Heating nest-boxes reveals an energetic contraint on incubation behaviour in great tits,Parus major

According to the ''energetic-bottleneck'' hypothesis, incubation in birds is constrained by the availability of energy. Hence, uniparental incubators are predicted to respond to a change in energy supply by adjusting, positively or negatively, the time spent warming the clutch. Energetic constraints on incubation in the great tit (Parus major) were demonstrated by heating nests, so that the night-time thermostatic component of daily energy expenditure in females was reduced by comparison with a control group. Birds in heated nests increased the time allocated to incubation during the day by 55 minutes, consistent with the predictions of the energetic-bottleneck hypothesis. Daily energy expenditure of all birds was inversely related to night-time ambient temperature, and did not differ between warmed and control birds on mild nights. When temperatures were low, however, escalation of daily costs was less for birds in heated nests. It is suggested that the balance of the energy budget may effect a proximate control on the constancy of incubation, with likely implications for reproductive success.     

Diet and reproductive function in wild female chimpanzees (Pan troglodytes schweinfurthii) at Kibale National Park, Uganda

Human female reproductive function is highly sensitive to current energetic condition, indicating adaptation to modulate reproductive effort in accordance with changing ecological conditions that might favor or disfavor the production of offspring. Here, we test the hypothesis that reproductive capacity in female chimpanzees is likewise limited by current energetic condition. We used 12 years of data on wild chimpanzees (Pan troglodytes schweinfurthii) in the Kanyawara community of Kibale National Park, Uganda, to examine the relationship of dietary quality, as assessed by fruit components of the diet, to the occurrence of sexually receptive females, concentrations of ovarian steroid hormones, and timing of conception. We found that the frequency of females having sexual swellings was positively related to the consumption of drupe fruits. Estrogen levels of both cycling and noncycling females increased during seasonal peaks in the consumption of drupe fruits. When average fruit consumption remained high across months, females conceived more quickly. These results support the hypothesis that cycling and conception in chimpanzees are contingent upon high energy balance, and they indicate that the availability of fruit is a key variable limiting reproductive performance in chimpanzees. Chimpanzees appear to share with humans a reproductive system that is primed to respond to proximate levels of energy acquisition.     

Human Ovarian Function and Reproductive Ecology: New Hypotheses

A series of eight hypotheses is presented, based on the results of current research, concerning the responsiveness of the human ovary to constitutional and environmental variables. These hypotheses are motivated by a theoretical position that seeks to understand human reproductive physiology as the product of natural selection. The hypotheses are: (1) Ovarian responsiveness occurs along a graded continuum. (2) The graded continuum of response forms a final common pathway for various "stresses." (3) Ovarian function tracks energy balance, not simply nutritional status. (4) Ovarian function tracks aerobic activity independently of energy balance. (5) Additive interactions characterize the interaction of constitutional and environmental factors modulating ovarian function. (6) Reproductive maturation is synchronized with skeletal maturation, especially of the pelvis. (7) Peak ovarian function is not ordinarily achieved until the early twenties. (8) Late reproductive maturation is associated with a slower rise in indices of ovarian function with age, and a lower level of ovarian function in adulthood. Together, these hypotheses provide for two, non-exclusive theories of facultative modulation of female reproductive effort. One theory views ovarian function as responsive to the prospects for positive reproductive outcome as these may be affected by maternal age, maturation, energy balance, and activity level. The second theory views ovarian function as responsive in a similar way to the need to maintain long-term maternal energy balance.     

