Energetic consequences of seasonal breeding in female Japanese macaques (Macaca fuscata)

Body fat and circulating leptin levels in the captive short-beaked echidna (Tachyglossus aculeatus)

It is possible that the reproductive strategy of the short-beaked echidna is related to seasonal changes in fat deposition and energy availability, regulated by seasonal changes in endocrine function. We predicted that circulating leptin levels would be directly proportional to adiposity during most of the year, but that a change in this relationship would occur during the pre-breeding season to allow increased fat deposition. To test this hypothesis, we made use of a captive colony of echidnas to describe and quantify changes in fat distribution and the adipostatic hormone leptin. First we assessed seasonal changes in circulating leptin levels, body mass and adiposity for three male and three female adult echidnas maintained on a standard diet. Second, we explored the relationship between circulating leptin levels and increased caloric intake for an additional five adult female echidnas that were provided with supplemented nutrition. Third we visualised fat distribution in male and female adult echidnas using magnetic resonance imaging (MRI) before and after the breeding season, to determine where fat is deposited in this species. For echidnas maintained on the standard diet, there were no seasonal changes in body mass, body fat or plasma leptin levels. However, female echidnas provided with supplemented nutrition had significantly elevated plasma leptin levels during the breeding season, compared to the pre-and post- breeding periods. MRI showed substantial subcutaneous fat depots extending dorso-laterally from the base of the skull to the base of the tail, in both sexes. Pre-breeding season, both sexes had considerable fat deposition in the pelvic/rump region, whilst the female echidna accumulated most fat in the abdominal region. This study shows that male and female echidnas accumulate body fat in the pelvic/rump and the abdominal regions, respectively and that circulating leptin may promote fattening in female echidnas during the breeding season by means of leptin resistance. However, further research is required to evaluate the precise relationship between seasonal changes in leptin and adiposity.

Decline in the Conception Rate of Wild Japanese Monkeys after the Fukushima Daiichi Nuclear Power Plant Accident

We examined the conception rate of wild Japanese monkeys (Macaca fuscata) in Fukushima City that were exposed to radiation as a result of the Fukushima Daiichi Nuclear Power Plant accident in March 2011. The conception rate in the year of delivery from 2009 to 2022 was estimated by dissecting individuals that were euthanized by the government for population control as a countermeasure against crop damage. To evaluate the effects of exposure, the cumulative exposure dose for each individual was calculated using the concentration of radiocesium deposited in the soil at the capture site and the concentration of radiocesium in muscle estimated from the aggregated transfer factor. There were no significant differences in conception rates across all age classes over time. In terms of conception rates by age class, there was a significant decrease post-exposure compared with pre-exposure in the age class ≥ 8 years, but no significant differences in the age class 5-7 years. The non-ovulation rate did not significantly differ between the pre- and post-exposure periods for any age class. Body fat index, which can affect fertility, was compared between the pre- and post-exposure periods, and no significant differences were found in either age class. In contrast, the median total cumulative exposure (cumulative internal exposure + cumulative external exposure) was significantly higher in the age class ≥ 8 years compared with the age class 5-7 years. These results suggest that the total cumulative exposure dose may be one of the reasons for the lower conception rate in the post-exposure period among the age class ≥ 8 years.

Seasonal variation in energy balance of wild Japanese macaques (Macaca fucata yakui) in a warm-temperate forest: a preliminary assessment in the coastal forest of Yakushima

