For individuals collaborating to rear offspring, effective organization of resource delivery is difficult because each carer benefits when the others provide a greater share of the total investment ...required. When investment is provided in discrete events, one possible solution is to adopt a turn-taking strategy whereby each individual reduces its contribution rate after investing, only increasing its rate again once another carer contributes. To test whether turn-taking occurs in a natural cooperative care system, here we use a continuous time Markov model to deduce the provisioning behavior of the chestnut-crowned babbler (Pomatostomus ruficeps), a cooperatively breeding Australian bird with variable number of carers. Our analysis suggests that turn-taking occurs across a range of group sizes (2-6), with individual birds being more likely to visit following other individuals than to make repeat visits. We show using a randomization test that some of this apparent turn-taking arises as a by-product of the distribution of individual inter-visit intervals ("passive" turn-taking) but that individuals also respond actively to the investment of others over and above this effect ("active" turn-taking). We conclude that turn-taking in babblers is a consequence of both their individual provisioning behavior and deliberate response rules, with the former effect arising through a minimum interval required to forage and travel to and from the nest. Our results reinforce the importance of considering fine-scale investment dynamics when studying parental care and suggest that behavioral rules such as turn-taking may be more common than previously thought.
Efficient host exploitation by parasites is frequently likely to depend on cooperative behaviour. Under these conditions, mixed-strain infections are predicted to show lower virulence (host ...mortality) than are single-clone infections, due to competition favouring non-contributing social 'cheats' whose presence will reduce within-host growth. We tested this hypothesis using the cooperative production of iron-scavenging siderophores by the pathogenic bacterium Pseudomonas aeruginosa in an insect host.
We found that infection by siderophore-producing bacteria (cooperators) results in more rapid host death than does infection by non-producers (cheats), and that mixtures of both result in intermediate levels of virulence. Within-host bacterial growth rates exhibited the same pattern. Crucially, cheats were more successful in mixed infections compared with single-clone infections, while the opposite was true of cooperators.
These data demonstrate that mixed clone infections can favour the evolution of social cheats, and thus decrease virulence when parasite growth is dependent on cooperative behaviours.
Cooperative breeding systems showcase the diversity of social trajectories within and among species, ranging from the extremes of eusocial insects where individuals become irreversibly specialized as ...fecund queens or sterile workers, to vertebrate systems where individuals maintain the flexibility to breed throughout life. Between these extremes lies a continuum with individuals exhibiting varying degrees of specialization in their behaviour. Most research on cooperative breeders, particularly on vertebrate systems, has focused on why helping has evolved, rather than addressing this diversity. Here, we present a framework to explain variation in the timing, extent and flexibility of phenotypic divergence across vertebrate and invertebrate cooperative systems. We base our framework on recent theory about how individuals integrate information about the environment from different sources (genes, parents and direct experiences) when establishing their developmental trajectory. We discuss how the timing and degree of divergence and specialization are influenced by the availability and reliability of information about later fitness options and by the extent to which individuals have control over their development. Throughout, we use this developmental perspective to draw broad comparisons across vertebrate and invertebrate systems, which are often considered separately.
•Cooperative systems showcase the diversity of specialization across species.•A developmental perspective using recent theory can shed light on this diversity.•Reliable early life information generates specialization and lack of sensitivity.•Developmental mode affects later life sensitivity to the environment.•Our perspective draws links across vertebrate and invertebrate cooperative systems.
Natal dispersal is an important life history trait driving variation in individual fitness, and therefore, a proper understanding of the factors underlying dispersal behaviour is critical to many ...fields including population dynamics, behavioural ecology and conservation biology. However, individual dispersal patterns remain difficult to quantify despite many years of research using direct and indirect methods. Here, we quantify dispersal in a single intensively studied population of the cooperatively breeding chestnut‐crowned babbler (Pomatostomus ruficeps) using genetic networks created from the combination of pairwise relatedness data and social networking methods and compare this to dispersal estimates from re‐sighting data. This novel approach not only identifies movements between social groups within our study sites but also provides an estimation of immigration rates of individuals originating outside the study site. Both genetic and re‐sighting data indicated that dispersal was strongly female biased, but the magnitude of dispersal estimates was much greater using genetic data. This suggests that many previous studies relying on mark–recapture data may have significantly underestimated dispersal. An analysis of spatial genetic structure within the sampled population also supports the idea that females are more dispersive, with females having no structure beyond the bounds of their own social group, while male genetic structure expands for 750 m from their social group. Although the genetic network approach we have used is an excellent tool for visualizing the social and genetic microstructure of social animals and identifying dispersers, our results also indicate the importance of applying them in parallel with behavioural and life history data.
