Antagonistic effect of helpers on breeding male and female survival in a cooperatively breeding bird.

1. Cooperatively breeding species are typically long lived and hence, according to theory, are expected to maximize their lifetime reproductive success through maximizing survival. Under these circumstances, the presence of helpers could be used to lighten the effort of current reproduction for parents to achieve higher survival. 2. In addition, individuals of different sexes and ages may follow different strategies, but whether male and female breeders and individuals of different ages benefit differently from the presence of helpers has often been overlooked. Moreover, only one study that investigated the relationship between parental survival and the presence of helpers used capture-mark-recapture analyses (CMR). These methods are important since they allow us to account for the non-detection of individuals that are alive in the population but not detected, and thus, the effects on survival and recapture probability to be disentangled. 3. Here, we used multi-event CMR methods to investigate whether the number of helpers was associated with an increase in survival probability for male and female breeders of different ages in the sociable weaver Philetairus socius. In this species, both sexes reduce their feeding rate in the presence of helpers. We therefore predicted that the presence of helpers should increase the breeders' survival in both sexes, especially early in life when individuals potentially have more future breeding opportunities. In addition, sociable weaver females reduce their investment in eggs in the presence of helpers, so we predicted a stronger effect of helpers on female than male survival. 4. As expected we found that females had a higher survival probability when breeding with more helpers. Unexpectedly, however, male survival probability decreased with increasing number of helpers. This antagonistic effect diminished as the breeders grew older. 5. These results illustrate the complexity of fitness costs and benefits underlying cooperative behaviours and how these may vary with the individuals' sex and age. They also highlight the need for further studies on the sex-specific effects of helpers on survival.Our research has received funding from the DST-NRF Centre of Excellence at the Percy FitzPatrick Institute of African Ornithology (South Africa), FEDER (Operational Programme for Competitiveness Factors – COMPETE) and Portuguese Foundation for Science and Technology (FCT; PTDC/BIA-BEC/103818/2008), Project “Biodiversity, Ecology and Global Change” co-financed by North Portugal Regional Operational Programme 2007/2013 (ON.2), under the NSRF, ERDF. to RC, the region Languedoc Roussillon to CD, the Natural Environment Research Council (UK) to BJH, St John's College, Cambridge and the University of Cape Town to CNS , and the European programme Marie Curie-IRSES (FP7-PEOPLE-2012-IRSES; ‘Cooperation’ 318994). This research was conducted within the International Associate Laboratory LIA “Biodiversity and Evolution”.This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1111/1365-2656.12377 Data are available from Dryad digital repository http://dx.doi.org/10.5061/dryad.mk44

Fine-scale genetic structure reflects sex-specific dispersal strategies in a population of sociable weavers (Philetairus socius).

Dispersal is a critical driver of gene flow, with important consequences for population genetic structure, social interactions and other biological processes. Limited dispersal may result in kin-structured populations in which kin selection may operate, but it may also increase the risk of kin competition and inbreeding. Here, we use a combination of long-term field data and molecular genetics to examine dispersal patterns and their consequences for the population genetics of a highly social bird, the sociable weaver (Philetairus socius), which exhibits cooperation at various levels of sociality from nuclear family groups to its unique communal nests. Using 20 years of data, involving capture of 6508 birds and 3151 recaptures at 48 colonies, we found that both sexes exhibit philopatry and that any dispersal occurs over relatively short distances. Dispersal is female-biased, with females dispersing earlier, further, and to less closely related destination colonies than males. Genotyping data from 30 colonies showed that this pattern of dispersal is reflected by fine-scale genetic structure for both sexes, revealed by isolation by distance in terms of genetic relatedness and significant genetic variance among colonies. Both relationships were stronger among males than females. Crucially, significant relatedness extended beyond the level of the colony for both sexes. Such fine-scale population genetic structure may have played an important role in the evolution of cooperative behaviour in this species, but it may also result in a significant inbreeding risk, against which female-biased dispersal alone is unlikely to be an effective strategy.The authors' research received funding from the Natural Environment Research Council (NERC, UK; NE/G018588/1 and NE/K015257/1) to BJH, the DST-NRF Centre of Excellence at the Percy FitzPatrick Institute of African Ornithology and the Portuguese Science and Technology Foundation (FCT PTDC/BIA-BEC/103818/2008) to RC, the CNRS and region Languedoc Roussillon to CD, St John’s College, Cambridge, and the University of Cape Town to CNS, and the European MC-IRSES (FP7-PEOPLE-2012-IRSES; ‘Cooperation’ 318994) to RC, CD, REvD and BJH.This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1111/mec.1330

