sociobiology, 2017Co-Authors: Cameron M Hudson, Gregory P Brown, Richard ShineAbstract:A potential prey item’s response to encountering a predator depends on aspects of the predator (e.g., its locomotor capacity), the local environment (e.g., proximity to shelter) and the physiological state of the prey item, but in addition, anti-predator tactics also vary geographically among different populations within wide-ranging species. Using standardised trials, we tested responses of cane Toads (Rhinella marina) to being placed on a laboratory runway and encouraged to flee. Overall, the Toads least capable of rapid locomotion were the ones most likely to respond to simulated predator attack by exuding toxins rather than attempting to escape. A toad’s willingness to move down the runway and its propensity to exude toxin from the parotoid glands rather than fleeing were repeatable in successive trials and influenced by the animal’s location of origin, morphology, previous experience, and parentage. We found that specimens from Australia were more willing to flee than were those from the native range (French Guiana) or Hawai’i; larger Toads, and those with relatively longer legs, were more willing to flee; captive-raised Toads were less willing to flee and more willing to exude toxin. Captive-raised offspring resembled their wild-caught parents both in propensity to run and in propensity to exude toxin. Thus, geographic divergence among cane toad populations in anti-predator responses reflects a complex combination of processes, including both developmental plasticity and heritability. The process of colonising novel environments exposes an organism to a host of different predators that exert selection on morphology, behaviour and physiology. Over time, this can lead to the evolution of novel phenotypes that are adapted to local conditions. Anthropogenically facilitated biological invasions provide a unique opportunity to study how species respond to colonisation of new environments. Here, we studied geographic variation in cane toad (Rhinella marina) anti-predator behaviours from a range of locations (including invasive and native populations) using standardised trials. Our results suggest that invasive Australian cane Toads have undergone a shift in their anti-predator response, becoming more willing to flee than are conspecifics from other areas. Location of origin, morphology, prior experience and parentage all played a role in shaping a toad’s anti-predator response, suggesting that the behaviour represents a combination of plastic and heritable variation.
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locomotor performance of cane Toads differs between native range and invasive populations
Royal Society Open Science, 2017Co-Authors: Georgia K Kosmala, Gregory P Brown, Keith A Christian, Richard ShineAbstract:Invasive species provide a robust opportunity to evaluate how animals deal with novel environmental challenges. Shifts in locomotor performance—and thus the ability to disperse—(and especially, the degree to which it is constrained by thermal and hydric extremes) are of special importance, because they might affect the rate that an invader can spread. We studied cane Toads ( Rhinella marina ) across a broad geographical range: two populations within the species9 native range in Brazil, two invasive populations on the island of Hawai9i and eight invasive populations encompassing the eastern, western and southern limits of the toad invasion in Australia. A toad9s locomotor performance on a circular raceway was strongly affected by both its temperature and its hydration state, but the nature and magnitude of those constraints differed across populations. In their native range, cane Toads exhibited relatively low performance (even under optimal test conditions) and a rapid decrease in performance at lower temperatures and hydration levels. At the other extreme, performance was high in Toads from southern Australia, and virtually unaffected by desiccation. Hawai9ian Toads broadly resembled their Brazilian conspecifics, plausibly reflecting similar climatic conditions. The invasion of Australia has been accompanied by a dramatic enhancement in the Toads9 locomotor abilities, and (in some populations) by an ability to maintain locomotor performance even when the animal is cold and/or dehydrated. The geographical divergences in performance among cane toad populations graphically attest to the adaptability of invasive species in the face of novel abiotic challenges.
