Development of guidelines for assessing obesity in captive chimpanzees (Pan troglodytes)

Age-related physiological dysregulation progresses slowly in semi-free-ranging chimpanzees

Background and objectives

Lifestyle has widespread effects on human health and aging. Prior results from chimpanzees (Pan troglodytes), one of humans' closest evolutionary relatives, indicate that these lifestyle effects may also be shared with other species, as semi-free-ranging chimpanzees fed a naturalistic diet show healthier values in several specific health biomarkers, compared with their sedentary, captive counterparts. Here, we examined how lifestyle factors associated with different environments affect rates of physiological aging in closely related chimpanzees.

Methodology

We compared physiological dysregulation, an index of biological aging, in semi-free-ranging chimpanzees in an African sanctuary versus captive chimpanzees in US laboratories. If the rate of aging is accelerated by high-calorie diet and sedentism, we predicted greater age-related dysregulation in the laboratory populations. Conversely, if costs of a wild lifestyle accelerate aging, then semi-free-ranging chimpanzees at the sanctuary, whose environment better approximates the wild, should show greater age-related dysregulation. We further tested whether dysregulation differed based on sex or body system, as in humans.

Results

We found that semi-free-ranging chimpanzees showed lower overall dysregulation, as well as lower age-related change in dysregulation, than laboratory chimpanzees. Males experienced lower dysregulation than females in both contexts, and the two populations exhibited distinct aging patterns based on body system.

Conclusions and implications

Our results support the conclusion that naturalistic living conditions result in healthier aging in chimpanzees. These data provide support for the proposal that lifestyle effects on human health and aging are conserved from deeper into our evolutionary history.

An overview of nutritional factors in the aetiopathogenesis of myocardial fibrosis in great apes

The main cause of mortality in great apes in zoological settings is cardiovascular disease (CVD), affecting all four taxa: chimpanzee (Pan troglodytes), bonobo (Pan paniscus), gorilla (Gorilla spp.) and orangutan (Pongo spp.). Myocardial fibrosis, the most typical histological characterisation of CVD in great apes, is non-specific, making it challenging to understand the aetiopathogenesis. A multifactorial origin of disease is assumed whereby many potential causative factors are directly or indirectly related to the diet, which in wild-living great apes mainly consists of high-fibre, low-carbohydrate and very low-sodium components. Diets of great apes housed in zoological settings are often different compared with the situation in the wild. Moreover, low circulating vitamin D levels have recently been recognised in great apes housed in more northern regions. Evaluation of current supplementation guidelines shows that, despite implementation of different dietary strategies, animals stay vitamin D insufficient. Therefore, recent hypotheses designate vitamin D deficiency as a potential underlying factor in the pathogenesis of myocardial fibrosis. The aim of this literature review is to: (i) examine important differences in nutritional factors between zoological and wild great ape populations; (ii) explain the potential detrimental effects of the highlighted dietary discrepancies on cardiovascular function in great apes; and (iii) elucidate specific nutrition-related pathophysiological mechanisms that may underlie the development of myocardial fibrosis. This information may contribute to understanding the aetiopathogenesis of myocardial fibrosis in great apes and pave the way for future clinical studies and a more preventive approach to great ape CVD management.

Body mass and growth rates in captive chimpanzees (Pan troglodytes) cared for in African wildlife sanctuaries, zoological institutions, and research facilities

Captive chimpanzees (Pan troglodytes) mature earlier in body mass and have a greater growth rate compared to wild individuals. However, relatively little is known about how growth parameters compare between chimpanzees living in different captive environments. To investigate, body mass was measured in 298 African sanctuary chimpanzees and was acquired from 1030 zoological and 442 research chimpanzees, using data repositories. An analysis of covariance, adjusting for age, was performed to assess same-sex body mass differences between adult sanctuary, zoological, and research populations. Piecewise linear regression was performed to estimate sex-specific growth rates and the age at maturation, which were compared between sexes and across populations using extra-sum-of-squares F tests. Adult body mass was greater in the zoological and resarch populations compared to the sanctuary chimpanzees, in both sexes. Male and female sanctuary chimpanzees were estimated to have a slower rate of growth compared with their zoological and research counterparts. Additionally, male sanctuary chimpanzees were estimated to have an older age at maturation for body mass compared with zoological and research males, whereas the age at maturation was similar across female populations. For both the zoological and research populations, the estimated growth rate was greater in males compared to females. Together, these data contribute to current understanding of growth and maturation in this species and suggest marked differences between the growth patterns of chimpanzees living in different captive environments.

