Short-term effects of an acute exposure to predatory cues on the spatial working and reference memory performance in a subterranean rodent

Navigational experience affect cognition: Spatial learning capabilities in captive and wild-born tuco-tucos

There is a growing recognition of the influence of both genetic and ecological context in shaping different cognitive traits. The hippocampal region is identified as a critical area for memory and learning in mammals, susceptible to modification by environmental influences. Although previous studies have identified the effects of various factors on cognitive parameters during early development, comparatively few research was conducted on wild species to analyze the role of natural environmental stimuli in the formation of spatial learning and memory abilities. Thus, to assess the importance of exposure to a complex and challenging environment during early development, we compared spatial learning performance of captive-born tuco-tucos with previous data obtained in our laboratory from wild-born adult tuco-tucos. The results showed that wild-born individuals learned faster, requiring less time to complete a labyrinth and making fewer errors than those who had no experience in their natural environment. These findings underscore the importance of considering ecological factors in understanding the evolution of brains and cognitive abilities.

Effects of acute maternal stress induced by predator cues on spatial learning and memory of offspring in the subterranean rodent Ctenomys talarum

One of the main selection pressures to which animals are exposed in nature is predation, which affects a wide variety of biological traits. When the mother experiences this stressor during pregnancy and/or lactation, behavioral and physiological responses may be triggered in the offspring as well. Thus, in order to broaden and deepen knowledge on the transgenerational effects of predation stress, we evaluated how maternal stress experienced during pregnancy and/or lactation affects the spatial abilities of progeny at the onset of adulthood in the subterranean rodent Ctenomys talarum. The results showed that, contrary to what was observed in other rodent species, maternal exposure to predator cues during pregnancy and lactation did not negatively affect the spatial abilities of the offspring, even registering some minor positive effects. Concomitantly, no effects of predatory cues on physiological parameters associated with stress were observed in the progeny. This difference in results between the present study and previous works on maternal stress highlights the importance of considering the species to be evaluated (strain, age and origin-wild or captive-) and the type of stressor used (artificial or natural, intensity of exposure) in the evaluation of the possible transgenerational effects of maternal stress.

Individual differences in behaviour are related to metabolism, stress response, testosterone, and immunity in the subterranean rodent Ctenomys talarum

The growth of personality research has led to the integration of consistent variation of individual behaviour in multidimensional approaches including physiological variables, which are required to continue building a more comprehensive theory about coping strategies. In this study, we used wild-caught males of Ctenomys talarum (tuco-tucos), a solitary subterranean rodent, to assess the relationships among personality traits and several physiological variables, namely stress response, testosterone, immunity, and energy metabolism. Subjects (n = 21) were used in experimental tests assessing behaviour, energy metabolism, testosterone levels, inflammatory cell-mediated and humoral immunity, and stress response to a simulated predator attack. The structural equation model explained a moderate portion of the variance of personality behaviours related to activity (52%), boldness (35%), and socioaversion (30%). More active and bold individuals showed higher oxygen consumption. While those subjects had lower baseline cortisol levels, there was no relationship between cortisol levels of the stress-induced response. Cell-mediated immune response was related to activity levels. Finally, testosterone only affected boldness. Despite some of these relationships diverge in direction to predicted ones, overall they support the existence of coping styles in male C. talarum; and are discussed in the light of current hypotheses and particular behavioural and ecological traits of tuco-tucos.

Effects of parasitism on antipredatory responses and defensive behaviors in the subterranean rodent Ctenomys talarum

Predation represents an important evolutionary force shaping specific adaptations. Prey organisms present behavioral adaptations that allow them to recognize, avoid, and defend themselves from their predators. In addition to predation, there is a growing consensus about the role of parasitism in the structuring of biological communities. In vertebrates, the effects on hosts include changes in daily activity, feeding, mate selection, reproduction, and modifications in responses to environmental stimuli. These behavioral variations can benefit the parasite (parasitic manipulation), benefit the host, or appear as a side effect of the infection. We evaluated the influence of parasitism on the behavioral and physiological responses of the tuco-tucos of the Talas (Ctenomys talarum Thomas, 1898) to predator cues. We found that individuals exposed to cat odors and immobilization entered less often and spent less time in the transparent arms of elevated maze, exhibiting a preference for protected areas (anxiogenic response). Additionally, we evaluated if the presence of parasites affected antipredatory behaviors in C. talarum (naturally parasitized, deparasitized, or inoculated with Eimeria sp.). We did not find differences among the groups with regards to responses to predator cues. Therefore, while exposure to predator cues triggered a stress response, the manipulation of parasite loads did not modify homeostasis under these experimental conditions.