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eliciting conditioned taste aversion in lizards live toxic prey are more effective than scent and taste cues alone
Integrative Zoology, 2017Co-Authors: Georgia Wardfear, David Pearson, Jonathan K Webb, Jai Thomas, Richard ShineAbstract:Conditioned taste aversion (CTA) is an adaptive learning mechanism whereby a consumer associates the taste of a certain food with symptoms caused by a toxic substance, and thereafter avoids eating that type of food. Recently, wildlife researchers have employed CTA to discourage native fauna from ingesting toxic cane Toads (Rhinella marina), a species that is invading tropical Australia. In this paper, we compare the results of 2 sets of CTA trials on large varanid lizards (“goannas,” Varanus panoptes). One set of trials (described in this paper) exposed recently-captured lizards to sausages made from cane toad flesh, laced with a nausea-inducing chemical (lithium chloride) to reinforce the aversion response. The other trials (in a recently-published paper, reviewed herein) exposed free-ranging lizards to live juvenile cane Toads. The effectiveness of the training was judged by how long a lizard survived in the wild before it was killed (fatally poisoned) by a cane toad. Both stimuli elicited rapid aversion to live Toads, but the CTA response did not enhance survival rates of the sausage-trained goannas after they were released into the wild. In contrast, the goannas exposed to live juvenile Toads exhibited higher long-term survival rates than did untrained conspecifics. Our results suggest that although it is relatively easy to elicit short-term aversion to toad cues in goannas, a biologically realistic stimulus (live Toads, encountered by free-ranging predators) is most effective at buffering these reptiles from the impact of invasive toxic prey.
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Using genetic data to predict the vulnerability of a native predator to a toxic invader
Endangered Species Research, 2016Co-Authors: Richard Shine, Supen Wang, George Madani, Kyle Armstrong, Libiao ZhangAbstract:Australia has no native toad species, and as a consequence, many Australian pre - dators lack resistance to the toxins of the invasive cane toad Rhinella marina, and die if they ingest one of these Toads. Resistance is conferred by a small and consistent genetic change, so genetic data can provide a rapid, non-invasive way to clarify the vulnerability of as-yet-unstudied taxa. To evaluate the hypothesis that a recent decline of ghost bat Macroderma gigas populations in tropical Australia is due to ingestion of cane Toads, we sequenced the H1-H2 extracellular domain of the sodium-potassium-ATPase. Two anuran-eating Asian relatives of the Australian species possess the genes that confer bufotoxin resistance, but the ghost bat does not. Like varanid lizards (major victims of the toad invasion), Australian ghost bats appear to have lost their physiological resistance to toad toxins but retained generalist foraging behaviours, potentially including a readiness to attack Toads as well as frogs. Our genetic data suggest that cane Toads may imperil populations of this iconic predator, and detailed behavioural and ecological studies are warranted.
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Toads in the backyard: why do invasive cane Toads (Rhinella marina) prefer buildings to bushland?
Population Ecology, 2016Co-Authors: Edna González-bernal, Gregory P Brown, Matthew J. Greenlees, Richard ShineAbstract:Like many invasive species, cane Toads (Rhinella marina) in Australia concentrate in the disturbed habitats created by human activity, rather than in pristine areas. We surveyed cane Toads in the wet–dry tropics of the Northern Territory to assess the abundances, body sizes, sexes, behaviour, hydration state and feeding rates of Toads around buildings compared to those in areas remote from buildings, and conducted experimental trials to assess the effects of building-related variables (lights and increased toad densities) on the foraging success of Toads. Toads around buildings were smaller than bushland conspecifics, and adult sex-ratios were female-biased. Toads were more sedentary around buildings than in the bush, but their feeding rates (based on direct observations and faeces production post-capture) were similar. That similarity, despite twofold-higher densities of competing Toads around building, reflected the strong enhancement of feeding rates due to artificial lights attracting insects (in our experimental trials, a threefold increase regardless of the number of competing Toads). Toads collected from around buildings were apparently in better hydric condition. Thus, access to water also may attract Toads to buildings. The relative scarcity of adult male Toads around buildings likely reflects waterbody-centred reproductive activities, whereas the concentration of females and juveniles around buildings is driven largely by access to the insects attracted by artificial light. We conclude that buildings enhance the persistence of cane toad populations and may facilitate their spread.
Jonathan K Webb - One of the best experts on this subject based on the ideXlab platform.
