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Richard Shine - One of the best experts on this subject based on the ideXlab platform.
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The Effects of Conspecific Alarm Cues on Larval Cane Toads (Rhinella marina)
Journal of Chemical Ecology, 2019Co-Authors: Michael R. Crossland, Angela A. Salim, Robert J. Capon, Richard ShineAbstract:Many aquatic organisms detect and avoid damage-released cues from conspecifics, but the chemical basis of such responses, and the effects of prolonged exposure to such cues, remain poorly understood. Injured Tadpoles of the cane toad ( Rhinella marina ) produce chemical cues that induce avoidance by conspecific Tadpoles; and chronic exposure to those cues decreases rates of tadpole survival and growth, and reduces body size at metamorphosis. Such effects suggest that we might be able to use the cane toads’ alarm cue for biocontrol of invasive populations in Australia. In the present study, we examined behavioral and ecological effects of compounds that are present in cane toad Tadpoles and thus, might trigger avoidance of crushed conspecifics. Four chemicals (L-Arg, L-Leu-L-Leu-OH, L-Leu-L-Ile-OH and suberic acid) induced behavioral avoidance in toad Tadpoles at some (but not all) dosage levels, so we then exposed toad larvae to these chemicals over the entire period of larval development. Larval survival and size at metamorphosis were decreased by chronic exposure to crushed conspecifics (consistent with earlier studies), but not by exposure to any of the four chemicals. Indeed, L-Arg increased body size at metamorphosis. We conclude that the behavioral response to crushed conspecifics by cane toad Tadpoles can be elicited by a variety of chemical cues, but that consistent exposure to these individual chemical cues does not affect tadpole viability or developmental trajectory. The optimal behavioral tactic of a tadpole may be to flee if it encounters even a single chemical cue likely to have come from an injured conspecific (indicative of predation risk), whereas the continuing presence of that single chemical (but no others) provides a less reliable signal of predation risk. Our data are consistent with results from studies on fish, that suggest a role for multiple chemicals in initiating alarm responses to damage-released cues.
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Ontogenetic Variation in the Chemical Defenses of Cane Toads (Bufo marinus): Toxin Profiles and Effects on Predators
Journal of Chemical Ecology, 2009Co-Authors: R. Andrew Hayes, Robert J. Capon, Michael R. Crossland, Mattias Hagman, Richard ShineAbstract:We conducted a quantitative and qualitative chemical analysis of cane toad bufadienolides—the cardioactive steroids that are believed to be the principal cane toad toxins. We found complex shifts in toxin composition through toad ontogeny: (1) eggs contain at least 28 dominant bufadienolides, 17 of which are not detected in any other ontogenetic stage; (2) Tadpoles present a simpler chemical profile with two to eight dominant bufadienolides; and (3) toxin diversity decreases during tadpole life but increases again after metamorphosis (larger metamorph/juvenile toads display five major bufadienolides). Total bufadienolide concentrations are highest in eggs (2.64 ± 0.56 μmol/mg), decreasing during tadpole life stages (0.084 ± 0.060 μmol/mg) before rising again after metamorphosis (2.35 ± 0.45 μmol/mg). These variations in total bufadienolide levels correlate with toxicity to Australian frog species. For example, consumption of cane toad eggs killed Tadpoles of two Australian frog species ( Limnodynastes convexiusculus and Litoria rothii ), whereas no Tadpoles died after consuming late-stage cane toad Tadpoles or small metamorphs. The high toxicity of toad eggs reflects components in the egg itself, not the surrounding jelly coat. Our results suggest a dramatic ontogenetic shift in the danger that toads pose to native predators, reflecting rapid changes in the types and amounts of toxins during toad development.
