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

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.

Left ventricular trabeculation in Hominidae: divergence of the human cardiac phenotype

Although the gross morphology of the heart is conserved across mammals, subtle interspecific variations exist in the cardiac phenotype, which may reflect evolutionary divergence among closely-related species. Here, we compare the left ventricle (LV) across all extant members of the Hominidae taxon, using 2D echocardiography, to gain insight into the evolution of the human heart. We present compelling evidence that the human LV has diverged away from a more trabeculated phenotype present in all other great apes, towards a ventricular wall with proportionally greater compact myocardium, which was corroborated by post-mortem chimpanzee (Pan troglodytes) hearts. Speckle-tracking echocardiographic analyses identified a negative curvilinear relationship between the degree of trabeculation and LV systolic twist, revealing lower rotational mechanics in the trabeculated non-human great ape LV. This divergent evolution of the human heart may have facilitated the augmentation of cardiac output to support the metabolic and thermoregulatory demands of the human ecological niche.

Quantifying maternal investment in mammals using allometry

Maternal investment influences the survival and reproduction of both mothers and their progeny and plays a crucial role in understanding individuals' life-history and population ecology. To reveal the complex mechanisms associated with reproduction and investment, it is necessary to examine variations in maternal investment across species. Comparisons across species call for a standardised method to quantify maternal investment, which remained to be developed. This paper addresses this limitation by introducing the maternal investment metric - MI - for mammalian species, established through the allometric scaling of the litter mass at weaning age by the adult mass and investment duration (i.e. gestation + lactation duration) of a species. Using a database encompassing hundreds of mammalian species, we show that the metric is not highly sensitive to the regression method used to fit the allometric relationship or to the proxy used for adult body mass. The comparison of the maternal investment metric between mammalian subclasses and orders reveals strong differences across taxa. For example, our metric confirms that Eutheria have a higher maternal investment than Metatheria. We discuss how further research could use the maternal investment metric as a valuable tool to understand variation in reproductive strategies.

Polyglucosan body disease in an aged chimpanzee (Pan troglodytes)

A 57-year-old female chimpanzee presented with a brief history of increasing lethargy and rapidly progressive lower-limb weakness that culminated in loss of use. Postmortem examination revealed no significant gross lesions in the nervous system or other organ systems. Histological analysis revealed round, basophilic to amphophilic polyglucosan bodies (PGBs) in the white and gray matter of the cervical, thoracic, lumbar, and coccygeal regions of spinal cord. Only rare PGBs were observed in forebrain samples. The lesions in the spinal cord were polymorphic, and they were positively stained with hematoxylin, periodic acid Schiff, Alcian blue, toluidine blue, Bielschowsky silver, and Grocott-Gomori methenamine-silver methods, and they were negative for von Kossa and Congo Red stains. Immunohistochemical evaluation revealed reactivity with antibodies to ubiquitin, but they were negative for glial fibrillary acidic protein, neuron-specific enolase, neurofilaments, tau protein, and Aβ protein. Electron microscopy revealed non-membrane-bound deposits composed of densely packed filaments within axons and in the extracellular space. Intra-axonal PGBs were associated with disruption of the axonal fine structure and disintegration of the surrounding myelin sheath. These findings are the first description of PGBs linked to neurological dysfunction in a chimpanzee. Clinicopathologically, the disorder resembled adult PGB disease in humans.

Getting to the Meat of It: The Effects of a Captive Diet upon the Skull Morphology of the Lion and Tiger

Zoo animals are crucial for conserving and potentially re-introducing species to the wild, yet it is known that the morphology of captive animals differs from that of wild animals. It is important to know how and why zoo and wild animal morphology differs to better care for captive animals and enhance their survival in reintroductions, and to understand how plasticity may influence morphology, which is supposedly indicative of evolutionary relationships. Using museum collections, we took 56 morphological measurements of skulls and mandibles from 617 captive and wild lions and tigers, reflecting each species' recent historical range. Linear morphometrics were used to identify differences in size and shape. Skull size does not differ between captive and wild lions and tigers, but skull and mandible shape does. Differences occur in regions associated with biting, indicating that diet has influenced forces acting upon the skull and mandible. The diets of captive big cats used in this study predominantly consisted of whole or partial carcasses, which closely resemble the mechanical properties of wild diets. Thus, we speculate that the additional impacts of killing, manipulating and consuming large prey in the wild have driven differentiation between captive and wild big cats.

Serum vitamin D in sanctuary chimpanzees (Pan troglodytes) in range countries: A pilot study

BACKGROUND

Vitamin D is essential for skeletal health, calcium homeostasis and general health. The major and more stable form of vitamin D in circulation is 25-hydroxyvitamin D (25-OH-D); this is the most valuable indicator of vitamin D status. There are studies on laboratory and zoo-housed chimpanzees; however, serum vitamin D status has not been documented in chimpanzees in range countries.

OBJECTIVES

(1) Determine the range of circulating 25-OH-D concentrations in chimpanzees in range countries. (2) Assess the influence of age, sex, and sun exposure on 25-OH-D serum concentrations.

METHODS

Opportunistic blood samples were obtained from 127 clinically healthy chimpanzees. Serum 25-OH-D concentration was measured with a commercially available competitive ELISA.

RESULTS

The median overall 25-OH-D concentration for chimpanzees in range countries was 46.24 nmol/L (range: 17.10-109.23 nmol/L). Males had a significantly lower concentration (40.15 nmol/L) than females (49.61 nmol/L), and infants (37.99 nmol/L) had a significantly lower concentration than adults (46.04 nmol/L). Concentrations of 25-OH-D in chimpanzees in sunnier habitats were significantly higher compared to thick tropical forest habitat.

CONCLUSION

The present constitutes a large dataset of serum 25-OH-D concentrations in range country sanctuary chimpanzees and contributes to document normal ranges. Age, sex, and sun exposure influenced serum concentrations of 25-OH-D in sanctuary chimpanzees.

How Sanctuary Chimpanzees (Pan troglodytes) Use Space after Being Introduced to a Large Outdoor Habitat

Wild chimpanzees live in large, mixed-sex groups that display a fission–fusion social organization. To provide a social environment more like that of wild chimpanzees, Chimp Haven integrated smaller groups of 3–4 individuals into one large group of 18 individuals. This large group was introduced to a 20,234.28 m2 forested habitat and associated indoor areas. This space was designed to allow the individual chimpanzees to choose their proximity to social companions and provide the group with a more natural environment in which they could express more species-typical behavior. The study took place over a 7-month period that began two weeks prior to the first groups being integrated and ended 4 months after the chimpanzees were released into the habitat. We collected data on the chimpanzees’ arboreal, terrestrial, indoor, and outdoor spatial use. The chimpanzees’ proximity to their nearest neighbor was also recorded, noting whether they were touching or within arm’s reach. Data were collected during daytime and nighttime hours and were utilized to make management decisions about potential group formations. We examined the data using generalized linear mixed models (GLMMs) with individual subjects as a random factor and months as a repeated measure for location and proximity results. There were significant differences in the use of arboreal and outside space over the 7-month time frame, with females more likely to use the arboreal space than males. The chimpanzees were more likely to utilize the habitat over time and increased their proximity to group mates. The results of this study indicate that the chimpanzees responded positively to living in large groups in a spacious naturalistic environment.