Foraging Success,Agonism, and Predator Alarms: Behavioral Predictors of Cortisol in <Emphasis Type="Italic">Lemur catta</Emphasis>

Primate social grouping is understood as an adaptive strategy for mitigating environmental selection pressures, but the relative importance of various pressures may vary. Physiological measures of well-being can show their short-term impacts and suggest their relative importance and capacity to provide ultimate or proximate control of group size. I examined correlations between pressures commonly proposed as causes of social grouping (foraging success, intergroup and intragroup agonism, and predation risk) and individual levels of fecal cortisol, a hormonal stress measure, in a free-ranging population of Lemur catta. I collected behavioral data on 45 female Lemur catta at Berenty Reserve, Madagascar, over 3 seasons (August 1999-July 2000) and determined individual cortisol levels from 474 fecal samples. Neither predator alarm rates nor intragroup agonism rates correlated with cortisol levels in any season. However, females with low daily food intake and high rates of escalated intergroup defense exhibited higher cortisol levels. The data suggest that acquisition and defense of food resources are principal challenges in Lemur catta, and may be important factors determining social grouping and other behavioral or life history adaptations.     

Stress in Yucatan spider monkeys: effects of environmental conditions on fecal cortisol levels in wild and captive populations

In the Yucatán Peninsula, spider monkeys Ateles geoffroyi yucatanensis are generally found in two contrasting conditions: large tracts of conserved forest or small fragments surrounded by human populations. In the present study, we analyzed fecal cortisol levels of spider monkeys to investigate whether environmental conditions have an influence on stress; specifically, we compared fecal cortisol across individuals living in conserved forests, fragmented forests and captive conditions (zoos and pets). Radioimmunoanalysis of fecal samples from 121 individuals indicated significant differences in mean cortisol for A. g. yucatanensis based on habitat type, with the lowest levels found in the conserved forest condition. The higher cortisol levels in both fragmented forest populations and in captive individuals may be the result of metabolic and behavioral stress. The mean male fecal cortisol concentration was significantly higher than that of females, and the fecal cortisol concentration was higher in the dry season compared with the wet season in a conserved habitat. Therefore, we emphasize the importance of considering sex and seasonality when monitoring fecal cortisol concentrations of spider monkeys, and more generally of frugivores, as they face a seasonal variation in food availability. Finally, our results suggest that forest fragmentation may create long-term stressors for spider monkeys, affecting the viability of populations living under such conditions.     

Reproductive tactics influence cortisol levels in individual male gray-cheeked mangabeys (Lophocebus albigena)

Concentration of the hormone cortisol is often used as an indicator of stress, and chronically high cortisol levels are often associated with poor health. Among group living animals that compete for resources, agonistic social interactions can be expected to contribute to variation in cortisol levels within and among individuals over time. Reproductive tactics of males can change with individual quality, relatedness, and social structure, and affect cortisol levels. In gray-cheeked mangabey (Lophocebus albigena) groups, male rank is an important factor in social interactions, and males also move between groups while actively competing for females or sneaking copulations. During a 20-month study we observed the social behavior and collected 461 fecal samples from 24 adult male gray-cheeked mangabeys from five groups in Kibale National Park, Uganda. Aggressive interactions and the presence of females at the peak of sexual swelling were associated with elevated cortisol concentrations in all males. Independently, dominant (i.e., highest-ranking) males within groups had higher cortisol concentrations than subordinate males, and immigrant males had higher cortisol concentrations than dominant males.     