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mass mortality of native anuran Tadpoles in tropical australia due to the invasive cane toad bufo marinus
Biological Conservation, 2008Co-Authors: Michael R. Crossland, Gregory P Brown, Marion Anstis, Catherine M Shilton, Richard ShineAbstract:Specific pathways of the ecological impact of invasive species remain poorly known. Although the spread of toxic cane toads (Bufo marinus) through tropical Australia is widely believed to have caused extensive mortality of native reptiles and mammals, effects of toad ingestion on native anurans have been virtually ignored. Our studies on the Adelaide River floodplain show that the most numerous vertebrate victims of toad invasion are native Tadpoles that die when they attempt to consume toad eggs. We documented 11 episodes of mass mortality, totalling >1300 Tadpoles of 10 species, in five waterbodies within a single wet-season shortly after the toads invaded. A causal link between toad breeding and tadpole mortality is supported by observations that: (1) in at least 9 of the 11 waterbodies involved, toads bred immediately prior to mortality events; (2) water quality was indistinguishable from that of control ponds, and Tadpoles placed in that water remained healthy; (3) dead Tadpoles showed no sign of disease; and (4) laboratory trials showed rapid, 100% mortality in native Tadpoles exposed to freshly-laid toad eggs. Despite these high mortality rates, toad invasion does not appear to threaten the viability of anuran populations because frogs often breed in ponds not used by toads, and because density-dependent growth and survival within tadpole communities mean that additional mortality may not reduce the total effective recruitment of metamorph frogs from a waterbody.
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Effects of the insecticide endosulfan and presence of congeneric Tadpoles on Australian treefrog (Litoria freycineti) Tadpoles.
Archives of Environmental Contamination and Toxicology, 2003Co-Authors: S. Broomhall, Richard ShineAbstract:The organochlorine insecticide endosulfan is extensively used in Australia and can often contaminate aquatic environments. However, its effects on Australian frog species are unknown. We exposed Tadpoles of the Australian treefrog Litoria freycineti to endosulfan for 96 hours. Tadpoles exposed to 0.03 or 1.3 μg/L endosulfan grew more slowly than control Tadpoles. Furthermore, feeding was inhibited in L. freycineti when the animals were observed halfway through their exposure to a concentration of 1.3 μg/L endosulfan for 96 h. This concentration (which periodically occurs in natural water bodies and rivers) also caused 17% tadpole mortality, and the survivors were more vulnerable to invertebrate (odonate) predation when tested 15 days after transfer to clean water. The presence of a sympatric species of tadpole, Litoria peronii, did not affect survivorship of L. freycineti, but reduced growth rates. Thus, short-term exposure to endosulfan in natural water bodies may influence tadpole viability either immediately or over an extended period.
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Competition between Tadpoles and mosquitoes: the effects of larval density and tadpole size
Australian Journal of Zoology, 2002Co-Authors: Allie Mokany, Richard ShineAbstract:Tadpoles and mosquito larvae compete for scarce resources in natural freshwater ecosystems, but factors determining the extent of competition between these two groups of organisms remain largely unstudied. Natural ponds display great variation both in the densities of larvae, and in the body sizes of Tadpoles. We set up replicated artificial pond experiments to examine the effects of population density and tadpole size on interactions between Tadpoles and mosquito larvae. We examined the effects of larval density in two systems of co-occurring Tadpoles and mosquito larvae, one from brackish-water ephemeral ponds (Crinia signifera with Ochlerotatus australis) and one from permanent freshwater ponds (Limnodynastes peronii with Culex quinquefasciatus). In both systems, increasing densities of larvae suppressed growth and development both of conspecifics and of the competing taxon. In the C. quinquefasciatus–L. peronii system, larger Tadpoles exerted more powerful suppression. Our results suggest that mosquito developmental rates and adult body sizes (and thus, the danger which mosquitoes pose to public health) may be reduced if natural water-bodies contain dense populations of large Tadpoles.
Shawn R Kuchta - One of the best experts on this subject based on the ideXlab platform.
