Aposematism is an antipredator strategy in which conspicuous coloration acts as a warning of chemical defenses to potential predators.Evidence suggests that aposematism largely functions under positive frequency-depen...Aposematism is an antipredator strategy in which conspicuous coloration acts as a warning of chemical defenses to potential predators.Evidence suggests that aposematism largely functions under positive frequency-dependent selection,which is thought to maintain uniformity of aposematic signals.Many studies of aposematic organisms have found evidence that color signals and defenses are positively correlated,indicating a quantitatively honest aposematic signal.Dendrobatid poison frogs represent a well-studied group of aposematic organisms that in addition to exhibiting a diversity of color signals also display unique defensive behaviors.Few studies have examined if both behavior and coloration act as quantitative honest signals of alkaloid defenses in poison frogs.We aimed to determine if coloration and behavior are quantitatively honest signals in the green and black poison frog(Dendrobates auratus)among 6 populations from Costa Rica.We(1)evaluated antipredator displays by using behavioral assays in the field,(2)assessed frog conspicuousness and pattern using digital images,and(3)quantified alkaloid profiles from frog skin secretions.We found that Pacific populations are less conspicuous in coloration,had greater quantities of alkaloids,and more frequently performed body-raising defensive behaviors when compared with Caribbean populations.Our results do not support the hypothesis that aposematic traits in D.auratus are quantitatively honest.Rather,our results suggest that phenotypic differences among populations may represent different phenotypic optima for advertising unprofitability to predators based on local environmental conditions,leading to the diversification of aposematic signals in this species.展开更多
Although the use of distinct colors to indicate unprofitability to predators(i.e.aposematism)is commonly thought of as an adaptation,our knowledge of its macroevolutionary effects is limited.Because aposematism is exp...Although the use of distinct colors to indicate unprofitability to predators(i.e.aposematism)is commonly thought of as an adaptation,our knowledge of its macroevolutionary effects is limited.Because aposematism is expected to decrease attacks by predators,we hypothesized that aposematic lineages should be larger on average than their non-aposematic sister groups because of the decreased probability of extinction and/or increased probability of speciation(i.e.increased diversification).The results of our sister-group analysis are consistent with the hypothesis that the evolution of aposematism is accompanied by increased diversification of lineages,with the aposematic focal group having more species in 11 of 14 pairs of sister groups.Despite the apparent advantages of reduced predation risk on diversification rates,the evolution of aposematism is relatively rare and reversions to a cryptic state are not uncommon.In addition to the difficulties in evolving a trait that initially decreases the survivorship of prey among naïve predators,we discuss other factors that may limit the apparent prevalence and success of aposematism.It is hoped that the results of our analysis will encourage further analyses of the phylogenetic relationships among aposematic groups and their relatives,and of the evolutionary time scales over which the benefits of aposematism are the greatest to lineages with this condition.展开更多
Color polymorphisms have been traditionally attributed to apostatic selection.The perception of color depends on the visual system of the observer.Theoretical models predict that differently perceived degrees of consp...Color polymorphisms have been traditionally attributed to apostatic selection.The perception of color depends on the visual system of the observer.Theoretical models predict that differently perceived degrees of conspicuousness by two predator and prey species may cause the evolution of polymorphisms in the presence of anti-apostatic and apostatic selection.The spider Gasteracantha cancriformis(Araneidae)possesses several conspicuous color morphs.In orb-web spiders,the prey attraction hypothesis states that conspicuous colors are prey lures that increase spider foraging success via flower mimicry.Therefore,polymorphism could be maintained if each morph attracted a different prey species(multiple prey hypothesis)and each spider mimicked a different flower color(flower mimicry hypothesis).Conspicuous colors could be a warning signal to predators because of the spider's hard abdomen and spines.Multiple predators could perceive morphs differently and exert different degrees of selective pressures(multiple predator hypothesis).We explored these 3 hypotheses using reflectance data and color vision modeling to estimate the chromatic and achromatic contrast of G.cancriformis morphs as perceived by several potential prey and predator taxa.Our results revealed that individual taxa perceive the conspicuousness of morphs differently.Therefore,the multiple prey hypothesis and,in part,the multiple predator hypothesis may explain the evolution of color polymorphism in G.cancriformis,even in the presence of anti-apostatic selection.The flower mimicry hypothesis received support by color metrics,but not by color vision models.Other parameters not evaluated by color vision models could also affect the perception of morphs and influence morph survival and polymorphism stability.展开更多