Energy metabolism and the evolution of reproductive suppression in the human female

Reproduction places severe demands on the energy metabolism in human females. When physical work entails higher energy expenditure, not enough energy will be left for the support of the reproductive processes and temporal suppression of the reproductive function is expected. While energy needed for reproduction may be obtained by increases in energy intake, utilization of fat reserves, or reallocation of energy from basal metabolism, several environmental or physiological constraints render such solutions unlikely. For human ancestors increases in energy intake were limited by availability of food, by labor of food preparation and by metabolic ceilings to energy assimilation. Energy stored as fat may support only a fraction of the requirements for reproduction (especially lactation). Effects of intense physical activity on basal metabolism may also interfere with fat accumulation during pregnancy. Finally, the female physiology may experience demands on increasing the basal metabolism as a consequence of physical activity and, at the same time, on decreasing the basal metabolism, when energy to support the ongoing pregnancy or lactation is inadequate. The resulting metabolic dilemmas could constitute a plausible cause for the occurrence of reproductive suppression in response to physical activity. It is, therefore, likely that allocating enough energy to the reproductive processes during periods when energy expenditure rises may be difficult due to physiological and bioenergetic constraints. Females attempting pregnancy in such conditions may compromise their lifetime reproductive output. A reproductive suppression occurring in low energy availability situations may thus represent an adaptive rather then a pathological response.     

Development of an early biomarker for the ovarian liability of selective estrogen receptor modulators in rats

Selective estrogen receptor modulators (SERMs) have the potential to treat estrogen sensitive diseases such as uterine leiomyoma and endometriosis, which are prevalent in reproductive age women. However, SERMs also increase the risk of developing ovarian cysts in this population, a phenomenon that is not seen in postmenopausal women. It is believed that current SERMs partially block estradiol's ability to downregulate gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus thereby interfering with estradiol's negative feedback, leading to increased ovarian stimulation by gonadotropins, and cyst formation. It has been postulated that a SERM with poor brain exposure would have less negative effect on the HPO axis, therefore reducing the risk of developing ovarian cysts. In order to test this hypothesis, we identified an early marker of SERM-dependent ovarian effects: upregulation of Cyp17a1 mRNA. SERMs known to cause ovarian cysts upregulate Cyp17a1 after only 4 days of dosing and suppression of the HPO axis prevented this regulation, indicating that ovarian expression of Cyp17a1 was secondary to SERM's effect on the brain. We then characterized three SERMs with similar binding affinity and antagonist effects on the uterus for their relative brain/plasma exposure and ovarian effects. We found that the degree of brain exposure correlated very well with Cyp17a1 expression.     

Adaptive variation in testosterone levels in response to immune activation: empirical and theoretical perspectives

High testosterone levels reflect investment in male reproductive effort through the ability to produce and maintain muscle tissue and thus augment mate attraction and competitive ability. However, high testosterone levels can also compromise survivorship by increasing risk of prostate cancer, production of oxygen radicals, risk of injury due to hormonally-augmented behaviors such as aggression, violence and risk taking, reduced tissue and organ maintenance, negative energy balance from adipose tissue catabolism, and suppression of immune functions. Here, I briefly discuss how inter- and intra-individual variation in human male testosterone levels is likely an adaptive mechanism that facilitates the allocation of metabolic resources, particularly in response to injury, illness or otherwise immune activation. Maintaining low testosterone levels in resource-limited and/or high pathogen-risk environments may avoid some immunosuppression and suspend energetically-expensive anabolic functions. Augmenting testosterone levels in the presence of fertile and receptive mates, areas of high food resource availability, and low disease risk habitats will function to maximize lifetime reproductive success.     

Energy expenditure and testosterone in free-living male yellow-pine chipmunks

The onset of mating in yellow-pine chipmunks (Tamias amoenus) follows emergence from a prolonged period of energy conservation during hibernation. Energy expenditures are greatly accelerated to meet the demands of the reproductive season. When emerging from hibernation, typical male chipmunks (breeders) have enlarged testes and a high level of plasma testosterone (T). However, certain males that do not participate in reproduction (nonbreeders) maintain small testes and low plasma T levels and emerge several weeks later than the breeders. The timing of the terminal arousal from hibernation and onset of mating are associated with increased plasma T levels. Experimental elevation of T levels in T. amoenus outside the mating season has been associated with a decrease in body mass, further suggesting an effect of T on energy balance. To test this hypothesis, we measured daily energy expenditure (DEE) in free-living, nonbreeding male chipmunks in the presence and absence of a T-implant. We also measured DEE in breeding males when endogenous T levels were high. DEE of the nonbreeders was not affected by our manipulation of plasma T, and the DEE of breeding males did not differ from that of nonbreeders. We conclude that energy expenditure on a daily basis in male yellow-pine chipmunks is not influenced by levels of T. However, on a seasonal basis, the earlier emergence from hibernation by breeding males, which appears to be influenced by T, represents an overall seasonal energy expenditure that exceeds that of nonbreeding males.     