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a trophic cascade initiated by an invasive vertebrate alters the structure of native reptile communities
Global Change Biology, 2020Co-Authors: Benjamin Feit, Tim Dempster, Tim S Jessop, Jonathan K Webb, Mike LetnicAbstract:Invasive vertebrates are frequently reported to have catastrophic effects on the populations of species which they directly impact. It follows then, that if invaders exert strong suppressive effects on some species then other species will indirectly benefit due to ecological release from interactions with directly impacted species. However, evidence that invasive vertebrates trigger such trophic cascades and alter community structure in terrestrial ecosystems remains rare. Here, we ask how the cane toad, a vertebrate invader that is toxic to many of Australia's vertebrate predators, influences lizard assemblages in a semi-arid rangeland. In our study area, the density of cane Toads is influenced by the availability of water accessible to Toads. We compared an index of the abundance of sand goannas, a large predatory lizard that is susceptible to poisoning by cane Toads and the abundances of four lizard families preyed upon by goannas (skinks, pygopods, agamid lizards and geckos) in areas where cane Toads were common or rare. Consistent with the idea that suppression of sand goannas by cane Toads initiates a trophic cascade, goanna activity was lower and small lizards were more abundant where Toads were common. The hypothesis that suppression of sand goannas by cane Toads triggers a trophic cascade was further supported by our findings that small terrestrial lizards that are frequently preyed upon by goannas were more affected by toad abundance than arboreal geckos, which are rarely consumed by goannas. Furthermore, the abundance of at least one genus of terrestrial skinks benefitted from allogenic ecosystem engineering by goannas where Toads were rare. Overall, our study provides evidence that the invasion of ecosystems by non-native species can have important effects on the structure and integrity of native communities extending beyond their often most obvious and frequently documented direct ecological effects.
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Not such silly sausages: Northern quolls exhibit aversion to Toads after training with toad sausages
2017Co-Authors: Naomi Indigo, Jonathan K Webb, James G. Smith, Ben L. PhillipsAbstract:The 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, 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 predatory responses when presented with a dead adult toad. Captive quolls that consumed a single toad sausage showed substantially reduced interest in cane Toads, interacting with them for less than half the time of their untrained counterparts and showing substantially 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 approximately 61% of quolls consumed toad-aversion baits when first encountered. Between 40-68% of these animals developed aversion to further bait consumption. Our results suggest that toad-aversion sausages can 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.
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eliciting conditioned taste aversion in lizards live toxic prey are more effective than scent and taste cues alone
Integrative Zoology, 2017Co-Authors: Georgia Wardfear, David Pearson, Jonathan K Webb, Jai Thomas, Richard ShineAbstract:Conditioned taste aversion (CTA) is an adaptive learning mechanism whereby a consumer associates the taste of a certain food with symptoms caused by a toxic substance, and thereafter avoids eating that type of food. Recently, wildlife researchers have employed CTA to discourage native fauna from ingesting toxic cane Toads (Rhinella marina), a species that is invading tropical Australia. In this paper, we compare the results of 2 sets of CTA trials on large varanid lizards (“goannas,” Varanus panoptes). One set of trials (described in this paper) exposed recently-captured lizards to sausages made from cane toad flesh, laced with a nausea-inducing chemical (lithium chloride) to reinforce the aversion response. The other trials (in a recently-published paper, reviewed herein) exposed free-ranging lizards to live juvenile cane Toads. The effectiveness of the training was judged by how long a lizard survived in the wild before it was killed (fatally poisoned) by a cane toad. Both stimuli elicited rapid aversion to live Toads, but the CTA response did not enhance survival rates of the sausage-trained goannas after they were released into the wild. In contrast, the goannas exposed to live juvenile Toads exhibited higher long-term survival rates than did untrained conspecifics. Our results suggest that although it is relatively easy to elicit short-term aversion to toad cues in goannas, a biologically realistic stimulus (live Toads, encountered by free-ranging predators) is most effective at buffering these reptiles from the impact of invasive toxic prey.
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predation on invasive cane Toads rhinella marina by native australian rodents
Journal of Pest Science, 2015Co-Authors: Michael R. Crossland, Jonathan K Webb, Elisa Cabreraguzman, David Pearson, Richard ShineAbstract:The success of an invasive species can be reduced by biotic resistance from the native fauna. For example, an invader that is eaten by native predators is less likely to thrive than one that is invulnerable. The ability of invasive cane Toads (Rhinella marina) to spread through Australia has been attributed to the toad's potent defensive chemicals that can be fatal if ingested by native snakes, lizards, marsupials and crocodiles. However, several taxa of native insects and birds are resistant to cane toad toxins. If native rodents are also capable of eating Toads (as suggested by anecdotal reports), these large, abundant and voracious predators might reduce toad numbers. Our field observa- tions and laboratory trials confirm that native rodents (Melomys burtoni, Rattus colletti and Rattus tunneyi) readily kill and consume cane Toads (especially small Toads), and are not overtly affected by toad toxins. Captive rodents did not decrease their consumption of Toads over successive trials, and ate Toads even when alternative food types were available. In combination with anecdotal reports, our data suggest that rodents (both native and invasive) are predators of cane Toads in Australia. Despite concerns about the decline of rodents following the invasion of Toads, our data suggest that the species we studied are not threatened by Toads as toxic prey, and no specific conser- vation actions are required to ensure their persistence.
