Molecular phylogeny of New World Myotis (Chiroptera, Vespertilionidae) inferred from mitochondrial and nuclear DNA genes.

Recent studies have shown that species in the genus Myotis have evolved a number of convergent morphological traits, many of which are more related to their mode of food procurement than to their phylogeny. Surprisingly, the biogeographic origins of these species are a much better predictor of phylogenetic relationships, than their morphology. In particular, a monophyletic clade that includes all New World species was apparent, but only a third of the 38 species have been analysed. In order to better understand the evolution of this clade, we present phylogenetic reconstructions of 17 Nearctic and 13 Neotropical species of Myotis compared to a number of Old World congeners. These reconstructions are based on mitochondrial cytochrome b (1140 bp), and nuclear Rag 2 genes (1148 bp). Monophyly of the New World clade is strongly supported in all analyses. Two Palaearctic sister species, one from the west (M. brandtii) and one from the east (M. gracilis), are embedded within the New World clade, suggesting that they either moved across the Bering Strait, or that they descended from the same ancestor that reached the New World. An emerging feature of these phylogenetic reconstructions is that limited faunal exchanges have occurred, including between the North and South American continents, further emphasizing the importance of biogeography in the radiation of Myotis. A fossil-calibrated, relaxed molecular-clock model was used to estimate the divergence time of New World lineages to 12.2+/-2.0 MYA. Early diversification of New World Myotis coincides with the sharp global cooling of the Middle Miocene. Radiation of the temperate-adapted Myotis may have been triggered by these climatic changes. The relative paucity of species currently found in South America might result from a combination of factors including the early presence of competitors better adapted to tropical habitats.

Leptin receptor expression increases in placenta, but not hypothalamus, during gestation in Mus musculus and Myotis lucifugus.

In addition to effects on appetite and metabolism, the hormone leptin is required for reproduction in mammals. Maternal plasma leptin is increased above non-pregnant levels in all mammals thus far examined, including humans. The increase in plasma leptin appears to result in part from upregulation of adipose leptin secretion (e.g., in mice), or from production and secretion of leptin from the placenta (e.g., in humans and some bats). The placenta may also modulate maternal leptin levels via production of a plasma leptin-binding protein (mice, humans). Thus, the placenta plays a coordinating role in regulation of maternal leptin during pregnancy. In this study, the hypothesis that the placenta is also a target organ for leptin in diverse taxa was tested by examining the expression of leptin receptors (Ob-R) in placentae from species of distantly related mammalian taxa, Mus musculus (the laboratory mouse) and Myotis lucifugus (the little brown myotis, also called the little brown bat). A partial sequence of M. lucifugus Ob-R cDNA was first obtained and found to share approximately 78-88% homology at the nucleotide level with known mammalian Ob-R cDNAs. Using probes and primers designed from this sequence, receptor expression was detected in numerous tissues of M. lucifugus, including placenta, which expressed two major receptor isoforms as judged by molecular size. In both species, Ob-R mRNA expression in placenta significantly increased from early to late gestation. Expression of Ob-R mRNA was not affected by cAMP treatment in vitro. The increase in Ob-R mRNA expression in placenta was specific, since Ob-R mRNA expression did not change during gestation in either species in hypothalamus, the major site of the central actions of leptin. Thus, Ob-R is expressed in placenta throughout gestation in mice and bats, and its expression increases over the course of gestation, which raises the possibility that leptin may exert temporally distinct effects on placental growth or function throughout gestation. Because similar placenta-specific changes in leptin receptor expression occurred in species from distantly related mammalian taxa which collectively comprise approximately 70% of all known mammalian species, it is possible that placental actions of leptin are conserved across mammals, even in those species (such as the Swiss-Webster strain of mouse) in which the placenta does not itself produce leptin.

Intersexual differences in energy expenditure of Anolis carolinensis lizards during breeding and postbreeding seasons.

