Female Solicitation and Male Rejection During Mating Events in Wild Chimpanzees

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Description
Humans are seemingly unique among the great apes with regard to their monogamous mating behavior. Since chimpanzees (Pan troglodytes) are humans closest living relative, understanding their actions may give insight into the evolutionary development of certain behaviors. In this paper,

Humans are seemingly unique among the great apes with regard to their monogamous mating behavior. Since chimpanzees (Pan troglodytes) are humans closest living relative, understanding their actions may give insight into the evolutionary development of certain behaviors. In this paper, the mating behavior of chimpanzees will be evaluated in hopes of better understanding any similarities or differences compared to that of humans. Wild male chimpanzees have shown to reject solicitations from females at full swelling. The hypothesis being tested was that a male chimpanzee will reject a female who solicits a mating event due to age, rank, and parity. Long term data from Gombe National Park in Tanzania, Africa was used to test this. As expected, parous females were less likely to be rejected than nulliparous females, rejection was more likely if several other swollen females were present, and rejection was less likely if the female was higher-ranking/older. Surprisingly, it was found that younger males were more likely to reject females than prime males were. This was most likely due to the fact that almost always, higher-ranking males were also present, which may have deterred young males from mating. The results also showed that there was no effect of male rank and female reproductive state on the probability of rejection. The findings of this study may help to show a potential evolutionary step towards conscious mate selection as seen in humans.
Date Created
2019-05
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Reflections of the Social Environment in Chimpanzee Memory: Applying Rational Analysis Beyond Humans

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Description

In cognitive science, the rational analysis framework allows modelling of how physical and social environments impose information-processing demands onto cognitive systems. In humans, for example, past social contact among individuals predicts their future contact with linear and power functions. These

In cognitive science, the rational analysis framework allows modelling of how physical and social environments impose information-processing demands onto cognitive systems. In humans, for example, past social contact among individuals predicts their future contact with linear and power functions. These features of the human environment constrain the optimal way to remember information and probably shape how memory records are retained and retrieved. We offer a primer on how biologists can apply rational analysis to study animal behaviour. Using chimpanzees (Pan troglodytes) as a case study, we modelled 19 years of observational data on their social contact patterns. Much like humans, the frequency of past encounters in chimpanzees linearly predicted future encounters, and the recency of past encounters predicted future encounters with a power function. Consistent with the rational analyses carried out for human memory, these findings suggest that chimpanzee memory performance should reflect those environmental regularities. In re-analysing existing chimpanzee memory data, we found that chimpanzee memory patterns mirrored their social contact patterns. Our findings hint that human and chimpanzee memory systems may have evolved to solve similar information-processing problems. Overall, rational analysis offers novel theoretical and methodological avenues for the comparative study of cognition.

Date Created
2016-08-03
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Chimpanzee Females Queue But Males Compete for Social Status

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Description

Dominance hierarchies are widespread in animal social groups and often have measureable effects on individual health and reproductive success. Dominance ranks are not static individual attributes, however, but instead are influenced by two independent processes: 1) changes in hierarchy membershi

Dominance hierarchies are widespread in animal social groups and often have measureable effects on individual health and reproductive success. Dominance ranks are not static individual attributes, however, but instead are influenced by two independent processes: 1) changes in hierarchy membership and 2) successful challenges of higher-ranking individuals. Understanding which of these processes dominates the dynamics of rank trajectories can provide insights into fitness benefits of within-sex competition. This question has yet to be examined systematically in a wide range of taxa due to the scarcity of long-term data and a lack of appropriate methodologies for distinguishing between alternative causes of rank changes over time. Here, we expand on recent work and develop a new likelihood-based Elo rating method that facilitates the systematic assessment of rank dynamics in animal social groups, even when interaction data are sparse. We apply this method to characterize long-term rank trajectories in wild eastern chimpanzees (Pan troglodytes schweinfurthii) and find remarkable sex differences in rank dynamics, indicating that females queue for social status while males actively challenge each other to rise in rank. Further, our results suggest that natal females obtain a head start in the rank queue if they avoid dispersal, with potential fitness benefits.

Date Created
2016-10-14
Agent