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Towards an understanding of cooperation in an African passerine bird

Final Report Summary - COOPERATION (Towards an understanding of cooperation in an African passerine bird)

This project was built around three main objectives. First, we wanted to build a consortium of researchers with complementary skills and thereby share knowledge between the researchers in order to reinforce a long-term research programme into several interlinked aspects of the behaviour and population ecology of sociable weavers Philetairus socius, a passerine bird from southern Africa that is used as the study model. Second we wanted to use a multidisciplinary approach to investigate the costs and benefits of cooperation in the study species by integrating longitudinal field-based data, genetics and physiology, in order to obtain a thorough estimations of individual fitness. Third, we intended to integrate the specialist knowledge of the different partners and long-term data on the model species in order to study the dynamics of this population and determine the influence of different social and environmental variables on dispersal decisions, population genetic structure and long-term meta-population trends.
The project brought together a large team of 21 researchers and students that were involved in studying several costs and benefits of cooperation and how this impacts population dynamics. This was a field-based project and the specific topics that we investigated were: 1) how maternal investment interacts with helper presence to test the ‘cryptic helper effects’ hypothesis); 2) how social hierarchy, age and genetic relatedness relate to cooperative investment; 3) physiological costs of helping; 5) social, genetic and environmental factors associated with dispersal and population trends; and 6) initiated the study of whether direct benefits, such as sexually selected benefits, may favour cooperative behaviour. These specific objectives could only be achieved by bringing together researchers with diverse and complementary skills on diverse fields such as cooperation, population dynamics, population genetics, bioacoustics and animal physiology. We gathered a large team of researchers and students from four different countries (Portugal, France, UK and South Africa) that worked together in the field – conducting experiments and gathering long-term data – and interacted and exchanged competencies in the lab, during visits to the other group members or during the annual meetings of the project.
As a result, the project achieved several main outcomes. These have moved forward our understanding of the benefits and costs of cooperation and provided some first insights into the population-level consequences of sociality. First, we provided evidence in favour of ‘cryptic helper effects’ in this species. In many cooperatively breeding species, the presence of helpers has little or no effects on reproductive output. We showed that females breeding with helpers produce smaller eggs, which does not impact the fledging weight of these offspring (Paquet et al 2013). However, it appears that producing smaller eggs is beneficial for females as females, but not males, enjoy greater survival when they are assisted by helpers (Paquet et al 2015). This work was the bulk of a PhD thesis by French student M. Paquet.
Second, it has been shown in several species that cooperation is favoured among close relatives through kin-selection. But other mechanisms are less understood. We showed that social hierarchy is marked in this species (Rat et al 2014) and that social status and/or age interact with genetic relatedness to determine investment in cooperation (van Dijk et al 2014; Rat 2015). Simultaneously, and as expected, higher social status provides enhanced access to resources, including more helpers (Rat et al in review). This work was part of the PhD of Univ of Cape Town (UCT) student M. Rat and Univ Sheffield (US) post-doc R. van Dijk.
Third, we wanted to take further the study of how important are non-kin selected benefits (i.e. direct benefits such as sexually selected benefits, which may favour the evolution of cooperation). A new collaboration and post-doc project was initiated (A. Tognetti, Institute for the Advance Study of Toulouse) to specifically investigate this topic (the work is ongoing). Furthermore, R Covas and C Doutrelant obtained two important research grants to work on this topic from the Portuguese and French research agencies, respectively.
While helping and sociality are expected to be associated with benefits for helpers and receivers of help, the paradox of cooperation lies in that cooperation is expected to be costly and hence investigating the balance between costs and benefits is paramount; yet, this not often undertaken, largely because the costs of cooperation are often neglected as most studies focus on the benefits. We investigated the physiological costs of helping through a field experiment combined with correlative data and found that helping is indeed costly at both a short- and long-term scale. This work was conducted as part of a post-doc project by UCT student S. Lardy.
A good understanding of the fine scale genetic structure of groups and how genetic and social factors affect dispersal decisions is essential to understand whether and how social factors may affect population processes. We studied, the genetic structure dispersal decisions and population trends of our study population (Altwegg et al 2014, van Dijk et al 2015, Lloyd 2016, Lloyd et al in review). We found strong genetic structure among colonies of our study model and a dispersal mechanism that conformed with avoidance of inbreeding, social competition and demographic sinks. We also unveiled important effects of aridity and temperature extremes on population trends (Altwegg et al 2014, Altwegg et al in prep, Mares et al in review). This part of the work was mostly integrated in the work developed by SANBI and UCT researcher R. Altwegg, US post-doc R. van Dijk and UCT MSc student K. Lloyd.
Hence, the final results of this project are on three main levels. First, the project significantly contributed to the training of researchers, particularly young researchers that benefited from high quality training and learning of specific skills available in the consortium (9 MSc and four PhD theses were concluded during this project, another PhD is ongoing, 3 post-doc projects were concluded and another two are ongoing; there were also several other early stage researchers involved in internships). Second, the scientific work conducted significantly contributed to advance our understanding of sociality in this species and more generally produced insights to understand to the evolution of sociality and its population-level consequences. Finally, the large multi-disciplinary group that we were able to bring together and the dynamics created lead to a substantial consolidation of our research and a marked increase in productivity. So fa we have published 10 papers and another six are either submitted or will be submitted during 2017. We also attracted considerable media attention having featured in two television documentaries and articles in the press. This growth and consolidation allowed us to successfully attract further funding from the national organisations in all three European countries involved.