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In response to seasonal variation in energy availability and thermal environment, physiological and endocrine mechanisms have evolved in temperate zone animals. Seasonal changes in hormone activity affect metabolism, body temperature, and reproductive activity. We examined the seasonal regulatory role of hormones on basal metabolic rate (BMR) and regulatory nonshivering thermogenesis (RNST) in 98 female and 17 male adult Eptesicus fuscus (big brown bat). We measured BMR, RNST, and plasma levels of thyroid hormone (T3), leptin, and cortisol in bats captured in maternity colonies in eastern Massachusetts from May to August (from arousal from the hibernation phase to the prehibernation phase). We hypothesized that all three hormones are seasonally primarily metabolic hormones and secondarily thermogenic hormones. In males, only BMR significantly changed seasonally. In females, all five variables significantly changed seasonally. The seasonal pattern of plasma leptin and cortisol levels correlated with the seasonal pattern of BMR, with an initial increase followed by a decrease, suggesting that leptin and cortisol are primarily metabolic hormones. The seasonal pattern of plasma T3 levels generally paralleled the basic seasonal pattern of RNST, with both increasing at the second half of the season, suggesting that T3 is primarily a thermogenic hormone. The observed decrease in plasma leptin levels may be necessary to allow for the observed seasonal decrease in BMR, with the similar cortisol pattern important for leptin regulation. While T3 is needed to maintain BMR, it may play a more critical role in the seasonal regulation of RNST than of BMR.

Reduced populations of Myotis lucifugus (Little Brown Myotis) devastated by white-nose syndrome (WNS) persist in eastern North America. Between 2009 and 2013, we recaptured 113 marked individuals that survived between 1 and 6 winters in New England since the arrival of WNS. We also observed signs of reproductive success in 57 recaptured bats.

As the human population continues to expand, increased encroachment on natural landscapes and wildlife habitats is expected. Organisms able to acclimate to human-altered environments should have a selective advantage over those unable to do so. Over the past two decades, bats have increasingly begun to roost and raise offspring in spaces beneath pre-cast concrete bridges. Few studies have examined the health or fitness of individuals living in these anthropogenic sites. In the present study, we examined birth size and postnatal growth, as surrogates of reproductive success, in Brazilian free-tailed bat pups born at a natural and a human-made roost. Based on putative stress-related conditions (noise from vehicular traffic, chemical pollutants and a modified social environment) present at bridges, we predicted that bats at these sites would have reduced reproductive success. Contrary to our prediction, pups born at a bridge site were on average heavier and larger at birth and grew faster than those born at a cave site. Also, both birth size and growth rates of pups differ between years. We attribute observed differences to a combination of roost-related conditions (i.e. roost temperature and proximity to foraging areas), climate and maternal effects with larger mothers raising larger pups. Thus, some bridge roosts, at least in the short term, are suitable, and in some cases may provide better conditions, for raising young bat pups than cave roosts.

Estimates of postnatal growth rates and age based on data collected from free-ranging little brown myotis (Myotis lucifugus) captured sequentially at the same colony in the same year were used to compare longitudinal (mark–recapture) and cross-sectional (grab) sampling methods. Analyses of these data indicate that cross-sectional sampling significantly underestimates growth rates for length of forearm, body mass, and length of epiphyseal gap. Equations based on cross-sectional samples significantly overestimated ages of young, as compared with equations based on the longitudinal method. These results support the hypothesis that cross-sectional sampling is unreliable for deriving postnatal growth curves for free-ranging bats and emphasize the importance of using longitudinal data to derive growth rates and estimates of age during the postnatal period.

We conducted a "common garden" experiment to compare aspects of thermoregulation and metabolism in wild and random-bred laboratory house mice (Mus domesticus) and their reciprocal crosses. Analysis of covariance (ANCOVA) indicated that, after accounting for effects of body mass and other appropriate covariates (e.g., age), wild (N = 12) and hybrid (N = 25) mice together tended to have higher (+9.7%; P = .0904) maximal nonshivering thermogenesis (max-NST) in response to norepinephrine injection than did lab mice (N = 18). Wild (-17.2%; P = .0941) and hybrid (wild dam:-23.1%; P = .0001; lab dam: -11.2%; P = .0749) mice also tended to have lower basal metabolic rates (BMRs) than did lab mice. As a consequence of these trends, wild and hybrid mice, analyzed together, had significantly higher (+ 18.2%; P = .0263) regulatory NST (max-NST minus BMR) than did lab mice. Paralleling the differences in regulatory NST, wild and hybrid mice together had significantly more (+21.2%; P = .0129) interscapular brown adipos...