In biparental systems, members of the same pair can vary substantially in the amount of parental care they provide to offspring. The extent of this asymmetry should depend on the relative costs and ...benefits of care. Individual variation in personality is likely to influence this trade-off, and hence is a promising candidate to explain differences in care. In addition, plasticity in parental care may also be associated with personality differences. Using exploration behaviour (EB) as a measure of personality, we investigated these possibilities using both natural and experimental data from a wild population of great tits (Parus major). Contrary to predictions, we found no association between EB and natural variation in provisioning behaviour. Nor was EB linked to responsiveness to experimentally increased brood demand. These results are initially surprising given substantial data from other studies suggesting personality should influence investment in parental care. However, they are consistent with a recent study showing selection on EB is weak and highly context-specific in the focal population. This emphasises the difficulty faced by personality studies attempting to make predictions based on previous work, given that personalities often vary among populations of the same species.
Lay Summary Just as a tenant is required to pay rent to a landlord, adult subordinates in animals are hypothesized to pay rent to dominants for being allowed to live on their territory. In this case, ...however, the currency is in food-to-nestlings. We found no evidence in chestnut-crowned babblers that individuals feeding nestlings attempt to signal their contributions to the dominant, as expected, and no evidence that they suffer retribution following experimental induction of defecting from helping.Alloparental care by distant/nonkin that accrue few kin-selected benefits requires direct fitness benefits to evolve. The pay-to-stay hypothesis, under which helpers contribute to alloparental care to avoid being expelled from the group by dominant individuals, offers one such explanation. Here, we investigated 2 key predictions derived from the pay-to-stay hypothesis using the chestnut-crowed babbler, Pomatostomus ruficeps, a cooperatively breeding bird where helping by distant/nonkin is common (18% of nonbreeding helpers). First, we found no indication that distant or nonkin male helpers advertised their contributions toward the primary male breeder. Helpers unrelated to both breeders were unresponsive to provisioning rates of the dominant male, whereas helpers that were related to either the breeding male or to both members of the pair were responsive. In addition, unrelated male helpers did not advertise their contributions to provisioning by disproportionately synchronizing their provisioning events with those of the primary male breeder or by provisioning nestlings immediately after him. Second, no helper, irrespective of its relatedness to the dominant breeders, received aggression when released back into the group following temporary removal for 1-2 days. We therefore find no compelling support for the hypothesis that pay-to-stay mechanisms account for the cooperative behavior of unrelated males in chestnut-crowned babblers.
1. Behavioural synchrony typically involves trade-offs. In the context of foraging, for example, synchrony may be suboptimal when individuals have different energy requirements but yield net benefits ...in terms of increased foraging success or decreased predation risk. 2. Behavioural synchrony may also be advantageous when individuals collaborate to achieve a common goal, such as raising young. For example, in several bird species, provisioners synchronize nest-feeding visits. However, despite the apparent prevalence of provisioning synchrony, it is not known whether it is adaptive or what its function might be. 3. Here, we propose a novel explanation for provisioning synchrony: it increases brood survival by decreasing the number of temporally separate nest visits and accordingly the chance that the nest will be detected by predators. Using cooperatively breeding pied babblers, we showed experimentally that provisioners synchronized nest visits by waiting for another provisioner before returning to the nest. Brood survival increased with provisioning synchrony. Provisioners were more likely to synchronize feeding visits for older nestlings as they were louder and possibly more conspicuous to predators. Finally, provisioners in large groups were more likely to wait for other provisioners and synchronized a higher proportion of all visits than those in smaller groups. Thus, provisioning synchrony may be one mechanism by which large groups increase brood survival in this species. 4. This study highlights a novel strategy that birds use to increase the survival of young and demonstrates the advantages of coordinated behaviour in social species.