Although the amount of energy that males and females invest in reproduction is an integral component of theories explaining the evolution of particular mating strategies, few studies have actually determined the amount of energy that each sex allocates to reproduction. We compared how energy is expended by male and female Anolis carolinensis lizards during both the breeding and postbreeding seasons. We used laboratory respirometry to determine resting metabolic rates (RMRs) of inactive, freshly captured lizards and the doubly labeled water technique to determine field metabolic rates (FMRs) of free-ranging lizards. Both RMRs and FMRs were influenced by body mass but not by sex. Season did not influence FMRs; however, RMRs of both sexes increased approximately 40% from the breeding to the postbreeding season. The seasonal increase in RMRs was attributed to a postreproductive increase in feeding rate and specific dynamic action. We used RMRs, FMRs, and thermal profiles of lizards to calculate energy budgets for breeding and postbreeding seasons. Energy budgets partitioned daily field energy (DFE; calculated from FMRs) into daily activity energy (DAE) and daily resting energy (DRE; calculated from RMRs). Energy expended for reproduction was estimated as DAE during the breeding season plus egg production (for females). Despite males having 40% greater body mass, females expended 46% more energy for reproduction than did males (906 and 619 J/d, respectively). Total metabolizable energy (TME=DFE+egg production for females) expended during the breeding season was similar for males and females (1,280 and 1,365 J/d, respectively). Although TME of females decreased 44% from the breeding to the postbreeding season (1,365 vs. 766 J/d), TME of males was similar during both seasons (1,280 vs. 1,245 J/d). There were both seasonal and sexual differences in DRE and DAE. Compared with most lizards from semiarid/desert habitats, A. carolinensis in a temperate habitat expends more total energy during the breeding season, allocates more energy to eggs, and appears to have more total energy available for reproduction.

Genetic consequences of polygyny and social structure in an Indian fruit bat, Cynopterus sphinx. I. Inbreeding, outbreeding, and population subdivision.

Population subdivision into behaviorally cohesive kin groups influences rates of inbreeding and genetic drift and has important implications for the evolution of social behavior. Here we report the results of a study designed to test the hypothesis that harem social structure promotes inbreeding and genetic subdivision in a population with overlapping generations. Genetic consequences of harem social structure were investigated in a natural population of a highly polygynous fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae), in western India. The partitioning of genetic variance within and among breeding groups was assessed using 10-locus microsatellite genotypes for 431 individually marked bats. Genetic analysis of the C. sphinx study population was integrated with field data on demography and social structure to determine the specific ways in which mating, dispersal, and new social group formation influenced population genetic structure. Microsatellite data revealed striking contrasts in genetic structure between consecutive offspring cohorts and between generations. Relative to the 1998 (dry-season) offspring cohort, the 1997 (wet-season) cohort was characterized by a more extensive degree of within-group heterozygote excess (F(IS) = -0.164 vs. -0.050), a greater degree of among-group subdivision (F(ST) = 0.123 vs. 0.008), and higher average within-group relatedness (r = 0.251 vs. 0.017). Differences in genetic structure between the two offspring cohorts were attributable to seasonal differences in the number and proportional representation of male parents. Relative to adult age-classes, offspring cohorts were characterized by more extensive departures from allelic and genotypic equilibria and a greater degree of genetic subdivision. Generational differences in F-statistics indicated that genetic structuring of offspring cohorts was randomized by natal dispersal prior to recruitment into the breeding population. Low relatedness among harem females (r = 0.002-0.005) was primarily attributable to high rates of natal dispersal and low rates of juvenile survivorship. Kin selection is therefore an unlikely explanation for the formation and maintenance of behaviorally cohesive breeding groups in this highly social mammal.

Genetic consequences of polygyny and social structure in an Indian fruit bat, Cynopterus sphinx. II. Variance in male mating success and effective population size.

Variance in reproductive success is a primary determinant of genetically effective population size (Ne), and thus has important implications for the role of genetic drift in the evolutionary dynamics of animal taxa characterized by polygynous mating systems. Here we report the results of a study designed to test the hypothesis that polygynous mating results in significantly reduced Ne in an age-structured population. This hypothesis was tested in a natural population of a harem-forming fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae), in western India. The influence of the mating system on the ratio of variance Ne to adult census number (N) was assessed using a mathematical model designed for age-structured populations that incorporated demographic and genetic data. Male mating success was assessed by means of direct and indirect paternity analysis using 10-locus microsatellite genotypes of adults and progeny from two consecutive breeding periods (n = 431 individually marked bats). Combined results from both analyses were used to infer the effective number of male parents in each breeding period. The relative proportion of successfully reproducing males and the size distribution of paternal sibships comprising each offspring cohort revealed an extremely high within-season variance in male mating success (up to 9.2 times higher than Poisson expectation). The resultant estimate of Ne/N for the C. sphinx study population was 0.42. As a result of polygynous mating, the predicted rate of drift (1/2Ne per generation) was 17.6% higher than expected from a Poisson distribution of male mating success. However, the estimated Ne/N was well within the 0.25-0.75 range expected for age-structured populations under normal demographic conditions. The life-history schedule of C. sphinx is characterized by a disproportionately short sexual maturation period scaled to adult life span. Consequently, the influence of polygynous mating on Ne/N is mitigated by the extensive overlap of generations. In C. sphinx, turnover of breeding males between seasons ensures a broader sampling of the adult male gamete pool than expected from the variance in mating success within a single breeding period.

