Dominance, social organisation and cooperation in the sociable weaver (Philetairus socius)

Includes bibliographical referencesSociality and cooperation are universal features of life, yet cooperative societies are highly vulnerable to conflicts-of-interests which may lead to societal collapse. Dominance may function as a central mechanism behind the maintenance of cooperative societies, because it may reduce conflict by the establishment of hierarchies, and may act in concert with kin selection, enforcement or signalling mechanisms to promote cooperation. Yet, the significance of dominance in the evolutionary routes that maintain cooperation remains poorly understood (Chapter 1). Sociable weavers Philetairus socius are highly social, cooperative passerines. The species is particularly prone to conflicts because of their year-round coloniality and thus year round sharing of resources. Using extensive field-data on individual behaviour, I examine in this thesis whether dominance may mitigate conflict and maintain cooperation, and how it may inform our understanding of the evolutionary mechanisms underlying cooperation. In Chapter2, I investigate whether hierarchies and phenotypic traits allowing the assessment of social status may have evolved to mediate conflicts. I show that weavers establish ordered hierarchies within colonies and that the size of a melanin-based plumage trait, the black bib, is correlated to social status. In Chapter 3, experimental manipulation supports my proposition of a status signalling function of the bib. In Chapter 4, I investigate the benefits of achieving high social status and whether these are shared with relatives through nepotism. Both dominants and their offspring gain enhanced access to resources. Dominants had more access to breeding positions, although this was not reflected by increased reproductive success. In Chapter 5, I explore how dominance and kinship predict individual cooperativeness to three tasks, nestling provisioning, nest construction and predator mobbing. I find that both explain variation in cooperativeness, yet some results follow opposite directions, revealing multiple routes to cooperation. Finally, in Chapter 6, I examine how dominance and kinship structure weavers' social network and whether network position are linked to cooperativeness. Social network analyses reveal that more central birds are more, related, dominant and cooperative. Chapter 7 concludes that dominance acts in concert with kinship to promote the societal lifestyle of sociable weavers highlighting the potential significance of dominance in the evolution of cooperation

Data from: Disruptive viability selection on a black plumage trait associated with dominance

Traits used in communication, such as colour signals, are expected to have positive consequences for reproductive success, but their associations with survival are little understood. Previous studies have mainly investigated linear relationships between signals and survival, but both hump-shaped and U-shaped relationships can also be predicted, depending on the main costs involved in trait expression. Furthermore, few studies have taken the plasticity of signals into account in viability selection analyses. The relationship between signal expression and survival is of particular interest in melanin-based traits, because their main costs are still debated. Here, we first determined the main factors explaining variability in a melanin-based trait linked to dominance: the bib size of a colonial bird, the sociable weaver Philetairus socius. We then used these analyses to obtain a measure representative of the individual mean expression of bib size. Finally, we used capture-recapture models to study how survival varied in relation to bib size. Variation in bib size was strongly affected by year and moderately affected by age, body condition and colony size. In addition, individuals bearing small and large bibs had higher survival than those with intermediate bibs, and this U-shaped relationship between survival and bib size appeared to be more pronounced in some years than others. These results constitute a rare example of disruptive viability selection, and point towards the potential importance of social costs incurred by the dominance signalling function of badges of status

Extreme and variable environmental temperatures are linked to reduction of social network cohesiveness in a highly social passerine

International audienceOrganisms living in hot, arid environments face important risks associated with hyperthermia and dehydration which are expected to become more severe with climate change. To mitigate these risks, individuals often modify behaviour, e.g. reducing activity and seeking shade. These behavioural modifications may affect interactions between individuals, with consequences for the social structure of groups. We tested whether the social structure of cooperative groups of sociable weavers (Philetairus socius) varied with environmental temperature. We recorded the nature and frequency of interactions at feeders positioned beneath three sociable weaver colonies (N = 49 identified birds) in the Kalahari Desert with respect to environmental temperatures over a 30‐day period. Using random forest models, we examined whether thermal conditions predicted variation in social network structure. We also conducted focal observations of individual weavers to assess functional links between temperature, intensity of heat dissipation behaviour (panting), and immediate effects on social behaviour. Our results suggest that the social structure of weaver colonies becomes less cohesive and more fragmented at extreme and variable environmental temperatures. These changes in network structure appear to be linked with individuals’ heat dissipation behaviour: extreme and variable temperatures were associated with increased panting, which was significantly correlated with an immediate reduction in the frequency of association. Collectively, our results indicate that interactions within groups could be disturbed by environmental temperature variation and extremes. Changing temperature regimes could therefore affect the functioning of animal societies by altering social networks