Food scarcity is a major challenge for primates living in temperate forests, where food availability varies markedly among seasons. In Japanese macaques, which are exclusively distributed in temperate zones, the fat accumulation ability has been highlighted as an adaptation for survival during the lean season and for reproductive success. However, the knowledge of energetic strategies of Japanese macaques has been mainly derived from data on cool-temperate forests, where fallback foods comprise winter buds and bark. Data on Japanese macaques in warm-temperate forests where fallback foods comprise mature leaves are still lacking. We aimed to identify seasonal variations in energy balance and the relative importance of ingestion rates (dry matter intake per feeding time), energy content of the food, and feeding time in energy intake of Japanese macaques in the coastal forest of Yakushima. We estimated energy balance of 6-12 adult females from October 2012 to October 2013. We estimated energy intake based on the data on feeding behavior and energy content of the diet and calculated energy expenditure based on the previously established relationship between body mass and total energy expenditure. We also quantified urinary C-peptide, which is a non-invasive biomarker of energetic conditions. We demonstrated that energy balance was more positive in the fruit/seed-feeding period than in the mature-leaf-feeding and fruit/fungi-feeding periods and that ingestion rates were the most important component of energy intake. The present study suggests that the fat accumulation ability is an essential adaptation in Japanese macaques even in warm-temperate forests.

On the sunny side of (new) life: Effect of sunshine duration on age at first reproduction in Japanese macaques (Macaca fuscata)

To produce offspring early in life is energetically demanding and depends greatly on environmental conditions. In female primates, age at first reproduction (AFR) has been associated with social parameters (e.g., population density and social rank), food availability and meteorological conditions (e.g., photoperiod, rainfall patterns, and temperature). Regarding the latter, less attention has been given to the influence of sunshine. In nonhuman primates, including the northern‐most distributed Japanese macaque (Macaca fuscata), sunbathing is an effective thermoregulatory strategy to maintain sufficient energy intake during harsh winter months. Furthermore, the energetic value of sunshine and its role in the synthesis of essential vitamins important for sexual development and overall fertility is well investigated using human and animal models. In the present study, we hypothesized that female's AFR is influenced by the amount of sunshine in a semi‐free‐ranging, provisioned a group of Japanese macaques. To test this, we gathered data on sunshine duration in the year females theoretically experienced the onset of puberty. This phase of the female life cycle is particularly prone to the effects of environmental conditions. In addition to the investigation of sunshine duration and other meteorological conditions (i.e., rainfall and temperature) we controlled for social parameters (i.e., group size and sex ratio) as potential covariates. We found a clear effect of sunshine duration on female AFR: Females who entered puberty in years with more sunshine reproduced for the first time at significantly younger ages than females who experienced less sunshine during this specific period of their development. Possible mechanisms for how the sunshine influences sexual maturation in Japanese macaques are discussed.

We investigated the influence of sunshine during the year of puberty onset on a female's age at first reproduction (AFR).

We used 20 years of birth data from a semi‐free‐ranging group of Japanese macaques and meteorological data provided online by local weather stations

We controlled for the influence of other meteorological conditions as well as for group size and socionomic sex ratio

Higher mean sunshine duration in the year of puberty onset significantly decreased females’ AFR.

Primate energy input and the evolutionary transition to energy-dense diets in humans

Humans and other large-brained hominins have been proposed to increase energy turnover during their evolutionary history. Such increased energy turnover is plausible, given the evolution of energy-rich diets, but requires empirical confirmation. Framing human energetics in a phylogenetic context, our meta-analysis of 17 wild non-human primate species shows that daily metabolizable energy input follows an allometric relationship with body mass where the allometric exponent for mass is 0.75 ± 0.04, close to that reported for daily energy expenditure measured with doubly labelled water in primates. Human populations at subsistence level (n = 6) largely fall within the variation of primate species in the scaling of energy intake and therefore do not consume significantly more energy than predicted for a non-human primate of equivalent mass. By contrast, humans ingest a conspicuously lower mass of food (-64 ± 6%) compared with primates and maintain their energy intake relatively more constantly across the year. We conclude that our hominin hunter-gatherer ancestors did not increase their energy turnover beyond the allometric relationship characterizing all primate species. The reduction in digestive costs due to consumption of a lower mass of high-quality food, as well as stabilization of energy supply, may have been important evolutionary steps enabling encephalization in the absence of significantly raised energy intakes.