Biological aging and the etiology of aneuploidy

A prevalent hypothesis concerning the cause of the rise in aneuploid conceptions with maternal age is that the changes that accompany normal ovarian aging increase the rate of meiotic errors in the oocyte. Biological aging of the ovary is accompanied by a decline in both the total oocyte pool and the number of antral follicles maturing per cycle, as well as changes in the levels of circulating reproductive hormones. The biological aging hypothesis predicts that aneuploidy rates should be higher in women with a prematurely reduced oocyte pool, and that women with trisomic conceptions should show signs of earlier ovarian aging than women of the same chronological age without trisomic conceptions. Comprehensive studies of aneuploidy in groups of women with known causes of premature ovarian failure remain to be done, though anecdotal evidence does suggest increased rates of pregnancy loss and aneuploidy. Smoking, which is a well-documented cause of earlier ovarian aging, is not associated with an increase in aneuploid conceptions. Evidence from women with unilateral ovariectomies is inconsistent. Support for the biological aging hypothesis was provided by one study showing that menopause occurred about a year earlier in women with a trisomic spontaneous abortion compared to women with chromosomally normal conceptions. Associations between high FSH and pregnancies with Down syndrome and chromosomally abnormal spontaneous abortions have also been reported. However, the most direct test of the hypothesis, which compared antral follicle counts and hormonal levels in women with trisomic pregnancies and those with chromosomally normal pregnancies, failed to find a difference in the expected direction. A prospective study of FSH levels in women with subfertility also failed to find an association with the rate of pregnancy loss. The bulk of evidence thus suggests that, if the processes of biological aging are indeed related to aneuploidy, they probably involve factors other than those measured by oocyte or antral follicle pool size and reproductive hormone levels.     

Genetic markers of ovarian follicle number and menopause in women of multiple ethnicities

Oocyte loss has a significant impact on fertility and somatic health. Yet, we know little about factors that impact this process. We sought to identify genetic variants associated with ovarian reserve (oocyte number as measured by antral follicle count, AFC). Based on recently published genome-wide scans that identified loci associated with age of menopause, we also sought to test our hypothesis that follicle number and menopausal age share underlying genetic associations. We analyzed menopause-related variants for association with follicle number in an independent population of approximately 450 reproductive-aged women of European and African ancestry; these women were assessed for AFC, anthropometric, clinical, and lifestyle factors. One SNP strongly associated with later menopausal age in Caucasian women (+1.07?±?0.11?years) in previous work was also associated with higher follicle counts in Caucasians (+2.79?±?1.67 follicles) in our study. This variant is within the Minichromosome Maintenance Complex Component 8 (MCM8) gene, which we found was expressed within oocytes in follicles of the human ovary. In genome-wide scans of AFC, we also identified one marginally genome-wide and several nominally significant SNPs within several other genes associated with follicle number in both ethnic groups. Further, there were overlapping variants associated with multiple ovarian reserve markers (AFC, serum hormone levels, menopausal age). This study provides the first evidence for direct genetic associations underlying both follicle number and menopause and identifies novel candidate genes. Genetic variants associated with ovarian reserve may facilitate discovery of genetic markers to predict reproductive health and lifespan in women.     