Weight management towards physiological and behavioral wellbeing for chimpanzees living under human care

Across a period of 54 months, several changes were made to the feeding protocols of 32 adult chimpanzees living at the Yerkes National Primate Research Center Field Station. Before implementing any changes in diet, baseline data were collected for 6 months. During Baseline (BS), the chimpanzees received unlimited amounts of primate biscuits twice a day and a limited amount of produce as enrichment. Treatment One (T1) dietary modifications included an increased amount of vegetables, primarily leafy greens, and biscuit feedings scheduled to occur an hour after vegetables were provided to the chimpanzees. T1 lasted for 1 year. At the end of T1, most of the chimpanzees had gained weight. Treatment Two (T2) occurred over the span of 3 years, during which all the chimpanzees were switched from unlimited, group-distributed primate biscuits to individually prescribed amounts of biscuits, fed in\dividually, and increased daily feedings of leafy greens. By the end of T2, 10 of 15 chimpanzees who were overweight or obese at the start of the project were within range of ideal body condition, and 4 of the remaining 5 were improved. All the chimpanzees who started the project within ideal range were still within ideal range. Significantly more time was invested in eating, foraging, and processing food during T2 (p < .05), more appropriately replicating the natural time budget for a chimpanzee. There were not any increases in abnormal, stress-related, or agonistic behaviors as a function of dietary modifications. Inactivity, however, was significantly higher (p < .05) during the later protocol, and locomotion was concurrently lower (p < .05).

From Farm to Fork: Crickets as Alternative Source of Protein, Minerals, and Vitamins

Globally, there is growing interest to integrate cricket-based ingredients (flour) into food products to combat food and nutrition insecurity. However, there is lack of information on in-depth nutrient profile of the two cricket species (Scapsipedus icipe and Gryllus bimaculatus), which are the most widely consumed in Africa. Here we determined the nutrient composition of two cricket species and compared them with published records of key animal and plant sources. Our results revealed that the crude protein contents of S. icipe and G. bimaculatus were similar (56.8 and 56.9%, respectively) and comparable to those of animal protein sources. Both cricket species had balanced amino acid profiles that are superior to that of animal and plant sources, except for histidine and cysteine. The protein digestibility of S. icipe and G. bimaculatus ranged between 80 and 88%, which is comparable to that of common plant foods but slightly lower than that of animal proteins. The iron, Zinc, and potassium contents were considerably higher in both cricket species compared to that of plant and animal sources. The calcium contents of both crickets (S. icipe and G. bimaculatus) was superior to that of plant and animal origin except for kidney beans and eggs, respectively. Riboflavin, thiamine, and folic acid concentrations of S. icipe and G. bimaculatus were superior to that of the conventional sources. Vitamin A levels were significantly higher in S. icipe compared to G. bimaculatus. This implies that S. icipe and G. bimaculatus can adequately contribute to our daily required nutrient intake. Thus, integrating cricket flours into ready-to-eat food products would address some of the most pressing nutritional deficiency challenges that many developing countries have to grapple with, particularly high risk to serious health problems such as anemia, poor pregnancy outcomes, hypertension, increased risk of morbidity and mortality, stunted growth and impaired physical and cognitive development. We conclude that edible crickets present unique opportunities for improving food and nutritional insecurity status of both resource-poor and Western populations.

Effects of Captivity on the Morphology of the Insertion Sites of the Palmar Radiocarpal Ligaments in Hominoid Primates

Simple Summary

In this manuscript, we report the results of our 3D geometric morphometric analyses of the distal radial epiphysis in wild and captive gorillas, chimpanzees, and orangutans. We have identified significant differences in the insertion sites of the palmar radiocarpal ligaments between the wild and captive specimens of each species that are likely related to the locomotor behaviors developed in captivity. We believe that our study deals with a subject of great social impact in today’s world: the well-being of animals living in captivity, especially hominoid primates. Our findings provide novel information on the effect of captivity on the anatomy and locomotor behavior of hominoid primates. We trust that this information can be a basis for improving the artificial spaces where these captive primates live by increasing their available space and providing structures that more closely simulate their natural environment.