Fruit availability, chimpanzee diet, and grouping patterns on Rubondo Island, Tanzania

We examined seasonal patterns of fruit availability, dietary quality, and group size in the descendants of an introduced chimpanzee population on Rubondo Island, Tanzania. The site has supported a free-ranging population without provisioning for 40 years. Our goals were to determine whether Rubondo chimpanzees experience periods of fruit shortage, and whether they respond to changes in fruit availability similarly to chimpanzees at endemic sites. We indexed the fruit availability of tree and liana species on transects stratified across three chimpanzee ranging areas. We used fecal analyses to evaluate seasonal changes in diet, and used data on party size and nesting group size to examine seasonal patterns of grouping. Tree fruit availability was positively correlated with rainfall, with a period of relative tree fruit scarcity corresponding with the long dry season. Liana fruit availability was not related to rainfall, and lianas exhibited less variable fruiting patterns across seasons. Fruits made up the majority of the chimpanzee diet, with lianas accounting for 35% of dietary fruit species. Fruits of the liana Saba comorensis were available during all months of phenological monitoring, but they were consumed more when tree fruit was scarce, suggesting that Saba comorensis fruits may be a fallback food for Rubondo chimpanzees. There were no increases in consumption of lower-quality plant parts between seasons, and there were no changes in group size between seasons. These results contrast with evidence from several endemic chimpanzee study sites, and indicate that Rubondo chimpanzees may have access to abundant and high-quality foods year round.     

Individual,social, and environmental factors affecting salivary and fecal cortisol levels in captive pied tamarins (Saguinus bicolor)

Pied tamarins (Saguinus bicolor) are endangered New World primates, and in captivity appear to be very susceptible to stress. We measured cortisol in 214 saliva samples from 36 tamarins and in 227 fecal samples from 27 tamarins, and investigated the effects of age, sex, pregnancy, rearing history, social status, weight, group composition, and enclosure type using generalized linear mixed models. There was no effect of age on either fecal or salivary cortisol levels. Female pied tamarins in late pregnancy had higher fecal cortisol levels than those in early pregnancy, or nonpregnant females, but there was no effect of pregnancy on salivary cortisol. Females had higher salivary cortisol levels than males, but there was no effect of rearing history. However, for fecal cortisol, there was an interaction between sex and rearing history. Hand‐reared tamarins overall had higher fecal cortisol levels, but while male parent‐reared tamarins had higher levels than females who were parent‐reared, the reverse was true for hand‐reared individuals. There was a trend towards lower fecal cortisol levels in subordinate individuals, but no effect of status on salivary cortisol. Fecal but not salivary cortisol levels declined with increasing weight. We found little effect of group composition on cortisol levels in either saliva or feces, suggesting that as long as tamarins are housed socially, the nature of the group is of less importance. However, animals in off‐show enclosures had higher salivary and fecal cortisol levels than individuals housed on‐show. We suggest that large on‐show enclosures with permanent access to off‐exhibit areas may compensate for the effects of visitor disturbance, and a larger number of tamarins of the same species housed close together may explain the higher cortisol levels found in tamarins living in off‐show accommodation, but further research is needed.     

Sources of variation in fecal cortisol levels in howler monkeys in belize

High cortisol levels are known to cause low fecundity and increased mortality; thus, the prospect of using cortisol as a measure of population health is an exciting one. However, because so many factors can interact to influence cortisol release, it can be difficult to interpret what exactly is creating changes to cortisol levels. This study investigates variation in fecal cortisol levels in a population of black howlers (Alouatta pigra) from 350 fecal samples collected from 33 individuals in more than 4 years. A general linear mixed model revealed that cortisol varied significantly with fruit availability and contact with tourists. When fruit availability was low, cortisol increased, likely because when fruit availability is low monkeys eat less fruit, thus obtaining less sugar. This result may simply reflect cortisol's metabolic function of mobilizing glucose. It also indicates that these monkeys may be experiencing periods of food stress throughout the year, which was earlier thought to be minimal for a primarily folivorous species. Presence of tourists was the only other factor found to lead to high cortisol; with exposure to tourists increasing stress levels. These results highlight the importance of understanding how physiological factors can influence cortisol, making it easier to interpret results and determine the external social or ecological stressors that may increase cortisol. Am. J. Primatol. 72:600–606, 2010. © 2010 Wiley‐Liss, Inc.     

