Relationships of basal metabolic rate, relative testis size and cycle length of spermatogenesis in shrews (Mammalia, Soricidae).

The aim of the present study was to determinate the cycle length of spermatogenesis in three species of shrew, Suncus murinus, Sorex coronatus and Sorex minutus, and to assess the relative influence of variation in basal metabolic rate (BMR) and mating system (level of sperm competition) on the observed rate of spermatogenesis, including data of shrew species studied before (Sorex araneus, Crocidura russula and Neomys fodiens). The dynamics of sperm production were determined by tracing 5-bromodeoxyuridine in the DNA of germ cells. As a continuous scaling of mating systems is not evident, the level of sperm competition was evaluated by the significantly correlated relative testis size (RTS). The cycle durations estimated by linear regression were 14.3 days (RTS 0.3%) in Suncus murinus, 9.0 days (RTS 0.5%) in Sorex coronatus and 8.5 days (RTS 2.8%) in Sorex minutus. In regression and multiple regression analyses including all six studied species of shrew, cycle length was significantly correlated with BMR (r2=0.73) and RTS (r2=0.77). Sperm competition as an ultimate factor obviously leads to a reduction in the time of spermatogenesis in order to increase sperm production. BMR may act in the same way, independently or as a proximate factor, revealed by the covariation, but other factors (related to testes size and thus to mating system) may also be involved.

Reexamination of the relationship of resting metabolic rate to fat-free mass and to the metabolically active components of fat-free mass in humans.

The ratio of resting metabolic rate (RMR) to fat-free mass (FFM) is often used to compare individuals of different body sizes. Because RMR has not been well described over the full range of FFM, a literature review was conducted among groups with a wide range of FFM. It included 31 data sets comprising a total of 1111 subjects: 118 infants and preschoolers, 323 adolescents, and 670 adults; FFM ranged from 2.8 to 106 kg. The relationship of RMR to FFM was found to be nonlinear and average slopes of the regression equations of the three groups differed significantly (P less than 0.0001). For only the youngest group did the intercept approach zero. The lower slopes of RMR on FFM, at higher measures of FFM, corresponded to relatively greater proportions of less metabolically active muscle mass and to lesser proportions of more metabolically active nonmuscle organ mass. Because the contribution of FFM to RMR is not constant, an arithmetic error is introduced when the ratio of RMR to FFM is used. Hence, alternative methods should be used to compare individuals with markedly different FFM.

Toxin jararhagin in low doses induces interstitial edema and increases the metabolic rate and red blood cells in mice

Jararhagin is a metalloproteinase from Bothrops jararaca responsible for hemorrhage, inflammation, necrosis and edema. Effects of low doses of the toxin were analyzed on the energy metabolism of mice as well as its physiological implications. Measures of O-2 consumption (VO2) were quantified after 4 and 24 h of the jarathagin administration during four weeks. Hematocrit and histology of the lungs were also analyzed after the end of the treatment. Results showed that animals that received subcutaneous doses of jararhagin had significant increase in VO2 from second (120 ng) and third weeks (60 ng) after 4 and 24 h, comparing to control, as well as in the number of erythrocytes after four weeks. Histology of the lungs showed interstitial edema within the alveolar septum. Results suggest that the jararhagin toxin caused an increase in VO2 and edema of intra-alveolar septum. The increase of the erythrocytes could be a physiological response to adjust the higher necessity of oxygen, due to diffusional abnormalities caused by the edema. Thus, low doses of jararhagin promote endothelial edema which lead to changes in several physiological conditions. (c) 2006 Elsevier Ltd. All rights reserved.

Effects of season, temperature, and body mass on the standard metabolic rate of tegu lizards (Tupinambis merianae)

This study examined how the standard metabolic rate of tegu lizards, a species that undergoes large ontogenetic changes in body weight with associated changes in life-history traits, is affected by changes in body mass, body temperature, season, and life-history traits. We measured rates of oxygen consumption ((V) over dot o(2)) in 90 individuals ranging in body mass from 10.4. g to 3.75 kg at three experimental temperatures ( 17 degrees, 25 degrees, and 30 degrees C) over the four seasons. We found that standard metabolic rate scaled to the power of 0.84 of body mass at all experimental temperatures in all seasons and that thermal sensitivity of metabolism was relatively low (Q(10) approximate to 2.0-2.5) over the range from 17 degrees to 30 degrees C regardless of body size or season. Metabolic rates did vary seasonally, being higher in spring and summer than in autumn and winter at the same temperatures, and this was true regardless of animal size. Finally, in this study, the changes in life-history traits that occurred ontogenetically were not accompanied by significant changes in metabolic rate.