Serum Leptin Levels in Obese Males During Over‐ and Underfeeding

Leptin levels in lean adults vary in response to short‐term alterations in energy balance. We tested whether leptin responded to short‐term changes in energy balance in obese males in a similar manner to lean individuals. We enrolled eight obese, healthy males in a 12‐day study composed of four consecutive dietary treatment periods of 3 days each: baseline eucaloric feeding followed by randomized crossover periods of overfeeding (130% of total energy expenditure (TEE)) or underfeeding (70% of TEE), separated by a eucaloric (100% of TEE) washout period. We measured TEE with doubly labeled water prior to baseline. Leptin levels were measured throughout the third day of each treatment and 24‐h weighted averaged were calculated. Subjects' ad libitum intake during a breakfast buffet following each treatment period was recorded. During underfeeding, leptin levels decreased by 21 ± 6% (P < 0.01) from the previous eucaloric period. During overfeeding, leptin levels increased by 25 ± 11% (P < 0.01) when subjects were underfed first, but did not increase (5 ± 8%, nonsignificant (n.s.)) when subjects were overfed first. Changes in ad libitum intake from baseline were calculated for each subject after over‐, under‐, and eucaloric feeding and did not to correlate with the changes in mesor leptin levels from baseline (R² = 0.006, n.s). Leptin levels in obese males were acutely responsive to negative energy balance, but not to positive energy balance unless subjects were previously underfed. Consequently, leptin levels in obese males do not respond to changes in energy intake in a manner that would protect against weight gain.     

Labor Saved,Calories Lost: The Energetic Impact of Domestic Labor‐saving Devices

Objective: As the prevalence of obesity has increased, so has sedentariness. Progressive sedentariness has been attributed to greater use of labor saving devices, such as washing machines, and less nonexercise walking (e.g., walking to work). However, there is a paucity of data to support this conclusion. In this study, we address the hypothesis that domestic mechanization of daily tasks has resulted in less energy expenditure compared with performing the same tasks manually. Research Methods and Procedures: Energy expenditure was measured in four groups of subjects (122 healthy adult men and women total) from Rochester, Minnesota. Energy expenditure was measured using indirect calorimetry while subjects performed structured tasks such as cleaning dishes and clothes, stair climbing, and work‐associated transportation, and these values were compared with the respective mechanized activity. Results: Energy expenditure was significantly greater and numerically substantial when daily domestic tasks were performed without the aid of machines or equipment (clothes washing: 45 ± 14 vs. 27 ± 9 kcal/d; dish washing: 80 ± 28 vs. 54 ± 19 kcal/d; transportation to work: 83 ± 17 vs. 25 ± 3 kcal/d; stair climbing: 11 ± 7 vs. 3 ± 1 kcal/d; p < 0.05). The combined impact of domestic mechanization was substantial and equaled 111 kcal/d. Discussion: The magnitude of the energetic impact of the mechanized tasks we studied was sufficiently great to contribute to the positive energy balance associated with weight gain. Efforts focused on reversing sedentariness have the potential to impact obesity.     

Trends over 5 decades in U.S. occupation-related physical activity and their associations with obesity

Background

The true causes of the obesity epidemic are not well understood and there are few longitudinal population-based data published examining this issue. The objective of this analysis was to examine trends in occupational physical activity during the past 5 decades and explore how these trends relate to concurrent changes in body weight in the U.S.

Methodology/Principal Findings

Analysis of energy expenditure for occupations in U.S. private industry since 1960 using data from the U.S. Bureau of Labor Statistics. Mean body weight was derived from the U.S. National Health and Nutrition Examination Surveys (NHANES). In the early 1960''s almost half the jobs in private industry in the U.S. required at least moderate intensity physical activity whereas now less than 20% demand this level of energy expenditure. Since 1960 the estimated mean daily energy expenditure due to work related physical activity has dropped by more than 100 calories in both women and men. Energy balance model predicted weights based on change in occupation-related daily energy expenditure since 1960 for each NHANES examination period closely matched the actual change in weight for 40–50 year old men and women. For example from 1960–62 to 2003–06 we estimated that the occupation-related daily energy expenditure decreased by 142 calories in men. Given a baseline weight of 76.9 kg in 1960–02, we estimated that a 142 calories reduction would result in an increase in mean weight to 89.7 kg, which closely matched the mean NHANES weight of 91.8 kg in 2003–06. The results were similar for women.

