Comparative biochemistry and physiology in Brazil: a critical appraisal.

Brazil stood out as the country with the highest number of submissions to the editorial project dedicated to Latin America by the journal Comparative Biochemistry and Physiology. Therefore, we felt that it was important to critically discuss the state of comparative biochemistry and physiology in this country. Our study is based on data collected from the ISI Web-of-Science. We analyzed publication trends through time, availability of novel approaches and techniques, patterns of collaboration among different geographical regions, patterns of collaboration with researchers abroad, and relative efforts dedicated to the study of biochemical and physiological adaptation of native fauna representing different terrestrial Brazilian biomes. Overall, our data shows that comparative biochemistry and physiology is a lively and productive discipline, but that some biases limit the scope of the field in Brazil. Some important limitations are the very heterogeneous distribution of research nuclei throughout the country and the absence of some important approaches, such as remote sensing and the use of molecular biology techniques in a comparative or evolutionary context. We also noticed that international collaboration far surpasses interregional collaboration, and discuss the possible causes and consequences of this situation. Finally, we found that Brazilian comparative biochemistry and physiology is biome-biased, as the Amazonian fauna has received far more attention than the whole pool of fauna representing other terrestrial biomes. We discuss the possible causes of these biases, and propose some directions that may contribute to invigorate the field in the country.

Control and regulatory mechanisms associated with thermogenesis in flying insects and birds.

Most insects and birds are able to fly. The chitin made exoskeleton of insects poses them several constraints, and this is one the reasons they are in general small sized animals. On the other hand, because birds possess an endoskeleton made of bones they may grow much larger when compared to insects. The two taxa are quite different with regards to their general "design" platform, in particular with respect to their respiratory and circulatory systems. However, because they fly, they may share in common several traits, namely those associated with the control and regulatory mechanisms governing thermogenesis. High core temperatures are essential for animal flight irrespective of the taxa they belong to. Birds and insects have thus evolved mechanisms which allowed them to control and regulate high rates of heat fluxes. This article discusses possible convergent thermogenic control and regulatory mechanisms associated with flight in insects and birds.

Intraspecific relationships between resting and activity metabolism in anuran amphibians: influence of ecology and behavior.

The aerobic capacity model, as well as other models for the evolution of aerobic metabolism and the origin of endothermy, requires a mechanistic link between rates of resting and activity oxygen consumption (VO2rest and VO2act). The existence of such link is still controversial, but studies with anuran amphibians support a correlation between VO2rest and VO2act at both the intraspecific and interspecific levels. Because results at the intraspecific level are based only on a few species, we test for the generality of a link between these two metabolic variables in anurans by studying the intraspecific correlational patterns between mass-independent VO2rest and VO2act in anurans. We focus on 21 Neotropical species from different geographical areas that include remarkable diversity in behavior and thermal ecology. Although uncorrelated, VO2rest and VO2act seem to be consistent among individuals. Diverse intraspecific phenotypic correlational trends were detected, indicating that the intraspecific relationships between VO2rest and VO2act might be very diverse in anurans. The three possible trends (positive, negative, and absent correlations) were observed and appeared to be predictable from ecological and behavioral variables that relate to evolutionary physiological shifts in anurans. Positive correlations between VO2rest and VO2act were more common in species with active lifestyles (e.g., intense vocal activity) and in species that call at low temperatures (e.g., winter or high-elevation specialists).

Seasonal metabolic depression, substrate utilisation and changes in scaling patterns during the first year cycle of tegu lizards (Tupinambis merianae).