Data for variability analyses

This dataset contains all bib size measurements obtained from photographies taken at captures and recaptures events in the field (without any transformation). The dataset also contains covariates used to model bib size variation with mixed models: sex, year, colony size, age, body mass, tarsus length, colony identity and individual identity. The file format is "csv" which can be easily opened with EXCEL (or equivalent) and R for processing

Data for capture-recapture analyses

This dataset contains individual encounter histories (2002-2012) starting the year of first photography, with covariates: sex, raw bib size measurements and their squared values (taken the year of first photography), standardized bib size measurements and their squared values (taken the year of first photography, and standardized within this year), mean adjusted bib sizes and their squared values, and individual identities (band numbers). The file format is "headed" (i.e. containing explicit label for each column) with "txt" extension, which is compatible with E-SURGE and easily convertible with EXCEL (or equivalent) or R for any other use

Analyse des réseaux sociaux appliquée à l’éthologie et l’écologie -- 1

En entendant les termes «  réseaux sociaux  », vous penserez probablement à Facebook ou Twitter. Dans ce livre, ce terme est évidemment à comprendre autrement. Les animaux interagissent et communiquent notamment au sujet de la nourriture et de la reproduction. Dans un milieu écologique donné, les espèces tissent des liens de compétition, d’exclusion, de prédation, de coopération. La façon dont les espèces et les individus interagissent influence le réseau qu’ils forment, réseau plus ou moins dense, centralisé ou modulaire. L’analyse de tels réseaux sociaux est un puissant outil mobilisé en éthologie et en écologie pour étudier la structure des sociétés à toute échelle, de l’individu à la population, entre individus de la même espèce ou d’espèces différentes, entre écosystèmes. Différentes interactions, intragroupes, intergroupes ou même interespèces (entre proies et prédateurs, par exemple) peuvent être analysées avec les mêmes méthodes. Cette généralité d’application signifie que nous pouvons étudier comment le comportement d’un individu ou d’une espèce influence le réseau, mais que nous pouvons également déterminer l’influence du réseau et de ses propriétés sur la survie et la reproduction des individus constituant un groupe ou une population. Ce type de boucle de rétroaction est essentiel dans la compréhension de l’émergence et de la stabilité des systèmes sociaux et écologiques. Cependant, la combinatoire qui résulte de ces interactions peut alors devenir considérable, et de fait, inextricable sans les outils adéquats (informatique, simulation numérique, modélisation, théorie des graphes, étude des systèmes complexes, etc.) que ce livre expose. Outre la présentation des enjeux scientifiques et appliqués de ces méthodes et démarches, on y lit la vitalité des interactions et convergences disciplinaires entre écologues, éthologues, généticiens des populations, informaticiens, mathématiciens…info:eu-repo/semantics/published

Dominance hierarchies and associated signalling in a cooperative passerine

In animal societies, individuals face the dilemma of whether to cooperate or to compete over a shared resource. Two intertwined mechanisms may help to resolve this enduring evolutionary dilemma by preventing conflicts and thereby mediating the costs of living in groups: the establishment of dominance hierarchies and the use of ‘badge-of-status’ for signalling dominance. We investigated these two mechanisms in the sociable weaver (Philetairus socius), a colonial and social passerine which cooperates over multiple tasks. We examined the sociable weavers’ dominance structure in 2 years by recording 2563 agonistic interactions between 152 individuals observed at a feeder at eight colonies. We tested which individual traits, including sex, age, relatedness and two melanin-based plumage traits, predicted variation in social status. First, using social network analysis, we found that colonies were structured by strongly ordered hierarchies which were stable between years. Second, medium-ranked birds engaged more in aggressive interactions than highly ranking individuals, suggesting that competition over food is most pronounced among birds of intermediate social status. Third, we found that colony size and kinship influenced agonistic interactions, so aggression was less pronounced in smaller colonies and among relatives. Finally, within- and between-individual variation in social status and the presence of an individual at the feeder were associated with variation in bib size, as predicted by the badge-of-status hypothesis. These results suggest that dominance hierarchies and bib size mediate conflicts in sociable weaver societies