Conclusion

Over the last 50 years in the U.S. we estimate that daily occupation-related energy expenditure has decreased by more than 100 calories, and this reduction in energy expenditure accounts for a significant portion of the increase in mean U.S. body weights for women and men.     

Female Reproductive Decline Is Determined by Remaining Ovarian Reserve and Age

The early decline and loss of female fertility in humans and other species represents an evolutionary paradox. Despite being born with a vast stock of oocytes, females encounter an exhaustion of ovarian reserve and sterility half way through their natural lives. Female reproductive ageing has been proposed to proceed as an ongoing decline in ovarian reserve, determined by remaining ovarian follicle number. However, despite extensive modelling, the respective contributions of intra-, inter-, and extra-ovarian signalling have not been fully characterised. It remains unclear whether reproductive ageing progresses simply as a pre-determined function of remaining ovarian follicles, or as an age-dependent process in humans. Here, we have analysed ovarian response to hormonal stimulation in women who have undergone surgical removal of a single ovary, in order to investigate the relative contributions of intra-, inter, and extra-ovarian signalling on reproductive ageing. Our data show that in unilaterally oophorectomised women, ovarian response to follicle stimulating hormone (FSH) declines beyond levels predicted by a total ovarian follicle pool model of reproductive ageing. Maintenance of ovarian function later in reproductive life, despite the removal of half of the total ovarian reserve, suggests a role for an extra-ovarian age-dependent regulation of reproductive decline. This highlights the need for further work to identify signalling factors that communicate age-related signals between the soma and the germline.     

State-dependent behaviour in breeding barn swallows (Hirundo rustica): consequences for reproductive effort

Life-history theory offers an explanation for the intraspecific variation in reproductive effort; increased levels of current reproductive success, for example, may trade off against residual reproductive value. Even where such trade-offs have been demonstrated, however, much variation in effort remains unexplained and the underlying causes are usually obscure. We examined body state, i.e. energy reserves, as a factor, which could moderate reproductive effort. Specifically, overnight heating and cooling treatments were used to adjust dawn energy reserves in female swallows attending their nests without impinging on the opportunities for foraging. Changes in reproductive effort were measured as 'daytime energy expenditure' (doubly labelled water technique) and the 'number of feeding visits' during brood rearing, which both relate positively to current reproductive success. Our experimental treatments and responses were then compared using the common currency of energy. In response to positive and negative state manipulations, female swallows increased and decreased, respectively, their daytime energy expenditure (and number of feeding visits). These responses to experimental manipulation of state provided evidence of a direct link between the energy expenditure, life history and behaviour, which has hitherto proved elusive. They allow that energy supply and expenditure play a regulatory role in reproductive effort, and indicate that units of energy expenditure probably carry fitness costs and benefits, which are context dependent.     

Fat distribution patterns in young amenorrheic females

The present study analyzes body fat distribution, a well-known and important indicator of reproductive capability, in young women between 18 and 28 years of age (mean=23.3 years) suffering from secondary amenorrhea and therefore temporary infertility resulting from self-starvation. Body composition parameters estimated by means of dual energy x-ray absorptiometry and the fat distribution index, indicating body shape, were compared with those of healthy controls. Although members of the infertile, amenorrheic group exhibited dramatically low body weight and total amount of body fat, and therefore a marked negative energy balance in comparison with the healthy controls, the sex-specific fat distribution patterns did not differ between infertile and fertile young women. In contrast, the lower the weight and total fat amount, the more gynoid the fat distribution, even in infertile women. This observation may be interpreted in an evolutionary sense: Our ancestors had to cope with frequent food shortages, even starvation, and therefore lengthy periods of negative energy balance. In addition to pregnancy and lactation, temporary infertility as a result of long-term negative energy balance was not an uncommon phenomenon in female life histories. Nevertheless, after a time of plenty, reproductive function recovered, and therefore the gynoid fat distribution patterns in temporarily infertile young women may be interpreted as signal of reproductive capability, which resumes after a time of surplus.     