An examination of factors potentially influencing birth distributions in golden snub-nosed monkeys (Rhinopithecus roxellana)

Many species of primates are considered seasonal breeders, but the set of factors, such as food availability, day length and temperature, that influence the timing of reproductive events for both wild and captive individuals remains unclear. Here, we examine the role of factors in shaping breeding patterns in Rhinopithecus roxellana, a temperate colobine primate. We used circular statistics to describe and compare the patterns of reproductive seasonality among individuals in 13 captive groups and two free ranging but provisioned groups at various locations throughout China. Almost 90% of births occurred in March, April and May in adult females residing in both free ranging (n = 131) and captive groups (n = 407). Births occurred principally in 2-4 months prior to the peak of food availability, while conceptions occurred in 1-2 months after the peak of food availability in free ranging but provisioned groups. Day length (latitude) had a significant effect on the timing of reproduction. However, females that experienced a wide variation of temperature between the lowest and highest monthly average temperature had a later conception date. These results support that day length and temperature might be factor influencing the timing of reproductive activity.

Multimodal Advertisement of Pregnancy in Free-Ranging Female Japanese Macaques (Macaca fuscata)

The role of multiple sexual signals in indicating the timing of female ovulation, and discrimination of this timing by males, has been particularly well studied among primates. However the exhibition of pregnancy signals, and how such signals might modulate male post-conception mating decisions, is still poorly understood. Here we aimed to determine if Japanese macaque males use changes in female sexual signals (behavioral, visual and auditory) to discriminate pregnancy and adjust their socio-sexual behaviors. We combined behavioral observations, digital photography and endocrinological (progestogen and estrogen) data, collected systematically during three one-month periods: the pre-conceptive period, the 1st month of pregnancy and the 2nd month of pregnancy. We analyzed variation in the probability of detecting male and female socio-sexual behaviors and estrus calls, as well as changes in female face color parameters, in relation to female reproductive state. Based on our focal observations, we found that males did not copulate during the pregnancy period, and that female socio-sexual behaviors generally decreased from the pre-conceptive to post-conceptive periods. Female face luminance decreased from the pre-conceptive month to the pregnancy period whereas face color only varied between the 1st and 2nd month of gestation. Our results suggest that Japanese macaque females display sexual cues of pregnancy that males might use to reduce energy wasted on non-reproductive copulations with pregnant females. We hypothesize that females advertize their pregnancy through changes in behavioral, visual and potential auditory signals that males can use to adjust their mating behaviors. We finish by discussing implications for male and female post-conception strategies.

Overwintering strategy of Yunnan snub-nosed monkeys: adjustments in activity scheduling and foraging patterns

Temperate forests are characterized by pronounced climatic and phenological seasonality. Primates inhabiting such environments experience prolonged resource scarcity and low ambient temperatures in winter and are expected to adjust time allocation and foraging behavior so as to maintain their energy balance. We analyzed the activity scheduling of a group of Yunnan snub-nosed monkeys (Rhinopithecus bieti) based on data collected over 20 months in the high-altitude (>3000 m) Samage Forest, Baimaxueshan Nature Reserve, PRC. The forest consists of evergreen conifers and oaks and deciduous broadleaf trees. The diet varied seasonally, with young leaves preferentially exploited in spring and fruits in summer. The monkeys subsisted on readily available fallback resources (mainly lichens) in winter [Grueter et al. in (Am J Phys Anthropol 140:700-715, 2009)]. We predicted that this switch to a relatively low-quality diet would prompt an increase in feeding effort and decrease in moving effort. We found that the monkeys spent significantly more time feeding in winter than in the other seasons. The monthly time devoted to feeding was also negatively correlated with temperature and positively with percentage of lichens in the diet. Time spent on moving did not vary among seasons or with temperature, but day-journey length was found to be longer on hotter days. Time spent resting was lower in winter and under colder conditions and was also negatively correlated with time spent feeding, indicating that resting time is converted into feeding time during times of ecological stress. These results indicate a strong effect of seasonality on time allocation patterns, constraints on inactivity phases, and the prevalence of an energy-conserving foraging strategy in winter, when costs of thermoregulation were high and the availability of preferred food was low.