Cooperation and population dynamics in the Sociable Weaver
The evolution of cooperation is a central problem in evolutionary biology because individuals cooperate to help others at a cost to themselves, violating a basic principle of natural selection. Kin-selection theory provides an explanation for cooperation among kin, but cooperative interactions among unrelated individuals are commonplace. This poses a major challenge, which is to demonstrate how non-kin selected mechanisms may drive the evolution of cooperation.
This project investigates the benefits, costs and consequences of cooperation using the Sociable Weaver Philetairus socius as a study model. Akin to traditional human societies, these weavers have an elaborate social structure with different levels of organisation – the family, the neighbourhood that surrounds the family nest, and the colony – and they also collaborate on multiple tasks. These features allow a comprehensive study of cooperation in the wild. Additionally, the project’s long-term demographic data now spans over 20 years, providing the possibility to investigate how sociality interacts with environmental factors to determine population dynamics.
The current main focus of the Sociable Weaver project is to investigate the possible direct benefits arising from cooperation and, especially, whether there are benefits obtained through social or sexual selection. Cooperation may be under social or sexual selection if the individuals that are more cooperative are preferred by others as social or sexual partners. This hypothesis has received support in humans, but remains largely untested in other animals. Rita Covas, Claire Doutrelant and their team have been conducting work towards addressing these questions on the Sociable Weaver population at Benfontein near Kimberley. Post-doc Nora Carlson (CIBIO, Portugal), PhD student André Ferreira (University of Montpellier) and MSc students Sandra Esteves and Inês Duarte (CIBIO, University of Porto) are all conducting projects related to these questions.
Another main topic in this research programme is how sociality interacts with environmental conditions to determine individual life-history strategies and population trends. Rita Fortuna (CIBIO, University of Porto) was awarded a PhD bursary from FCT, Portugal to investigate how social and environmental factors influence female reproductive strategies and the consequences for offspring and colony dynamics.
Activities in 2017
- The 2017 bumper breeding season lasted nine months, during which 150 pairs in 13 colonies attempted to breed, producing a whopping 3 419 eggs. Of these, only 527 resulted in fledged young, essentially because of massive predation by snakes.
- Monitoring the adults at the nest produced over 2 000 videos that are still being analysed by project technician Liliana Silva (CIBIO). The data will be key to analysing breeder and helper strategies. However, to improve data collection efficiency we started developing an alternative way to automatically collect nest attendance behaviour using PIT-tags and RFID readers.
- A collaboration between project technician Franck Théron (CNRS) and Jérémy Tornos (CNRS) produced a programme to enter breeding data directly in the field using a tablet. This was a major advance as it drastically reduced the time associated with data-entry and fieldwork planning.
- During the annual captures, a record number of 694 adults was caught by a team of 13 people.
- André Ferreira (PhD, U. Montpellier) and Sandra Esteves (MSc, CIBIO) conducted personality tests on 322 individuals to examine whether there is consistent variation in behavioural traits in this species and how that interacts with cooperative behaviour.
- Inês Duarte (MSc, CIBIO) collected data on dominance hierarchies at five colonies for her project on the relationship between social status and cooperative investment.
- Nora Carlson (Postdoc, CIBIO) successfully conducted a first season of field experiments to investigate the effect of a female audience on cooperative behaviour.
- André Ferreira, in collaboration with Damien Farine (Max Planck Institute, Germany), developed an automated system to collect associations between birds based on PIT-tags and RFID readers. This will allow the collection of large-volume data to study social networks in this species.
- Rita Fortuna (PhD, CIBIO) started fieldwork on the effect of helpers and environmental conditions on maternal effects.
- Franck Théron finished compiling the project’s data into an integrated database. The breeding data now spans 10 years and contains over 18 000 records.
- An article about the Sociable Weaver Project was published in National Geographic (Portuguese edition).
- A new post-doc, a new PhD student and two new MSc students joined the project.
- A paper was published in Royal Society Open Science, revealing that temperature plays a crucial role in determining the onset of breeding and breeding duration in Sociable Weavers; and a paper in African Journal of Ecology described the collective foraging behaviour of Sociable Weavers.
- A new automated data collection system using PIT-tags and RFID readers is now in use at five colonies and a new electronic note book allows efficient data capture directly in the field.
Impact of the project
The long-term nature of this project allows unique insights to understand the evolution of cooperation and the mechanisms that allow it to persist. The demographic data allow for examination of the factors affecting population dynamics in relation to environmental change.
The Foundation for Science and Technology (FCT), Portugal; French Research Agency; ANR, France; DST-NRF CoE grant
Dr Rita Covas (FIAO, UCT and CIBIO, U. Porto)
Dr Claire Doutrelant (FIAO, UCT and CNRS, France)
Dr Nora Carlson (CIBIO, U. Porto)
Dr Sophie Lardy (FIAO, UCT and CNRS)