An increase in minimum metabolic rate and not activity explains field metabolic rate changes in a breeding seabird

The field metabolic rate (FMR) of a free-ranging animal can be considered as the sum of its maintenance costs (minimum metabolic rate, MMR) and additional costs associated with thermoregulation, digestion, production and activity. However, the relationships between FMR and BMR and how they relate to behaviour and extrinsic influences is not clear. In seabirds, FMR has been shown to increase during the breeding season. This is presumed to be the result of an increase in foraging activity, stimulated by increased food demands from growing chicks, but few studies have investigated in detail the factors that underlie these increases. We studied free-ranging Australasian gannets (Morus serrator) throughout their 5 month breeding season, and evaluated FMR, MMR and activity-related metabolic costs on a daily basis using the heart rate method. In addition, we simultaneously recorded behaviour (flying and diving) in the same individuals. FMR increased steadily throughout the breeding season, increasing by 11% from the incubation period to the long chick-brooding period. However, this was not accompanied by either an increase in flying or diving behaviour, or an increase in the energetic costs of activity. Instead, the changes in FMR could be explained exclusively by a progressive increase in MMR. Seasonal changes in MMR could be due to a change in body composition or a decrease in body condition associated with changing the allocation of resources between provisioning adults and growing chicks. Our study highlights the importance of measuring physiological parameters continuously in free-ranging animals in order to understand fully the mechanisms underpinning seasonal changes in physiology and behaviour.

Context-dependent correlation between resting metabolic rate and daily energy expenditure in wild chipmunks

Several empirical studies have shown that variation in daily energy expenditure (DEE) and resting metabolic rate (RMR) is influenced by environmental and individual factors, but whether these shared influences are responsible for, or independent of, relationships between DEE and RMR remains unknown. The objectives of this study were to (i) simultaneously evaluate the effects of environmental and individual variables on DEE and RMR in free-ranging eastern chipmunks (Tamias striatus) and (ii) quantify the correlation between DEE and RMR before and after controlling for common sources of variation. We found that the influence of individual factors on DEE and RMR is most often shared, whereas the influence of environmental factors tends to be distinct. Both raw and mass-adjusted DEE and RMR were significantly correlated, but this correlation vanished after accounting for the shared effect of reproduction on both traits. However, within reproductive individuals, DEE and RMR remained positively correlated after accounting for all other significant covariates. The ratio of DEE to RMR was significantly higher during reproduction than at other times of the year and was negatively correlated with ambient temperature. DEE and RMR appear to be inherently correlated during reproduction, but this correlation does not persist during other, less energy-demanding periods of the annual cycle.

Genetic correlation between resting metabolic rate and exploratory behaviour in deer mice (Peromyscus maniculatus)

According to the ‘pace-of-life’ syndrome hypothesis, differences in resting metabolic rate (RMR) should be genetically associated with exploratory behaviour. A large number of studies reported significant heritability for both RMR and exploratory behaviour, but the genetic correlation between the two has yet to be documented. We used a quantitative genetic approach to decompose the phenotypic (co)variance of several metabolic and behavioural measures into components of additive genetic, common environment and permanent environment variance in captive deer mice. We found significant additive genetic variance for two mass-independent metabolic measures (RMR and the average metabolic rate throughout the respirometry run) and two behavioural measures (time spent in centre and distance moved in a novel environment). We also detected positive additive genetic correlation between mass-independent RMR and distance moved (rA = 0.78 ± 0.23). Our results suggest that RMR and exploratory behaviour are functionally integrated traits in deer mice, providing empirical support for one of the connections within the pace-of-life syndrome hypothesis.

Exploration strategies map along fast-slow metabolic and life-history continua in muroid rodents

1Personality is highly relevant to ecology and the evolution of fast–slow metabolic and life-history strategies. One of the most important personality traits is exploratory behaviour, usually measured on an animal introduced to a novel environment (e.g. open-field test).2Here, we use a unique comparative dataset on open-field exploratory behaviour of muroid rodents to test a key assumption of a recent evolutionary model, i.e. that exploration thoroughness is positively correlated to age at first reproduction (AFR). We then examine how AFR and exploratory behaviour are related to basal metabolic rate (BMR).3Inter-specific variation in exploratory behaviour was positively correlated with AFR. Both AFR and exploration behaviour were negatively correlated with BMR. These results remained significant when taking phylogeny into account.4We suggest that species occupying unproductive and unpredictable environments simultaneously benefit from high exploration, low BMR and delayed AFR because exploration increases the likelihood of finding scarce resources, whereas low BMR and delayed reproduction enhance survival during frequent resources shortages.5This study provides the first empirical evidence for a link between personality, life-history, phylogeny and energy metabolism at the inter-specific level. The superficial-thorough exploration continuum can be mapped along the fast–slow metabolic and life-history continua.

Testing dynamic variance-sensitive foraging using individual differences in basal metabolic rates of zebra finches

Social foragers can alternate between searching for food (producer tactic), and searching for other individuals that have located food in order to join them (scrounger tactic). Both tactics yield equal rewards on average, but the rewards generated by producer are more variable. A dynamic variance-sensitive foraging model predicts that social foragers should increase their use of scrounger with increasing energy requirements and/or decreased food availability early in the foraging period. We tested whether natural variation in minimum energy requirements (basal metabolic rate or BMR) is associated with differences in the use of producer–scrounger foraging tactics in female zebra finches Taeniopygia guttata. As predicted by the dynamic variance-sensitive model, high BMR individuals had significantly greater use of the scrounger tactic compared with low BMR individuals. However, we observed no effect of food availability on tactic use, indicating that female zebra finches were not variance-sensitive foragers under our experimental conditions. This study is the first to report that variation in BMR within a species is associated with differences in foraging behaviour. BMR-related differences in scrounger tactic use are consistent with phenotype-dependent tactic use decisions. We suggest that BMR is correlated with another phenotypic trait which itself influences tactic use decisions.

Basal metabolic rate of canidae from hot deserts to cold arctic climates

Canids form the most widely distributed family within the order Carnivora, with members present in a multitude of different environments from cold arctic to hot, dry deserts. We reviewed the literature and compared 24 data sets available on the basal metabolic rate (BMR) of 12 canid species, accounting for body mass and climate, to examine inter- and intraspecific variations in mass-adjusted BMR between 2 extreme climates (arctic and hot desert). Using both conventional and phylogenetically independent analysis of covariance, we found that canids from the arctic climate zone had significantly higher mass-adjusted BMR than species from hot deserts. Canids not associated with either arctic or desert climates had an intermediate and more variable mass-adjusted BMR. The climate effect also was significant at the intraspecific level in species for which we had data in 2 different climates. Arctic and desert climates represent contrasting combinations of ambient temperatures and water accessibility that require opposite physiological adaptations in terms of metabolism. The fact that BMR varies within species when individuals are subjected to different climate regimes further suggests that climate is an important determinant of BMR.

Effect of pregnancy for females born small on later life metabolic disease risk

There is a strong inverse relationship between a females own birth weight and her subsequent risk for gestational diabetes with increased risk of developing diabetes later in life. We have shown that growth restricted females develop loss of glucose tolerance during late pregnancy with normal pancreatic function.