Many aposematic insect species advertise their toxicity to potential predators using olfactory and auditory signals, in addition to visual signals, to produce a multimodal warning display. The olfactory signals in the...Many aposematic insect species advertise their toxicity to potential predators using olfactory and auditory signals, in addition to visual signals, to produce a multimodal warning display. The olfactory signals in these displays may have interesting effects, such as eliciting innate avoidance against novel colored prey, or improving learning and memory of defended prey. However, little is known about the effects of such ancillary signals when they are auditory rather than olfactory. The few studies that have investigated this question have provided conflicting results. The current study sought to clarify and extend understanding of the effects of prey auditory signals on avian predator responses. The domestic chick Gallus gallus domesticus was used as a model avian predator to examine how the defensive buzzing sound of a bumblebee Bombus terrestris affected the chick＇s innate avoidance behavior, and the learning and memory of prey avoidance. The results demonstrate that the buzzing sound had no effect on the predator＇s responses to unpalatable aposematically colored crumbs, suggesting that the agitated buzzing of B. terrestris may provide no additional protection from avian predators .展开更多
Predators efficiently learn to avoid one type of warning signal rather than several, making colour polymorphisms un- expected. Aposematic wood tiger moth males Parasemia plantaginis have either white or yellow hindwin...Predators efficiently learn to avoid one type of warning signal rather than several, making colour polymorphisms un- expected. Aposematic wood tiger moth males Parasemia plantaginis have either white or yellow hindwing coloration across Eu- rope. Previous studies indicate that yellow males are better defended from predators, while white males have a positively frequency-dependent mating advantage. However, the potential frequency-dependent behavioural differences in flight between the morphs, as well as the role of male-male interactions in inducing flying activity, have not been previously considered. We ran an outdoor cage experiment where proportions of both male morphs were manipulated to test whether flying activity was frequency- dependent and differed between morphs. The white morph was significantly more active than the yellow one across all treatments, and sustained activity for longer. Overall activity for both morphs was considerably lower in the yellow-biased environment, suggesting that higher proportions of yellow males in a population may lead to overall reduced flying activity. The activity of the yellow morph also followed a steeper, narrower curve than that of the white morph during peak female calling activity. We sug- gest that white males, with their presumably less costly defences, have more resources to invest in flight for predator escape and finding mates. Yellow males, which are better protected but less sexually selected, may instead compensate their lower flight ac- tivity by ＇flying smart＇ during the peak female-calling periods. Thus, both morphs may be able to behaviourally balance the trade-off between warning signal selection and sexual selection. Our results emphasize the greater need to investigate animal behaviour and colour polymorphisms in natural or semi-natural environments [Current Zoology 61 （4）： 765-772, 2015].展开更多
Toxic insects advertise their defended state to potential predators using warning displays. Frequently these displays use cues through more than one sensory modality, and combine color, smell and sound to produce a mu...Toxic insects advertise their defended state to potential predators using warning displays. Frequently these displays use cues through more than one sensory modality, and combine color, smell and sound to produce a multimodal warning display. Signalling through more than one sensory pathway may enhance the rate of avoidance learning, and the memorability of the learned avoidance. A common insect warning odor, pyrazine, has previously been shown to increase the rate of learned avoidance of unpalatable yellow prey by domestic chicks （GaUus gallus domesticus）, and the odor also improved memory of this learned avoidance. However, to date no research has examined this response to pyrazine odor using wild birds under natural conditions. This study used wild robins （Erithacus rubecula） to investigate whether wild birds avoided yellow baits that smelled of pyrazine more strongly than those presented with no odor. The results provide some evidence that pyrazine odor does increase the level of protection an aposematic insect gains from a wild avian predator, but that the effect of pyrazine on learned avoidance was much weaker than was found with domestic chicks .展开更多