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why does vulnerability to toxic invasive cane Toads vary among populations of australian freshwater crocodiles
Animal Conservation, 2013Co-Authors: Ruchira Somaweera, Tim Dempster, Richard Shine, Jonathan K Webb, Mike LetnicAbstract:The ecological impact of an invasive species can be heterogeneous through space and time. One such case in Australia involves native freshwater crocodiles Crocodylus johnstoni, which are highly sensitive to invasive cane Toads Rhinella marina in some areas, whereas other populations experience little or no mortality from ingestion of the toxic Toads. We studied the impact of toad invasion on three crocodile populations: one crashed, one showed a minor decrease and one appeared unaffected. We tested three hypotheses for the cause of this spatial variation in impact: differences among populations in toad–crocodile encounter rates (proximity of Toads to crocodiles during spotlight surveys), differences in crocodile feeding responses (trials of prey preference in the laboratory) and differences in crocodile physiology (reduction of swim speed after receiving a dose of toad toxin). We found little divergence among populations in any of these traits: crocodiles from the three populations all encountered cane Toads in the wild, and exhibited similar feeding responses and toxin tolerances. Thus, we cannot confidently identify causation for the impact heterogeneity. Reliance on alternative food resources and an ability to rapidly learn taste aversion may have allowed crocodiles to deal with toad arrival in Lake Argyle and the Daly River. Future work could usefully evaluate potential explanations for the failure of these adaptive mechanisms in the severely affected (Victoria River) population. We suggest that spatial variation in the availability of alternative prey (and thus the willingness of crocodiles to attack a novel toxic prey item) may have contributed to that variation in impact.
Gregory P Brown - One of the best experts on this subject based on the ideXlab platform.
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evolutionary shifts in anti predator responses of invasive cane Toads rhinella marina
Behavioral Ecology and Sociobiology, 2017Co-Authors: Cameron M Hudson, Gregory P Brown, Richard ShineAbstract:A potential prey item’s response to encountering a predator depends on aspects of the predator (e.g., its locomotor capacity), the local environment (e.g., proximity to shelter) and the physiological state of the prey item, but in addition, anti-predator tactics also vary geographically among different populations within wide-ranging species. Using standardised trials, we tested responses of cane Toads (Rhinella marina) to being placed on a laboratory runway and encouraged to flee. Overall, the Toads least capable of rapid locomotion were the ones most likely to respond to simulated predator attack by exuding toxins rather than attempting to escape. A toad’s willingness to move down the runway and its propensity to exude toxin from the parotoid glands rather than fleeing were repeatable in successive trials and influenced by the animal’s location of origin, morphology, previous experience, and parentage. We found that specimens from Australia were more willing to flee than were those from the native range (French Guiana) or Hawai’i; larger Toads, and those with relatively longer legs, were more willing to flee; captive-raised Toads were less willing to flee and more willing to exude toxin. Captive-raised offspring resembled their wild-caught parents both in propensity to run and in propensity to exude toxin. Thus, geographic divergence among cane toad populations in anti-predator responses reflects a complex combination of processes, including both developmental plasticity and heritability. The process of colonising novel environments exposes an organism to a host of different predators that exert selection on morphology, behaviour and physiology. Over time, this can lead to the evolution of novel phenotypes that are adapted to local conditions. Anthropogenically facilitated biological invasions provide a unique opportunity to study how species respond to colonisation of new environments. Here, we studied geographic variation in cane toad (Rhinella marina) anti-predator behaviours from a range of locations (including invasive and native populations) using standardised trials. Our results suggest that invasive Australian cane Toads have undergone a shift in their anti-predator response, becoming more willing to flee than are conspecifics from other areas. Location of origin, morphology, prior experience and parentage all played a role in shaping a toad’s anti-predator response, suggesting that the behaviour represents a combination of plastic and heritable variation.