Intraspecific variability in the basal metabolic rate: Testing the food habits hypothesis

Several competing hypotheses attempt to explain how environmental conditions affect mass-independent basal metabolic rate (BMR) in mammals. One of the most inclusive and yet debatable hypotheses is the one that associates BMR with food habits, including habitat productivity. These effects have been widely investigated at the interspecific level under the assumption that for any given species all traits are fixed. Consequently, the variation among individuals is largely ignored. Intraspecific analysis of physiological traits has the potential to compensate for many of the pitfalls associated with interspecific analyses and, thus, to be a useful approach for evaluating hypotheses regarding metabolic adaptation. In this study, we investigated the effects of food quality, availability, and predictability on the BMR of the leaf-eared mouse Phyllotis darwini. BMR was measured on freshly caught animals from the field, since they experience natural seasonal variations in environmental factors ( and, hence, variations in habitat productivity) and diet quality. BMR was significantly correlated with the proportion of dietary plants and seeds. In addition, BMR was significantly correlated with monthly habitat productivity. Path analysis indicated that, in our study, habitat productivity was responsible for the observed changes in BMR, while diet per se had no effect on this variable.

The relationship between diet quality and basal metabolic rate in endotherms: Insights from intraspecific analysis

In this article, we review intraspecific studies of basal metabolic rate (BMR) that address the correlation between diet quality and BMR. The food-habit hypothesis stands as one of the most striking and often-mentioned interspecific patterns to emerge from studies of endothermic energetics. Our main emphasis is the explicit empirical comparison of predictions derived from interspecific studies with data gathered from within-species studies in order to explore the mechanisms and functional significance of the putative adaptive responses encapsulated by the food-habit hypothesis. We suggest that, in addition to concentrating on the relationship among diet quality, internal morphology, and BMR, new studies should also attempt to unravel alternative mechanisms that shape the interaction between diet and BMR, such as enzymatic plasticity, and the use of energy-saving mechanisms, such as torpor. Another avenue for future study is the measurement of the effects of diet quality on other components of the energy budget, such as maximum thermogenic and sustainable metabolic rates. It is possible that the effects of diet quality operate on such components rather than directly on BMR, which might then push or pull along changes in these traits. Results from intraspecific studies suggest that the factors responsible for the association between diet and BMR at an ecological timescale might not be the same as those that promoted the evolution of this correlation. Further analyses should consider how much of a role the proximate and ultimate processes have played in the evolution of BMR.

Diet, phylogeny, and basal metabolic rate in phyllostomid bats

Aside from the pervasive effects of body mass, much controversy exists as to what factors account for interspecific variation in basal metabolic rates (BMR) of mammals; however, both diet and phylogeny have been strongly implicated. We examined variation in BMR within the New World bat family Phyllostomidae, which shows the largest diversity of food habits among mammalian families, including frugivorous, nectarivorous, insectivorous, carnivorous and blood-eating species. For 27 species, diet was taken from the literature and BMR was either measured on animals captured in Brazil or extracted from the literature. Conventional (nonphylogenetic) analysis of covariance (ANCOVA), with body mass as the covariate, was first used to test the effects of diet on BMR. In this analysis, which assumes that all species evolved simultaneously from a single ancestor (i.e., a star phylogeny), diet exerted a strong effect on mass-in-dependent BMR: nectarivorous bats showed higher mass-independent BMR than other bats feeding on fruits, insects or blood. In phylogenetic ANCOVAs via Monte Carlo computer simulation, which assume that species are part of a branching hierarchical phylogeny, no statistically significant effect of diet on BMR was observed. Hence, results of the nonphylogenetic analysis were misleading because the critical values for testing the effect of diet were underestimated. However, in this sample of bats, diet is perfectly confounded with phylogeny, because the four dietary categories represent four separate subclades, which greatly reduces statistical power to detect a diet (= subclade) effect. But even if diet did appear to exert an influence on BMR in this sample of bats, it would not be logically possible to separate this effect from the possibility that the dietary categories differ for some other reason (i.e., another synapomorphy of one or more of the subclades). Examples such as this highlight the importance of considering phylogenetic relationships when designing new comparative studies, as well as when analyzing existing data sets. We also discuss some possible reasons why BMR may not coadapt with diet. © by Urban & Fischer Verlag.

Age and gender influence the cardiorespiratory function and metabolic rate of broiler chicks during normocapnia and hypercapnia

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Steelhead trout Oncorhynchus mykiss metabolic rate is affected by dietary Aloe vera inclusion but not by mounting an immune response against formalin-killed Aeromonas salmonicida

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)