The night sky is the venue of an ancient acoustic battle between echolocating bats and their insect prey. Many tiger moths （Lepidoptera： Arctiidae） answer the attack calls of bats with a barrage of high frequency c...The night sky is the venue of an ancient acoustic battle between echolocating bats and their insect prey. Many tiger moths （Lepidoptera： Arctiidae） answer the attack calls of bats with a barrage of high frequency clicks. Some moth species use these clicks for acoustic aposematism and mimicry, and others for sonar jamming, however, most of the work on these defensive functions has been done on individual moth species. We here analyze the diversity of structure in tiger moth sounds liom 26 spe- cies collected at three locations in North and South America. A principal components analysis of the anti-bat tiger moth sounds reveals that they vary markedly along three axes： （1） frequency, （2） duty cycle （sound production per unit time） and frequency modulation, and （3） modulation cycle （clicks produced during flexion and relaxation of the sound producing tymbal） structure. Tiger moth species appear to cluster into two distinct groups： one with low duty cycle and few clicks per modulation cycle that supports an acoustic aposematism function, and a second with high duty cycle and many clicks per modulation cycle that is con- sistent with a sonar jamming function. This is the first evidence from a community-level analysis to support multiple functions for tiger moth sounds. We also provide evidence supporting an evolutionary history for the development of these strategies. Further- more, cross-correlation and spectrogram correlation measurements failed to support a ＂phantom echo＂ mechanism underlying sonar jamming, and instead point towards echo interference [Current Zoology 56 （3）： 358-369, 2010].展开更多
Batesian mimicry is the process in which harmless species adopt the appearance of a dangerous, aposematic species.In some prey species,both Batesian mimetic and non-Batesian morphs coexist,presupposing that both morph...Batesian mimicry is the process in which harmless species adopt the appearance of a dangerous, aposematic species.In some prey species,both Batesian mimetic and non-Batesian morphs coexist,presupposing that both morphs have to be evolutionarily advantageous.The viperine snake, Natrix maura,exhibits a zigzag dorsal pattern and antipredatory behavior that mimics European vipers.This snake also has a striped dorsal pattern that coexists with the zigzag pattern.We have examined whether individuals belonging to different geographically structured clades were more likely to exhibit a certain dorsal pattern,and whether the zigzag pattern has a protective function by exposing artificial snakes to predation in natural environments,in addition to comparing antipredatory behavior between zigzag and striped snakes also in natural environments.Our results indicate that the striped pattern was not geographically structured,but habitat-dependent.Aerial predators less frequently attacked zigzag plasticine models than striped or unpatterned models.We detected a shift in antipredator behavior between the 2 morphs,as Batesian mimicking N.maura responded to an approaching potential predator by remaining immobile or fleeing at shorter distances than did striped ones.We conclude that Batesian mimics maintain the cryptic and aposematic value by resembling vipers,whereas in open habitats the non-Batesian mimic has altered its antipredator behavior to maintain its fitness.展开更多
A laboratory colony of Coleomegilla maculata (De Geer) was selected for a novel phenotypic color trait. The phenotype was paler in color than the wild type, although not as pale as a previously described mutant strain...A laboratory colony of Coleomegilla maculata (De Geer) was selected for a novel phenotypic color trait. The phenotype was paler in color than the wild type, although not as pale as a previously described mutant strain, yellow (ye), and retained dark pigmentation in the eyes. This selected strain was named gold. Mendelian breeding experiments indicate a recessive biallelic inheritance. The strain has decreased fitness characteristics based on measurements of egg production and pupa size.展开更多