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locomotor performance of cane Toads differs between native range and invasive populations
Royal Society Open Science, 2017Co-Authors: Georgia K Kosmala, Gregory P Brown, Keith A Christian, Richard ShineAbstract:Invasive species provide a robust opportunity to evaluate how animals deal with novel environmental challenges. Shifts in locomotor performance—and thus the ability to disperse—(and especially, the degree to which it is constrained by thermal and hydric extremes) are of special importance, because they might affect the rate that an invader can spread. We studied cane Toads ( Rhinella marina ) across a broad geographical range: two populations within the species9 native range in Brazil, two invasive populations on the island of Hawai9i and eight invasive populations encompassing the eastern, western and southern limits of the toad invasion in Australia. A toad9s locomotor performance on a circular raceway was strongly affected by both its temperature and its hydration state, but the nature and magnitude of those constraints differed across populations. In their native range, cane Toads exhibited relatively low performance (even under optimal test conditions) and a rapid decrease in performance at lower temperatures and hydration levels. At the other extreme, performance was high in Toads from southern Australia, and virtually unaffected by desiccation. Hawai9ian Toads broadly resembled their Brazilian conspecifics, plausibly reflecting similar climatic conditions. The invasion of Australia has been accompanied by a dramatic enhancement in the Toads9 locomotor abilities, and (in some populations) by an ability to maintain locomotor performance even when the animal is cold and/or dehydrated. The geographical divergences in performance among cane toad populations graphically attest to the adaptability of invasive species in the face of novel abiotic challenges.
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Toads in the backyard: why do invasive cane Toads (Rhinella marina) prefer buildings to bushland?
Population Ecology, 2016Co-Authors: Edna González-bernal, Gregory P Brown, Matthew J. Greenlees, Richard ShineAbstract:Like many invasive species, cane Toads (Rhinella marina) in Australia concentrate in the disturbed habitats created by human activity, rather than in pristine areas. We surveyed cane Toads in the wet–dry tropics of the Northern Territory to assess the abundances, body sizes, sexes, behaviour, hydration state and feeding rates of Toads around buildings compared to those in areas remote from buildings, and conducted experimental trials to assess the effects of building-related variables (lights and increased toad densities) on the foraging success of Toads. Toads around buildings were smaller than bushland conspecifics, and adult sex-ratios were female-biased. Toads were more sedentary around buildings than in the bush, but their feeding rates (based on direct observations and faeces production post-capture) were similar. That similarity, despite twofold-higher densities of competing Toads around building, reflected the strong enhancement of feeding rates due to artificial lights attracting insects (in our experimental trials, a threefold increase regardless of the number of competing Toads). Toads collected from around buildings were apparently in better hydric condition. Thus, access to water also may attract Toads to buildings. The relative scarcity of adult male Toads around buildings likely reflects waterbody-centred reproductive activities, whereas the concentration of females and juveniles around buildings is driven largely by access to the insects attracted by artificial light. We conclude that buildings enhance the persistence of cane toad populations and may facilitate their spread.
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The impact of lungworm parasites on rates of dispersal of their anuran host, the invasive cane toad
Biological Invasions, 2016Co-Authors: Gregory P Brown, Crystal Kelehear, Ligia Pizzatto, Richard ShineAbstract:Translocation of native-range parasites to control invasive species is effective only if the parasite substantially impairs either the viability or dispersal rate of the invasive host. Lungworms ( Rhabdias pseudosphaerocephala ) of cane Toads ( Rhinella marina ) were introduced to Australia from the toad’s native range, along with the Toads, and have been suggested as a potential biocontrol of invasive Toads due to various negative impacts on toad viability. We conducted two radio-telemetry studies on a tropical floodplain to specifically assess the parasite’s impact on toad dispersal. First, a retrospective correlative analysis of data from field-collected animals showed that Toads infected with lungworms moved farther, not less, than uninfected conspecifics. Second, an experimental study (comparing movements of experimentally infected Toads vs. uninfected controls) showed that lungworms did not modify rates of toad dispersal. In addition, experimental infection with lungworms did not elicit an immune response substantial enough to influence dispersal behaviour. Thus, we conclude that increasing lungworm densities at the invasion front as an attempt at biocontrol would not slow down the spread of cane Toads.