Acoustic divergence in two cryptic Hipposideros species: a role for social selection?

We present evidence that a relatively widespread and common bat from South East Asia comprises two morphologically cryptic but acoustically divergent species. A population of the bicoloured leaf-nosed bat (Hipposideros bicolor) from Peninsular Malaysia exhibits a bimodal distribution of echolocation call frequencies, with peaks in the frequency of maximum energy at ca. 131 and 142 kHz. The two phonic types are genetically distinct, with a cytochrome b sequence divergence of just under 7%. We consider the mechanisms by which acoustic divergence in these species might arise. Differences in call frequency are not likely to effect resource partitioning by detectable prey size or functional range. However, ecological segregation may be achieved by differences in microhabitat use; the 131kHz H. bicolor is characterized by significantly longer forearms, lower wing loading, a lower aspect ratio and a more rounded wingtip, features that are associated with greater manoeuvrability in flight that may enable it to forage in more cluttered environments relative to the 142 kHz phonic type. We suggest that acoustic divergence in these species is a consequence of social selection for a clear communication channel, which is mediated by the close link between the acoustic signal and receptor systems imposed by the highly specialized nature of the hipposiderid and rhinolophid echolocation system.

Hyperleptinemia in pregnant bats is characterized by increased placental leptin secretion in vitro.

Hyperleptinemia is a common feature of pregnancy in mammals. The source of increased plasma leptin is uncertain. We examined leptin secretory rates in vitro to test the hypothesis that leptin secretion is upregulated during pregnancy. Two species of insectivorous bats were examined, Myotis lucifugus and Eptesicus fuscus, because of their unique reproductive cycle. Body mass and plasma leptin significantly increased with gestation and decreased during lactation. Adiposity increased in midgestation, then decreased in late gestation and lactation and was not significantly correlated with plasma leptin in pregnant or early lactating individuals. Leptin secretion in vitro per gram of adipose tissue tended to increase with gestation but was not significantly correlated with plasma leptin in the same individuals. Leptin secretion from placentae, however, increased with gestation and was significantly correlated with plasma leptin from the same individuals. In suckling pups, plasma leptin was high shortly after birth, then decreased to low levels that were not correlated with adiposity thereafter. We conclude that in bats, the placenta is a major source of circulating leptin during pregnancy, and that adiposity and plasma leptin levels are decoupled during three different periods of intense metabolic demand (pregnancy, early lactation, and neonatal growth).

Interspecific and intraspecific variation in proximate, mineral, and fatty acid composition of milk in Old World fruit bats (Chiroptera: Pteropodidae).

We examine the effect of body mass on milk composition among Old World fruit bats, including Pteropus pumilus (0.175 kg), Pteropus rodricensus (0.265 kg), Pteropus hypomelanus (0.571 kg), and Pteropus vampyrus (1.133 kg). We describe intra- and interspecific differences in the proximate composition of milk among these four species and the minerals and fatty acids in the milk of the latter two species. There were no differences between species in the concentrations of dry matter, fat, or lactose in milk. However, there were significant, although small, differences in the protein content of milk among species, with protein being significantly greater in P. rodricensus than in P. pumilus and P. hypomelanus and protein being significantly less in P. hypomelanus than in P. rodricensus and P. vampyrus. There were no differences in mineral content between P. hypomelanus and P. vampyrus in milk minerals, but minor differences were evident in fatty acids 12:0, 14:0, 18:0, 18:1n11, and 18:2n6. Our findings suggest that milk composition is relatively constant across lactation for most proximate, mineral, and fatty acid components. We found a significant increase in dry matter and energy across lactation in the concentration of dry matter and energy in P. pumilus and fat in P. hypomelanus. In P. hypomelanus, we found a significant increase in the concentration of fatty acids 10:0 and 20:1n9 and a significant decrease in Iso15 and 20:1n7. No other differences associated with day of lactation were found. These findings suggest that milk composition is generally similar within the genus Pteropus, despite a 6.5-fold difference in body mass between species that we evaluated.