The hypothesis was tested that the reproductive performance of voles would be reduced when fed diets containing tannins either because of increased metabolic rates, decreased intake, or decreased digestive efficiency. We fed a ration containing 4% tannic acid (TA) (dry mass basis) to 24 pair of prairie voles (Microtus ochrogaster) and compared reproductive performance (litter size, birth weights, body mass of the young until weaning, and mass changes in the dams) to that of 24 pair of prairie vole fed a control ration. We also compared the intake rates, digestive efficiency, and metabolic rates [as measured by Vo2 consumption (cm(3)/hr)] of dams and young fed both rations. Voles consuming 4% TA diets produced litters of similar size and mass as did voles fed the control ration. Furthermore, the mass of the young of dams fed the tannic acid ration were similar to the young of dams consuming the control ration through day 19 postpartum. However, dams consuming the tannic acid ration lost mass throughout lactation while the control dams maintained mass. Because the Vo2 rates of both treated and control dams and litters were similar, we conclude increased metabolic costs were not the reason for the observed mass loss but, rather, reduced digestive efficiency, reduced intake of digestible dry mass, and apparent digestible nitrogen.

To better understand intraspecific variation in basal metabolic rate (BMR), we examined environmental, physiological, and/or cellular bases for residual variation in BMR in big brown bats, Eptesicus fuscus. We measured BMR and plasma levels of thyroid hormone (T(3)) and leptin in bats captured in maternity colonies in eastern Massachusetts (MA; northern population) and in Alabama and Georgia (ALGA; southern population) to assess macrogeographic (between- or among-population) and microgeographic (within-population) variation in those traits. After accounting for effects of body mass, stage of pregnancy, and within-population variation, bats from the northern population did not differ significantly in BMR, T(3), or leptin values from those in the southern population. However, after accounting for the effects of body mass and stage of pregnancy, a test for differences in all traits among colonies from both populations was significant. For BMR, bats differed significantly among the northern colonies. Moreover, after removing the effects of body mass and stage of pregnancy, bats from the AL colony had significantly higher BMR than did bats from all other colonies except one in MA, and they had significantly higher T(3) levels but lower leptin levels than did bats from two other colonies. The presence of among-colony and within-population variation for these traits suggests that proximate (nonevolutionary) factors (e.g., microhabitat differences such as roost type) play an important role in shaping intraspecific variation in BMR and its hormone correlates.

Hibernating animals deposit adipose tissue before hibernation to withstand long periods of reduced energy intake. Normally, adiposity is positively correlated with increased secretion from adipose tissue of the satiety hormone, leptin. During the prehibernatory phase of the little brown bat, Myotis lucifugus, body mass and adiposity increased to a maximum within 12 days. Leptin secretion from adipose tissue in vitro and plasma leptin, however, increased before the increase in adiposity, then significantly decreased when adiposity increased. Basal metabolic rate (BMR) decreased when plasma leptin was increasing. This was followed by an increase in nonshivering thermogenic capacity and brown adipose tissue mass. We conclude that in the early prehibernatory phase, BMR decreases despite increasing plasma leptin levels, suggesting a state of relative leptin resistance at that time. At later stages, adiposity increases as BMR continues to decrease, and plasma leptin becomes dissociated from adiposity. Thus, in M. lucifugus, hibernation may be achieved partly by removing the metabolic signal of leptin during the fattening period of prehibernation.

We conducted a "common garden" experiment to compare aspects of exercise physiology and voluntary wheel-running behavior in wild and random-bred (i.e., non-inbred) laboratory house mice and their reciprocal crosses. Analysis of covariance indicated that, after effects of body mass and other appropriate covariates (e.g., age at testing) were accounted for, wild (range 2.46-3.30 m/s, n = 12) and hybrid (range 1.69-3.30 m/s, n = 24) mice exhibited forced maximal sprint running speeds that averaged approximately 50% higher than those of random-bred laboratory mice (range 1.11-2.12 m/s, n = 19). Wild and hybrid mice also had significantly higher (+22%) mass-corrected maximal rates of oxygen consumption (VO2max) during forced exercise and greater (+12%) relative ventricle masses than lab mice. Wild and hybrid mice also showed statistically higher swimming endurance times relative to body mass than lab mice, although these differences were insignificant when body mass was not used as a covariate. No significant differences were found for relative gastrocnemius muscle mass, liver mass, hematocrit, or blood hemoglobin content. During a 7-day test on voluntary activity wheels, both wild and hybrid mice ran significantly more total revolutions (+101%), ran at higher average velocities when they were active (+69%), and exhibited higher maximum revolutions in any single 1-min period (+41% on the 7th day of testing), but the total number of active 1-min intervals did not differ significantly among groups. In general, the behavioral and/or whole organisms performance traits showed greater differences than the lower-level traits; thus, during the domestication of house mice, behavior may have evolved more rapidly than physiology.