Effect of Postpartum Exercise on Mothers and their Offspring: A Review of the Literature

Epidemiological studies suggest that childbearing may contribute to the development of obesity. In the past 12 years, several cross‐sectional and randomized trials have addressed the effect of postpartum exercise on weight loss and/or energy balance in mostly lactating women. These studies suggest that moderate exercise without specific calorie restriction does not promote greater weight or fat loss. This may be because exercise may promote greater energy intake and/or reduced energy expenditure from nonexercise physical activity (thus preventing negative energy balance), but further research is needed. Regular exercise, however, is likely to have other important health benefits after childbirth. A few published studies suggest that postpartum exercise improves aerobic fitness, high‐density lipoprotein‐cholesterol levels, and insulin sensitivity. Exercise may also enhance psychological well‐being, but controlled clinical studies are needed. Although two published studies have addressed whether exercise training attenuates lactation‐induced bone loss, better controlled studies are needed to determine whether postpartum weight‐bearing exercise can improve bone mineral density in lactating and nonlactating women alike. In lactating women, several studies have collectively determined that neither acute nor regular exercise has adverse effects on a mother's ability to successfully breast‐feed. It needs to be determined whether a woman's participation in regular exercise after childbirth will improve her ability to mother or instill lifetime habits of regular physical activity in either herself or her offspring. Overall, published studies have established the importance of regular exercise during the postpartum period. More research, however, is needed in this important area.     

Energetics of the annual reproductive cycle in female sticklebacks, Gasterosteus aculeatus L.

Laboratory studies on the thrce-spined stickleback provided predictive equations for the relationships between food consumption, faecal production and growth, and between respiration rate and body weight. These equations were used to estimate the energy income and expenditure at monthly intervals during the annual reproductive cycle of females of mean length from two populations. In winter only a small percentage of the energy income was invested in ovarian or somatic growth, and the latter was negative in some cases. Routine respiration and faecal losses accounted for a high proportion of the energy income. In spring a higher proportion of the energy income was partitioned into somatic and ovarian growth while routine respiration accounted for a smaller proportion of the energy income.     

That’s hot: golden spiny mice display torpor even at high ambient temperatures

Golden spiny mice (Acomys russatus) living in the Judean desert are exposed to extended periods of food and water shortage. We investigated their thermal and metabolic response to three weeks of 50 % food reduction at ambient temperatures of 23, 27, 32 and 35 °C by long term records of metabolic rate and body temperature in the laboratory. At all ambient temperatures, A. russatus responded to starvation by a reduction of daily energy expenditure. At 32 and 35 °C, this metabolic adjustment fully compensated the reduced food availability and they maintained their energy balance at a slightly reduced body mass. At lower ambient temperatures, they could not fully compensate for the reduced food availability and kept a negative energy balance. The reduction of daily energy expenditure was largely achieved by the occurrence of daily torpor. Torpor even occurred at high ambient temperatures of 32 and 35 °C during which metabolic depression was not associated with a marked decrease of body temperature. The results show that the occurrence of daily torpor is not necessarily linked to cold exposure and the development of a pronounced hypothermia, but may even occur as depression of metabolic rate in a hot environment.     

动物生殖抑制研究进展：理论模型、方式和机制

生殖抑制指原本具有生育能力的动物个体因特定外界环境或生理条件而减少或丧失生殖能力的现象,有时是受环境变化的主动调控,更多的是出现在其他个体影响下的被动抑制,极端情况发生在社会性动物的永久性抑制,即永久无法生殖或无法生殖成熟。研究发现非社会性动物也有生殖的推迟及可恢复性的生殖抑制,生殖抑制影响着动物种群数量动态、维持和进化。随着多学科的发展,生殖抑制机理研究取得了诸多进展。从阐述生殖抑制的概念出发,解析生殖抑制的形态、激素和分子生理特征,总结了生殖抑制的原因、作用,终述现有的理论模型以及不同物种方面的最新进展,并就生殖抑制在生物资源管理方面的应用价值进行了展望,旨在丰富生殖抑制的理论,扩展应用实践,为后续的生物资源管理提供理论参考。