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.

Ecological variation in adult social play reveals a hidden cost of motherhood for wild chimpanzees.

Though common among humans, social play by adults is an uncommon occurrence in most animals, even between parents and offspring.1,2,3 The most common explanation for why adult play is so rare is that its function and benefits are largely limited to development, so that social play has little value later in life.3,4,5,6 Here, we draw from 10 years of behavioral data collected by the Kibale Chimpanzee Project to consider an alternative hypothesis: that despite its benefits, adult play in non-humans is ecologically constrained by energy shortage or time limitations. We further hypothesized that, since they may be the only available partners for their young offspring, mother chimpanzees pay greater costs of play than other adults. Our analysis of nearly 4,000 adult play bouts revealed that adult chimpanzees played both among themselves and with immature partners. Social play was infrequent when diet quality was low but increased with the proportion of high-quality fruits in the diet. This suggests that adults engage in play facultatively when they have more energy and/or time to do so. However, when diet quality was low and most adult play fell to near zero, play persisted between mothers and offspring. Increased use of play by adult chimpanzees during periods of resource abundance suggests that play retains value as a social currency beyond development but that its costs constrain its use. At the same time, when ecological conditions constrain opportunities for young to play, play by mothers fills a critical role to promote healthy offspring development.

Observational approaches to chimpanzee behavior in an African sanctuary: Implications for research, welfare, and capacity-building.

Research in African ape sanctuaries has emerged as an important context for our understanding of comparative cognition and behavior. While much of this work has focused on experimental studies of cognition, these animals semi-free-range in forest habitats and therefore can also provide important information about the behavior of primates in socioecologically-relevant naturalistic contexts. In this "New Approaches" article, we describe a project where we implemented a synthetic program of observational data collection at Ngamba Island Chimpanzee Sanctuary in Uganda, directly modeled after long-term data collection protocols at the Kibale Chimpanzee Project in Uganda, a wild chimpanzee field site. The foundation for this project was a strong partnership between sanctuary staff, field site staff, and external researchers. We describe how we developed a data-collection protocol through discussion and collaboration among these groups, and trained sanctuary caregivers to collect novel observational data using these protocols. We use these data as a case study to examine: (1) how behavioral observations in sanctuaries can inform primate welfare and care practices, such as by understanding aggression within the group; (2) how matched observational protocols across sites can inform our understanding of primate behavior across different contexts, including sex differences in social relationships; and (3) how more robust collaborations between foreign researchers and local partners can support capacity-building in primate range countries, along with mentoring and training students more broadly.