Animals can avoid predation by masquerading as objects that are not food to their predators. Alder moth Acronicta alni larvae go through an impressive ontogenetic change from masquerade to highly conspicuous appearanc...Animals can avoid predation by masquerading as objects that are not food to their predators. Alder moth Acronicta alni larvae go through an impressive ontogenetic change from masquerade to highly conspicuous appearance： early larval stages resemble bird droppings but in the last instar the larval coloration changes into striking yellow-and-black stripes. We hypothe- sized that such a change may be driven by differential predation favoring dissimilar anti-predator strategies in different life stages We show with a series of laboratory assays that larvae are distasteful to birds regardless of their developmental stage, suggesting that ontogenetic color change is not driven by the differential chemical defense. Birds showed higher variance in hesitation to- ward conspicuous prey; some individuals hesitated long time before attacking whereas all birds attacked instantly masqueraded prey. We also found that the activity level of the larvae increased with age, which fits to the fact that larvae need to move from foliage to pupation sites. In the field by using artificial larvae resembling the two life-history stages we found predation risk to vary during the season： In early summer larger yellow-and-black larvae were attacked most, whereas later in the summer small ＇bird-dropping-larvae＇ suffered the highest predation. We conclude that the ontogenetic switch from masquerading to aposema- tism is adaptive most likely because actively moving prey cannot mimic immotile objects and thus, aposematism during the ac- tive and vulnerable period when larvae are searching for pupation sites becomes beneficial展开更多
Chemical defenses are frequently accompanied by salient color patterns actively avoided by predators,a phe-nomenon referred to as aposematism.However,the production of both chemical defenses and pigments is costly,and...Chemical defenses are frequently accompanied by salient color patterns actively avoided by predators,a phe-nomenon referred to as aposematism.However,the production of both chemical defenses and pigments is costly,and is thus expected to be reduced under mild predator pressure.In this work,I compared the size and coloration of parotoid glands(2 dorsal,external swollen structures that secrete toxins in toads)of male and female Epidalea calamita toads from agrosystems and from pine groves.I also quantified the predator attacks received by plas-ticine toad models,whose“parotoid glands”differed in size and color conspicuousness,exposed in each habitat.Predators avoided models with large and conspicuous parotoid glands,but models in agrosystems were more of-ten attacked.Concerning actual toads,agrosystem and male individuals had larger parotoid glands,presumably implying greater production of chemical defenses than in pine grove and female conspecifics.Thesefindings are aligned with previous research suggesting that both agrosystem toads and males in this system are subjected to a more intense predator pressure.Difference between parotoid gland and dorsum coloration was greater in agrosys-tem toads.A marked internal pattern could function as an aposematic signal,which could counteract increased predator pressure.展开更多
基金funded by 2 grants awarded to KPB(Animal Behavior Society,Student Research Grant and Sigma Xi,Grants-in-Aid of Research)funding from John Carroll University.
文摘Aposematism is an antipredator strategy in which conspicuous coloration acts as a warning of chemical defenses to potential predators.Evidence suggests that aposematism largely functions under positive frequency-dependent selection,which is thought to maintain uniformity of aposematic signals.Many studies of aposematic organisms have found evidence that color signals and defenses are positively correlated,indicating a quantitatively honest aposematic signal.Dendrobatid poison frogs represent a well-studied group of aposematic organisms that in addition to exhibiting a diversity of color signals also display unique defensive behaviors.Few studies have examined if both behavior and coloration act as quantitative honest signals of alkaloid defenses in poison frogs.We aimed to determine if coloration and behavior are quantitatively honest signals in the green and black poison frog(Dendrobates auratus)among 6 populations from Costa Rica.We(1)evaluated antipredator displays by using behavioral assays in the field,(2)assessed frog conspicuousness and pattern using digital images,and(3)quantified alkaloid profiles from frog skin secretions.We found that Pacific populations are less conspicuous in coloration,had greater quantities of alkaloids,and more frequently performed body-raising defensive behaviors when compared with Caribbean populations.Our results do not support the hypothesis that aposematic traits in D.auratus are quantitatively honest.Rather,our results suggest that phenotypic differences among populations may represent different phenotypic optima for advertising unprofitability to predators based on local environmental conditions,leading to the diversification of aposematic signals in this species.