ADRENAL FUNCTION IN WILD AND REHABILITATED PACIFIC HARBOR SEALS (PHOCA VITULINA RICHARDII) AND IN SEALS WITH PHOCINE HERPESVIRUS-ASSOCIATED ADRENAL NECROSIS

Adrenal function in harbor seals (Phoca vitulina richardii) was evaluated using adrenocorticotrophic hormone (ACTH) stimulation tests and fecal cortisol levels. The effect of ACTH administration on plasma cortisol and aldosterone levels in five free-living and 14 rehabilitated harbor seal pups was determined using enzyme immunoassay and radioimmunoassay, respectively. In free-living seals, injection of ACTH caused a significant increase in mean plasma cortisol but not of mean aldosterone levels 60 min postinjection. In these seals, mean initial plasma aldosterone was significantly higher than initial levels in rehabilitated seals, while initial cortisol levels were similar. Of the rehabilitated seals, eight died with adrenal cortical necrosis associated with herpesvirus inclusions, while six lived to be released. In the seals that were released, both mean initial cortisol levels and response to ACTH decreased through rehabilitation. In the seals that died, mean initial cortisol and response to ACTH increased through rehabilitation. The differences between initial cortisol levels in seals that lived and those that died were significant at weeks two and four of rehabilitation but not at the week of admission. There was considerable individual variation in initial plasma aldosterone levels and responses to ACTH, although initial aldosterone levels were significantly higher in rehabilitated seals that died than in seals that lived. Seals with adrenal necrosis associated with herpesvirus infection did not have decreased adrenal hormone responses to ACTH. Differences between initial hormone levels and responses to ACTH in different groups of seals may be associated with differing stress levels. Fecal cortisol assays were not a useful method of assessing adrenal function in these seals, as measured levels did not correlate with plasma cortisol levels.     

Factors affecting fecal glucocorticoid levels in semi-free-ranging female mandrills (Mandrillus sphinx)

Subordinate female cercopithecine primates often experience decreased reproductive success in comparison with high-ranking females, with a later age at sexual maturity and first reproduction and/or longer interbirth intervals. One explanation that has traditionally been advanced to explain this is high levels of chronic social stress in subordinates, resulting from agonistic and aggressive interactions and leading to higher basal levels of glucocorticoids. We assessed the relationships among fecal cortisol levels and reproductive condition, dominance rank, degree of social support, and fertility in female mandrills (Mandrillus sphinx) living in a semi-free-ranging colony in Franceville, Gabon. Lower-ranking females in this colony have a reproductive disadvantage relative to higher-ranking females, and we were interested in determining whether this relationship between dominance rank and reproductive success is mediated through stress hormones. We analyzed 340 fecal samples from 19 females, collected over a 14-month period. We found that pregnant females experienced higher fecal cortisol levels than cycling or lactating females. This is similar to results for other primate species and is likely owing to increased metabolic demands and interactions between the hypothalamus-pituitary-adrenal axis, estrogen, and placental production of corticotrophin releasing hormones during pregnancy. There was no influence of dominance rank on fecal cortisol levels, suggesting that subordinate females do not suffer chronic stress. This may be because female mandrills have a stable social hierarchy, with low levels of aggression and high social support. However, we found no relationship between matriline size, as a measure of social support, and fecal cortisol levels. Subordinates may be able to avoid aggression from dominants in the large enclosure or may react only transiently to specific aggressive events, rather than continuously expecting them. Finally, we found no relationship between fecal cortisol levels and fertility. There was no difference in fecal cortisol levels between conceptive and nonconceptive cycles, and no significant relationship between fecal cortisol level and either the length of postpartum amenorrhea or the number of cycles before conception. This suggests that the influence of dominance rank on female reproductive success in this population is not mediated through chronic stress in subordinate females, and that alternative explanations of the relationship between social rank and reproduction should be sought.     