Abstract

The environmental conditions of captive hominoid primates can lead to modifications in several aspects of their behavior, including locomotion, which can then alter the morphological characteristics of certain anatomical regions, such as the knee or wrist. We have performed tridimensional geometric morphometrics (3D GM) analyses of the distal radial epiphysis in wild and captive gorillas, chimpanzees, and orangutans. Our objective was to study the morphology of the insertion sites of the palmar radiocarpal ligaments, since the anatomical characteristics of these insertion sites are closely related to the different types of locomotion of these hominoid primates. We have identified significant differences between the wild and captive specimens that are likely related to their different types of locomotion. Our results indicate that the habitat conditions of captive hominoid primates may cause them to modify their locomotor behavior, leading to a greater use of certain movements in captivity than in the wild and resulting in the anatomical changes we have observed. We suggest that creating more natural environments in zoological facilities could reduce the impact of these differences and also increase the well-being of primates raised in captive environments.

Taste detection threshold of human (Homo sapiens) subjects and taste preference threshold of black-handed spider monkeys (Ateles geoffroyi) for the sugar substitute isomalt

The artificial sweetener isomalt is widely used due to its low caloric, non-diabetogenic and non-cariogenic properties. Although the sweetening potency of isomalt has been reported to be lower than that of sucrose, no data on the sensitivity of humans for this polyol are available. Using an up-down, two-alternative forced choice staircase procedure we therefore determined taste detection thresholds for isomalt in human subjects (n = 10; five females and five males) and compared them to taste preference thresholds, determined using a two-bottle preference test of short duration, in a highly frugivorous nonhuman primate, the spider monkey (n = 4; one female, three males). We found that both species detected concentrations of isomalt as low as 20 mM. Both humans and spider monkeys are less sensitive to isomalt than to sucrose, which is consistent with the notion of the former being a low-potency sweetener. The spider monkeys clearly preferred all suprathreshold concentrations tested over water, suggesting that, similar to humans, they perceive isomalt as having a purely sweet taste that is indistinguishable from that of sucrose. As isomalt, like most sweet-tasting polyols, may elicit gastric distress when consumed in large quantities, the present findings may contribute to the choice of appropriate amounts and concentrations of this sweetener when it is employed as a sugar substitute or food additive for human consumption. Similarly, the taste preference threshold values of spider monkeys for isomalt reported here may be useful for determining how much of it should be used when it is employed as a low-caloric sweetener for frugivorous primates kept on a vegetable-based diet, or when medication needs to be administered orally.

Healthy cardiovascular biomarkers across the lifespan in wild-born chimpanzees (Pan troglodytes)

Chimpanzees (Pan troglodytes) are a crucial model for understanding the evolution of human health and longevity. Cardiovascular disease is a major source of mortality during ageing in humans and therefore a key issue for comparative research. Current data indicate that compared to humans, chimpanzees have proatherogenic blood lipid profiles, an important risk factor for cardiovascular disease in humans. However, most work to date on chimpanzee lipids come from laboratory-living populations where lifestyles diverge from a wild context. Here, we examined cardiovascular profiles in chimpanzees living in African sanctuaries, who range semi-free in large forested enclosures, consume a naturalistic diet, and generally experience conditions more similar to a wild chimpanzee lifestyle. We measured blood lipids, body weight and body fat in 75 sanctuary chimpanzees and compared them to publicly available data from laboratory-living chimpanzees from the Primate Aging Database. We found that semi-free-ranging chimpanzees exhibited lower body weight and lower levels of lipids that are risk factors for human cardiovascular disease, and that some of these disparities increased with age. Our findings support the hypothesis that lifestyle can shape health indices in chimpanzees, similar to effects observed across human populations, and contribute to an emerging understanding of human cardiovascular health in an evolutionary context. This article is part of the theme issue 'Evolution of the primate ageing process'.

