ABSTRACT Foraging underground poses a number of important challenges for fossorial animals, such ... more ABSTRACT Foraging underground poses a number of important challenges for fossorial animals, such as amphisbaenians. For instance, visual detection and identification of prey is often hampered by low light conditions and poor eye sight. In response, many fossorial animals have switched to other sensory systems, such as chemoreception. We tested the ability of the amphisbaenian Trogonophis wiegmanni to detect and discriminate between different prey types based on chemical cues alone. Results of a laboratory experiment showed that amphisbaenians were able to detect prey using chemoreception, as indicated by an increase in chemosensory tongue-flick responses to swabs bearing chemicals from prey in comparison with blank controls. Also, differential tongue-flick rates to chemicals from different prey types indicated that at least some prey types may be discriminated from others based on chemosensory cues. These results suggest that T. wiegmanni amphisbaenians use chemoreception when foraging.
Background: In spite that chemoreception is important in sexual selection for many animals, such ... more Background: In spite that chemoreception is important in sexual selection for many animals, such as reptiles, the mechanisms that confer reliability to chemical signals are relatively unknown. European green lizards (Lacerta viridis) have substantial amounts of a-tocopherol (= vitamin E) in their femoral secretions. Because vitamin E is metabolically important and can only be attained from the diet, its secretion is assumed to be costly. However, its role in intraspecific communication is unknown. Methodology/Principal Findings: Here, we experimentally show that male European green lizards that received a dietary supplement of vitamin E increased proportions of vitamin E in their femoral secretions. Furthermore, our experiments revealed that females preferred to use areas scent marked by males with experimentally increased vitamin E levels in their secretions. Finally, female preferences were stronger when vitamin E differences between a pair of males' secretions were larger. Conclusions/Significance: Our results demonstrate that female green lizards are able to discriminate between males based on the vitamin E content of the males' femoral secretions. We suggest that the possible cost of allocating vitamin E to secretions, which might be dependent on male quality, may be a mechanism that confers reliability to scent marks of green lizards and allows their evolution as sexual signals.
Background: Many animals produce elaborated sexual signals to attract mates, among them are commo... more Background: Many animals produce elaborated sexual signals to attract mates, among them are common chemical sexual signals (pheromones) with an attracting function. Lizards produce chemical secretions for scent marking that may have a role in sexual selection. In the laboratory, female rock lizards (Iberolacerta cyreni) prefer the scent of males with more ergosterol in their femoral secretions. However, it is not known whether the scent-marks of male rock lizards may actually attract females to male territories in the field. Methodology/Principal Findings: In the field, we added ergosterol to rocks inside the territories of male lizards, and found that this manipulation resulted in increased relative densities of females in these territories. Furthermore, a higher number of females were observed associated to males in manipulated plots, which probably increased mating opportunities for males in these areas. Conclusions/Significance: These and previous laboratory results suggest that female rock lizards may select to settle in home ranges based on the characteristics of scent-marks from conspecific males. Therefore, male rock lizards might attract more females and obtain more matings by increasing the proportion of ergosterol when scent-marking their territories. However, previous studies suggest that the allocation of ergosterol to secretions may be costly and only high quality males could afford it, thus, allowing the evolution of scent-marks as an honest sexual display.
Many studies have shown the importance of colorful ornamentation in mate choosiness or intrasexua... more Many studies have shown the importance of colorful ornamentation in mate choosiness or intrasexual conflict. However, research on color ornaments has focused mainly on birds, lizards or fish, but remains practically unknown in other animal groups such as turtles. In addition, female ornaments and their relation with sexual selection also remain almost unknown. Here, we measured the coloration of the shell and the limb stripes of male and female Spanish terrapins Mauremys leprosa and explored the existence of sexual dichromatism and the relation of color characteristics with body size and health state estimated from the immune response to the injection of an antigen (phytohaemagglutinin test). Our results showed that shell coloration, which could be constrained by natural selection to be cryptic, changed with body size, but did not differ between sexes. In contrast, females had brighter and less ultraviolet-saturated and more orange-saturated limb stripes than males. In females, interindividual variation in limb stripe coloration was related with body size and immune response suggesting that this coloration may inform honestly about multiple traits that could be important in sexual selection. In contrast, coloration of limb stripes of males was duller than in females, and was not related with any trait suggesting that coloration is not important in sexual selection for males.
Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 2009
Sexual signals can be evolutionarily stable if they are honest and condition dependent or costly ... more Sexual signals can be evolutionarily stable if they are honest and condition dependent or costly to the signaler. One possible cost is the existence of a trade-off between maintaining the immune system and the elaboration of ornaments. We experimentally challenged the immune system of male Iberian wall lizards, Podarcis hispanica, with a bacterial antigen (lipopolysaccharide) without pathogenic effects to explore whether the immune activation affected sexually dimorphic visual ornaments. Ventrolateral coloration changed in all males, but immune activation affected some characteristics of coloration of experimental males (i.e., challenged males failed to increase brightness and medium wavelengths over time as control males did, and the proportion of yellow pigments decreased after the immune activation) but not others (i.e., proportion of blue, green and red pigments changed equally in all males). Results suggested the existence of a trade-off between physiological regulation of the immune system and the allocation of essential compounds (probably carotenoids) to sexual ornaments. We suggest that this trade-off may allow one to honestly signal individual male quality via characteristics of coloration in lizards, which may have an important role in both intra-and intersexual selection processes.
Vertebrate males often show breeding colours that may function as reliable signals of status in i... more Vertebrate males often show breeding colours that may function as reliable signals of status in intrasexual competition. In many lacertid lizards, males show a conspicuous row of small but distinctive blue spots that runs along their body side on the outer margin of the belly. However, no study has examined the role of these blue spots. We first analysed in a field population of the Iberian rock lizard, Lacerta monticola, the relationships between number of blue spots and some morphological traits, which are known to be related to males’ fighting ability. The number of spots seems to be an character showing ontogenetic change as large (generally older) males showed more blue spots than small (generally younger) males. Males with a higher body condition also showed a higher number of blue spots. Thus, a higher number of blue spots may be used to signal size, age or body condition. Many contiguous blue spots would result in a visual artefact consisting of a continuous blue band, which...
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit:
Prey should balance cost and benefits when deciding optimal refuge use. In ectotherms, such as li... more Prey should balance cost and benefits when deciding optimal refuge use. In ectotherms, such as lizards, body temperature can decrease in cold refuges, which has negative effects on physiological and locomotor performance. Thus, refuge use of ectotherms should be influenced by the thermal environment as well as by the body size-dependent thermal inertia of each individual. We simulated predator attacks to Schreiber's Green lizards (Lacerta schreiberi) and analyzed their refuge use. Results indicated that temperatures outside and inside a refuge had opposite effects on refuge use decisions. Thus, when initial external temperatures were higher and lizards had higher thermal inertia, lizards could spend longer times inside refuges before reaching a 'critical' low body temperature. However, when refuge temperature was low lizards did not decrease refuge use. If low refuge temperatures increased risk upon emerging because lizards had lower escape performance, lizards would need to compensate by remaining in a refuge for longer to scan the surroundings before emerging to ensure that the risk of a new attack decreased. Therefore, when deciding refuge use, L. schreiberi lizards seem to consider physiological costs of being at low temperatures and also the risk of emerging with low escape performance.
Some mate choice theories propose that only male signals that are honest and condition-dependent ... more Some mate choice theories propose that only male signals that are honest and condition-dependent can be stable, while another hypothesis states that males evolve signals that exploit the sensory system of females. However, sensory traps might evolve into honest signals if they are differentially costly for males. We tested whether a pre-existing sensory bias for food chemicals explained chemosensory preferences of female Iberian rock lizards for male scents. We manipulated hunger levels of females and found that food-deprived females had increased chemosensory responses to chemical stimuli from both invertebrate prey and femoral secretions of males, but not to control water. Further tests suggested that cholesta-5,7dien-3-ol (provitamin D 3), a lipid found in both prey and males' scent, may be one of the chemicals eliciting these responses. Moreover, hungry females spent more time on scent marks of males that had experimentally increased cholesta-5,7-dien-3-ol than on scent marks of males alone, whereas for control females this effect was not significant. We suggest that preexisting sensory bias for essential nutrients (i.e., provitamin D) may be the origin of similar female responses to male chemicals. However, previous studies have suggested that the allocation of these chemicals to ornaments is costly and only high quality males can afford it. Therefore, preexisting sensory bias for essential nutrients may further allow the evolution and maintenance of honest sexual displays.