Dissociation of leptin secretion and adiposity during prehibernatory fattening in little brown bats.

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.

Steroid-dependent up-regulation of adipose leptin secretion in vitro during pregnancy in mice.

Circulating leptin levels are elevated during the later stages of pregnancy in mammals, suggesting that maternal leptin may play a role in maintenance of pregnancy and/or preparation for parturition and lactation. The regulation and source of circulating leptin during pregnancy remains undetermined, but leptin mRNA levels increase in adipose tissue during this time in some species. Considerable controversy exists whether placenta is also a leptin-secreting tissue during pregnancy. Here, we directly demonstrate that leptin secretion rates from mouse adipose tissue in vitro are decreased during early pregnancy and up-regulated during late pregnancy and lactation. Changes in leptin secretion rates in vitro paralleled those of circulating leptin in vivo during gestation. Subcutaneous implants of estradiol or corticosterone into lactating mice for 48 h stimulated adipose leptin secretion rates in vitro to the level of that in pregnant mice. However, corticosterone, but not estradiol, increased leptin secretion when added to isolated adipose tissue in vitro. Placentae obtained at two stages of pregnancy did not secrete leptin in vitro, either when acutely isolated or when dissociated into cells for long-term cultures. Placental tissue (or cells) secreted progesterone, however, demonstrating placental viability. We conclude that hyperleptinemia during late pregnancy in mice primarily results from corticosterone-dependent up-regulation of leptin secretion from adipose tissue, and that the placenta does not contribute to leptin secretion. The initial decrease in leptin secretory rates from adipose tissue during early pregnancy may facilitate energy storage for the subsequent, increased metabolic demands of later pregnancy and lactation.

Resource partitioning in rhinolophoid bats revisited.

We assessed the ecomorphological structure of a guild of rhinolophoid bats in a Malaysian rainforest first described by Heller and von Helversen (1989). These authors found that the distribution of echolocation call frequencies used by 12 syntopic species was more even than expected from allometric relationships or in randomly generated communities, and that the observed minimal ratio was greater than expected by chance alone. In this study we were able to expand their guild to 15 species, but in doing so it became apparent that call frequencies might be less evenly distributed across the total frequency range than previously proposed. We replicated Heller and von Helversen's (1989) analyses with the full 15-species complement but were unable to support their suggestion that rhinolophoid bats exhibit resource partitioning through differences in frequency bands. We adopted a multivariate approach and incorporated measures of body size and wing morphology into the analysis. We used phylogenetic autocorrelation to ensure that the species were statistically independentand principal component analysis to describe the morphological space occupied by the 15 species in the community and four additional species representing the extremes of phenotypic variation. We derived interspecific Euclidean distances and tested the mean values and SDs of these distances against those of 100 guilds of "synthetic" species created randomly within the principal component space. The guild of Rhinolophoidea was not distributed randomly in multivariate space. Instead we found evidence of morphological overdispersion of the most similar species, which suggests niche differentiation in response to competition. Less similar species were nearer in morphological space than expected, and we suggest this is a consequence of ecological constraints on parameter combinations. Despite this underdispersion, many of the more distant neighbours were evenly rather than randomly spaced or clumped in morphospace, suggesting that, given the environmental constraints on morphology, species in this guild do experience limits to their similarity. Finally, we tested the influence of the relative abundance of species on morphological displacement, and found no evidence that abundant, spatially correlated species reduce interspecific overlap in morphological space.

Plasma leptin decreases during lactation in insectivorous bats.

We previously demonstrated high leptin levels during late pregnancy in little brown bats (Myotis lucifugus). We now extend these observations to a second species, the big brown bat (Eptesicus fuscus), and also report that leptin increases after the first trimester of pregnancy. Leptin decreased to baseline 1 week following parturition, with a half-time decay of 2 days. During lactation, leptin was significantly correlated with body mass in E. fuscus, but not in M. lucifugus. No circadian pattern of leptin was observed in M. lucifugus. The decrease in post-partum leptin in bats may be partly explained by loss of putative placental leptin. The continued decrease may reflect depletion of body fat during this energy demanding period, at least in Eptesicus. Changes in leptin during lactation appeared to be independent of circadian effects and time of sampling. Our study provides additional evidence that leptin increases during pregnancy and declines during lactation in a free-ranging mammal, supporting the hypothesis that leptin plays important but yet undetermined roles in reproduction.