Validation and utility of a body condition scoring system for chimpanzees (Pan troglodytes)

Obesity is a problem in captive chimpanzee colonies that can lead to increased risk for disease; therefore, implementation of effective weight management strategies is imperative. To properly implement a weight management program, captive managers should be able to noninvasively identify and assess overweight or obese individuals. Traditional means of categorizing obese individuals involve sedating the animals to obtain body weights or skin fold measurements. The current study aimed to validate a noninvasive, subjective body condition score (BCS) system for captive chimpanzees. The system utilizes a 10-point scale, with one rated as "emaciated," five as "normal," and 10 as "extremely obese." Between 2013 and 2014, 158 chimpanzees were weighed and scored using this system (a) while sedated and (b) while awake in their social group within 1-3 days of sedation ("In-group" ratings). We found high inter-rater reliability between In-group raters, as well as between sedated and In-group scores. BCSs, which require observation only, were significantly positively correlated with weight (an objective measure of obesity often requiring anesthetization), supporting the scale's validity. The BCS system identified 36 individuals as "overweight," while the use of weights alone identified only 26 individuals as "overweight." Furthermore, the BCS system was able to classify individuals of the same sex and weight as having different BCSs, ranging from normal to overweight. Lastly, using focal animal behavioral observations from 2016 to 2018 (N = 120), we found that In-group BCS predicted individual levels of inactive behavior more than 2 years later, demonstrating the predictive validity of the scale. These results illustrate the utility of the BCS system as a noninvasive, reliable, and valid technique that may be more sensitive than traditional methods in identifying and quantifying obesity in chimpanzees. This system can be a useful tool for captive managers to monitor and manage the weight of chimpanzees and other nonhuman primates.

Large Lemurs: Ecological, Demographic and Environmental Risk Factors for Weight Gain in Captivity

Simple Summary

Excessive body mass, i.e., being overweight or obese, is a health concern. Some lemur species are prone to extreme weight gain in captivity, yet for others a healthy body condition is typical. The first aim of our study was to examine possible ecological explanations for these species’ differences in susceptibility to captive weight gain across 13 lemur species. Our second aim was to explore demographic and environmental risk factors across individuals from the four best-sampled species. We found a potential ecological explanation for susceptibility to captive weight gain: being adapted to unpredictable wild food resources. Additionally, we also revealed one environmental and four demographic risk factors, e.g., increasing age and, for males, being housed with only fixed climbing structures. Our results indicate targeted practical ways to help address weight issues in affected animals, e.g., by highlighting at-risk species for whom extra care should be taken when designing diets; and by providing a mixture of flexible and fixed climbing structures within enclosures.

Abstract

Excessive body mass, i.e., being overweight or obese, is a health concern associated with issues such as reduced fertility and lifespan. Some lemur species are prone to extreme weight gain in captivity, yet others are not. To better understand species- and individual-level effects on susceptibility to captive weight gain, we use two complementary methods: phylogenetic comparative methods to examine ecological explanations for susceptibility to weight gain across species, and epidemiological approaches to examine demographic and environment effects within species. Data on body masses and living conditions were collected using a survey, yielding useable data on 675 lemurs representing 13 species from 96 collections worldwide. Data on species-typical wild ecology for comparative analyses came from published literature and climate databases. We uncovered one potential ecological risk factor: species adapted to greater wild food resource unpredictability tended to be more prone to weight gain. Our epidemiological analyses on the four best-sampled species revealed four demographic and one environmental risk factors, e.g., for males, being housed with only fixed climbing structures. We make practical recommendations to help address weight concerns, and describe future research including ways to validate the proxy we used to infer body condition.

Food preferences and nutrient composition in zoo-housed ring-tailed lemurs, Lemur catta

The aim of the present study was to assess the occurrence of spontaneous food preferences in zoo-housed ring-tailed lemurs and to analyze whether these preferences correlate with nutrient composition. Using a two-alternative choice test three female and one male Lemur catta were repeatedly presented with all possible binary combinations of 12 types of food which are part of their diet in captivity and found to display the following rank order of preference: apple > sweet potato > melon > beetroot > carrot > egg > eggplant > pumpkin > cucumber > tomato > cabbage > mealworm. Correlational analyses revealed a highly significant positive correlation between this food preference ranking and the total carbohydrate and sucrose contents of the foods (p < 0.01, respectively). No other significant correlations with any other macro- or micronutrient were found. These results suggest that zoo-housed ring-tailed lemurs are not opportunistic, but selective feeders with regard to maximizing their net gain of energy as only the content of carbohydrates, but not the contents of total energy, proteins or lipids significantly correlated with the displayed food preferences. Further, we found that ring-tailed lemurs that were raised on a vegetable-based diet did not significantly differ in their food preferences, and in particular in their predilection for food items high in carbohydrates, from animals that had previously been fed a fruit-based diet. This suggests that the lemurs' preference for carbohydrate-rich food items may be innate and not affected by experience with different diets.