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predator mediated selection and the impact of developmental stage on viability in wood frog Tadpoles rana sylvatica
BMC Evolutionary Biology, 2011Co-Authors: Ryan Calsbeek, Shawn R KuchtaAbstract:Background: Complex life histories require adaptation of a single organism for multiple ecological niches. Transitions between life stages, however, may expose individuals to an increased risk of mortality, as the process of metamorphosis typically includes developmental stages that function relatively poorly in both the pre- and postmetamorphic habitat. We studied predator-mediated selection on Tadpoles of the wood frog, Rana sylvatica ,t o identify this hypothesized period of differential predation risk and estimate its ontogenetic onset. We reared Tadpoles in replicated mesocosms in the presence of the larval odonate Anax junius, a known tadpole predator. Results: The probability of tadpole survival increased with increasing age and size, but declined steeply at the point in development where hind limbs began to erupt from the body wall. Selection gradient analyses indicate that natural selection favored Tadpoles with short, deep tail fins. Tadpoles resorb their tails as they progress toward metamorphosis, which may have led to the observed decrease in survivorship. Path models revealed that selection acted directly on tail morphology, rather than through its indirect influence on swimming performance. Conclusions: This is consistent with the hypothesis that tail morphology influences predation rates by reducing the probability a predator strikes the head or body.
Geoffrey R Smith - One of the best experts on this subject based on the ideXlab platform.
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combined effects of malathion and nitrate on early growth abnormalities and mortality of wood frog rana sylvatica Tadpoles
Ecotoxicology, 2011Co-Authors: S V Krishnamurthy, Geoffrey R SmithAbstract:Use of pesticides and other agro-chemicals adversely influence amphibians either directly by killing them or by inducing sublethal, chronic effects. Many studies have investigated the effect of mixtures of pesticides or fertilizers. We studied the combined effects of nitrate and malathion ([(dimethoxy phosphino thioyl] butanediotae) on the early growth, expression of abnormalities, and mortality of Wood Frog (Rana sylvatica) Tadpoles in a laboratory experiment. Tadpoles were treated with factorial combinations of 0, 8, and 16 mg NO3–N l−1 and 0, 250, 500, and 1,000 μg malathion l−1 for a period of 14 days. Feeding behaviour, total length, mean tadpole mass, frequencies of abnormalities, and survivorship in each treatment were recorded. Malathion showed a significant negative influence on all parameters and strongly influenced the frequencies of morphological anomalies. In contrast, nitrate alone did not produce any significant effects on behavior, total length, tadpole mass, or the frequency of abnormalities during the experiment. Malathion and nitrate had an interactive effect on tadpole length and mass, but did not affect any other parameters. Our results suggest that exposure to malathion, even at relatively low concentrations can have serious negative consequences for Wood Frog Tadpoles. In addition, our results also indicate that there was little synergistic interaction between malathion and nitrate exposure under laboratory conditions.
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Effects of mosquitofish and ammonium nitrate on activity of green frog (Lithobates clamitans) Tadpoles: a mesocosm experiment
Journal of Freshwater Ecology, 2011Co-Authors: Geoffrey R Smith, Andrew J. Terlecky, Christopher B. Dayer, Allison Boyd, Michael E. Ogle, Christopher J. DibbleAbstract:We conducted a mesocosm experiment that allowed us to examine the effects of mosquitofish (Gambusia affinis) and ammonium nitrate on the activity of green frog (Lithobates clamitans) Tadpoles under the more natural conditions of a mesocosm as opposed to a laboratory experiment. The proportion of active Tadpoles was lower in the presence of mosquitofish than when mosquitofish were not present. There was no effect of ammonium nitrate or interaction between mosquitofish and ammonium nitrate on tadpole activity. These results suggest that green frog Tadpoles reduce their activity levels in the presence of mosquitofish, but the ability of ammonium nitrate to mediate the outcome of potential predator–prey interactions between green frog Tadpoles and mosquitofish appears to be limited, at least at the ecologically relevant concentration we studied.
