Phenotypic plasticity in the energy metabolism of a small Andean rodent: Effect of short-term thermal acclimation and developmental conditions.

The study of phenotypic variation within species in response to different environments is a central issue in evolutionary and ecological physiology. Particularly, ambient temperature is one of the most important factors modulating interactions between animals and their environment. Phyllotis xanthopygus, a small Andean rodent, exhibits intraspecific differences along an altitudinal gradient in traits relevant to energy balance that persist after acclimation to common experimental temperatures. Therefore, we aim to explore geographic variations in energetic traits of P. xanthopygus and to assess the contribution of phenotypic plasticity to population differences. We compared metabolic rate and thermal conductance in response to different acclimation temperatures in animals collected at distinct altitudes (F0 generation) and in their offspring, born and raised under common-garden conditions (F1 generation). We found intraspecific differences in resting metabolic rate (RMR) of animals collected at different altitudes that were no longer evident in the F1 generation. Furthermore, although both generations showed the same pattern of RMR flexibility in response to acclimation temperature, its magnitude was lower for the F1 individuals. This suggests that developmental conditions affect the short-term acclimation capacity of this trait during adulthood. On the other hand, thermal conductance (C) showed irreversible plasticity, as animals raised in the laboratory at stable warm conditions had a relatively higher C than the animals from the field, showing no adjustments to thermal acclimation during adulthood in either group. In sum, our results support the hypothesis that the developmental environment shapes energetic traits, emphasizing the relevance of incorporating ontogeny in physiological studies.

Developmental environment influences activity levels in a montane rodent, Phyllotis xanthopygus.

Ambient temperature and thermal variability play a crucial role in diverse aspects of organisms' biology. In the current context of climate change, it is critical to understand how temperature impacts traits that could affect fitness. In Phyllotis xanthopygus, a small altricial rodent inhabiting an altitudinal gradient in the Andes Mountains of Argentina, the behavioral response to temperature varies between populations from different altitudes. Animals from high altitude (cold environment) reduce their activity rate at high temperatures, in contrast to animals from low altitude (relatively warmer environment). The goal of this study was to unveil the mechanism underlying such intraspecific behavioral variability in P. xanthopygus. We characterized activity rates under different thermal treatments both for wild-reared and lab-reared animals. As we expected, the intraspecific variability shown by animals raised at different altitudes in the field disappeared in animals raised under homogenous conditions in the laboratory. Our results are indicative of ontogenetic plasticity in P. xanthopygus and suggest that the behavioral versatility of adult individuals to deal with thermal challenges is shaped by the range of environmental conditions experienced during their early life. This adds to the list of features that modulate the biological performance of individuals and could influence the relative vulnerability of populations inhabiting different elevations under the global disturbance of climate change.

Are there different vigilance strategies between types of social units in Lama guanicoe?

Group vigilance is a cooperative behaviour in social species that reduces individual risk of predation. Lama guanicoe is a social species of camelid performing cooperative vigilance, but little is known about the vigilance behaviour of different social units. We analysed the vigilance behaviour in different types of social units of L. guanicoe, to better understand the complexity of this behaviour. The best supported models for both the frequency of vigilance and the proportion of time vigilant included the type and size of social units as the most important predictors that affect the vigilance behaviour. Solitary males devoted proportionally more time in vigilance behaviour than family, mixed or bachelor groups, whereas females in female groups spent more time vigilant than guanacos in mixed groups. Frequency of vigilance was higher in family individuals and solitary males than in bachelor or mixed groups. It is likely that that in family and females groups, the presence of offspring would increase the vigilance behaviour to detect possible predators. Topography and habitat characteristics that determine the predation risk, affected vigilance behaviour of mixed groups and solitary males. Our results suggest that vigilance behaviour should not be generalized for this species, since there are differences between the types of social units, probably related to intrinsic characteristics of each one and the perception of risk.

Spatial and seasonal dynamic of abundance and distribution of guanaco and livestock: insights from using density surface and null models.

Monitoring species abundance and distribution is a prerequisite when assessing species status and population viability, a difficult task to achieve for large herbivores at ecologically meaningful scales. Co-occurrence patterns can be used to infer mechanisms of community organization (such as biotic interactions), although it has been traditionally applied to binary presence/absence data. Here, we combine density surface and null models of abundance data as a novel approach to analyze the spatial and seasonal dynamics of abundance and distribution of guanacos (Lama guanicoe) and domestic herbivores in northern Patagonia, in order to visually and analytically compare the dispersion and co-occurrence pattern of ungulates. We found a marked seasonal pattern in abundance and spatial distribution of L. guanicoe. The guanaco population reached its maximum annual size and spatial dispersion in spring-summer, decreasing up to 6.5 times in size and occupying few sites of the study area in fall-winter. These results are evidence of the seasonal migration process of guanaco populations, an increasingly rare event for terrestrial mammals worldwide. The maximum number of guanacos estimated for spring (25,951) is higher than the total population size (10,000) 20 years ago, probably due to both counting methodology and population growth. Livestock were mostly distributed near human settlements, as expected by the sedentary management practiced by local people. Herbivore distribution was non-random; i.e., guanaco and livestock abundances co-varied negatively in all seasons, more than expected by chance. Segregation degree of guanaco and small-livestock (goats and sheep) was comparatively stronger than that of guanaco and large-livestock, suggesting a competition mechanism between ecologically similar herbivores, although various environmental factors could also contribute to habitat segregation. The new and compelling combination of methods used here is highly useful for researchers who conduct counts of animals to simultaneously estimate population sizes, distributions, assess temporal trends and characterize multi-species spatial interactions.

Cooperative vigilance: the guanaco's (Lama guanicoe) key antipredator mechanism.

The concept of sociality has been associated with the effectiveness of antipredator mechanisms, like cooperative vigilance and the dilution effect. Lama guanicoe (guanaco) is a social native herbivore in South America and a social species. The objectives of this study were to evaluate the antipredator responses of different-sized groups of guanacos in areas with varying predation risks and to determine antipredator mechanisms in guanacos. For this, we measured different antipredator responses to a potential predator (human subjects). Detection of predator and flight distances from predator both increased with a greater number of guanacos per group and with greater distances among guanacos within the social group. Both buffer distance and flight time decreased with a greater number of guanacos per group, but increased with greater distances among guanacos inside the social group. Solitary adult males moved shorter distance and mixed groups moved greater distances. Flight distances were greater in areas with tall and dense vegetation than in areas with low vegetation. Buffer distance and flight time were shorter in undulating land than on flat lands, and groups were usually observed on hill slopes. Our results suggest that the benefit of social grouping in guanacos is the increased probability of avoiding predator with cooperative vigilance and not with the dilution effect. This means that a predator could be detected earlier when approaching a guanaco group than when approaching a solitary individuals and could thus be avoided.