Low-ranking individuals present high and unstable fecal cortisol levels in provisioned free-ranging adult male rhesus macaques (<Emphasis Type="Italic">Macaca mulatta</Emphasis>) during the birth season in a mountain area of northern China

Social hierarchy commonly exists in animal societies, affecting both the endocrine functioning and the behavior of animals. In nonhuman primates, the relationship between social rank and cortisol levels varies across species and even within species. Here, we assessed the relationships between social rank and fecal cortisol levels in adult male Taihangshan macaques (rhesus macaques, Macaca mulatta tcheliensis) from the provisioned, free-ranging Wulongkou-2 (WLK-2) group inhabiting Wulongkou Scenic Area, Jiyuan, China. From March to May 2014, we recorded 195 agonistic behaviors and collected 54 fresh fecal samples from eight adult male Taihangshan macaques. Males were assigned a social rank according to an agonistic behavior matrix, and enzyme-linked immunosorbent assay was then used to measure the cortisol concentration in the fecal samples. We found that social rank among the eight male Taihangshan macaques in WLK-2 group followed a strict linear hierarchy, and that fecal cortisol levels were significantly higher and more variable in low-ranking males than in more dominant individuals. Age was not significantly associated with social rank or fecal cortisol levels. Our results suggest that social rank and maintenance of the social hierarchy within the WLK-2 group is a chronic stressor, with low-ranking males maintaining heightened stress levels and enlarged reactive scope relative to dominant males. This provides new support for the theory that social environment can influence endocrine functioning.     

Behavioral and hormonal response of common marmosets, <Emphasis Type="Italic">Callithrix jacchus</Emphasis>, to two environmental conditions

Captive animals of several species change their behavioral pattern and hormonal profile in response to physical (for example, cage size and temperature) and social (for example, group size and social isolation) modification of their environment. To evaluate the effect of environmental change in captivity, the affiliative (contact/proximity and allogrooming) and individual (approach, leaving, scent mark, locomotion, and autogrooming) behavior of five family groups of common marmosets, Callithrix jacchus, were recorded on weekdays (non-quiet) and at the weekend (quiet) for two months. In addition, fecal samples were collected for four of these groups to measure their cortisol levels under both conditions. The behavioral pattern and hormonal profile of breeding pairs and their offspring were modified by different management routines used in the experimental conditions. We found that the animals spent more time in affiliative interactions at the weekend, whereas on weekdays, they showed more individual behaviors. Moreover, cortisol levels of breeding pairs and their offspring were higher on weekdays, suggesting that common marmosets living in captivity react to environmental modification by changing their behavioral and hormonal pattern.     

Seasonal effects on plasma cortisol concentrations in the Bedouin buck: circadian studies and response to ACTH

Our work aims at the exploration of cortisol secretion in the Bedouin goat, native to the Algerian Sahara desert, to understand the mechanisms of adaptation to extreme hot climates. In the present study, diurnal and seasonal variations of cortisol concentrations were measured in basal conditions, as well as the response to ACTH stimulation tests across seasons in bucks. The plasma concentrations of cortisol showed no diurnal cycle but a large variation across seasons. The highest levels occurred in summer and winter when the environmental conditions are at their extreme levels. The rectal temperature showed nychthemeral and seasonal variations, and BW was also different across seasons with highest values in summer and lowest in winter. The results obtained after administration of two doses (2 or 10 μg/kg BW) of synthetic ACTH to three different age groups (kids, adults and elderly animals) showed a strong increase in plasma cortisol concentrations under all conditions with maximum levels achieved between 15 and 120 min. The analysis of the area under the cortisol curve showed no significant difference between the responses to the two doses of ACTH and between age groups, but showed seasonal variations with the lowest response in autumn than in other seasons. We conclude that season significantly affects secretion of cortisol in both basal state and under ACTH stimulation. However, the variation of adrenal reactivity to ACTH is not sufficient to explain seasonal differences, and in particular the summer peak in basal circulating cortisol concentrations. Further research should focus on the respective contribution of environmental factors (such as day length, temperature, humidity) and the mechanisms involved in cortisol regulation.     