Milk composition and lactational output in the greater spear-nosed bat, phyllostomus hastatus.

Growth rates of mammalian young are closely linked to the ability of the mother to provide nutrients; thus, milk composition and yield provide a direct measure of maternal investment during lactation in many mammals. We studied changes in milk composition and output throughout lactation in a free-ranging population of the omnivorous bat, Phyllostomus hastatus. Fat and dry matter of milk increased from 9 to 21% and from 21 to 35% of wet mass, respectively, throughout lactation. Energy increased from 6 to 9 kJ.g-1 wet mass, primarily due to the increase in fat concentration. Total sugar levels decreased slightly but non-significantly. Mean sugar level was 4.0% of wet mass. Protein concentration increased from 6 to 11% of wet mass at peak lactation and then decreased as pups approached weaning age. Total milk energy output until pups began to forage was 3609 kJ. Milk levels of Mg, Fe, Ca, K, and Na averaged 0.55 %/- 0.26, 0.23 +/- 0.2, 8.75 +/- 4.17, 5.42 +/- 2.11, and 9.87 +/- 4.3 mg.g-1 dry matter, respectively. Of the minerals studied, calcium appears to be most limiting in this species. The high degree of variability in foraging time, milk composition and milk yield between individuals at the same stage of lactation could potentially yield high variance in reproductive success among females of this polygynous species.

Leptin, corticotropin-releasing hormone (CRH), and neuropeptide Y (NPY)in free-ranging pregnant bats.

Leptin, the product of the obese gene first identified in mice, restores fertility in obese mice, and accelerates puberty in mice. We hypothesized that leptin's putative role in reproduction may extend to pregnancy and lactation. Leptin levels were determined in Myotis lucifugus, the little brown bat, a free-ranging mammal with a seasonal breeding cycle. The present study shows that plasma levels of leptin progressively rise during pregnancy, supporting a potential role for leptin in the maintenancy of pregnancy. In contrast, leptin was significantly lower during lactation, a time when most mammals, including bats, demonstrate reduced fertility. In addition to its possible roles in reproduction, leptin appears important in regulation of energy balance. M. lucifugus spontaneously fasts for up to 16 h each day during the active season, which allowed us to test the hypothesis that acute fasting was associated with decreased leptin. Leptin was significantly lower in fasted (lactating) bats, compared to those that recently returned from nightly foraging. Although postprandial lactating bats had a significantly higher fat index than fasted bats, plasma leptin and body fat were not significantly correlated, and were only weakly correlated (r2 = 0.26) when both pregnant and lactating females were included in the analysis. Similar changes during pregnancy, lactation, and the daily feeding cycle were observed in the hypothalamic neuropeptide, corticotropin-releasing hormone (CRH), which is believed to play an important role in energy balance and reproduction. By contrast, neuropeptide Y (NPY) increased during pregnancy but did not change during fasting. These results suggest that leptin's putative role in reproduction may extend to pregnancy and lactation, and that spontaneous, acute fasting results in decreased circulating levels of leptin in M. lucifugus.

High plasma cholesterol, but low triglycerides and plaque-free arteries, in Mexican free-tailed bats.

Female mammals typically become hyperphagic from mid- to late pregnancy and during lactation. Mexican free-tailed bats, Tadarida brasiliensis mexicana, double their nightly food intake from late pregnancy to peak lactation and consume an insect diet that is exceptionally high in fat. During late pregnancy and throughout lactation, fasting plasma levels of cholesterol in this insectivorous bat are high (215 +/- 8 mg/dl) and are nearly 10-fold higher than in three species of Old World frugivorous bats. Fasting triglycerides were unexpectedly low in T. brasiliensis (25 +/- 2 mg/dl), despite evidence of high fat intake during nightly feeding bouts (postprandial cholesterol and triglycerides, 268 +/- 18 and 122 +/- 20 mg/dl, respectively). High-density lipoprotein (HDL) cholesterol levels were extraordinarily high (124 +/- 5 mg/dl) and unaffected by feeding. Low-density lipoprotein cholesterol levels were correspondingly low (86 +/- 7 mg/dl). This unusual plasma lipid profile was not associated with coronary or aortic atherosclerosis, nor was there evidence of hyperglycemia or hyperinsulinemia. A high-fat diet and high levels of cholesterol in T. brasiliensis are not correlated with cardiovascular disease or (possibly) insulin resistance. Among several possible factors that might account for these observations, nightly bouts of powered flight (commuting and foraging for food) may contribute to elevated HDL cholesterol, which may protect this species from developing atherosclerosis.