Idiopathic Myocardial Fibrosis in Captive Chimpanzees (Pan troglodytes)

Cardiovascular disorders and predominantly idiopathic myocardial fibrosis are frequently associated with mortality among zoo-housed chimpanzees (Pan troglodytes). Formalin-fixed whole hearts of deceased chimpanzees housed in zoos (n = 33) and an African sanctuary (n = 2) underwent detailed macroscopic and histopathologic examination using a standardized protocol. Archived histological slides from the hearts of 23 additional African sanctuary-housed chimpanzees were also examined. Myocardial fibrosis (MF) was identified in 30 of 33 (91%) of the zoo-housed chimpanzees but none of the 25 sanctuary-housed chimpanzees. MF was shown to be characterized by both interstitial and replacement fibrosis. Immunophenotyping demonstrated that the fibrotic lesions were accompanied by the increased presence of macrophages, alpha smooth muscle actin-positive myofibroblasts, and a minimal to mild T-cell-dominant leukocyte infiltration. There was no convincing evidence of cardiotropic viral infection or suggestion that diabetes mellitus or vitamin E or selenium deficiency were associated with the presence of the lesion. However, serum vitamin D concentrations among zoo-housed chimpanzees were found to be lower in seasons of low ultraviolet light levels.

Behavioral responses of three lemur species to different food enrichment devices

Environmental enrichment is a tool used to promote the welfare and well-being of captive animals by encouraging the display of species-specific behaviors and reducing the stress or boredom induced by captive environments. Lemurs are highly endangered, yet few studies have analyzed the behavioral impacts of enrichment on captive populations. We studied the impacts of two novel enrichment devices on three lemur species (ring-tailed lemurs [Lemur catta], red-ruffed lemurs [Varecia rubra], and Coquerel's sifaka [Propithecus coquereli]) to determine both the overall and species-specific impacts of enrichment on lemur behavior. We recorded lemur behavior using the continuous sampling method to obtain behavior duration and analyzed our results using ANOVA Repeated Measures. Results showed enrichment effectiveness differed for each species and that different enrichment devices had varying impacts on lemur behavior across all species. We attributed the differences in species-specific responses to the unique locomotor patterns and methods of diet acquisition of each species, and the variances in behavioral responses across all species to the characteristics of each device. Our study highlights the importance of species-specific enrichment and encourages further research in this field in order to maximize the positive effects of enrichment, which in turn has the potential to affect the overall well-being of captive populations.

A SYSTEMATIC REVIEW OF THE LITERATURE RELATING TO CAPTIVE GREAT APE MORBIDITY AND MORTALITY

Wild bonobos (Pan paniscus), chimpanzees (Pan troglodytes), Western gorillas (Gorilla gorilla), and orangutans (Pongo pygmaeus, Pongo abelii) are threatened with extinction. In order to help maintain a self-sustaining zoo population, clinicians require a sound understanding of the diseases with which they might be presented. To provide an up-to-date perspective on great ape morbidity and mortality, a systematic review of the zoological and veterinary literature of great apes from 1990 to 2014 was conducted. This is the first review of the great ape literature published since 1990 and the first-ever systematic literature review of great ape morbidity and mortality. The following databases were searched for relevant articles: CAB Abstracts, Web of Science Core Collection, BIOSIS Citation Index, BIOSIS Previews, Current Contents Connect, Data Citation Index, Derwent Innovations Index, MEDLINE, SciELO Citation Index, and Zoological Record. A total of 189 articles reporting on the causes of morbidity and mortality among captive great apes were selected and divided into comparative morbidity-mortality studies and case reports-series or single-disease prevalence studies. The content and main findings of the morbidity-mortality studies were reviewed and the main limitations identified. The case reports-case series and single-disease prevalence studies were categorized and coded according to taxa, etiology, and body system. Subsequent analysis allowed the amount of literature coverage afforded to each category to be calculated and the main diseases and disorders reported within the literature to be identified. This review concludes that reports of idiopathic and infectious diseases along with disorders of the cardiovascular, respiratory, and gastrointestinal body systems were particularly prominent within the great ape literature during 1990-2014. However, recent and accurate prevalence figures are lacking and there are flaws in those reviews that do exist. There is therefore a critical need for a robust, widespread, and more up-to-date review of mortality among captive great apes.