Terrestrial predator alarm vocalizations are a valid monitor of stress in captive brown capuchins (Cebus apella)

The vocal behavior of captive animals is increasingly exploited as an index of well‐being. Here we show that the terrestrial predator alarm (TPA) vocalization, a robust and acoustically distinctive anti‐predation vocal response present in many mammal and bird species, offers useful information on the relative well‐being and stress levels of captive animals. In a 16‐week experiment evaluating the effects of varying levels of physical environmental enrichment (control < toys < foraging box < foraging box and toys) in the cages of eight singly housed adult male brown capuchins, we quantified the 1) emission rate of TPAs, 2) proportions of normal and abnormal behavior sample intervals, and 3) fecal and plasma cortisol levels. Variation in TPA emission across the experimental conditions was significant. We found significant reductions in the mean TPA production rate by the group in the enriched (toys, foraging box, and foraging box and toys) compared to the control condition; pre‐ and post‐experimental conditions, however, did not differ from the control condition. Mean TPA production by the group was also significantly positively correlated to mean group levels of fecal cortisol and proportion of abnormal behavior sample intervals, and significantly negatively correlated to the average proportion of normal behavior sample intervals in the group. Based on group means, plasma cortisol levels were positively, but not significantly, related to increasing TPA rate. At the level of the responses of an individual subject, however, the covariation between the vocal and non‐vocal behavioral measures and the cortisol assays seldom attained significance. Nevertheless, the direction of the relationships among these parameters within individual subjects typically mirrored those correlations based on group means. At both the group mean and individual levels, our results are consistent with the interpretation that in conditions of low environmental enrichment the study subjects were more stressed, and therefore more reactive to the presence of a threatening terrestrial stimulus (human observer), than when in more enriched conditions. We suggest that protocols to evaluate the effectiveness of enrichment for captive species other than brown capuchins could also profitably exploit TPAs as a first‐line monitor or as corroboratory evidence of current well‐being. Zoo Biol 18:295–312, 1999. © 1999 Wiley‐Liss, Inc.     

The effects of observer presence on the behavior of Cebus capucinus in Costa Rica

We report on the responses of Cebus capucinus in the Santa Rosa Sector of the Area de Conservación Guanacaste, Costa Rica, to the presence of observers over a 4-week period. Study groups were habituated to different degrees: (1) Cerco de Piedra (CP): continuous observations began in 1984; (2) Exclosure (EX): focus of an 18-month study on males from 1998 to 1999; and (3) NBH: never studied/followed but the group frequently encounters researchers. We collected three types of data: group scans (group state was coded as calm or agitated at observer presence), focal animal data (observer-directed behaviors were recorded), and fecal cortisol levels. The two less-habituated groups (NBH and EX) differed significantly from the habituated group (CP) in their behavioral and cortisol responses, and they showed an increase in habituation over the study period (agitation and cortisol levels both dropped). Individuals in NBH also decreased their responses to observers during focal follows; however, at the end of the study the responses of the two less-habituated groups (NBH and EX) remained elevated in comparison to the habituated group (CP), suggesting the need for further habituation. Unlike capuchin groups that rarely encounter humans, NBH and EX never fled from observers and they rarely emitted observer-directed alarm calls. We suggest that the permanence of habituation and the ability to habituate animals passively through a neutral human presence are both important considerations for researchers conducting studies in areas where animal safety from poachers, etc. cannot be guaranteed.     

马尾松毛虫对马尾松和湿地松的选择与适应研究

用马尾松老叶、新叶,湿地松老叶、新叶,当年生马尾松新叶、湿地松新叶和当年生以20％和40％β-蒎烯处理过的马尾松新叶作食料饲养马尾松毛虫。结果表明：马尾松毛虫幼虫在第1代发生期取食马尾松老叶、马尾松新叶、湿地松老叶和湿地松新叶等4种不同质量的食料后,因其食料中10种必需氨基酸含量和挥发性物质β-蒎烯含量的不同,导致幼虫的存活率差异显著。其中,取食马尾松老叶的幼虫成活率最高（44％）,依次为马尾松新叶（32.7％）、湿地松老叶（4％）,而取食湿地松新叶的幼虫全部死亡。通过马尾松针叶增加外援β-蒎烯喂养马尾松毛虫实验,表明增加了外源β-蒎烯的松针饲养的马尾松毛虫幼虫与用同样松针未增加外源β-蒎烯饲养的幼虫相比,死亡率明显提高;松树中β-蒎烯含量的增加与幼虫成活率呈显著负相关。由此,我们阐明了马尾松与湿地松对马尾松毛虫的抗虫机制。     