文摘Although the use of distinct colors to indicate unprofitability to predators(i.e.aposematism)is commonly thought of as an adaptation,our knowledge of its macroevolutionary effects is limited.Because aposematism is expected to decrease attacks by predators,we hypothesized that aposematic lineages should be larger on average than their non-aposematic sister groups because of the decreased probability of extinction and/or increased probability of speciation(i.e.increased diversification).The results of our sister-group analysis are consistent with the hypothesis that the evolution of aposematism is accompanied by increased diversification of lineages,with the aposematic focal group having more species in 11 of 14 pairs of sister groups.Despite the apparent advantages of reduced predation risk on diversification rates,the evolution of aposematism is relatively rare and reversions to a cryptic state are not uncommon.In addition to the difficulties in evolving a trait that initially decreases the survivorship of prey among naïve predators,we discuss other factors that may limit the apparent prevalence and success of aposematism.It is hoped that the results of our analysis will encourage further analyses of the phylogenetic relationships among aposematic groups and their relatives,and of the evolutionary time scales over which the benefits of aposematism are the greatest to lineages with this condition.
文摘Color polymorphisms have been traditionally attributed to apostatic selection.The perception of color depends on the visual system of the observer.Theoretical models predict that differently perceived degrees of conspicuousness by two predator and prey species may cause the evolution of polymorphisms in the presence of anti-apostatic and apostatic selection.The spider Gasteracantha cancriformis(Araneidae)possesses several conspicuous color morphs.In orb-web spiders,the prey attraction hypothesis states that conspicuous colors are prey lures that increase spider foraging success via flower mimicry.Therefore,polymorphism could be maintained if each morph attracted a different prey species(multiple prey hypothesis)and each spider mimicked a different flower color(flower mimicry hypothesis).Conspicuous colors could be a warning signal to predators because of the spider's hard abdomen and spines.Multiple predators could perceive morphs differently and exert different degrees of selective pressures(multiple predator hypothesis).We explored these 3 hypotheses using reflectance data and color vision modeling to estimate the chromatic and achromatic contrast of G.cancriformis morphs as perceived by several potential prey and predator taxa.Our results revealed that individual taxa perceive the conspicuousness of morphs differently.Therefore,the multiple prey hypothesis and,in part,the multiple predator hypothesis may explain the evolution of color polymorphism in G.cancriformis,even in the presence of anti-apostatic selection.The flower mimicry hypothesis received support by color metrics,but not by color vision models.Other parameters not evaluated by color vision models could also affect the perception of morphs and influence morph survival and polymorphism stability.
文摘Many aposematic insect species advertise their toxicity to potential predators using olfactory and auditory signals, in addition to visual signals, to produce a multimodal warning display. The olfactory signals in these displays may have interesting effects, such as eliciting innate avoidance against novel colored prey, or improving learning and memory of defended prey. However, little is known about the effects of such ancillary signals when they are auditory rather than olfactory. The few studies that have investigated this question have provided conflicting results. The current study sought to clarify and extend understanding of the effects of prey auditory signals on avian predator responses. The domestic chick Gallus gallus domesticus was used as a model avian predator to examine how the defensive buzzing sound of a bumblebee Bombus terrestris affected the chick＇s innate avoidance behavior, and the learning and memory of prey avoidance. The results demonstrate that the buzzing sound had no effect on the predator＇s responses to unpalatable aposematically colored crumbs, suggesting that the agitated buzzing of B. terrestris may provide no additional protection from avian predators .