Socially dominant males often signal their status to rival males and/or females. We tested the hy... more Socially dominant males often signal their status to rival males and/or females. We tested the hypotheses that Lacerta monticola femoral gland secretions and copulatory plugs convey chemical information about male identity and dominance status. We estimated male dominance status by staging male-male agonistic encounters in a neutral arena. We then conducted two experiments to compare male tongue-flick behavior toward chemical stimuli consisting of cotton swabs bearing (1) deionized water (control), the lizard's own femoral secretions, and the femoral secretions of another male and (2) phosphate-buffered saline solution (control), the lizard's own plug products, and the plug products of another male. Results indicate that males discriminated their own femoral secretions and plugs from those of other males. They also discriminated morphological attributes of other males that were associated with dominance status based on chemical cues arising from femoral secretions and discriminated the dominance status of other males based on chemical cues arising from the plugs. Femoral secretions that convey information about male identity and dominance status may be hypothesized to function in the establishment of L. monticola dominance hierarchies through scent-marking of territories. We suggest that copulatory plugs and femoral secretions may allow males to scent-mark the female body and postulate that this behavior may influence male and female reproductive decisions under selective pressures of sperm competition.
Sexual selection favors more conspicuous male displays, whereas natural selection (via predator p... more Sexual selection favors more conspicuous male displays, whereas natural selection (via predator pressure) favors less conspicuous displays. However, this trade-off might be altered if males with more conspicuous displays could compensate behaviorally for their increased conspicuousness by acting more cautiously toward predators. The aim of this study was to explore in 2 species of Iberian rock lizards whether or not conspicuous coloration was associated with antipredatory behavior and whether conspicuousness-dependent regulation of antipredatory behavior existed. Our results suggested that male lizards may compensate for the negative effects of conspicuous sexual coloration on predation risk by modulating their antipredatory behavior (time inside refuges, false alarms, etc). We found that male Iberolacerta monticola, but not male Iberolacerta cyreni, compensated for the negative effects of blue lateral ocelli, which increased visual conspicuousness. However, male lizards did not compensate for relatively unexposed ventral spots. We also found that male I. monticola in better condition and with more blue lateral ocelli were shier, whereas male I. cyreni in better condition and with more ventral spots were bolder. These 2 lizard species live in habitats that differ in refuge availability and in the number of potential predators, which may promote differences in the trade-off between predation risk and social behavior and may explain the observed interspecific differences in antipredatory behavior. This suggests that regulation of antipredatory behavior may also function as a condition-dependent cost promoting costly (honest) sexual signaling in some species.
Many antipredator adaptations are induced by the prey's ability to recognize chemical cues from p... more Many antipredator adaptations are induced by the prey's ability to recognize chemical cues from predators. However, predator recognition often requires learning by prey individuals. Iberian green frog tadpoles (Pelophylax perezi) have the ability to learn new potential predators. Here, we tested the memory capabilities of Iberian green frog tadpoles. We conditioned tadpoles with chemicals cues from a non-predatory fish in conjunction with conspecific alarm cues, and examined whether tadpoles retained their conditioned response (reduction of activity level). We found that conditioned tadpoles reduced their activity levels in subsequent exposures to the nonpredatory fish cues alone. Tadpoles were able to remember this association and reduced movement rate at least for 9 days after. The ability to learn and memorize potential predators may be especially important for the survivorship of prey species that are likely to find a high variety of predators. However, after those 9 days, there was a lack of response to the non-predatory fish cues alone in the absence of reinforcement. This could be explained if tadpoles behave according to the threat-sensitive predator avoidance hypothesis, and the perceived risk to the learning cue diminished over time, or it could be due to an apparent forgetting process to avoid non-adaptative responses to chemical cues of non-dangerous species that were randomly paired with alarm cues. Thus, this study demonstrates that green frog tadpoles in the absence of reinforcement remember the chemical cues of a learned predator only for a limited time that may be adaptative in a threat-sensitive context.
