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Our planet is undergoing fast environmental changes, which are referred as global change. In this new scenario, it is of paramount relevance to understand the mechanistic basis of animal responses to environmental change. Here we analyze to what extent seasonal changes in the digestive function of the lizard Liolaemus moradoensis is under endogenous (i.e., hard wired) or exogenous (i.e., environmentally determined) control. For this purpose we compared animals collected in the field during autumn, winter and summer, against (experimental) specimens collected in the field at the beginning of autumn and reared in the laboratory under simulated summer conditions until winter. We found that different aspects of the digestive function are under different types of control: small intestine length appears to be under endogenous control (i.e., experimental animals were similar to winter animals), small intestine mass appears to be under exogenous control (i.e., experimental animals were similar to summer animals), and specific enzyme activities did not change throughout the year. Thus, we suspect that processes related with gut length, such as cell division, may be under endogenous control, while others related with gut mass, such as enterocyte size and content, may be determined by exogenous factors, such as the presence of food in the intestinal lumen. Faced with accelerated changing conditions, the ability of vertebrates to cope will be closely related with their plasticity in fitness-associated traits. More studies aimed at determining the levels and limits of physiological flexibility will be necessary to understand this phenomenon., (Copyright © 2011 Elsevier Inc. All rights reserved.)

The understanding of animal functioning in fluctuating environments is a major goal of physiological and evolutionary ecology. In temperate terrestrial habitats, one of the most pervasive changes in environmental conditions is that associated with the seasonal change along the year. In this study, we describe the pattern of seasonal variation in the size of nine internal organs in the lizard Liolaemus moradoensis from the Andes Mountains of Central Chile. We observed that the size of digestive organs was greater during summer in comparison to other seasons. Dry masses of liver and fat bodies reached maximum values during summer and minimum during spring. We suspect that lowest spring values are related with build-up costs of energetically expensive organs (e.g., digestive, muscle mass) at the end of the hibernation period. Dry mass of the heart and lungs did not show a clear pattern of variation, suggesting that cardiac and pulmonary performance were maintained throughout the year. The dry mass of kidneys was greater during winter than during summer, a result observed in other hibernating lizards but for which there is no clear explanation. Finally, the dry mass of testes showed a maximum value during autumn and a progressive reduction toward summer, indicating that reproduction occurs during autumn. When represented in a bivariate space, acquisition (digestive), distribution (heart, lungs and kidneys), storage (liver and fat bodies), and expenditure (testes) organs generate four clusters. In general terms, observed seasonal pattern of change in organ size is in agreement with those reported for other lizard species that inhabit highly fluctuating environments., (© 2010 Wiley-Liss, Inc.)

A large number of physiological acclimation studies assume that flexibility in a certain trait is both adaptive and functionally important for organisms in their natural environment; however, it is not clear how an organism's capacity for temperature acclimation translates to the seasonal acclimatization that these organisms must accomplish. To elucidate this relationship, we measured BMR and TEWL rates in both field-acclimatized and laboratory-acclimated adult rufous-collared sparrows (Zonotrichia capensis). Measurements in field-acclimatized birds were taken during the winter and summer seasons; in the laboratory-acclimated birds, we took our measurements following 4 weeks at either 15 or 30 degrees C. Although BMR and TEWL rates did not differ between winter and summer in the field-acclimatized birds, laboratory-acclimated birds exposed to 15 degrees C exhibited both a higher BMR and TEWL rate when compared to the birds acclimated to 30 degrees C and the field-acclimatized birds. Because organ masses seem to be similar between field and cold-acclimated birds whereas BMR is higher in cold-acclimated birds, the variability in BMR cannot be explained completely by adjustments in organ masses. Our findings suggest that, although rufous-collared sparrows can exhibit thermal acclimation of physiological traits, sparrows do not use this capacity to cope with minor to moderate fluctuations in environmental conditions. Our data support the hypothesis that physiological flexibility in energetic traits is a common feature of avian metabolism.

One of the most fundamental questions in organismal ecology is how animals work in a continuously changing environment. In order to contribute to the current understanding of this question, this study evaluated seasonal changes in digestive enzymes activities, organs size, and energy reserves in Liolaemus nigroviridis, a medium-size lizard that inhabit extreme environments in the Andes range. We found that digestive enzymes (trehalase, maltase, and aminopeptidase-N) hydrolytic activities, dry masses of digestive organs and liver, and energy reserve (dry mass of fat bodies and tail energy density) were greater during summer than during winter months. By contrast, dry mass of the kidneys, lungs, heart, and gonads were greater during winter (though significance was reach only for the last two organs). In summary, obtained results reinforce the idea that hibernation is connected with phenotypic adjustments at different organizational levels, which in turn, potentially affects rates of energy acquisition and expenditure, organisms' fitness, and, ultimately, ecological and evolutionary success of species living in highly seasonal environments. We suggest that, owing to the pressing need to explain and predict the impact of climatic change on the biota, more studies destined to determine the levels and limits of physiological flexibility are necessary., ((c) 2009 Wiley-Liss, Inc.)