文摘Predators efficiently learn to avoid one type of warning signal rather than several, making colour polymorphisms un- expected. Aposematic wood tiger moth males Parasemia plantaginis have either white or yellow hindwing coloration across Eu- rope. Previous studies indicate that yellow males are better defended from predators, while white males have a positively frequency-dependent mating advantage. However, the potential frequency-dependent behavioural differences in flight between the morphs, as well as the role of male-male interactions in inducing flying activity, have not been previously considered. We ran an outdoor cage experiment where proportions of both male morphs were manipulated to test whether flying activity was frequency- dependent and differed between morphs. The white morph was significantly more active than the yellow one across all treatments, and sustained activity for longer. Overall activity for both morphs was considerably lower in the yellow-biased environment, suggesting that higher proportions of yellow males in a population may lead to overall reduced flying activity. The activity of the yellow morph also followed a steeper, narrower curve than that of the white morph during peak female calling activity. We sug- gest that white males, with their presumably less costly defences, have more resources to invest in flight for predator escape and finding mates. Yellow males, which are better protected but less sexually selected, may instead compensate their lower flight ac- tivity by ＇flying smart＇ during the peak female-calling periods. Thus, both morphs may be able to behaviourally balance the trade-off between warning signal selection and sexual selection. Our results emphasize the greater need to investigate animal behaviour and colour polymorphisms in natural or semi-natural environments [Current Zoology 61 （4）： 765-772, 2015].
文摘Toxic insects advertise their defended state to potential predators using warning displays. Frequently these displays use cues through more than one sensory modality, and combine color, smell and sound to produce a multimodal warning display. Signalling through more than one sensory pathway may enhance the rate of avoidance learning, and the memorability of the learned avoidance. A common insect warning odor, pyrazine, has previously been shown to increase the rate of learned avoidance of unpalatable yellow prey by domestic chicks （GaUus gallus domesticus）, and the odor also improved memory of this learned avoidance. However, to date no research has examined this response to pyrazine odor using wild birds under natural conditions. This study used wild robins （Erithacus rubecula） to investigate whether wild birds avoided yellow baits that smelled of pyrazine more strongly than those presented with no odor. The results provide some evidence that pyrazine odor does increase the level of protection an aposematic insect gains from a wild avian predator, but that the effect of pyrazine on learned avoidance was much weaker than was found with domestic chicks .
基金support from the Richter Foundation(JRB)a Wake Forest University Dean's Fellowship (AJC)from the National Science Foundation #IBN-0135825 (WEC)
文摘The night sky is the venue of an ancient acoustic battle between echolocating bats and their insect prey. Many tiger moths （Lepidoptera： Arctiidae） answer the attack calls of bats with a barrage of high frequency clicks. Some moth species use these clicks for acoustic aposematism and mimicry, and others for sonar jamming, however, most of the work on these defensive functions has been done on individual moth species. We here analyze the diversity of structure in tiger moth sounds liom 26 spe- cies collected at three locations in North and South America. A principal components analysis of the anti-bat tiger moth sounds reveals that they vary markedly along three axes： （1） frequency, （2） duty cycle （sound production per unit time） and frequency modulation, and （3） modulation cycle （clicks produced during flexion and relaxation of the sound producing tymbal） structure. Tiger moth species appear to cluster into two distinct groups： one with low duty cycle and few clicks per modulation cycle that supports an acoustic aposematism function, and a second with high duty cycle and many clicks per modulation cycle that is con- sistent with a sonar jamming function. This is the first evidence from a community-level analysis to support multiple functions for tiger moth sounds. We also provide evidence supporting an evolutionary history for the development of these strategies. Further- more, cross-correlation and spectrogram correlation measurements failed to support a ＂phantom echo＂ mechanism underlying sonar jamming, and instead point towards echo interference [Current Zoology 56 （3）： 358-369, 2010].
