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Seasonal changes in environmental conditions may induce reversible physiological adjustments in organisms. We studied the acclimatization for multiple stressors in energy expenditure and water balance in Galea leucoblephara, a diurnal hystricognath rodent native to South America that experiences significant changes in temperature, precipitation, and food availability among seasons. We conducted a field study in the Monte Desert of Mendoza, Argentina, where we evaluated adult individuals' physiological status during two contrasting seasons in terms of climate and primary productivity. Reduced temperature, rainfall, and primary productivity during winter were associated with a decrease of 70% in basal metabolic rate (BMR), 30% in total evaporative water loss (TEWL), and 9% in body mass (Mb). In contrast, higher water availability, high temperature, and primary productivity during summer, induced significant increases in energy expenditure and evaporative water loss. As expected, the proportion of dietary items consumed by G. leucoblephara varied seasonally, resulting in a more diverse diet during summer. Our results illustrate how G. leucoblephara can cope with high seasonal contrasts in water availability, temperature, and food availability by modifying its physiological performance. Our data provide support for the hypothesis of physiological flexibility in energetic traits and water balance in response to the environmental challenges of the Monte Desert. [ABSTRACT FROM AUTHOR]

Hummingbirds (family Trochilidae) are among the smallest endothermic vertebrates representing an extreme, among birds, in their physiological design. They are unique in their ability to sustain hovering flight, one of the most energetically demanding forms of locomotion. Given that hovering metabolic rate (HMR) in hummingbirds scales allometrically as [M.sup.0.78] (M is mass), we tested the hypothesis that variation in HMR may be correlated with variation in maximal enzyme activities ([V.sub.max] values) of key enzymes in glucose and fatty acid oxidation pathways in the flight muscles of four species of hummingbirds ranging in body mass from 4 to 20 g. We also estimated metabolic flux rates from respirometric data obtained during hovering flight. The data are striking in the lack of correlation between [V.sub.max] values and flux rates at most steps in energy metabolism, particularly at the hexokinase and carnitine palmitoyltransferase reactions. In the context of hierarchical regulation analysis, this finding suggests that metabolic regulation (resulting from variation in substrate, product, or allosteric regulator concentrations) dominates as the proximate explanation for the interspecific variation in flux. On the other hand, we found no evidence of hierarchical regulation of flux, which results from variation in [V.sub.max] and is based on variation in enzyme concentration [E]. The evolutionary conservation of pathways of energy metabolism suggests that 'one size fits all' among hummingbirds. Les colibris (famille des Trochilides) sont parmi des plus petits vertebras endothermes, et presentent une physiologie extreme chez les oiseaux. Le vol sur place, l'une des formes de locomotion les plus couteuses, est une caracteristique qui leur est propre. Sachant que le cout metabolique du vol sur place (HMR) chez les colibris est fonction allometrique de [M.sup.0,78] (M est la masse), nous avons teste l'hypothese selon laquelle HMR pourrait etre correle aux changements d'activite maximale ([V.sub.max])d'enzymes jouant un role cle dans les processus d'oxydation du glucose et des acides gras dans les muscles du vol chez quatre especes de colibris dont la masse varie de 4 a 20 g. En parallele, nous avons egalement estime les flux metaboliques a partir de donnees de respirometrie mesurees durant le vol sur place. Contrairement a notre hypothese, aucune correlation entre [V.sub.max] et les flux metaboliques n'a ete trouvee, en particulier pour les reactions metaboliques impliquant l'hexokinase et la carnitine palmityl transferase. Dans le cadre d'une analyse de regulation hierarchique, ces resultats indiquent que la regulation metabolique (provenant de changements de substrat, produit ou effecteur allosterique) explique le mieux les variations interspecifiques de flux metabolique. D' un autre cote, nous n' avons mis en evidence aucun signe de regulation hierarchique du flux metabolique, c'est-a-dire aucun changement de [V.sub.max] du a un changement de concentration en enzymes [E], provenant d'une regulation de l'expression genique. La conservation au fil de revolution de ces processus metaboliques suggere l'existence d'une << taille metabolique unique ' chez les colibris., Introduction Hummingbirds (Trochilidae) are characterized by their small size, extreme physiological design, and extraordinary aero-acrobatics. Trochilidae represent one of the largest avian families, comprising 330 species that weigh between 2 [...]

Maternal effects, the environment that mothers provide to their offspring, their provision of nutrients and the environment that offspring of the same clutch share, are recognized as an important influence on offspring fitness. The changes observed in quantitative genetic parameters in a half-sib design where mothers are fed with varying nutrient content diets, are presented.

The transition from trot to gallop in quadruped mammals has been widely hypothesized to be a strategy to minimize the energetic costs of running. Experimental evidence from horses running on treadmills, however, suggests that gait change is not triggered by energetic factors but by mechanical factors, when the musculoskeletal forces reach a critical value. An alternative hypothesis to the previous two to explain gait transition has been proposed based on the relationship among the forces that act on a body while moving. For terrestrial locomotion, gait transition is predicted to occur at speeds when the ratio of inertial to gravitational forces, known as the Froude number, reaches a critical value. All experiments to test these hypotheses have used relatively large species and the results, therefore, may not be applicable to small mammals, as they are probably constrained in their morphology and locomotion in different ways than larger mammals. In this study we evaluate the effects of loads on the locomotor energetics and gait transitions of degus (Octodon degus; Rodentia: Caviomorpha) running on a treadmill. The trot-gallop transition speed did not vary when rodents were experimentally loaded indicating that the forces applied to the musculoskeletal system do not trigger the gait transition. On the other hand, the transition speed was not associated to an energetic minimum indicating that changes of gait are not energetically determined. Experimentally loaded individuals switched to gallop at the same Froude number as controls, suggesting that the relationship between inertial and gravitational forces are important in determining the trot-gallop transition, even when the Froude number alone is not enough to describe the kinetics and kinematics of either walking or running gaits.

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Studies focusing on physiological variation among individuals, and its possible evolutionary consequences, are scarce. A trait can only be a target of natural selection if it is consistent over time, that is, a trait must be repeatable. In ectotherms it has been suggested that standard metabolic rate (MR) is related to Darwinian fitness, since it reflects energy usage and expenditure. The metabolic rate of the cricket Hophlosphyrum griseus was determined at three ambient temperatures. Repeatability of MR was estimated by product-moment correlation on residuals of body mass, as well as the thermal sensitivity of MR on an individual basis (individual Q[sub 10]). The MR of H. griseus was significantly repeatable (r=0.53) and highly dependent on ambient temperature, and its sensitivity (Q[sub 10]) was dependent on the temperature range. Our estimation of MR repeatability was high in comparison to published studies in vertebrates. Ours is the second report of repeatability (i.e. consistency over time of an individual's performance ranking within a population) of any aspect of energy metabolism in an insect, and also the first study to report significant repeatability of MR. Individual Q[sub 10] values revealed important interindividual variation, which reflects the existence of intrapopulational variability in the thermal sensitivity of MR. In addition, individual Q[sub 10] values were negatively correlated between temperature ranges. This means that crickets having low Q[sub 10] at low temperatures, presented high Q[sub 10] at high temperatures, and vice versa. Our results suggest that MR could be of selective value in insects, showing consistency over time and intrapopulational variability in its thermal dependence. Nevertheless, its heritability remains to be determined. [ABSTRACT FROM AUTHOR]