According to the "barrel model", an organism may be represented by a container, with input energy constraints (foraging, digestion, and absorption) symbolized by funnels connected in tandem, and energy outputs (maintenance, growth, and reproduction) symbolized by a series of spouts arranged in parallel. Animals can respond to changes in environmental conditions, through adjustments in the size of the funnels, the fluid stored inside the barrel, or the output flow through the spouts. In the present study, we investigate the interplay among these processes through the analysis of seasonal changes in organ size and metabolic rate in a lizard species (Liolaemus bellii) that inhabits extremely seasonal environments in the Andes range. We found that digestive organ size showed the greatest values during spring and summer, that is, during the foraging seasons. Energy reserves were larger during summer and autumn, and then decreased through winter and spring, which was correlated with overwintering maintenance and reproductive costs. Standard metabolic rate was greater during the high-activity seasons (spring and summer), but this increase was only noticeable at higher environmental temperatures. The ability of many lizard species to reduce their maintenance cost during the cold months of the year, beyond what is expected from temperature decrease, is probably related to their success in coping with highly fluctuating environments. Here, we demonstrate that this ability is correlated with high physiological flexibility, which allows animals to adjust energy acquisition, storing and expenditure processes according to current environmental conditions.

Animals process and allocate energy at different seasons at variable rates, depending on their breeding season and changes in environmental conditions and resulting physiological demands. Overall total energy expenditure, in turn, should either increase in some seasons due to special added demands (e.g. reproduction) or it could simply remain at about the same level, in which case the animals must show compensatory rebalancing of other expenditures that can be reduced. To test for the alternative hypotheses of seasonal variability or compensation, we measured total daily energy expenditure (DEE) in free-living degus (Octodon degus) at four seasons and followed this with determinations of basal metabolic rate (BMR) in the laboratory in the same individuals. DEE varied seasonally but was only significantly different (lower) in summer (non-breeding season), with a DEE:BMR ratio of only 1.6, whereas autumn, winter and spring DEE values were statistically indistinguishable from one another and showed DEE:BMR ratios ranging from 1.9 to 2.2. Our values of DEE in the field fall within the broad range of allometric expectation for herbivorous mammals in general, but the ratios of DEE:BMR are lower than expected. This, together with the lack of strong major shifts in total levels of DEE, suggests that degus are showing compensatory shifts among various categories of energy expenditure that allow them to manage their overall energy balance by minimizing total expenditure.

We investigated seasonal patterns of plasma glucocorticosteroids (GCs) in both sexes and testosterone (T) in males in relation to the annual cycle in central Chile of a natural population of the degu (Octodon degus), a caviomorph rodent. We wanted to find out which GCs are present in degus, whether their seasonal variation suggests suppressive or synergistic interrelationships with T, and whether seasonal variation in GC levels indicates a relationship with energy mobilization and demands of reproduction. Degus mated in late autumn, and female body mass increased in pregnancy and remained high during lactation and throughout spring. Over the subsequent period of summer drought both sexes declined to a minimal body mass before the next mating season. Cortisol appears to be the principal GC in degus. In fact cortisol levels were so high that the extremely low levels of corticosterone measured were probably largely due to the cross-reactivity of our corticosterone antiserum with cortisol. Titers of cortisol in females exceeded 1000 ng/ml at lactation in the spring of 2 years; cortisol declined greatly following lactation and during the summer and reached its lowest mean level of about 500 ng/ml at mating. Males were more difficult to capture than females and thus our sampling was limited, but male cortisol levels were similar to those of females during the times of year when we measured them. Male T levels remained within a low range all year, but at mating, when mean T was highest (0.16 ng/ml) and when most males had detectable T, degus showed their lowest cortisol levels. The minimal cortisol level of males during mating represents a possible suppressive effect of T, as described in other mammals. At the time of their spring emergence, 60% of juvenile males had detectable T levels comparable to those of adults, suggesting important organizational effects of T at that time in their maturation. Peak cortisol titers in both sexes were associated with lactation in females, when energy mobilization, production, and body mass were at their greatest., (Copyright 1999 Academic Press.)