Body condition scoring system for greater one-horned rhino (Rhinoceros unicornis): Development and application

Preventing obesity in zoo animals is increasingly recognized as an important husbandry objective. To achieve this goal, body condition scoring (BCS) systems are available for an ever-increasing number of species. Here, we present a BCS for the greater one-horned rhinoceros (Rhinoceros unicornis) based on an evaluation (on a scale from 1 to 5) of seven different body regions, and report resulting scores for 62 animals from 27 facilities, based on digital photographs. In animals above 4 years of age, this BCS correlated with the body mass:shoulder height ratio. Although differences between the sexes for individual regions were noted (with consistently higher scores in males for the neck and shoulder and in parous females for the abdomen), the average BCS of all regions did not differ significantly between males (4.3 ± 0.4) and females (4.1 ± 0.5). Linking the BCS to results of a questionnaire survey and studbook information, there were no differences in BCS between animals with and without foot problems or between parous and non-parous females. In a very limited sample of 11 females, those eight that had been diagnosed with leiomyoma in a previous study had a higher BCS (range 3.9-4.9) than the three that had been diagnosed as leiomyoma-free (range 3.5-3.7). The BCS was correlated to the amount of food offered as estimated from the questionnaire. Adjusting the amounts and the nutritional quality of the diet components is an evident measure to maintain animals at a target BCS (suggested as 3-3.5). Zoo Biol. 35:432-443, 2016. © Wiley Periodicals, Inc.

Comparative Pathology of Aging Great Apes: Bonobos, Chimpanzees, Gorillas, and Orangutans

The great apes (chimpanzees, bonobos, gorillas, and orangutans) are our closest relatives. Despite the many similarities, there are significant differences in aging among apes, including the human ape. Common to all are dental attrition, periodontitis, tooth loss, osteopenia, and arthritis, although gout is uniquely human and spondyloarthropathy is more prevalent in apes than humans. Humans are more prone to frailty, sarcopenia, osteoporosis, longevity past reproductive senescence, loss of brain volume, and Alzheimer dementia. Cerebral vascular disease occurs in both humans and apes. Cardiovascular disease mortality increases in aging humans and apes, but coronary atherosclerosis is the most significant type in humans. In captive apes, idiopathic myocardial fibrosis and cardiomyopathy predominate, with arteriosclerosis of intramural coronary arteries. Similar cardiac lesions are occasionally seen in wild apes. Vascular changes in heart and kidneys and aortic dissections in gorillas and bonobos suggest that hypertension may be involved in pathogenesis. Chronic kidney disease is common in elderly humans and some aging apes and is linked with cardiovascular disease in orangutans. Neoplasms common to aging humans and apes include uterine leiomyomas in chimpanzees, but other tumors of elderly humans, such as breast, prostate, lung, and colorectal cancers, are uncommon in apes. Among the apes, chimpanzees have been best studied in laboratory settings, and more comparative research is needed into the pathology of geriatric zoo-housed and wild apes. Increasing longevity of humans and apes makes understanding aging processes and diseases imperative for optimizing quality of life in all the ape species.

Distinguishing between determinate and indeterminate growth in a long-lived mammal

BACKGROUND

The growth strategy of a species influences many key aspects of its life-history. Animals can either grow indeterminately (throughout life), or grow determinately, ceasing at maturity. In mammals, continued weight gain after maturity is clearly distinguishable from continued skeletal growth (indeterminate growth). Elephants represent an interesting candidate for studying growth because of their large size, long life and sexual dimorphism. Objective measures of their weight, height and age, however, are rare.