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Effects of light and group size on the activity of wood frog Tadpoles ( Rana sylvatica ) and their response to a shadow stimulus
Acta Herpetologica, 2009Co-Authors: Katherine V. Mcclure, Jordan W. Mora, Geoffrey R SmithAbstract:Tadpoles are known to behaviorally respond to cues from aquatic predators. However, there are several additional factors that might affect tadpole behavior. We examined the influence of light conditions and group size on the activity of wood frog ( Rana sylvatica ) Tadpoles and their response to a simulated non-aquatic predator (i.e., a shadow stimulus). Activity levels of undisturbed wood frog Tadpoles were higher in larger groups (15 Tadpoles) than in the smaller groups (5 Tadpoles). Activity following exposure to a simulated aerial predator (i.e., a shadow stimulus) was also higher in the larger groups of Tadpoles than in the smaller groups. Light conditions did not influence activity level in undisturbed Tadpoles, but did affect the response to the shadow stimulus, with the greatest responses being observed under bright light conditions. Our results suggest that the factors influencing tadpole activity can include a diverse range of factors and cues, including lighting conditions and group size.
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behavioral responses of american toad and bullfrog Tadpoles to the presence of cues from the invasive fish gambusia affinis
Biological Invasions, 2008Co-Authors: Geoffrey R Smith, Christopher B. Dayer, Allison Boyd, Kristen E WinterAbstract:The introduction of non-native predators is thought to have important negative effects on native prey populations. The susceptibility of native prey to non-native or introduced predators may depend on their ability to respond appropriately to the presence of these non-native predators. We conducted a laboratory based behavioral experiment to examine the response of American toad (Bufo americanus) and bullfrog (Rana catesbeiana) Tadpoles to the presence of cues from the introduced mosquitofish (Gambusia affinis), a potential tadpole predator. Neither the American toad Tadpoles nor the bullfrog Tadpoles responded behaviorally to the presence of mosquitofish cues. If Tadpoles are unable to respond to the presence of mosquitofish cues appropriately, then their ability to avoid predation by mosquitofish may be compromised and this may contribute to the impacts of mosquitofish on some tadpole populations.
Michael R. Crossland - One of the best experts on this subject based on the ideXlab platform.
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The Effects of Conspecific Alarm Cues on Larval Cane Toads (Rhinella marina)
Journal of Chemical Ecology, 2019Co-Authors: Michael R. Crossland, Angela A. Salim, Robert J. Capon, Richard ShineAbstract:Many aquatic organisms detect and avoid damage-released cues from conspecifics, but the chemical basis of such responses, and the effects of prolonged exposure to such cues, remain poorly understood. Injured Tadpoles of the cane toad ( Rhinella marina ) produce chemical cues that induce avoidance by conspecific Tadpoles; and chronic exposure to those cues decreases rates of tadpole survival and growth, and reduces body size at metamorphosis. Such effects suggest that we might be able to use the cane toads’ alarm cue for biocontrol of invasive populations in Australia. In the present study, we examined behavioral and ecological effects of compounds that are present in cane toad Tadpoles and thus, might trigger avoidance of crushed conspecifics. Four chemicals (L-Arg, L-Leu-L-Leu-OH, L-Leu-L-Ile-OH and suberic acid) induced behavioral avoidance in toad Tadpoles at some (but not all) dosage levels, so we then exposed toad larvae to these chemicals over the entire period of larval development. Larval survival and size at metamorphosis were decreased by chronic exposure to crushed conspecifics (consistent with earlier studies), but not by exposure to any of the four chemicals. Indeed, L-Arg increased body size at metamorphosis. We conclude that the behavioral response to crushed conspecifics by cane toad Tadpoles can be elicited by a variety of chemical cues, but that consistent exposure to these individual chemical cues does not affect tadpole viability or developmental trajectory. The optimal behavioral tactic of a tadpole may be to flee if it encounters even a single chemical cue likely to have come from an injured conspecific (indicative of predation risk), whereas the continuing presence of that single chemical (but no others) provides a less reliable signal of predation risk. Our data are consistent with results from studies on fish, that suggest a role for multiple chemicals in initiating alarm responses to damage-released cues.