The tegus increase in body mass after hatching until early autumn, when the energy intake becomes gradually reduced. Resting rates of oxygen consumption in winter drop to 20% of the values in the active season ((O(2))=0.0636 ml g(-1) h(-1)) and are nearly temperature insensitive over the range of 17-25 degrees C (Q(10)=1.55). During dormancy, plasma glucose levels are 60% lower than those in active animals, while total protein, total lipids and beta-hydroxybutyrate are elevated by 24%, 43% and 113%, respectively. In addition, a significant depletion of liver carbohydrate (50%) and of fat deposited in the visceral fat bodies (24%) and in the tail (25%) and a slight loss of skeletal muscle protein (14%) were measured halfway through the inactive period. Otherwise, glycogen content is increased 4-fold in the brain and 2.3-fold in the heart of dormant lizards, declining by the onset of arousal. During early arousal, the young tegus are still anorexic, although (O(2)) is significantly greater than winter rates. The fat deposits analysed are further reduced (62% and 45%, respectively) and there is a large decrease in tail muscle protein (50%) together with a significant increase in glycogen (2-3-fold) and an increase in plasma glucose (40%), which suggests a role for gluconeogenesis as a supplementary energy source in arousing animals. No change is detectable in citrate synthase activity, but beta-hydroxyacyl CoA dehydrogenase activities are strongly affected by season, reaching a 3-fold and 5-fold increase in the liver tissue of winter and arousing animals, respectively, and becoming reduced by half in skeletal muscle and heart of winter animals compared with late fall or spring active individuals. From hatching to late autumn, the increase of the fat body mass relatively to body mass is disproportionate (b=1.44), and the mass exponent changes significantly to close to 1.0 during the fasting period. The concomitant shift in the (O(2)) mass exponent in early autumn (b=0.75) to values significantly greater than 1.0 in late autumn and during winter dormancy indicates an allometric effect on the degree of metabolic depression related to the size of the fat stores and suggests greater energy conservation in the smaller young.

Adaptive thermogenesis in hummingbirds.

The occurrence of non-shivering thermogenesis in birds has long been a controversial issue. Although birds are endothermic vertebrates, sharing with mammals (placental mammals and marsupials) a common ancestor, they do not possess brown adipose tissue or a similar type of tissue, unlike their mammalian counterparts. Some bird species are, however, able to withstand very low ambient temperatures (-70 degrees C) or undergo periods of heterothermia, and there is now good experimental evidence showing that non-shivering thermogenesis may indeed occur in birds under such conditions. The skeletal muscles of birds, particularly the flight muscles, occupy a significant fraction (approximately 30 %) of the total body mass, and recent results have shown that they are likely to be the main sites for non-shivering thermogenesis. The precise mechanisms involved in adaptive thermogenesis in birds are still not fully understood. The translocation of Ca(2+) between intracellular compartments and the cystosol mediated by the sarcoplasmic reticulum Ca(2+)-ATPase, uncoupled from ATP synthesis, is one mechanism whereby chemi-osmotic energy can be converted into heat, and it has been proposed as one of the possible mechanisms underlying non-shivering thermogenesis in birds on the basis of data obtained mainly from ducklings acclimatized to cold conditions. The recent characterization of an uncoupling protein homolog in avian skeletal muscle and the expression of its mRNA at different stages of the torpor/rewarming cycle of hummingbirds indicate that it has the potential to function as an uncoupling protein and could play a thermogenic role during rewarming in these birds.

Temperature effects on energy metabolism: a dynamic system analysis.

Q(10) factors are widely used as indicators of the magnitude of temperature-induced changes in physico-chemical and physiological rates. However, there is a long-standing debate concerning the extent to which Q(10) values can be used to derive conclusions about energy metabolism regulatory control. The main point of this disagreement is whether or not it is fair to use concepts derived from molecular theory in the integrative physiological responses of living organisms. We address this debate using a dynamic systems theory, and analyse the behaviour of a model at the organismal level. It is shown that typical Q(10) values cannot be used unambiguously to deduce metabolic rate regulatory control. Analytical constraints emerge due to the more formal and precise equation used to compute Q(10), derived from a reference system composed from the metabolic rate and the Q(10). Such an equation has more than one unknown variable and thus is unsolvable. This problem disappears only if the Q(10) is assumed to be a known parameter. Therefore, it is concluded that typical Q(10) calculations are inappropriate for addressing questions about the regulatory control of a metabolism unless the Q(10) values are considered to be true parameters whose values are known beforehand. We offer mathematical tools to analyse the regulatory control of a metabolism for those who are willing to accept such an assumption.