Travel Time Predicts Fecal Glucocorticoid Levels in Free-Ranging Howlers (Alouatta palliata)

Environmental stressors impact physiology in many animal species. Accordingly, the monitoring of fecal glucocorticoid metabolites (fGCM) has been increasingly used to evaluate the physiological costs of habitat disturbance on wild animal populations, providing a powerful tool for conservation and management. Several studies have suggested that primates in forest fragments have higher fGCM levels than those in continuous forests, yet the proximate causes of fGCM variation remain to be identified. In previous studies of Mexican howlers (Alouatta palliata mexicana) in Los Tuxtlas, Mexico, we found that individuals living in a smaller and more disturbed forest fragment consumed significantly less fruit and had a significantly higher feeding effort than those living in a bigger, more conserved forest fragment. Here, we aimed to examine the effects of fruit consumption and travel time on fGCM levels in the same two groups of howlers, during three sampling sessions that differed markedly in fruit availability. We found that fGCM levels (N?=?202 fecal samples) were higher in the howler group living in the smaller forest fragment and varied seasonally in both focal groups, being lowest when fruit consumption was highest. However, our results suggest that travel time is the main factor predicting fGCM levels in howlers, and that although fruit consumption may be negatively related to fGCM levels, this relationship is probably mediated by the strong effect that fruit consumption has on travel time. Our results provide important insight into the proximate causes of fGCM variation in primates in fragments and highlight the potential conservation significance of studies showing that habitat loss and transformation can lead to increases in travel time in wild primates.     

Fecal cortisol levels in free-ranging female chacma baboons: relationship to dominance, reproductive state and environmental factors

Savannah baboons are one of the few mammalian species that do not exhibit seasonal reproduction patterns and are therefore ideally suited to study the effect of female reproductive states (cycling, pregnant, lactating) on cortisol levels independent of seasonal factors. Fecal samples from 10 free-ranging female chacma baboons (Papio hamadryas ursinus), collected during a period of 17 months, were analyzed using a steroid-extraction method. Reproductive state had a significant effect on fecal cortisol, with lowest levels found in estrous females. Fertility was not related to fecal cortisol levels; we found no significant differences between samples collected on conceptive and nonconceptive cycles. Environmental factors explained most of the variance of fecal cortisol levels. Cortisol measures were strongly correlated with seasonal differences such as daylight duration, temperature and the amount of time that baboons spent resting. We measured higher cortisol levels during winter months and suggest that this could be related to shorter resting periods and to the cold minimum ambient temperatures at this study site. Finally, we found no relationship between social rank nor the rate of agonistic interactions with basal fecal cortisol levels.     

季节和等级顺位对雄性黄山短尾猴粪样皮质醇水平的影响

在长期的进化选择压力下,灵长类动物大多数群居生活,群体中的动物个体也面临来自群内成员强度不一的社会压力,压力大小的重要生理指标通常用其体内的皮质醇水平的变化来衡量.季节性繁殖的黄山短尾猴(Macaca thibetana),群体内的个体有严格的社会等级,是研究等级顺位与社会压力水平之间关系的理想研究对象.我们采集13只...     