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Ontogenetic Variation in the Chemical Defenses of Cane Toads (Bufo marinus): Toxin Profiles and Effects on Predators
Journal of Chemical Ecology, 2009Co-Authors: R. Andrew Hayes, Robert J. Capon, Michael R. Crossland, Mattias Hagman, Richard ShineAbstract:We conducted a quantitative and qualitative chemical analysis of cane toad bufadienolides—the cardioactive steroids that are believed to be the principal cane toad toxins. We found complex shifts in toxin composition through toad ontogeny: (1) eggs contain at least 28 dominant bufadienolides, 17 of which are not detected in any other ontogenetic stage; (2) Tadpoles present a simpler chemical profile with two to eight dominant bufadienolides; and (3) toxin diversity decreases during tadpole life but increases again after metamorphosis (larger metamorph/juvenile toads display five major bufadienolides). Total bufadienolide concentrations are highest in eggs (2.64 ± 0.56 μmol/mg), decreasing during tadpole life stages (0.084 ± 0.060 μmol/mg) before rising again after metamorphosis (2.35 ± 0.45 μmol/mg). These variations in total bufadienolide levels correlate with toxicity to Australian frog species. For example, consumption of cane toad eggs killed Tadpoles of two Australian frog species ( Limnodynastes convexiusculus and Litoria rothii ), whereas no Tadpoles died after consuming late-stage cane toad Tadpoles or small metamorphs. The high toxicity of toad eggs reflects components in the egg itself, not the surrounding jelly coat. Our results suggest a dramatic ontogenetic shift in the danger that toads pose to native predators, reflecting rapid changes in the types and amounts of toxins during toad development.
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mass mortality of native anuran Tadpoles in tropical australia due to the invasive cane toad bufo marinus
Biological Conservation, 2008Co-Authors: Michael R. Crossland, Gregory P Brown, Marion Anstis, Catherine M Shilton, Richard ShineAbstract:Specific pathways of the ecological impact of invasive species remain poorly known. Although the spread of toxic cane toads (Bufo marinus) through tropical Australia is widely believed to have caused extensive mortality of native reptiles and mammals, effects of toad ingestion on native anurans have been virtually ignored. Our studies on the Adelaide River floodplain show that the most numerous vertebrate victims of toad invasion are native Tadpoles that die when they attempt to consume toad eggs. We documented 11 episodes of mass mortality, totalling >1300 Tadpoles of 10 species, in five waterbodies within a single wet-season shortly after the toads invaded. A causal link between toad breeding and tadpole mortality is supported by observations that: (1) in at least 9 of the 11 waterbodies involved, toads bred immediately prior to mortality events; (2) water quality was indistinguishable from that of control ponds, and Tadpoles placed in that water remained healthy; (3) dead Tadpoles showed no sign of disease; and (4) laboratory trials showed rapid, 100% mortality in native Tadpoles exposed to freshly-laid toad eggs. Despite these high mortality rates, toad invasion does not appear to threaten the viability of anuran populations because frogs often breed in ponds not used by toads, and because density-dependent growth and survival within tadpole communities mean that additional mortality may not reduce the total effective recruitment of metamorph frogs from a waterbody.
Ryan Calsbeek - One of the best experts on this subject based on the ideXlab platform.
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predator mediated selection and the impact of developmental stage on viability in wood frog Tadpoles rana sylvatica
BMC Evolutionary Biology, 2011Co-Authors: Ryan Calsbeek, Shawn R KuchtaAbstract:Background: Complex life histories require adaptation of a single organism for multiple ecological niches. Transitions between life stages, however, may expose individuals to an increased risk of mortality, as the process of metamorphosis typically includes developmental stages that function relatively poorly in both the pre- and postmetamorphic habitat. We studied predator-mediated selection on Tadpoles of the wood frog, Rana sylvatica ,t o identify this hypothesized period of differential predation risk and estimate its ontogenetic onset. We reared Tadpoles in replicated mesocosms in the presence of the larval odonate Anax junius, a known tadpole predator. Results: The probability of tadpole survival increased with increasing age and size, but declined steeply at the point in development where hind limbs began to erupt from the body wall. Selection gradient analyses indicate that natural selection favored Tadpoles with short, deep tail fins. Tadpoles resorb their tails as they progress toward metamorphosis, which may have led to the observed decrease in survivorship. Path models revealed that selection acted directly on tail morphology, rather than through its indirect influence on swimming performance. Conclusions: This is consistent with the hypothesis that tail morphology influences predation rates by reducing the probability a predator strikes the head or body.