Mediating male-male interactions: the role of the UV-blue crest coloration in blue tits

This is the postprint version of the article. The published article can be located here: http://link.springer.com/article/10.1007/s00265-010-0995-z?nullBadges of status, usually color patches, are hypothesised to serve as important signals within natural populations by communicating individual’s fighting ability or aggressiveness before an interaction ever takes place. These signals, which may evolve via sexual and/or social selection, mediate intra-specific competition by influencing the outcome or escalation of contests between individuals. The last 10 years saw the rise of interest in the role of Ultraviolet (UV)-based coloration in intra-sexual communication. However, the rare experimental studies that tested this hypothesis found opposite results, which may originate from the different methodological procedures used to assess badge of status theory. We present here the results of an experiment testing whether male blue tits (Cyanistes caeruleus) respond differently to unfamiliar conspecifics presenting contrasted UV crest coloration. In an aviary, we simultaneously presented two caged blue tits with enhanced (UV+) or reduced (UV-) crest coloration to a focal bird. We found that focal males acted more aggressively towards the UV- males than UV+ males. In addition, focal males fed more often close to males that were similar in brightness or duller than themselves. We conclude that, in blue tits, UV-blue crest coloration affects both social and aggressive responses towards unfamiliar individuals, and thus it has some properties of a badge of status

Interaction des effets du comportement de signalisation, de la lumière ambiante et de la couleur du plumage chez un oiseau tempéré, la Mésange bleue Parus caeruleus

Individuals can increase their conspicuousness to conspecifics while minimizing their probability of detection by predators by choosing the time and location of their display. Conspicuousness arises from the contrast between the light reflected by the colour patches, and the light reflected by the visual background in ambient light used for displays. Conspicuousness also depends on the discrimination abilities of both conspecifics and predators. We investigated whether different light environments are present in temperate woodlands, and whether male Blue Tits use this variability to optimize intraspecific conspicuousness while reducing the probability of detection by predators. We measured refl ectance of plumage and visual backgrounds, irradiance of available light environments during the breeding period. We used measures of photoreceptor sensitivity of the Blue Tit Parus caeruleus and of a bird approaching that of its main predator the European sparrowhawk Accipiter nisus. We found different light environments in space and time (during the day and throughout the year) that birds could exploit and select for sexual signalling. The blue crown colour appears to be more conspicuous in early/late light environments but during the day it appears to be least conspicuous in woodland shade for both conspecifics and predators. Male Blue Tits, by displaying more intensively at dawn during the breeding period, would optimize intraspecifi c communication without minimizing detectability by predators. Inversely, by choosing to sing mainly in woodland shade during the day, male Blue Tits reduce the probability of visual detection by predators but also their visibility to conspecificsLes individus peuvent maximiser leur visibilité par rapport aux congénères tout en minimisant leur probabilité d'être détectés par leurs prédateurs en choisissant le moment et le lieu de leur comportement de signalisation. La visibilité d'un patron de couleur d'un individu est déterminée d'une part par le contraste entre la lumière reflétée par les différents signaux colorés du patron et la lumière reflétée par le fond visuel dans la lumière ambiante où est effectué le comportement de signalisation. Elle est déterminée d'autre part par la capacité de détection de ce contraste par les systèmes visuels des congénères et des prédateurs. Nous avons étudié tout d'abord si différents environnements lumineux peuvent se distinguer dans une forêt tempérée d'un parc urbain, et ensuite si les mâles de Mésange bleue utilisent cette variabilité pour optimiser leur visibilité intraspécifique tout en réduisant la probabilité de détection par les prédateurs. Nous avons mesuré la réflectance des différentes régions du plumage et des fonds visuels, l'irradiance des environnements lumineux disponibles pendant la période de reproduction, et nous avons utilisé les mesures de la sensibilité des photorécepteurs de la Mésange bleue Parus caeruleus et ceux d'un oiseau ayant un système visuel similaire à celui de son principal prédateur l'Epervier d'Europe Accipiter nisus. Nous avons trouvé des environnements lumineux différents dans le temps et dans l'espace (au cours d'une journée et au long de l'année) que les oiseaux pourraient exploiter et sélectionner pour la signalisation sexuelle. Nous avons trouvé que la couleur de la calotte paraît être plus visible dans l'environnement lumineux aube/crépuscule pour les congénères et prédateurs. Par ailleurs, cette couleur apparaît moins visible dans l'ombre de bois pendant le jour pour les congénères comme pour les prédateurs. Les mâles de Mésange bleue, en se signalant plus intensivement à l'aube durant la période de reproduction, optimiseraient la communication intraspécifique sans minimiser leur détectabilité par leurs prédateurs. Au contraire, en choisissant de chanter principalement dans l'ombre de la végétation au cours de la journée, les mâles de Mésange bleue réduisent la probabilité d'une détection visuelle par leurs prédateurs mais aussi leur visibilité aux congénères