Female Spider Monkeys (<Emphasis Type="Italic">Ateles geoffroyi</Emphasis>) Cope with Anthropogenic Disturbance Through Fission–Fusion Dynamics

Most primates live in habitats with some level of anthropogenic disturbance, and such disturbances have a larger impact on frugivorous primates that are more sensitive to ecological disruptions than folivores. Fecal glucocorticoid metabolites provide insight into how the external environment affects internal physiological state, and thus provide information on how anthropogenic pressures become embodied. Here, I examine how subgroup size and glucocorticoids vary with high and low fruit abundance, and how fruit abundance, subgroup size, and activity budget affect fecal glucocorticoid metabolites in female spider monkeys (Ateles geoffroyi) living in an anthropogenically disturbed habitat. I measured these variables via behavioral, ecological, and fecal sampling for 15 months in 17 female spider monkeys at El Zota Biological Field Station. Subgroup size was significantly larger during periods of high fruit abundance, but glucocorticoids did not differ between periods of low and high fruit abundance. Monthly fruit abundance predicted subgroup sizes significantly, but did not predict fecal glucocorticoid concentrations. Increased resting time and reproductive state predicted fecal glucocorticoid concentrations significantly, but travel and foraging time had no significant effect on glucocorticoid concentrations. Individual resting time over the study period correlated negatively with glucocorticoid concentrations. These results suggest that spider monkeys cope with variation in fruit abundance by adjusting subgroup size, and that these adjustments may mitigate environmental stress in this mildly seasonal environment. The large, relatively productive forest size at this site, and the availability of anthropogenic food sources, enable this population of spider monkeys to cope with human-induced habitat disturbance.     

Seasonal glucose uptake in marmots (Marmota flaviventris): the role of pancreatic hormones.

1. Glucose uptake was measured throughout the year in marmots (Marmota flaviventris) by the hyperglycemic clamp technique. During each 2 hr experiment, the plasma glucose level was maintained at 215 mg/dl while blood samples were collected and analysed for glucose, insulin, glucagon, cortisol and catecholamines. 2. Glucose uptake was calculated from the glucose infusion rate, changes in the glucose pool (using a correction factor), and urinary glucose excretion. 3. In autumn, animals peaked in body weight (greater than 4.0 kg) and ceased to feed. Basal plasma insulin levels in autumn were significantly elevated over all other seasons (P less than 0.01) and glucose uptake in autumn was 9.7 +/- 2.4 mg/min which was significantly lower (P less than 0.05) than summer (21.7 +/- 2.4 mg/min) during the steady state phase of the glucose clamp (90-120 min). 4. Plasma glucagon levels declined during the clamp in all seasons but there was no significant difference between seasons. Plasma cortisol and catecholamine (norepinephrine and epinephrine) levels remained unchanged under basal and experimental conditions throughout the seasons. 5. During glucose infusion, beta-hydroxybutyrate levels were suppressed suggesting that lipolysis was reduced during the experiment. 6. These results suggest that the marmot exhibits seasonal changes in glucose uptake; the lowest rate of glucose uptake occurring in the autumn after the animals peak in body weight and cease to feed.     

METABOLIC RESPONSES ON THE EARLY SHIFT

Shiftwork has been associated with a higher propensity for the development of metabolic disorders and obesity. The aim of the study was to investigate concentrations of glucose, cortisol, and insulin among fixed night workers (n?=?9), fixed early morning workers (n?=?6), and day workers (n?=?7). Food intake was recorded for 7 days using a diary. Blood samples were collected every 4?h over the course of 24?h, yielding six samples. Total carbohydrate intake was lowest (p?<?.0005), whereas fat (p?=?.03) and protein (p?<?.0005) were highest on the early morning shifts. Early morning workers also had overall elevated cortisol levels relative to the other two groups. Cortisol levels appeared to be more influenced by time since waking prior to the shift than by time-of-day. Cortisol was highest for the early morning group than the day group 12?h after waking, and both the early morning and night groups had higher levels than the day group 16?h after waking (p?<?.05 in all cases). In contrast, the homesostatsis model assessment of insulin resistance (HOMA-IR) appeared to be more influenced by time-of-day than by time since waking prior to the shift. The early morning group had higher levels of HOMA-IR at 08:00?h than the other groups (p?<?.05). In conclusion, the early morning group had the highest overall concentrations of cortisol and tended to have higher levels of HOMA-IR, indicating that more attention should be given to these workers. Moreover, all three groups showed pronounced cortisol levels on awakening, suggesting that they may have adjusted to their awaking time. (Author: heloguarita@rgnutri.com.br)