ABSTRACT Foraging underground poses a number of important challenges for fossorial animals, such ... more ABSTRACT Foraging underground poses a number of important challenges for fossorial animals, such as amphisbaenians. For instance, visual detection and identification of prey is often hampered by low light conditions and poor eye sight. In response, many fossorial animals have switched to other sensory systems, such as chemoreception. We tested the ability of the amphisbaenian Trogonophis wiegmanni to detect and discriminate between different prey types based on chemical cues alone. Results of a laboratory experiment showed that amphisbaenians were able to detect prey using chemoreception, as indicated by an increase in chemosensory tongue-flick responses to swabs bearing chemicals from prey in comparison with blank controls. Also, differential tongue-flick rates to chemicals from different prey types indicated that at least some prey types may be discriminated from others based on chemosensory cues. These results suggest that T. wiegmanni amphisbaenians use chemoreception when foraging.
Background: In spite that chemoreception is important in sexual selection for many animals, such ... more Background: In spite that chemoreception is important in sexual selection for many animals, such as reptiles, the mechanisms that confer reliability to chemical signals are relatively unknown. European green lizards (Lacerta viridis) have substantial amounts of a-tocopherol (= vitamin E) in their femoral secretions. Because vitamin E is metabolically important and can only be attained from the diet, its secretion is assumed to be costly. However, its role in intraspecific communication is unknown. Methodology/Principal Findings: Here, we experimentally show that male European green lizards that received a dietary supplement of vitamin E increased proportions of vitamin E in their femoral secretions. Furthermore, our experiments revealed that females preferred to use areas scent marked by males with experimentally increased vitamin E levels in their secretions. Finally, female preferences were stronger when vitamin E differences between a pair of males' secretions were larger. Conclusions/Significance: Our results demonstrate that female green lizards are able to discriminate between males based on the vitamin E content of the males' femoral secretions. We suggest that the possible cost of allocating vitamin E to secretions, which might be dependent on male quality, may be a mechanism that confers reliability to scent marks of green lizards and allows their evolution as sexual signals.
Background: Many animals produce elaborated sexual signals to attract mates, among them are commo... more Background: Many animals produce elaborated sexual signals to attract mates, among them are common chemical sexual signals (pheromones) with an attracting function. Lizards produce chemical secretions for scent marking that may have a role in sexual selection. In the laboratory, female rock lizards (Iberolacerta cyreni) prefer the scent of males with more ergosterol in their femoral secretions. However, it is not known whether the scent-marks of male rock lizards may actually attract females to male territories in the field. Methodology/Principal Findings: In the field, we added ergosterol to rocks inside the territories of male lizards, and found that this manipulation resulted in increased relative densities of females in these territories. Furthermore, a higher number of females were observed associated to males in manipulated plots, which probably increased mating opportunities for males in these areas. Conclusions/Significance: These and previous laboratory results suggest that female rock lizards may select to settle in home ranges based on the characteristics of scent-marks from conspecific males. Therefore, male rock lizards might attract more females and obtain more matings by increasing the proportion of ergosterol when scent-marking their territories. However, previous studies suggest that the allocation of ergosterol to secretions may be costly and only high quality males could afford it, thus, allowing the evolution of scent-marks as an honest sexual display.
Many studies have shown the importance of colorful ornamentation in mate choosiness or intrasexua... more Many studies have shown the importance of colorful ornamentation in mate choosiness or intrasexual conflict. However, research on color ornaments has focused mainly on birds, lizards or fish, but remains practically unknown in other animal groups such as turtles. In addition, female ornaments and their relation with sexual selection also remain almost unknown. Here, we measured the coloration of the shell and the limb stripes of male and female Spanish terrapins Mauremys leprosa and explored the existence of sexual dichromatism and the relation of color characteristics with body size and health state estimated from the immune response to the injection of an antigen (phytohaemagglutinin test). Our results showed that shell coloration, which could be constrained by natural selection to be cryptic, changed with body size, but did not differ between sexes. In contrast, females had brighter and less ultraviolet-saturated and more orange-saturated limb stripes than males. In females, interindividual variation in limb stripe coloration was related with body size and immune response suggesting that this coloration may inform honestly about multiple traits that could be important in sexual selection. In contrast, coloration of limb stripes of males was duller than in females, and was not related with any trait suggesting that coloration is not important in sexual selection for males.
Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 2009
Sexual signals can be evolutionarily stable if they are honest and condition dependent or costly ... more Sexual signals can be evolutionarily stable if they are honest and condition dependent or costly to the signaler. One possible cost is the existence of a trade-off between maintaining the immune system and the elaboration of ornaments. We experimentally challenged the immune system of male Iberian wall lizards, Podarcis hispanica, with a bacterial antigen (lipopolysaccharide) without pathogenic effects to explore whether the immune activation affected sexually dimorphic visual ornaments. Ventrolateral coloration changed in all males, but immune activation affected some characteristics of coloration of experimental males (i.e., challenged males failed to increase brightness and medium wavelengths over time as control males did, and the proportion of yellow pigments decreased after the immune activation) but not others (i.e., proportion of blue, green and red pigments changed equally in all males). Results suggested the existence of a trade-off between physiological regulation of the immune system and the allocation of essential compounds (probably carotenoids) to sexual ornaments. We suggest that this trade-off may allow one to honestly signal individual male quality via characteristics of coloration in lizards, which may have an important role in both intra-and intersexual selection processes.
Vertebrate males often show breeding colours that may function as reliable signals of status in i... more Vertebrate males often show breeding colours that may function as reliable signals of status in intrasexual competition. In many lacertid lizards, males show a conspicuous row of small but distinctive blue spots that runs along their body side on the outer margin of the belly. However, no study has examined the role of these blue spots. We first analysed in a field population of the Iberian rock lizard, Lacerta monticola, the relationships between number of blue spots and some morphological traits, which are known to be related to males’ fighting ability. The number of spots seems to be an character showing ontogenetic change as large (generally older) males showed more blue spots than small (generally younger) males. Males with a higher body condition also showed a higher number of blue spots. Thus, a higher number of blue spots may be used to signal size, age or body condition. Many contiguous blue spots would result in a visual artefact consisting of a continuous blue band, which...
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit:
Prey should balance cost and benefits when deciding optimal refuge use. In ectotherms, such as li... more Prey should balance cost and benefits when deciding optimal refuge use. In ectotherms, such as lizards, body temperature can decrease in cold refuges, which has negative effects on physiological and locomotor performance. Thus, refuge use of ectotherms should be influenced by the thermal environment as well as by the body size-dependent thermal inertia of each individual. We simulated predator attacks to Schreiber's Green lizards (Lacerta schreiberi) and analyzed their refuge use. Results indicated that temperatures outside and inside a refuge had opposite effects on refuge use decisions. Thus, when initial external temperatures were higher and lizards had higher thermal inertia, lizards could spend longer times inside refuges before reaching a 'critical' low body temperature. However, when refuge temperature was low lizards did not decrease refuge use. If low refuge temperatures increased risk upon emerging because lizards had lower escape performance, lizards would need to compensate by remaining in a refuge for longer to scan the surroundings before emerging to ensure that the risk of a new attack decreased. Therefore, when deciding refuge use, L. schreiberi lizards seem to consider physiological costs of being at low temperatures and also the risk of emerging with low escape performance.
Some mate choice theories propose that only male signals that are honest and condition-dependent ... more Some mate choice theories propose that only male signals that are honest and condition-dependent can be stable, while another hypothesis states that males evolve signals that exploit the sensory system of females. However, sensory traps might evolve into honest signals if they are differentially costly for males. We tested whether a pre-existing sensory bias for food chemicals explained chemosensory preferences of female Iberian rock lizards for male scents. We manipulated hunger levels of females and found that food-deprived females had increased chemosensory responses to chemical stimuli from both invertebrate prey and femoral secretions of males, but not to control water. Further tests suggested that cholesta-5,7dien-3-ol (provitamin D 3), a lipid found in both prey and males' scent, may be one of the chemicals eliciting these responses. Moreover, hungry females spent more time on scent marks of males that had experimentally increased cholesta-5,7-dien-3-ol than on scent marks of males alone, whereas for control females this effect was not significant. We suggest that preexisting sensory bias for essential nutrients (i.e., provitamin D) may be the origin of similar female responses to male chemicals. However, previous studies have suggested that the allocation of these chemicals to ornaments is costly and only high quality males can afford it. Therefore, preexisting sensory bias for essential nutrients may further allow the evolution and maintenance of honest sexual displays.