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invasive cane Toads social facilitation depends upon an individual s personality
PLOS ONE, 2014Co-Authors: Edna Gonzalezbernal, Gregory P Brown, Richard ShineAbstract:Individual variation in behavioural traits (including responses to social cues) may influence the success of invasive populations. We studied the relationship between sociality and personality in invasive cane Toads (Rhinella marina) from a recently established population in tropical Australia. In our field experiments, we manipulated social cues (the presence of a feeding conspecific) near a food source. We captured and compared Toads that only approached feeding sites where another toad was already present, with conspecifics that approached unoccupied feeding sites. Subsequent laboratory trials showed correlated personality differences (behavioural syndromes) between these two groups of Toads. For example, Toads that approached already-occupied rather than unoccupied feeding sites in the field, took longer to emerge from a shelter-site in standardized trials, suggesting these individuals are ‘shy’ (whereas Toads that approached unoccupied feeding stations tended to be ‘bold’). Manipulating hunger levels did not abolish this difference. In feeding trials, a bold toad typically outcompeted a shy toad under conditions of low prey availability, but the outcome was reversed when multiple prey items were present. Thus, both personality types may be favored under different circumstances. This invasive population of Toads contains individuals that exhibit a range of personalities, hinting at the existence of a wide range of social dynamics in taxa traditionally considered to be asocial.
Ben L. Phillips - One of the best experts on this subject based on the ideXlab platform.
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Not such silly sausages: Northern quolls exhibit aversion to Toads after training with toad sausages
2017Co-Authors: Naomi Indigo, Jonathan K Webb, James G. Smith, Ben L. PhillipsAbstract:The 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, 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 predatory responses when presented with a dead adult toad. Captive quolls that consumed a single toad sausage showed substantially reduced interest in cane Toads, interacting with them for less than half the time of their untrained counterparts and showing substantially 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 approximately 61% of quolls consumed toad-aversion baits when first encountered. Between 40-68% of these animals developed aversion to further bait consumption. Our results suggest that toad-aversion sausages can 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.
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an invasive species induces rapid adaptive change in a native predator cane Toads and black snakes in australia
Proceedings of The Royal Society B: Biological Sciences, 2006Co-Authors: Ben L. Phillips, Richard ShineAbstract:Rapid environmental change due to human activities has increased rates of extinction, but some species may be able to adapt rapidly enough to deal with such changes. Our studies of feeding behaviour and physiological resistance to toxins reveal surprisingly rapid adaptive responses in Australian black snakes (Pseudechis porphyriacus) following the invasion of a lethally toxic prey item, the cane toad (Bufo marinus). Snakes from toad-exposed localities showed increased resistance to toad toxin and a decreased preference for Toads as prey. Separate laboratory experiments suggest that these changes are not attributable to learning (we were unable to teach naive snakes to avoid toxic prey) or to acquired resistance (repeated sub-lethal doses did not enhance resistance). These results strongly suggest that black snake behaviour and physiology have evolved in response to the presence of Toads, and have done so rapidly. Toads were brought to Australia in 1935, so these evolved responses have occurred in fewer than 23 snake generations.
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Toxic tucker: the potential impact of Cane Toads on Australian reptiles
Pacific Conservation Biology, 2006Co-Authors: James G. Smith, Ben L. PhillipsAbstract:Cane Toads Bufo marinus are a highly successful invasive species, having invaded more than twenty countries in the last 150 years. In Australia, they currently occupy more than 1 million square kilometres. Toads are highly toxic and Australian predators have no evolutionary history with the cardiac toxins in toad skin. As such, Toads constitute a novel and extremely toxic prey for Australia's predators. Australia's reptiles are perhaps the largest group likely to be affected by the invasion of the toad. By examining species distributions, we conclude that 59% of agamids, 85% of the varanids and all of Australia's crocodiles and freshwater turtles are potentially at risk from Toads. We then assayed eleven species of reptile; one freshwater turtle (Chelidae), two crocodiles (Crocodylidae), two dragons (Agamidae), one python (Pythonidae) and five species of monitor (Varanidae) for resistance to toad toxin. We found a high level of variation between species in resistance to toad toxin but in all cases (except for one species of crocodile) all species were easily capable of eating a toad large enough to kill them. We conclude that Toads pose a real and ongoing threat to the majority of Australian reptile species we examined.
