How environmental unpredictability and harshness affect chimpanzees (Pan troglodytes) in risk-choice and temporal discounting tasks.

Animals need to adjust their decision-making strategies to the ecological challenges of their environment. Variation in ecological unpredictability and harshness thus seem to affect their decisions in the wild. In our study, we combine methods from human life history theory and previous comparative work with chimpanzees to investigate whether current variability in ecological factors such as reward unpredictability and harshness affect chimpanzees' decision-making strategies in two value-based scenarios. We presented chimpanzees with choices varying in the probability of obtaining food rewards (risk-choice task) and in their temporal availability (temporal discounting task). These scenarios were preceded by different sets of priming phases mimicking variability in resource unpredictability (predictable or unpredictable rewards) and harshness (abundant or scarce rewards). In addition, we implemented a social manipulation to explore whether variations in unpredictable gains and losses affected chimpanzees' performance in both tasks. We found that chimpanzees were only affected by the social manipulation in the risk-choice scenario. Specifically, after a period of constant food losses chimpanzees became less risk prone. We discuss how different types of negative experiences affect chimpanzees' decisions. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

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'.

Forgetting in chimpanzees (Pan troglodytes): What is the role of interference?

Humans are constantly acquiring new information and skills. However, forgetting is also a common phenomenon in our lives. Understanding the lability of memories is critical to appreciate how they are formed as well as forgotten. Here we investigate the lability of chimpanzees' short-term memories and assess what factors cause forgetting in our closest relatives. In two experiments, chimpanzees were presented with a target task, which involved remembering a reward location, followed by the presentation of an interference task-requiring the recollection of a different reward location. The interference task could take place soon after the presentation of the target task or soon before the retrieval of the food locations. The results show that chimpanzees' memories for the location of a reward in a target task were compromised by the presentation of a different food location in an interference task. Critically, the temporal location of the interference task did not significantly affect chimpanzees' performance. These pattern of results were found for both Experiment 1-when the retention interval between the encoding and retrieval of the target task was 60 seconds- and Experiment 2-when the retention interval between the encoding and retrieval of the target task was 30 seconds. We argue that the temporal proximity of the to-be-remembered information and the interference item during encoding is the factor driving chimpanzees' performance in the present studies.