Socially dominant males often signal their status to rival males and/or females. We tested the hy... more Socially dominant males often signal their status to rival males and/or females. We tested the hypotheses that Lacerta monticola femoral gland secretions and copulatory plugs convey chemical information about male identity and dominance status. We estimated male dominance status by staging male-male agonistic encounters in a neutral arena. We then conducted two experiments to compare male tongue-flick behavior toward chemical stimuli consisting of cotton swabs bearing (1) deionized water (control), the lizard's own femoral secretions, and the femoral secretions of another male and (2) phosphate-buffered saline solution (control), the lizard's own plug products, and the plug products of another male. Results indicate that males discriminated their own femoral secretions and plugs from those of other males. They also discriminated morphological attributes of other males that were associated with dominance status based on chemical cues arising from femoral secretions and discriminated the dominance status of other males based on chemical cues arising from the plugs. Femoral secretions that convey information about male identity and dominance status may be hypothesized to function in the establishment of L. monticola dominance hierarchies through scent-marking of territories. We suggest that copulatory plugs and femoral secretions may allow males to scent-mark the female body and postulate that this behavior may influence male and female reproductive decisions under selective pressures of sperm competition.
Sexual selection favors more conspicuous male displays, whereas natural selection (via predator p... more Sexual selection favors more conspicuous male displays, whereas natural selection (via predator pressure) favors less conspicuous displays. However, this trade-off might be altered if males with more conspicuous displays could compensate behaviorally for their increased conspicuousness by acting more cautiously toward predators. The aim of this study was to explore in 2 species of Iberian rock lizards whether or not conspicuous coloration was associated with antipredatory behavior and whether conspicuousness-dependent regulation of antipredatory behavior existed. Our results suggested that male lizards may compensate for the negative effects of conspicuous sexual coloration on predation risk by modulating their antipredatory behavior (time inside refuges, false alarms, etc). We found that male Iberolacerta monticola, but not male Iberolacerta cyreni, compensated for the negative effects of blue lateral ocelli, which increased visual conspicuousness. However, male lizards did not compensate for relatively unexposed ventral spots. We also found that male I. monticola in better condition and with more blue lateral ocelli were shier, whereas male I. cyreni in better condition and with more ventral spots were bolder. These 2 lizard species live in habitats that differ in refuge availability and in the number of potential predators, which may promote differences in the trade-off between predation risk and social behavior and may explain the observed interspecific differences in antipredatory behavior. This suggests that regulation of antipredatory behavior may also function as a condition-dependent cost promoting costly (honest) sexual signaling in some species.
Many antipredator adaptations are induced by the prey's ability to recognize chemical cues from p... more Many antipredator adaptations are induced by the prey's ability to recognize chemical cues from predators. However, predator recognition often requires learning by prey individuals. Iberian green frog tadpoles (Pelophylax perezi) have the ability to learn new potential predators. Here, we tested the memory capabilities of Iberian green frog tadpoles. We conditioned tadpoles with chemicals cues from a non-predatory fish in conjunction with conspecific alarm cues, and examined whether tadpoles retained their conditioned response (reduction of activity level). We found that conditioned tadpoles reduced their activity levels in subsequent exposures to the nonpredatory fish cues alone. Tadpoles were able to remember this association and reduced movement rate at least for 9 days after. The ability to learn and memorize potential predators may be especially important for the survivorship of prey species that are likely to find a high variety of predators. However, after those 9 days, there was a lack of response to the non-predatory fish cues alone in the absence of reinforcement. This could be explained if tadpoles behave according to the threat-sensitive predator avoidance hypothesis, and the perceived risk to the learning cue diminished over time, or it could be due to an apparent forgetting process to avoid non-adaptative responses to chemical cues of non-dangerous species that were randomly paired with alarm cues. Thus, this study demonstrates that green frog tadpoles in the absence of reinforcement remember the chemical cues of a learned predator only for a limited time that may be adaptative in a threat-sensitive context.
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