文摘Batesian mimicry is the process in which harmless species adopt the appearance of a dangerous, aposematic species.In some prey species,both Batesian mimetic and non-Batesian morphs coexist,presupposing that both morphs have to be evolutionarily advantageous.The viperine snake, Natrix maura,exhibits a zigzag dorsal pattern and antipredatory behavior that mimics European vipers.This snake also has a striped dorsal pattern that coexists with the zigzag pattern.We have examined whether individuals belonging to different geographically structured clades were more likely to exhibit a certain dorsal pattern,and whether the zigzag pattern has a protective function by exposing artificial snakes to predation in natural environments,in addition to comparing antipredatory behavior between zigzag and striped snakes also in natural environments.Our results indicate that the striped pattern was not geographically structured,but habitat-dependent.Aerial predators less frequently attacked zigzag plasticine models than striped or unpatterned models.We detected a shift in antipredator behavior between the 2 morphs,as Batesian mimicking N.maura responded to an approaching potential predator by remaining immobile or fleeing at shorter distances than did striped ones.We conclude that Batesian mimics maintain the cryptic and aposematic value by resembling vipers,whereas in open habitats the non-Batesian mimic has altered its antipredator behavior to maintain its fitness.
文摘A laboratory colony of Coleomegilla maculata (De Geer) was selected for a novel phenotypic color trait. The phenotype was paler in color than the wild type, although not as pale as a previously described mutant strain, yellow (ye), and retained dark pigmentation in the eyes. This selected strain was named gold. Mendelian breeding experiments indicate a recessive biallelic inheritance. The strain has decreased fitness characteristics based on measurements of egg production and pupa size.
文摘Animals can avoid predation by masquerading as objects that are not food to their predators. Alder moth Acronicta alni larvae go through an impressive ontogenetic change from masquerade to highly conspicuous appearance： early larval stages resemble bird droppings but in the last instar the larval coloration changes into striking yellow-and-black stripes. We hypothe- sized that such a change may be driven by differential predation favoring dissimilar anti-predator strategies in different life stages We show with a series of laboratory assays that larvae are distasteful to birds regardless of their developmental stage, suggesting that ontogenetic color change is not driven by the differential chemical defense. Birds showed higher variance in hesitation to- ward conspicuous prey; some individuals hesitated long time before attacking whereas all birds attacked instantly masqueraded prey. We also found that the activity level of the larvae increased with age, which fits to the fact that larvae need to move from foliage to pupation sites. In the field by using artificial larvae resembling the two life-history stages we found predation risk to vary during the season： In early summer larger yellow-and-black larvae were attacked most, whereas later in the summer small ＇bird-dropping-larvae＇ suffered the highest predation. We conclude that the ontogenetic switch from masquerading to aposema- tism is adaptive most likely because actively moving prey cannot mimic immotile objects and thus, aposematism during the ac- tive and vulnerable period when larvae are searching for pupation sites becomes beneficial
文摘Chemical defenses are frequently accompanied by salient color patterns actively avoided by predators,a phe-nomenon referred to as aposematism.However,the production of both chemical defenses and pigments is costly,and is thus expected to be reduced under mild predator pressure.In this work,I compared the size and coloration of parotoid glands(2 dorsal,external swollen structures that secrete toxins in toads)of male and female Epidalea calamita toads from agrosystems and from pine groves.I also quantified the predator attacks received by plas-ticine toad models,whose“parotoid glands”differed in size and color conspicuousness,exposed in each habitat.Predators avoided models with large and conspicuous parotoid glands,but models in agrosystems were more of-ten attacked.Concerning actual toads,agrosystem and male individuals had larger parotoid glands,presumably implying greater production of chemical defenses than in pine grove and female conspecifics.Thesefindings are aligned with previous research suggesting that both agrosystem toads and males in this system are subjected to a more intense predator pressure.Difference between parotoid gland and dorsum coloration was greater in agrosys-tem toads.A marked internal pattern could function as an aposematic signal,which could counteract increased predator pressure.
