Primate News of the Week

Apes only provide food to conspecifics that have previously assisted them


Source : Max Planck Institutes for Evolutionary Anthropology and for Mathematics in the Sciences in Leipzig
Summary: A behavioral experiment was set up to understand Chimpanzee cooperation. A chimpanzee was given the choice of either providing food to itself and a partner or only providing food for itself. Chimpanzee were more generous to those that had risked obtaining no food in order to assist them. Chimpanzees also gave up extra food in order to reward their conspecifics for their support. They also appear to adjust the amount of reward they give depending on how much assistance their partner has provided.
Read more:
Journal Reference: Chimpanzees return favors at a personal cost. PNAS 2017 ; published ahead of print June 19, 2017, DOI: 10.1073/pnas.1700351114

Wild monkeys use loud calls to assess the relative strength of rivals

Source: University of Michigan
Summary: Gelada males use loud calls in order to gain information about their opponents condition. This allows them to decide whether or not to escalate contests. Geladas live in groups of one male units in which one male monopolizes the females. Bachelor males will attempt to compete with the male to gain reproductive access to females. The leader male uses loud calls in order to deter these bachelor males.
Read more via Phys:
Journal Reference: Marcela E. Bentez et al. Evidence for mutual assessment in a wild primate, Scientific Reports (2017). DOI: 10.1038/s41598-017-02903-w

Chimpanzees modify grooming behavior when near high ranking members


Source: University of Kent
Summary: Grooming is an incredibly important aspect to Chimp interactions. Lower ranking individuals will often groom higher ranking individuals in order to receive benefits such as protection. This study took place at the Budongo Forest Reserve in Western Uganda and found that when a chimp of higher rank is being groomed nearby, the grooming chimp will stop sooner. The chimps also appeared to stop grooming sooner if there was a larger group nearby rather than a smaller group. This study suuggests an economic oriented biological market theory involved in considering the benefits and costs while engaging in grooming.
Read more:
Journal Reference: Nicholas E. Newton-Fisher et al. Grooming decisions under structural despotism: the impact of social rank and bystanders among wild male chimpanzees, Animal Behaviour (2017). DOI: 10.1016/j.anbehav.2017.04.012

Chimpanzee ‘super strength’ and what is might mean in human muscle evolution


Source: University of Massachusetts at Amherst
Summary: Contrary to anecdotes of chimps being 7 to 8 times stronger than humans a recent study has shown chimps are only 1.35 times higher dynamic force and power output compared to similar sized human muscle.
Read more:
Journal Reference: Matthew C. O’Neill, Brian R. Umberger, Nicholas B. Holowka, Susan G. Larson, Peter J. Reiser. Chimpanzee super strength and human skeletal muscle evolution. Proceedings of the National Academy of Sciences, 2017; 201619071 DOI: 10.1073/pnas.1619071114

Looking for trouble: Territorial aggressions and trespesses pay off among primates

Source: Arizoma State University
Summary: Patrols involve multiple individuals (mainly males) travel to a neighboring territory and if they find a member of a rival group they will attack and occasionally kill the rival group member. The chimps in these patrols appear to actively search out the rival group members suggesting a risk with uncertain gains. another interesting aspect is some members are allowed to not participate and they are not ostracized or punished for not patrolling. In a study of the 200 member chimp Ngogo community in Uganda the cooperation needed for patrols was investigated. The study found that higher ranking males were more likely to participate likely due to the better health and those with more offspring and thus a more long term gain.
Journal Reference: Kevin E. Langergraber el al., “Group augmentation, collective action, and territorial boundary patrols by male chimpanzees,” PNAS (2017).



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