Time allocation to resources by three species of rats (Rattus spp.) in a radial arm maze

Abstract ContextIntroduced rats (Rattus spp.) can pose a serious threat to native flora and fauna, especially on islands where most species have evolved in the absence of terrestrial predators. Effective detection and eradication methods for introduced rats are essential to the maintenance of insular ecosystem integrity. Thus, it is important to better understand the behaviour of rats when they first arrive in a new setting. AimsTo determine whether rats would find some novel stimuli to be significantly more attractive than other novel stimuli. MethodsAn eight-arm radial maze was used to study the behaviour of three species of Rattus finding themselves in a novel environment with various familiar and unfamiliar stimuli. Key resultsAlthough there were some differences in responses by species and by sex, most rats sought out and spent considerable time in the den box, suggesting an immediate need for security when in an unfamiliar setting. Rats also sought out faeces of conspecifics, suggesting the need for social contact or reproduction. The rats, which had not been food deprived, did not seem interested in food sources, although there was some attraction to the water source. ImplicationsThe management implications of the present study’s results are two-fold. First, appears that detection of newly arriving rats on islands would be aided by strategic placement of den boxes that are highly acceptable to rats. Managers could then inspect the den boxes periodically (or use a remote sensing system) for evidence of rat presence. Second, the den boxes could be scented with the faeces of other rats to further attract invading rats to the den boxes. This protocol might also hold the rats near the invasion site for a longer period of time before they begin seeking other shelter, food sources or mates. These protocols could give managers increased opportunities to detect any newly invading rats, and potentially increase the available time to deploy a rapid response to the invasion, before the animals begin to widely disperse. Of course, the rats will ultimately seek a source of palatable food, so placing durable, yet palatable, rodenticide bait in the den boxes might further decrease the probability of the invaders establishing a self-sustaining population.

Immune challenge but not dietary restriction affects spatial learning in the wild subterranean rodent Ctenomys talarum

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.

Retinal photoreceptors of two subterranean tuco-tuco species (Rodentia, Ctenomys): morphology, topography, and spectral sensitivity

Traditionally, vision was thought to be useless for animals living in dark underground habitats, but recent studies in a range of subterranean rodent species have shown a large diversity of eye features, from small subcutaneous eyes to normal-sized functional eyes. We analyzed the retinal photoreceptors in the subterranean hystricomorph rodents Ctenomys talarum and Ctenomys magellanicus to elucidate whether adaptation was to their near-lightless burrows or rather to their occasional diurnal surface activity. Both species had normally developed eyes. Overall photoreceptor densities were comparatively low (95,000-150,000/mm(2) in C. magellanicus, 110,000-200,000/mm(2) in C. talarum), and cone proportions were rather high (10-31% and 14-31%, respectively). The majority of cones expressed the middle-to-longwave-sensitive (L) opsin, and a 6-16% minority expressed the shortwave-sensitive (S) opsin. In both species the densities of L and S cones were higher in ventral than in dorsal retina. In both species the tuning-relevant amino acids of the S opsin indicate sensitivity in the near UV rather than the blue/violet range. Photopic spectral electroretinograms were recorded. Unexpectedly, their sensitivity profiles were best fitted by the linear summation of three visual pigment templates with lambda(max) at 370 nm (S pigment, UV), at 510 nm (L pigment), and at 450 nm (an as-yet unexplained mechanism). Avoiding predators and selecting food during the brief aboveground excursions may have exerted pressure to retain robust cone-based vision in Ctenomys. UV tuning of the S cone pigment is shared with a number of other hystricomorphs.