The social network of preferences among group members can affect the distribution and consequences of collective behaviours. However, the behavioural contexts and taxa in which social network ...structure has been described are still limited because such studies require extensive data. Here, we highlight the use of an automated passive integrated transponder (PIT)-tag monitoring system for social network analyses and do so in a novel context—nestling provisioning in an avian cooperative breeder, for which direct observation of social behaviours is difficult. First, we used observers and cameras to arrive at a suitable metric of nest visit synchrony in the PIT-tag data. Second, we validated the use of this metric for social network analyses using internal nest video cameras. Third, we used hierarchical regression models with ‘sociality’ parameter to investigate structure of networks collected from multiple groups. Use of PIT tags led to nest visitation duration and frequency being obtained with a high degree of accuracy for all group members, except for the breeding female for whom accurate estimations required the use of a video camera due to her high variability in visitation time. The PIT-tag dataset uncovered significant variability in social network structure. Our results highlight the importance of combining complementary observation methods when conducting social network analyses of wild animals. Our methods can also be generalised to multiple contexts in social systems wherever repeated encounters with other individuals in closed space have ecological implications.
Humans are commonly concerned with social status, and often cooperate in the presence of others in an attempt to signal their potential as a social or reproductive partner. Whether or not cooperation ...might signal prestige in nonhuman animals is seldom tested and poorly understood. We investigated whether male chestnut-crowned babblers, Pomatostomus ruficeps, that are unrelated to the breeding female, and hence most likely to benefit from signalling their parenting ability to her, strategically adjust their actual or perceived contributions to nestling rearing. Male contributions to nestling rearing were unaffected by either their reproductive status (breeder versus nonbreeder) or, in the case of nonbreeding helpers, their relatedness to the breeding female (related versus unrelated). In addition, we found little support for the possibility that current breeders or unrelated helpers adjusted their nestling provisioning rates in the presence of actual or potential reproductive competition in the group, at least in a manner consistent with the social prestige hypothesis. Finally, we found no evidence to suggest that unrelated (breeding or nonbreeding) males attempted to increase the breeding female’s perception of their provisioning behaviour by timing their feeds to her presence. We conclude that, in chestnut-crowned babblers, patterns of male provisioning behaviour are not obviously consistent with advertising their parenting ability, and that social prestige is likely to have limited power in explaining male care in this system.
•In chestnut-crowned babblers of Australia, 1–10 males provision the same nestlings.•We tested if males try to advertise their parenting ability to the breeding female.•Patterns of offspring provisioning by males were not consistent with this hypothesis.•Potential partners neither provided more food nor coincided feeds with the female.•We thus found no evidence that male care in this system functions as a signal.
Recent theoretical and empirical work suggests that coordinating offspring provisioning plays a significant role in stabilizing cooperative care systems, with benefits to developing young. However, a ...warming and increasingly extreme climate might be expected to make contributions to, and so coordination of, care more challenging, particularly in cooperative breeding systems comprising multiple carers of varying age and pairwise relatedness. Here we investigated the interplay between breeding phenology, meteorological conditions and carer number on the individual rates and group-level coordination of nestling care in the cooperatively breeding chestnut-crowned babbler (Pomatostomus ruficeps) in outback south-eastern Australia. From 3 months since the last meaningful rain event, dominant male breeders and—to a lesser extent—related helpers showed reductions in their provisioning rates and increases in their day-to-day variation. Further, on days with high mean wind speed, dominant males contributed less and helpers were less likely to visit the nest on such days. Helpers also showed reduced visitation rates on days with high mean temperature. Provisioning rates were independent of the number of carers, and increasing numbers of carers failed to mitigate the detrimental effects of challenging environment on patterns of provisioning. Those helpers that were unrelated to broods often failed to help on a given day and tended to help at a low rate when they did contribute, with socio-environmental predictors having limited explanatory power. Given the marked variation in individual contributions to offspring care and the variable explanatory power of the socio-environmental predictors tested, babblers unsurprisingly had low levels of nest visitation synchrony. Large groups visited the nest more asynchronously on days of high mean temperature, suggesting that meteorological impacts on individual provisioning have consequences for group-level coordination. Our study has implications for the consequences of climate change on patterns of provisioning, the minimal role of group size in buffering against these challenges and the stabilization of cooperative care.
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