Glucocorticoids participate in the behavioral and physiological responses generated under stressful circumstances coming from different sources—physical and/or psychological. In mammals, the ...increases of these hormones are mediated by the activation of the hypothalamic–pituitary–adrenal axis. This response occurs after exposure to novel and unpredictable situations that lead to the loss of homeostasis, for example, a direct encounter with predators or their cues. However, the relationship between the physiological and behavioral responses is still a complex issue in vertebrates. We evaluate the effects of an experimental manipulation of glucocorticoid levels on the generation of the behavioral and physiological response to stress by predation in the subterranean rodent
C. talarum
. We found that when tuco-tucos encountered predator cues—fur odor, and largely, immobilization—they responded physiologically by secreting cortisol. This response was accompanied by an associated behavioral response. However, when the increase in plasma cortisol originated exogenously by the injection of cortisol, a behavioral response was not observed. Finally, inhibition of glucocorticoids’ synthesis was effective in weakening the behavioral effects produced by immobilization. In conclusion, in tuco-tucos, predator cues act as stress factors that trigger differential increases in plasma cortisol and a behavioral response associated with the appearance of anxiety states.
Subterranean Rodents Begall, Sabine; Burda, Hynek; Schleich, Cristian E
2007, 2007-07-02
eBook, Book
Across the globe, about 250 species of rodents spend most of their lives in safe and stable, but dark, oxygen-poor and carbon dioxide-rich burrows, deprived of most of the sensory cues available ...aboveground. They have become fully specialized for a unique way of life in which foraging and breeding take place underground. The systematic research into adaptations of subterranean dwellers is only about two decades old, but it has rapidly intensified within the last few years, bringing insight into many aspects of the biology and evolution at different organization levels. Subterranean Rodents presents achievements from the last years of research on these rodents, divided into five sections: ecophysiology, sensory ecology, life histories, behavioural ecology and demography, environmental and economical impact, molecular ecology and evolution. It is a must for all researchers working in this field and will be of interest to zoologists, physiologists, morphologists, ecologists, and evolutionary biologists.
Predation is a strong selective force, and prey species may show specific adaptations that allow recognition, avoidance, and defense against predators. Facing a situation of predatory risk, anxiety ...constitutes a reaction of adaptive value, allowing to evaluate the potential risk of this encounter as well as to generate a physiological and behavioral response. Previous studies in the subterranean rodent Ctenomys talarum revealed that exposure to predator odors (urine or fur) generates an anxiety state and induces behavioral changes. However, no differences between the responses generated by both odor sources were observed, although fur odors may indicate a higher level of predatory immanence. Therefore, the aim of this study was to evaluate the behavioral and physiological responses of C. talarum to different intensities of predator odors (urine and fur) and to the repeated exposition to the same odorous stimulus. When comparing the highest behavioral effects elicited by both predatory odors on C. talarum, our study supports the assumption that fur odors are more anxiogenic than urine, while the former provoked significant changes in the distance traveled, the number of arm entries and time in transparent arms in the elevated plus maze; cat urine only caused slight changes on those behavioral parameters. Furthermore, we also found that the intensity of natural predator odor presented to tuco‐tucos has a role on the appearance of defensive behaviors, although an amount‐dependent relationship between predator odor and anxiety levels was not observed. Finally, while individuals exposed for 1 day to fur odor displayed an evident anxiety state, those exposed repeatedly for 5 consecutive days did not differ with the control group in their behavioral response, indicating a clear habituation to the predatory cue. In our intensity and habituation experiments, we did not find differences in the measured physiological parameters among control individuals, exposed to different cues intensity (urine and fur odor) and exposed only once or for 5 days to fur odor. These results provide valuable evidence that the types of predatory odor, along with the frequency of exposition, are important determinants of the appearance, strength, and extinction of defensive behaviors in the subterranean rodent C. talarum.
