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.
When multiple individuals contribute to rearing the same offspring, conflict is expected to occur over the relative amounts invested by each carer. Existing models of biparental care suggest that ...this conflict should be resolved by partially compensating for changes by coinvestors, but this has yet to be explicitly modeled in cooperative breeders over a range of carer numbers. In addition, existing models of biparental and cooperative care ignore potential variation in both the relative costs of offspring production to mothers and in maternal allocation decisions. If mothers experience particularly high costs during offspring production, this might be expected to affect their investment strategies during later offspring care. Here, we show using a game-theoretical model that a range of investment tactics can result depending on the number of carers and the relative costs to the mother of the different stages within the breeding attempt. Additional carers result in no change in investment by individuals when production costs are low, as mothers can take advantage of the greater potential investment by increasing offspring number; however, this tactic ultimately results in a decrease in care delivered to each offspring. Conversely, when production costs prevent the mother from increasing offspring number, our model predicts that other individuals should partially compensate for additional carers and hence offspring should each receive a greater amount of care. Our results reinforce the importance of considering investment across all stages in a breeding attempt and provide some explanatory power for the variation in investment rules observed across cooperative 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.
In bi-parental care systems each parent shares benefits with its unrelated partner from the common investment in offspring, but pays an individual cost of providing that care, leading to sexual ...conflict. However, several recent empirical studies have shown that coordinating behaviours like synchronisation (e.g., arriving at similar times) and alternation (taking turns in providing care) at the nest lead to increased investment overall, presumably to reduce conflict through policing or synergistic benefits. Ecological conditions should impact the costs and benefits of bi-parental care, yet there exists a gap in research on the relationship between ecological conditions and patterns of parental care behaviour beyond visitation rate. Here we provide an examination of how bi-parental provisioning behaviours, i.e., pair feeding rate and feeding consistency, and the degree to which parents synchronise or take turns, differ under contrasting ecological conditions in populations of blue tits (Cyanistes caeruleus) spanning a 1,000 m altitudinal gradient. We found that blue tit pairs synchronised and alternated more than expected by chance, and that care patterns were modified by ecology. Pairs synchronised more in woodland-pasture edges than in woodland interiors, and alternated more and fed more frequently at lower altitude compared to higher altitude nests. Variation in bi-parental coordination behaviours did not have a significant impact on fledging success but more synchronous nests had heavier chicks in woodland habitats. Taken as a whole, our results show that patterns of care are influenced by ecological conditions and that their interplay may change the outcome of sexual conflict.
One of the primary functions of animal aggregations is defence against predators. Many social animals enjoy reduced predation risk as a result of grouping, and individuals within groups can benefit ...from information transferred by their group‐mates about a potential predator. We present evidence that a tactile interaction behaviour we term “nudging” substantially modified group responses to a potential threat in a highly social catfish, Corydoras aeneus. These catfish deployed nudges during flight responses, and these nudges were associated with a greater likelihood of group cohesion following a threat event. Increased nudging behaviour also resulted in longer flight responses, a potentially costly outcome in natural contexts. In addition, individuals that perceived the threat first were more likely to initiate nudges, implying that nudges could be used to alert group‐mates to the presence of a threat. Taken together, our results suggest that tactile communication plays an important role in mediating anti‐predator benefits from sociality in these fish.
In any system where multiple individuals jointly contribute to rearing offspring, conflict is expected to arise over the relative contributions of each carer. Existing theoretical work on the ...conflict over care has: (a) rarely considered the influence of tactical investment during offspring production on later contributions to offspring rearing; (b) concentrated mainly on biparental care, rather than cooperatively caring groups comprising both parents and helpers; and (c) typically ignored relatedness between carers as a potential influence on investment behavior. We use a gametheoretical approach to explore the effects of female production tactics and differing group relatedness structures on the expected rearing investment contributed by breeding females, breeding males, and helpers in cooperative groups. Our results suggest that the breeding female should pay higher costs overall when helpful helpers are present, as she produces additional offspring to take advantage of the available care. We find that helpers related to offspring through the breeding female rather than the breeding male should contribute less to care, and decrease their contribution as group size increases, because the female refrains from producing additional offspring to exploit them. Finally, within-group variation in helper relatedness also affects individual helper investment rules by inflating the differences between the contributions to care of dissimilar helpers. Our findings underline the importance of considering maternal investment decisions during offspring production to understand investment across the entire breeding attempt, and provide empirically testable predictions concerning the interplay between maternal, paternal and helper investment and how these are modified by different relatedness structures.
Sexual conflict is inescapable when two parents care for offspring, because providing care is personally costly, while the benefits of successful reproduction are shared. Previous models that treat ...parental investment as a continuous trait, with stable levels of effort negotiated between parents over evolutionary or behavioral time, generally predict that sexual conflict will lead to under-investment in the young, as each parent stands to gain by leaving its partner to bear a greater share of the costs of care. More recently, a model of parental investment as repeated discrete contributions suggested that a more efficient outcome can be reached through parents adopting a simple strategy of conditional cooperation by “turn-taking”: only investing after each contribution by their partner. However, while empirical work suggests that parental visits are significantly alternated in a number of natural systems, all examples thus far exhibit imperfect turn-taking rather than the strict rule predicted by theory. To help bridge this gap, we here present a more realistic mathematical model of parental turn-taking, incorporating (i) errors in parents' ability to monitor the contributions of their partner, (ii) time-dependent costs and benefits of delivering care, (iii) differences between partners in payoffs (and consequently in behavior), (iv) differences between partners in the accuracy with which they can monitor one another's behavior, and (v) shared costs of care. We illustrate how the degree of conditional cooperation is influenced by each of these factors, and discuss ways in which our model could be tested empirically.
Biotelemetry devices provide unprecedented insights into the spatial behaviour and ecology of many animals. Quantifying the potential effects of attaching such devices to animals is essential, but ...certain effects may appear only in specific or particularly stressful contexts. Here we analyse the effects of radio transmitter attachment on great tits Parus major tagged over three environmentally dissimilar years, as part of a project studying social‐ and communication networks. When we radio‐tagged birds before breeding, only those tagged in the coldest spring tended to be less likely to breed than control birds. Breeding probability was independent of relative transmitter weight (between 5 and 8% bodyweight). When we radio‐tagged both parents during nestling provisioning (transmitter weight between 6 and 8%), tagged parents were more likely than control parents to desert their brood in two out of three years, while in the other year no tagged parents deserted. Tagged parents provisioning larger broods were most likely to desert, especially during lower average temperatures. Video analyses did not reveal any transmitter effects on provisioning behaviour of parents in the year with no desertion. We conclude that radio tagging before breeding did not lead to negative effects, regardless of transmitter weight, but that decisions about radio‐tagging both parents during nestling provisioning need to be made with exceptional care, taking both environmental context and transmitter weight into account. Reporting results from long‐term radio‐tracking studies comprising several environmentally variable years is crucial to understand and predict potential transmitter effects and maximise the tremendous potential of biotelemetry.
Discussions about congressional earmarking often focus on their direct costs in the federal government's appropriations bills. This article shows that this conventional view neglects the ...administrative costs of earmarking by examining the extensive transaction and opportunity costs that come with the political, budgetary, and programmatic management of these earmarked projects in Congress and in the Office of Naval Research. One policy conclusion from this study is that the executive branch should make these costs transparent, as they remain largely hidden from public discussion and the consideration of the federal budget.
PDF
