Cooperation and population dynamics in the Sociable Weaver
The aptly named Sociable Weaver Philetairus socius is a highly social species that is endemic to the Kalahari region of southern African. As the common name suggests, these weavers work together to accomplish diverse tasks, from building their highly distinctive thatched nests to help raising the chicks and defending the nest and colony mates from predators. Their fascinating social structure and different types of cooperative behaviours make them an ideal study model to investigate the benefits and costs of sociality and the evolutionary mechanisms that allow cooperation to evolve and be maintained.
Cooperation among family members is relatively easy to explain, since close kin share a large proportion of genes, and hence by helping close relatives achieving higher survival or reproductive output, the cooperative individual is contributing to spread its own genes in the population. In Sociable Weavers, many cooperative interactions take place among family members. For example, older offspring help the parents feed their siblings, clean the nest and contribute to maintain the family’s nest chamber. However, some cooperative behaviours such as the communal nest building that allows the colony structure to be maintained is conducted by related and unrelated individuals, and nest defence against predators may also involve relatives and non-relatives of the nests under attack.
Currently, one of the main focuses of the Sociable Weaver Project, led by Rita Covas in collaboration with Claire Doutrelant, is to investigate whether there are benefits of cooperating that go beyond kin selection. In particular, we are interested in finding out whether more cooperative individuals are preferentially chosen as mates or as social partners. This could lead to higher reproductive success or higher survival and provide an additional mechanism favouring investment in cooperative tasks as opposed to cheating. Research being undertaken at our study site in Benfontein, near Kimberley is collecting data on cooperative investment, patterns of social association and mating patterns to investigate these hypotheses.
Another of our main research interests is the interaction between sociality and environmental conditions. Do social factors influence individual life-history strategies and population trends? We have been investigating the role of maternal investment in relation to social and climactic factors and how these influence individual fitness. In addition, we use the project’s long-term demographic data to investigate questions related to how environmental change affects crucial population parameters and how this interacts with social factors to determine population outcomes. Under the current climate change scenario, the frequency and intensity of extreme weather events such as droughts and heat waves is predicted to increase, and cooperative species may be better equipped to cope with these extreme adverse conditions than non-cooperative species.
Activities in 2018
- The 2017-2018 breeding season lasted eight months. The Sociable Weavers at the 14 study colonies produced 1 166 eggs. But as a result of predation and other losses, only 352 chicks fledged.
- Post-doc Nora Carlson conducted an experiment to investigate whether male helpers are more cooperative in the presence of females by simulating the presence of different audiences using playbacks.
- During the annual captures in Aug-Sept we captured all the colonies known in our study area (a total of 28 colonies and 1 147 birds). This will allow us to study the movement between these colonies and the factors influencing dispersal and colony size trends.
- We started to collect social network data in an automatic way using a system based on PIT-tags and RFID readers developed by PhD student André Ferreira in collaboration with Damien Farine (Max Planck Institute). This system is now operating at five colonies and a paper on social networks was submitted for publication.
- Two MSc students joined the project to study the effects of cooperation and breeding group size on the survival of helpers (Louis Bliard, U. Montpellier) and on the interactive effects of climate and social factors on reproductive output (António Vieira, CIBIO, U. Porto).
- A strong drought, probably in combination with unusually high temperatures, prevented the normal breeding activity that should have started in September 2018, and therefore seriously affected our research effort, which is largely based around reproduction.
- A paper published by Rita Covas and Claire Doutrelant in Trends in Ecology and Evolution appeared online in December 2018.
- A paper by former MSc student Liliana Silva showing a cost of dominance for Sociable Weaver females was published in Animal Behaviour.
- Rita Covas gave a talk at the Oppenheimer De Beers Group Research Conference Conference in Johannesburg.
- PhD student Rita Fortuna presented her work at both the European Conference on Behavioural Biology in Liverpool, UK and at the Oppenheimer De Beers Group Research Conference in Johannesburg.
- Post-doc Pietro D’Amelio joined the project in Sept on a contract from U. Paris-Sud. Pietro has been awarded a Claude Leon fellowship through UCT from April 2019.
- MSc students Sandra Esteves and Inês Duarte graduated from CIBIO, U. Porto. Their projects focused on personality syndromes and the link between cooperation and dominance, respectively.
- Two new MSc students António Vieira (CIBIO, U. Porto) and Louis Bliard, (U. Montpellier) joined the project.
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 Fanny Rybak (U. Paris-Sud, France)
Dr Nora Carlson (CIBIO, U. Porto)
Dr Pietro D’Amelio (U. Paris-Sud, France)
Dr Damien Farine (Max Planck Institute, Germany
Students: André Ferreira (PhD, U. Montpellier); Rita Fortuna (PhD, U. Porto), Inês Duarte (MSc, CIBIO), Sandra Esteves (MSc, CIBIO), António Vieira (MSc, CIBIO), Louis Bliard (MSc, U. Montpellier)
Research Assistants: Franck Théron, Liliana Silva, Rita Leal, Ryan Olinger, Barbara Alonso, Corey Jeal, Cécile Vansteenberghe, Annick Lucas, Samuel Perret.