Stable long-term individual variation in chimpanzee technological efficiency
Abstract
Using tools to access hard-to-reach and high-quality resources, such as termites, honey, and nuts, initiated a fundamental adaptive shift in human and nonhuman primate cognitive and behavioural evolution. Variation in the efficiency of extracting calorie-rich and nutrient-dense resources directly impacts energy expenditure, and potentially has significant repercussions for cultural transmission where model selection biases are employed during skill acquisition. Assessing variation in efficiency is key to understanding the evolution of complex behavioural traits in primates. Yet, individual-level differences beyond age- and sex-class in primate extractive foraging efficiency have never been investigated. Here, we used 25 years (1992– 2017) of video data of the Bossou chimpanzee community (Guinea), to investigate whether individual differences in nut-cracking efficiency exist across the life span of chimpanzees aged ≥ 6 years. Data from 3,882 oil-palm nut-cracking bouts from over 800 hours of observation were collected. We found long-term stable and reliable individual differences in four (out of five) measures of efficiency. We found no sex effect, challenging previous research on a female bias in chimpanzee tool use. These life-long differences in extractive foraging impacts daily energy budgets, which potentially have significant individual fitness and life history consequences. Additionally, the establishment of long-term individual variation in chimpanzee stone tool use has implications for interpreting archaeological records of hominins. Our findings highlight the importance of longitudinal data from long-term field sites when investigating underlying cognitive and behavioural diversity across individual lifespans and between populations.
Copyright and License
The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-ND 4.0 International license.
Acknowledgement
We thank the Direction Générale de la Recherche Scientifique et de l’Innovation Technologique (DGERSIT) and the Institut de Recherche Environnementale de Bossou (IREB) in Guinea for research authorisation. The video data for this research was provided by Tetsuro Matsuzawa and Kyoto University, Japan. The original video archive was digitised, organised, and systematised by Daniel Schofield, Department of Engineering Science, University of Oxford. Special thanks to all the field researchers and assistants at Bossou, specifically Henry Didier Camara, Cé Vincent Mami, Gouanou Zogbila, Boniface Zogbila, Jules Doré, Guana Goumy, Tino Camara, Pascal Goumy, Paquílé Cherif, Jiles Gondo Doré, and Marcel Doré. Thank you to all the researchers who contributed to the Bossou archive since its inception. Thank you to Alexander Mielke for help cataloguing the Bossou video archive. Thank you to Dora Biro and Katarina Almeida Warren for feedback. Thank you to Zhangzhuoran Dai and Victoire Martignac for being independent, hypothesis-blind coders for the inter-rater reliability analyses.
Funding
This research was supported by the Clarendon Fund (University of Oxford, UK), Keble College Sloane-Robinson Clarendon Scholarship (University of Oxford, UK), the Boise Trust Fund (University of Oxford, UK) to S.B., and by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan, (grant nos. 12002009, 16002001, 20002001, 24000001, and 16H06283) to T.M.. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.
Contributions
S.B. conceived of the study, designed, and coordinated the study, collected data, participated in the analysis and visualisation of the data, and wrote the manuscript. E.C. provided supervision, participated in the design of the study, and commented on the manuscript. A.J.D. analysed and visualised the data and commented on the manuscript. T.M. collected the original data set and commented on the manuscript. S.C. collected the original data set, provided supervision, participated in the design of the study, and commented on the manuscript.
Data Availability
https://github.com/arranjdavis/chimpanzee_nut_cracking_efficiency
Code Availability
https://github.com/arranjdavis/chimpanzee_nut_cracking_efficiency
Conflict of Interest
The authors declare no competing interests.
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Additional details
- University of Oxford
- 12002009
- Ministry of Education, Culture, Sports, Science and Technology
- 16002001
- Ministry of Education, Culture, Sports, Science and Technology
- 20002001
- Ministry of Education, Culture, Sports, Science and Technology
- 24000001
- Ministry of Education, Culture, Sports, Science and Technology
- 16H06283
- Ministry of Education, Culture, Sports, Science and Technology