RESULTS

We investigate evidence for indeterminate growth in the Asian elephant Elephas maximus using a longitudinal dataset from a semi-captive population. We fit growth curves to weight and height measurements, assess sex differences in growth, and test for indeterminate growth by comparing the asymptotes for height and weight curves. Our results show no evidence for indeterminate growth in the Asian elephant; neither sex increases in height throughout life, with the majority of height growth completed by the age of 15 years in females and 21 years in males. Females show a similar pattern with weight, whereas males continue to gain weight until over age 50. Neither sex shows any declines in weight with age.

CONCLUSIONS

These results have implications for understanding mammalian life-history, which could include sex-specific differences in trade-offs between size and reproductive investment.

The influence of body mass index, age and sex on inflammatory disease risk in semi-captive Chimpanzees

Obesity and ageing are emerging issues in the management of captive primates, including Chimpanzees, Pan troglodytes. Studies on humans show that obesity and old age can independently increase the risk of inflammatory-associated diseases indicated by elevated levels of pro-inflammatory cells and proteins in the blood of older or obese compared to levels in younger or non-obese individuals. In humans, sex can influence the outcomes of these risks. Health management of these problems in chimpanzee populations requires an understanding of similarities and differences of factors influencing inflammatory disease risks in humans and in chimpanzees. We examined the relationship between age, sex and Body Mass Index (BMI) with hematological biomarkers of inflammatory disease risk established for humans which include the neutrophil to lymphocyte ratio (NLR), and neutrophil, white blood cell (WBC), platelet microparticle and platelet counts. We found that higher values of NLR, neutrophil count and platelet microparticle count were associated with higher BMI values and older age indicating increased inflammation risk in these groups; a similar pattern to humans. There was a strong sex by age interaction on inflammation risk, with older males more at risk than older females. In contrast to human studies, total WBC count was not influenced by BMI, but like humans, WBC and platelet counts were lower in older individuals compared to younger individuals. Our findings are similar to those of humans and suggest that further insight on managing chimpanzees can be gained from extensive studies of ageing and obesity in humans. We suggest that managing BMI should be an integral part of health management in captive chimpanzee populations in order to partially reduce the risk of diseases associated with inflammation. These results also highlight parallels in inflammation risk between humans and chimpanzees and have implications for understanding the evolution of inflammation related diseases in apes.

Scaling of convex hull volume to body mass in modern primates, non-primate mammals and birds

The volumetric method of ‘convex hulling’ has recently been put forward as a mass prediction technique for fossil vertebrates. Convex hulling involves the calculation of minimum convex hull volumes (vol_CH) from the complete mounted skeletons of modern museum specimens, which are subsequently regressed against body mass (M_b) to derive predictive equations for extinct species. The convex hulling technique has recently been applied to estimate body mass in giant sauropods and fossil ratites, however the biomechanical signal contained within vol_CH has remained unclear. Specifically, when vol_CH scaling departs from isometry in a group of vertebrates, how might this be interpreted? Here we derive predictive equations for primates, non-primate mammals and birds and compare the scaling behaviour of M_b to vol_CH between groups. We find predictive equations to be characterised by extremely high correlation coefficients (r² = 0.97–0.99) and low mean percentage prediction error (11–20%). Results suggest non-primate mammals scale body mass to vol_CH isometrically (b = 0.92, 95%CI = 0.85–1.00, p = 0.08). Birds scale body mass to vol_CH with negative allometry (b = 0.81, 95%CI = 0.70–0.91, p = 0.011) and apparent density (vol_CH/M_b) therefore decreases with mass (r² = 0.36, p<0.05). In contrast, primates scale body mass to vol_CH with positive allometry (b = 1.07, 95%CI = 1.01–1.12, p = 0.05) and apparent density therefore increases with size (r² = 0.46, p = 0.025). We interpret such departures from isometry in the context of the ‘missing mass’ of soft tissues that are excluded from the convex hulling process. We conclude that the convex hulling technique can be justifiably applied to the fossil record when a large proportion of the skeleton is preserved. However we emphasise the need for future studies to quantify interspecific variation in the distribution of soft tissues such as muscle, integument and body fat.