Changes in milk composition during lactation in three species of insectivorous bats.

Changes in milk composition are described for three species of free-ranging insectivorous bats (Myotis lucifugus, M. velifer, and Tadarida brasiliensis) from early to mid (peak) lactation. Dry matter and energy concentrations in milk increased from early to mid-lactation. In M. lucifugus and T. brasiliensis, but not M. velifer, these increases were due largely to a rise in fat concentration, since protein and carbohydrate remained relatively constant. Energy content of milk (kJ.g-1) for each species from early through mid-lactation was related to dry matter (DM) as follows: M. lucifugus (y = 0.31 DM-0.32, r2 = 0.68), M. velifer (y = 0.48 DM-5.08, r2 = 0.99), and T. brasiliensis (y = 0.37 DM-1.51, r2 = 0.61). Comparison of the effect of sampling method on milk composition of T. brasiliensis indicated that fat, dry matter, and energy concentrations increased significantly from pre-dawn to pre-noon samples. Relatively high fat and low water levels in T. brasiliensis milk may reflect the limited access that lactating females have to free water, as well as need to minimize mass of stored milk during long foraging trips. Conversely, lower fat concentrations and higher water levels in milk in M. lucifugus and M. velifer may relate to the propensity for colonies of these two species to roost and forage near bodies of water. In addition, differences in milk fat concentrations observed among the three species may correlate to daily suckling schedules.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary energetics of the insectivorous Mexican free-tailed bat (Tadarida brasiliensis) during pregnancy and lactation.

Stomach content analysis of 20 pregnant (x body mass=13.4 g) and 18 lactating (x body mass=11.5 g) female Tadarida brasiliensis revealed that the diet, expressed as percent volume, consists largely of lepidopterans, coleopterans, hymenopterans, and dipterans, in decreasing order of importance. We found no significant difference in the diet of pregnant and lactating females when expressed as percent volume. However, when expressed as percent frequency, proportionately more pregnant females fed on lepidopterans, coleopterans, and dipterans than did lactating bats, and proportionately more lactating females fed on hymenopterans. We found no significant differences in the percentages of water, lean dry mass, fat, and energy density in the stomach contents of pregnant and lactating females. Water in stomach contents averaged 62.7% and fat and lean dry mass averaged 22.2% and 15.2%, respectively (expressed as percentage of wet mass); energy density averaged 31.2 kJ g-1 dry mass. This relatively high energy density of stomach contents, as compared to whole insects, can be attributed to the consumption of insects high in fat (especially flying ants) and the abdomens only of moths and beetles (other body parts being discarded). Estimates of nightly food intake increased markedly from mid- to late pregnancy, stabilized or decreased during late pregnancy, and increased again during early to mid-lactation. Average nightly feeding rate doubled from pregnancy to lactation and increased threefold during the first half of lactation. By adjusting our gravimetric estimates of nightly feeding rate upwards by 40% (based on estimates of field metabolic rate), we estimate that the average nightly energy intake of female T. brasiliensis ranges from 57 kJ day-1 in early lactation to 104 kJ day-1 in mid-lactation. These estimates represent nightly feeding rates averaging 39% and 73% of a female's body mass in the period from early to mid-lactation, respectively.

Further characterization of the pituitary-adrenocortical responses to stress in Chiroptera.