Maternal effects in relation to helper presence in the cooperatively breeding sociable weaver

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

Begging and feeding responses vary with relatedness and sex of provisioners in a cooperative breeder

Begging behaviour can provide information on offspring hunger levels and be used by parents to adjust food provisioning efforts. In cooperative breeders, helpers also provide care by feeding the young. However, how helpers of different sex and relatedness to the offspring respond to begging behaviour has rarely been studied in cooperatively breeding species, which limits our understanding of the indirect and/or direct benefits that helpers may obtain by responding to offspring demand. Here, we used a cooperatively breeding bird, the sociable weaver, Philetairus socius, to investigate how nest intervisit intervals of breeders and different types of helpers, distinguished by sex and relatedness, varied with acoustic begging. Moreover, we tested whether these different classes of provisioners experienced distinct levels of begging. Our results show that only breeding males, but not breeding females or helpers of any sex and relatedness to the nestlings, returned faster to the nest to feed after experiencing more begging calls. When contrasted directly, we confirmed a statistically supported difference in responses to begging between male and female breeders. Surprisingly, second-order relatives experienced more begging calls than the other classes of more related helpers and breeders. These results show that we might find differences in how provisioners respond to begging levels when classifying group members according to their potential fitness gains. In sociable weavers, the benefits and costs of adjusting feeding efforts to begging seem to differ with sex and life history stage. Experimental and more detailed investigations on begging-feeding interactions are necessary to understand the origin and prevalence of these differences across cooperatively breeding systems. (c) 2021 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/)

Egg components and offspring survival vary with group size and laying order in a cooperative breeder

Prenatal resource allocation to offspring can be influenced by maternal environment and offspring value, and affect offspring survival. An important pathway for flexible maternal allocation is via egg components such as nutrients and hormones. In cooperative breeders, females with helpers may increase resource allocation to eggs-'differential allocation'-or reduce it-'load-lightening'. Yet, helper effects on egg composition have been poorly studied. Moreover, it is unknown how helpers' presence modulates laying order effects on egg content and survival. Here, we investigated how maternal allocation varied with group size and laying order in the cooperatively breeding sociable weaver (Philetairus socius). We estimated interactive effects of helpers and laying order on allocation to egg mass, yolk nutrients-yolk mass, proteins, lipids, carotenoids, vitamin A and vitamin E-and hormones-testosterone, androstenedione, and corticosterone. Results concurred with the 'differential allocation' predictions. Females with more helpers produced later-laid eggs with heavier yolks and more lipids, and laid eggs overall richer in lipids. Proteins, antioxidants, and hormones were not found to vary with helper number. We then analyzed how helper number modulated laying order effects on survival. Females with more helpers did not specifically produce later-laid eggs with higher survival, but eggs laid by females with more helpers were overall more likely to fledge. These findings show that some egg components (yolk mass, lipids) can positively vary according to females' breeding group size, which may improve offspring fitness

Variation in clutch size in relation to nest size in birds

Peer reviewe

Testing the sexual and social benefits of cooperation in animals

International audienc