Browsing by Author "Doutrelant, Claire"

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    Dominance, social organisation and cooperation in the sociable weaver (Philetairus socius)
    (2015) Rat, Margaux Emilie Therese; Ryan, Peter G; Covas, Rita; Doutrelant, Claire; van Dijk, Rene E
    Sociality 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.
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    An experimental approach to assess the role of nest predation in the population dynamics of the sociable weaver (Philetairus socius)
    (2016) Lloyd, Kyle; Altwegg, Res; Covas, Rita; Doutrelant, Claire; Maciejewski, Kristi
    Predation is a widespread population process that has been shown to affect the distribution, abundance and dynamics of populations in ecosystems. This is the first study that used an experimental approach to assess the effect of nest predation on the population dynamics of the sociable weaver (Philetairus socius), a keystone species in the semi-arid savannas of the Kalahari and Namib regions. Snakes were excluded from five colonies for five breeding seasons and two colonies for three breeding seasons, with another eight colonies acting as the controls. Reproductive output, colony size, dispersal events and several environmental variables were measured between 2010 and 2015. This was done to determine (1) what effect nest predator exclusion had on reproductive output; (2) how this related to colony and population size trends by using a matrix-projection metapopulation model; (3) how protected colonies influence movement patterns; and (4) if nest predation had a compensatory or positive effect by reducing the intraspecific competition of a colony. The fourth aim was investigated by tracking the foraging paths of eight colonies of varying sizes, with foraging distance acting as a proxy for intraspecific competition. Colonies that were protected from snake predation produced, on average, more than double the number of fledglings per female per breeding season that were produced in unprotected colonies. However, the magnitude of this effect decreased with increasing colony size of protected colonies, most likely due to the negative effects that large colony sizes have on reproductive output. Increasing aridity was found to have a negative effect on reproductive output and warmer winter minimum temperatures were found to have a positive effect. My results suggested that protecting a subset of colonies in the metapopulation may be sufficient in preventing population declines under climate change conditions. The protected colonies played an important role in structuring and connecting the movement network of the metapopulation, whilst colony size explained the migration rates of colonies. However, predation was not found to have a compensatory effect in reducing the intraspecific competition (measured as foraging distance) of a colony. Instead, foraging distance was probably determined by the ability to thermoregulate under hot and humid conditions. To fully understand the effects of nest predation on sociable weaver population dynamics, future studies need to investigate the response of snake predators to sociable weaver behaviour and environmental conditions.
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    Maternal effects in relation to helper presence in the cooperatively breeding sociable weaver
    (Public Library of Science, 2013) Paquet, Matthieu; Covas, Rita; Chastel, Olivier; Parenteau, Charline; Doutrelant, Claire
    In egg laying species, breeding females may adjust the allocation of nutrients or other substances into eggs in order to maximise offspring or maternal fitness. Cooperatively breeding species offer a particularly interesting context in which to study maternal allocation because helpers create predictably improved conditions during offspring development. Some recent studies on cooperative species showed that females assisted by helpers produced smaller eggs, as the additional food brought by the helpers appeared to compensate for this reduction in egg size. However, it remains unclear how common this effect might be. Also currently unknown is whether females change egg composition when assisted by helpers. This effect is predicted by current maternal allocation theory, but has not been previously investigated. We studied egg mass and contents in sociable weavers ( Philetairus socius ). We found that egg mass decreased with group size, while fledgling mass did not vary, suggesting that helpers may compensate for the reduced investment in eggs. We found no differences in eggs’ carotenoid contents, but females assisted by helpers produced eggs with lower hormonal content, specifically testosterone, androstenedione (A4) and corticosterone levels. Taken together, these results suggest that the environment created by helpers can influence maternal allocation and potentially offspring phenotypes.