Previous studies on bats from this laboratory have revealed the presence of exceptionally high circulating levels of glucocorticoids in two species of the sub-order Megachiroptera. In the present study, the following questions were asked: (1) what effect does the routine handling and examination of captive bats have on the activity of their hypothalamic-pituitary-adrenocortical (HPA) axis?; (2) are the unusually high plasma levels of cortisol and corticosterone found in Pteropus hypomelanus associated with high levels of circulating adrenocorticotropic hormone (ACTH)?; (3) are there diurnal changes in stress responsivity in this species?; and (4) how do levels of glucocorticoids in P. hypomelanus compare with those found in other species of Chiroptera (both micro and megachiropteran species)? Of five species examined, P. hypomelanus had slightly higher total glucocorticoid levels than P. pumulis, but approximately 8-fold higher levels than in three species of Microchiroptera (Artibeus jamaicensis, Carollia perspicillata, and Myotis lucifigus). There was a pronounced diurnal rhythm in glucocorticoid levels in one species (M. lucifigus) for which this was determined. A 1-h period of restraint stress increased glucose and glucocorticoid levels in P. pumulis, and also increased ACTH and glucocorticoids in P. hypomelanus. Fifteen minutes of routine handling (weighting, measuring, etc.) elicited a significant rise in plasma glucocorticoids in P. hypomelanus to combined peak (cortisol plus corticosterone) levels of over 1,000 ng/ml (100 micrograms%). There was no significant difference in the response to handling in bats tested in the morning or evening. Basal ACTH levels as detected by radioimmunoassay were low in P. hypomelanus, in spite of high steroid levels.(ABSTRACT TRUNCATED AT 250 WORDS)

The cost of hovering and forward flight in a nectar-feeding bat, Glossophaga soricina, estimated from aerodynamic theory.

Energy expenditure during flight in animals can best be understood and quantified when both theoretical and empirical approaches are used concurrently. This paper examines one of four methods that we have used to estimate the cost of flight in a neotropical nectar-feeding bat Glossophaga soricina (Phyllostomidae), namely the use of kinematic and morphological data and aerodynamic theory to estimate the mechanical power requirements (power output) for hovering and horizontal forward flight. A hot-wire anemometer was used to measure induced velocity (the velocity of air accelerated by the wings) during hovering in order to estimate induced power. Our estimate of aerodynamic power (the sum of induced, profile and parasite powers) required for a 0.0105 kg G. soricina to hover is 0.15 W and our estimate of the inertial power (the power required to oscillate the wings) is 0.19 W. Thus, the total mechanical power for hovering is 0.34 W or 32.4 W kg-1. The mechanical power required for horizontal forward flight, near the minimum power flight speed (4.2 ms-1) for a 0.0117 kg bat is 0.14 W (12.3 W kg-1), of which 0.10 W is aerodynamic power and 0.042 W is inertial power. Comparison with our results on metabolic power requirements estimated from nectar intake gives a mechanical efficiency of 0.15 for hovering flight and 0.11 for forward flight near the minimum power speed.

Basal, diurnal, and stress-induced levels of glucose and glucocorticoids in captive bats.

Plasma levels of glucocorticoids and glucose were measured in three species of fruit bats (Chiroptera) sampled from captive populations. Three species of Old World bats (Pteropus vampyrus, P. Hypomelanus, and Rousettus aegyptiacus) had plasma levels of glucose that were within the normal mammalian range (80-100 mg/dl), with no difference between males and females. All animals had detectable levels of one or both of the major glucocorticoids (cortisol and corticosterone) found in mammals. Steroid levels were highest in P. hypomelanus (cortisol: 1,269 +/- 207 ng/ml; corticosterone; 590 +/- 154 ng/ml) and lowest in R. aegyptiacus (corticosterone: 36 +/- 4 ng/ml; cortisol not determined). Diurnal changes in these steroids and the effects of handling and restraint stress were further investigated in P. hypomelanus. Experimental animals were captured in their roost quarters, bled once by venupuncture within 3 min, placed singly into a small holding chamber for 50-60 min, and bled again. This procedure was performed at four different times over the course of 24 h with different groups of animals. Glucose was at a minimum just before and a maximum just after the period of food presentation. Cortisol levels remained relatively constant throughout the day-roosting period and significantly declined to their lowest level in the period following food presentation. As expected, the effects of handling and isolation caused a significant increase in both plasma cortisol and glucose levels. When individual P. hypomelanus were subjected to 3 h restraint stress in small plastic wire-mesh restraining devices, cortisol levels rose approximately 800% by 2 h, with the first significant increase at 20 min.(ABSTRACT TRUNCATED AT 250 WORDS)