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adapting to an invasive species toxic cane Toads induce morphological change in australian snakes
Proceedings of the National Academy of Sciences of the United States of America, 2004Co-Authors: Ben L. Phillips, Richard ShineAbstract:The arrival of invasive species can devastate natural ecosystems, but the long-term effects of invasion are less clear. If native organisms can adapt to the presence of the invader, the severity of impact will decline with time. In Australia, invasive cane Toads (Bufo marinus) are highly toxic to most snakes that attempt to eat them. Because snakes are gape-limited predators with strong negative allometry for head size, maximum relative prey mass (and thus, the probability of eating a toad large enough to be fatal) decreases with an increase in snake body size. Thus, the arrival of Toads should exert selection on snake morphology, favoring an increase in mean body size and a decrease in relative head size. We tested these predictions with data from specimens of four species of Australian snakes, collected over >80 years. Geographic information system layers provided data on the duration of toad exposure for each snake population, as well as environmental variables (latitude, precipitation, and temperature). As predicted, two toad-vulnerable species (Pseudechis porphyriacus and Dendrelaphis punctulatus) showed a steady reduction in gape size and a steady increase in body length with time since exposure to Toads. In contrast, two species at low risk from Toads (Hemiaspis signata and Tropidonophis mairii) showed no consistent change in these morphological traits as a function of the duration of toad exposure. These results provide strong evidence of adaptive changes in native predators as a result of the invasion of toxic prey.
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assessing the potential impact of cane Toads on australian snakes
Conservation Biology, 2003Co-Authors: Gregory P Brown, Ben L. Phillips, Richard ShineAbstract:Cane Toads (Bufo marinus) are large, highly toxic anurans that were introduced into Australia in 1937. Anecdotal reports suggest that the invasion of Toads into an area is followed by dramatic declines in the abundance of terrestrial native frog-eating predators, but quantitative studies have been restricted to nonpredator taxa or aquatic predators and have generally reported minimal impacts. Will Toads substantially affect Australian snakes? Based on geographic distributions and dietary composition, we identified 49 snake taxa as potentially at risk from Toads. The impact of these feral prey also depends on the snakes' ability to survive after ingesting toad toxins. Based on decrements in locomotor (swimming) performance after ingesting toxin, we estimate the LD50 of toad toxins for 10 of the at-risk snake species. Most species exhibited a similar low ability to tolerate toad toxins. Based on head widths relative to sizes of Toads, we calculate that 7 of the 10 taxa could easily ingest a fatal dose of toxin in a single meal. The exceptions were two colubrid taxa (keelbacks ( Tropidonophis mairii) and slatey-grey snakes ( Stegonotus cucullatus)) with much higher resistance to toad toxins (up to 85-fold) and one elapid (swamp snakes ( Hemiaspis signata)) with low resistance but a small relative head size and thus low maximum prey size. Overall, our analysis suggests that cane Toads threaten populations of approximately 30% of terrestrial Australian snake species.
Matthew J. Greenlees - One of the best experts on this subject based on the ideXlab platform.
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Toads in the backyard: why do invasive cane Toads (Rhinella marina) prefer buildings to bushland?
Population Ecology, 2016Co-Authors: Edna González-bernal, Gregory P Brown, Matthew J. Greenlees, Richard ShineAbstract:Like many invasive species, cane Toads (Rhinella marina) in Australia concentrate in the disturbed habitats created by human activity, rather than in pristine areas. We surveyed cane Toads in the wet–dry tropics of the Northern Territory to assess the abundances, body sizes, sexes, behaviour, hydration state and feeding rates of Toads around buildings compared to those in areas remote from buildings, and conducted experimental trials to assess the effects of building-related variables (lights and increased toad densities) on the foraging success of Toads. Toads around buildings were smaller than bushland conspecifics, and adult sex-ratios were female-biased. Toads were more sedentary around buildings than in the bush, but their feeding rates (based on direct observations and faeces production post-capture) were similar. That similarity, despite twofold-higher densities of competing Toads around building, reflected the strong enhancement of feeding rates due to artificial lights attracting insects (in our experimental trials, a threefold increase regardless of the number of competing Toads). Toads collected from around buildings were apparently in better hydric condition. Thus, access to water also may attract Toads to buildings. The relative scarcity of adult male Toads around buildings likely reflects waterbody-centred reproductive activities, whereas the concentration of females and juveniles around buildings is driven largely by access to the insects attracted by artificial light. We conclude that buildings enhance the persistence of cane toad populations and may facilitate their spread.