Mitochondrial genetics and obesity: evolutionary adaptation and contemporary disease susceptibility

Obesity is a leading risk factor for a variety of metabolic diseases including cardiovascular disease, diabetes, and cancer. Although in its simplest terms, obesity may be thought of as a consequence of excessive caloric intake and sedentary lifestyle, it is also evident that individual propensity for weight gain can vary. The etiology of individual susceptibility to obesity seems to be complex-involving a combination of environmental-genetic interactions. Herein, we suggest that the mitochondrion plays a major role in influencing individual susceptibility to this disease via mitochondrial-nuclear interaction processes and that environmentally influenced selection events for mitochondrial function that conveyed increased reproductive and survival success during the global establishment of human populations during prehistoric times can influence individual susceptibility to weight gain and obesity.

Exploring diagonal gait using a forward dynamic three-dimensional chimpanzee simulation

Primates are unusual among terrestrial quadrupedal mammals in that at walking speeds they prefer diagonal rather than lateral gaits. A number of reasons have been proposed for this preference in relation to the arboreal ancestry of modern primates: stability, energetic cost, neural control, skeletal loading, and limb interference avoiding. However, this is a difficult question to explore experimentally since most primates only occasionally use anything other than diagonal gaits. An alternative approach is to produce biologically realistic computer simulations of primate gait that enable the constraints of biomechanical loading and the energetics of different modes of locomotion to be explored. In this paper we describe such a model for the chimpanzee Pan troglodytes. The simulation is able to produce spontaneous quadrupedal locomotion, and the footfall sequences generated are split between lateral and diagonal footfall sequences with no obvious energetic benefit associated with either option. However, out of 10 successful simulation runs, 5 were lateral sequence/lateral couplet gaits indicating a preference for a specific lateral footfall sequence with a relatively tightly constrained phase difference between the fore- and hindlimbs. This suggests that the choice of diagonal walking gaits in chimpanzees is not a simple mechanical phenomenon and that diagonal walking gaits in primates are selected for by multiple factors.

Hypertension increases with aging and obesity in chimpanzees (Pan troglodytes)

Cardiovascular disease is a primary cause of morbidity and mortality in captive chimpanzees. Four years of blood pressure (BP) data were analyzed from a captive former laboratory population of 201 healthy adult chimpanzees with assessment of age and obesity on elevated BP. Five different measures of obesity were compared: abdominal girth, basal metabolic rate, body-mass index (BMI), body weight, and surface area. Systolic BP varied by sex. Obesity did not influence male BP. For females, obesity was a significant determinant of BP. The best measure of female obesity was basal metabolic rate and the worst was BMI. Median systolic BP of healthy weight females (<54.5 kg) was significantly lower (128 mmHg) than overweight or obese females (140 mmHg), but both were lower than all males (147 mmHg). For diastolic BP, neither sex nor any of the five obesity measures was significant. But age was highly significant, with geriatric chimpanzees (>30 years) having higher median diastolic BP (74 mmHg) than young adults of 10-29 years of age (65 mmHg). By these criteria, 80% of this population is normotensive, 7% prehypertensive, and 13% hypertensive. In summary, systolic BP intervals required adjustment for obesity among females but not males. Diastolic BP required adjustment for advanced age (≥30 years). Use of these reference intervals can facilitate timely clinical care of captive chimpanzees.

Diagnosis and prevalence of uterine leiomyomata in female chimpanzees (Pan troglodytes)

Uterine leiomyomata are common, affecting 70-80% of women between 30 and 50 years of age. Leiomyomata have been reported for a variety of primate species, although prevalence rates and treatments have not been widely reported. The prevalence, diagnosis, and treatment of uterine leiomyomata in the Alamogordo Primate Facility and the Keeling Center for Comparative Medicine and Research were examined. Uterine leiomyomata were diagnosed in 28.4% of chimpanzees with an average age at diagnosis of 30.4 ± 8.0 years. Advanced age (>30 years) was related to an increase in leiomyomata and use of hormonal contraception was related to a decrease in leiomyomata. As the captive chimpanzee population ages, the incidence of leiomyomata among female chimpanzees will likely increase. The introduction of progesterone-based contraception for nonbreeding research and zoological chimpanzees may reduce the development of leiomyomata. Finally, all chimpanzee facilities should institute aggressive screening programs and carefully consider treatment plans.