Subterranean rodents are able to dig long straight tunnels. Keeping the course of such "runways" is important in the context of optimal foraging strategies and natal or mating dispersal. These ...tunnels are built in the course of a long time, and in social species, by several animals. Although the ability to keep the course of digging has already been described in the 1950s, its proximate mechanism could still not be satisfactorily explained. Here, we analyzed the directional orientation of 68 burrow systems in five subterranean rodent species (
,
,
,
, and
) on the base of detailed maps of burrow systems charted within the framework of other studies and provided to us. The directional orientation of the vast majority of all evaluated burrow systems on the individual level (94%) showed a significant deviation from a random distribution. The second order statistics (averaging mean vectors of all the studied burrow systems of a respective species) revealed significant deviations from random distribution with a prevalence of north-south (
), NNW-SSE (
), and NE-SW (
mole-rats) oriented tunnels. Burrow systems of
were randomly oriented. We suggest that the Earth's magnetic field acts as a common heading indicator, facilitating to keep the course of digging. This study provides a field test and further evidence for magnetoreception and its biological meaning in subterranean mammals. Furthermore, it lays the foundation for future field experiments.
Abstract Several lines of evidence suggest that learning and triggering an immune response are both metabolically expensive and thus likely to be subject to nutritional trade-offs between them and ...other competing demands. Therefore, we evaluated if an immune challenge with a novel antigen affects spatial learning in the subterranean rodent Ctenomys talarum under two different dietary conditions. The results showed that immune-challenged animals were affected in their spatial learning capabilities, increasing the number of errors and marginally the time required to reach the goal of a complex labyrinth. No effect of the dietary restriction nor interaction between factors were observed. This work provides support for the existence of a trade-off between the costs of the immune defense and learning abilities, indicating that when investment is required to fight infection, fewer resources are available for learning. The absence of effect of nutritional condition on this trade-off suggests that other physiological processes, besides cognition, may be limited by the energetic resources necessary to the more immediately critical immune response.
Predatory risk is recognized as an important factor that impacts on behavior, distribution, and reproduction of animals. Facing the presence of predators’ cues, preys have developed a series of ...anti-predatory behaviors that involve trade-offs between costs and benefits. Faced with the clear advantage of reducing the immediate risk of predation, preys are forced to modify their performance in other activities. The most documented of them is undoubtedly the foraging. In the presence of predators or their cues in the environment, a compromise between food and safety arises, so that the prey restricts the time searching for food, limits it to protected sites, or increase the vigilance, thus impacting foraging success and consequently in reproductive performance and long-term survival. However, the influence of several factors, like nutritional condition (fed or food deprived) or predator experience, on preys’ feeding choices has been comparatively less studied. Therefore, the aim of this work was to evaluate
Ctenomys talarum
’s feeding behavior under the presence of predator cues (cat urine) considering (1) their nutritional condition and (2) a recent experience of a failed predatory event. The results of this work show that tuco-tucos can distinguish cues indicative of the presence of a predator and prefer to feed in areas where predator cues are not present (safe sites). Also, recent predatory experiences influenced foraging decisions, increasing the time without activity previous to a new feeding excursion. In conclusion, these results demonstrate the importance of the perception of predatory risk in the foraging behavior of
C. talarum
.
Spatial learning, the cognitive ability that allows animals to efficiently locate food, partners or avoid predators, can be affected by various factors such as stress. Stressors represent a threat to ...the animal's homeostasis and trigger a set of physiological and behavioral changes known as stress response. The herbivorous rodent Ctenomys talarum (tuco‐tuco) inhabits underground complex gallery systems. Dispersal as well as food collection occurs on the surface, where they are exposed to terrestrial and aerial predators. We evaluated the effect of a natural stress factor, predation, on spatial learning of C. talarum. Additionally, we collected data on neutrophil/lymphocyte ratio, hematocrit, blood glucose, and plasma cortisol to assess physiological levels of stress. The acute exposure to direct cues indicating the presence of a predator (immobilization + cat urine) increased the time needed to reach the goal in a longitudinal labyrinth. The number of errors also increased albeit the difference was only marginally significant. The chronic exposure to predator cues (immobilization, cat urine, and cat fur) presented in an unpredictable order significantly increased both time and errors committed by tuco‐tucos during learning trials in the labyrinth. Results show the strong impact of predatory stress on the spatial abilities of C. talarum, a key cognitive process involved in most of their vital activities. They also highlight the importance of investigating wild species as regards the development of antipredatory defensive behaviors that contribute both to the avoidance of deleterious consequences of a direct attack and the influence on food search and mate localization performance.
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