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the impact of invasive cane Toads on native wildlife in southern australia
Ecology and Evolution, 2015Co-Authors: Christopher J Jolly, Richard Shine, Matthew J. GreenleesAbstract:Commonly, invaders have different impacts in different places. The spread of cane Toads (Rhinella marina: Bufonidae) has been devastating for native fauna in tropical Australia, but the Toads' impact remains unstudied in temperate-zone Australia. We surveyed habitat characteristics and fauna in campgrounds along the central eastern coast of Australia, in eight sites that have been colonized by cane Toads and another eight that have not. The presence of cane Toads was associated with lower faunal abundance and species richness, and a difference in species composition. Populations of three species of large lizards (land mullets Bellatorias major, eastern water dragons Intellagama lesueurii, and lace monitors Varanus varius) and a snake (red-bellied blacksnake Pseudechis porphyriacus) were lower (by 84 to 100%) in areas with Toads. The scarcity of scavenging lace monitors in toad-invaded areas translated into a 52% decrease in rates of carrion removal (based on camera traps at bait stations) and an increase (by 61%) in numbers of brush turkeys (Alectura lathami). The invasion of cane Toads through temperate-zone Australia appears to have reduced populations of at least four anurophagous predators, facilitated other taxa, and decreased rates of scavenging. Our data identify a paradox: The impacts of cane Toads are at least as devastating in southern Australia as in the tropics, yet we know far more about toad invasion in the sparsely populated wilderness areas of tropical Australia than in the densely populated southeastern seaboard.
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Cane Toads on cowpats: commercial livestock production facilitates toad invasion in tropical australia.
PloS one, 2012Co-Authors: Edna González-bernal, Gregory P Brown, Matthew J. Greenlees, Richard ShineAbstract:Habitat disturbance and the spread of invasive organisms are major threats to biodiversity, but the interactions between these two factors remain poorly understood in many systems. Grazing activities may facilitate the spread of invasive cane Toads (Rhinella marina) through tropical Australia by providing year-round access to otherwise-seasonal resources. We quantified the cane toad’s use of cowpats (feces piles) in the field, and conducted experimental trials to assess the potential role of cowpats as sources of prey, water, and warmth for Toads. Our field surveys show that cane Toads are found on or near cowpats more often than expected by chance. Field-enclosure experiments show that cowpats facilitate toad feeding by providing access to dung beetles. Cowpats also offer moist surfaces that can reduce dehydration rates of Toads and are warmer than other nearby substrates. Livestock grazing is the primary form of land use over vast areas of Australia, and pastoral activities may have contributed substantially to the cane toad’s successful invasion of that continent.
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adjusting to a toxic invader native australian frogs learn not to prey on cane Toads
Behavioral Ecology, 2010Co-Authors: Matthew J. Greenlees, Benjamin L. Phillips, Richard ShineAbstract:Biological invasions provide opportunities to study novel behavioral interactions between predators and their prey. To withstand detrimental effects from a potentially lethal invader, a native taxon must somehow adjust to the invader’s presence. Cane Toads (Bufo marinus) are highly toxic to native Australian anurans and constitute a major threat if consumed. We recorded the responses of Australian marbled frogs (Limnodynastes convexiusculus) during their first encounters with edible-sized cane Toads. The frogs exhibited rapid avoidance learning: toad-exposed frogs were less likely to attack subsequently encountered cane Toads (and hence more likely to survive). Among-clutch variance in learning rates and in physiological tolerance to toad toxins was low, suggesting that genetically based adaptive changes to frog feeding responses will be slow (especially given that rapid learning reduces mortality and thus reduces the fitness decrement of initial willingness to attack a toad). Hence, rapid taste aversion learning is the primary mechanism enabling marbled frogs to persist in the presence of a potentially fatal invader. In combination with previous work, our study shows that some native predators adjust to the threat posed by cane toad invasion via taste aversion learning, whereas others show genetically based modification of feeding responses. More generally, both learning and adaptation enable vulnerable native taxa to survive the arrival of a toxic invasive species. Key words: behavior, Bufo marinus, frog, invasive species, learning, predator. [Behav Ecol]
