Cooperative Breeding Research Papers - Academia.edu (original) (raw)

Suppose that a large number of individuals are randomly matched into groups where each group plays a finite symmetric game. Individuals breed true according to their individual material payoffs, but the expected number of surviving... more

Suppose that a large number of individuals are randomly matched into groups where each group plays a finite symmetric game. Individuals breed true according to their individual material payoffs, but the expected number of surviving offspring may depend on the material payoff vector to the whole group. We show that the mean-field equation for the induced population dynamic is equivalent to the replicator dynamic for a game with payoffs derived from those in the original game. We apply this selection dynamic to a number of examples, including prisoners' dilemma games, coordination games, hawk-dove games, a prisoners' dilemma with a punishment option, and common-pool games. For each of these, we provide conditions under which our selection dynamic leads to other outcomes than those obtained under the usual replicator dynamic. By way of a revealedpreference argument, we show how our selection dynamic can explain certain stable behaviors that are consistent with individuals having social preferences.

As yet, cooperative breeding has been described only for some fish species. However, evidence is accumulating that it is widespread among Lake Tanganyika cichlids. We studied the cooperative breeding system of the substrate breeding... more

As yet, cooperative breeding has been described only for some fish species. However, evidence is accumulating that it is widespread among Lake Tanganyika cichlids. We studied the cooperative breeding system of the substrate breeding cichlid Neolamprologus savoryi. Breeding groups typically consisted of a large breeding male with one to four breeding females and three to 33 helpers (mean group size: 14.3 members). Group size was significantly related to breeding male and female body sizes, and larger males had more breeding females and larger sized male helpers. The size of the largest female in the group was positively related to the number and sizes of secondary breeding females and female helpers. In case of multiple breeding females, these females usually divided the group's territory into sub-territories, each with its own helpers (subgroups). Interspersed between groups, independent fish were detected defending an individual shelter (4.4% of all fish). In 9% of the groups no breeding female was present. All group members participated in territory defence and maintenance, and showed submissive behaviours to larger group members. As expected, the level of between-subgroup conflicts was high compared with the level of within-subgroup conflicts. We compare these results with data available from other cooperatively breeding fishes.

The queenless ant Pristomyrmex pungens has an unusual social structure, in which all workers reproduce parthenogenetically and help others. Laboratory experiments manipulating the proportion of post-reproductive foragers in the colony at... more

The queenless ant Pristomyrmex pungens has an unusual social structure, in which all workers reproduce parthenogenetically and help others. Laboratory experiments manipulating the proportion of post-reproductive foragers in the colony at various rates suggested that colonies with 5-10% forager ratios had the maximum efficiency per-worker. This result suggests that the cooperative colonies may be maintained by colony-level natural selection. Non-cooperative mutants that oviposit but do not forage should increase in relative frequency in the colony in the short term. However, decreased colony productivity and the resulting competition among colonies might eliminate colonies dominated by such mutants in the long term. P. pungens has a viscous population without migration between colonies, which may facilitate this process.

Social foraging strategies and their association with learning and innovation abilities have been studied extensively in flocking birds, but their importance for cooperatively breeding birds has remained relatively unexplored. The high... more

Social foraging strategies and their association with learning and innovation abilities have been studied extensively in flocking birds,
but their importance for cooperatively breeding birds has remained relatively unexplored. The high degree of sociality typical of cooperative
societies may indicate an important role of social foraging for learning and innovation. We studied 1) social foraging strategies
and 2) the acquisition of a novel foraging skill in 16 groups of wild, cooperatively breeding Arabian babblers (Turdoides squamiceps).
In Experiment 1, we provided a foraging grid of 96 feeding wells to each group, allowing them either to search for food individually
(producer) or to join other birds (scrounger). Subordinates scrounged significantly more than dominant individuals, spent longer on
the foraging grid, and had a higher proportion of their foraging steps rewarded (due to the effect of successful scrounging). However,
scrounging was not related to poor learning ability because almost all the individuals that learned the novel foraging skill in Experiment
2 (removing a rubber lid to reach food) were scroungers. These findings suggest that group members differ in their foraging strategies
and learning abilities according to their rank and that subordinate group members may be more opportunistic and flexible in their
behavior than dominants, making use of both scrounging and novel foraging opportunities.

Male reproductive cooperation is rare in nature: expectations from evolutionary theory suggest that males should be competitors for reproductive opportunities and provide little parental care. Counter to this expectation, in cooperatively... more

Male reproductive cooperation is rare in nature: expectations from evolutionary theory suggest that males should be competitors for reproductive opportunities and provide little parental care. Counter to this expectation, in cooperatively polyandrous mating systems, multiple adult males mate with a single breeding female and subsequently cooperate to rear her young. This raises the question of the fitness benefits of parental care, as males may be providing care to offspring that are not their own. Here, I use genetic and demographic data from a multiyear field study of Geoffroy’s tamarin, Saguinus geoffroyi, to test predictions of the indirect and direct fitness benefits hypotheses. I found that polyandrous males within a group were related at levels consistent with filial or fraternal relationships (r = 0.36–0.44) and could also share paternity (40% of groups had >2 male sires). Sharing of paternity occurred both within litters and over multiyear associations that remained stable throughout the study period of 2–3 years. However, remaining groups had a single sire, perhaps owing to the ability of males to prevail in sperm competition. These results suggest the joint role of indirect and direct fitness benefits in male–male cooperation in tamarins, in contrast to other cooperatively polyandrous species. The high average relatedness of polyandrous males may be consistent with fraternal cooperative polyandry in this species, as observed in certain human societies, providing a novel example that should enhance comparative studies of the evolution of male–male cooperation in reproduction.

Theory on the evolution of egalitarianism and its relevance to anthropology is described in three sections. The first section carefully defines and delimits usage of the term egalitarianism in anthropology, outlines the form of social... more

Theory on the evolution of egalitarianism and its relevance to anthropology is described in three sections. The first section carefully defines and delimits usage of the term egalitarianism in anthropology, outlines the form of social organization empirically observed in egalitarian societies, and clarifies the difference between egalitarian and acephalous societies. The second section describes multidisciplinary perspectives on the egalitarian disposition and behaviors found in humans, and how these contrast with those of nonhuman primates. Theories on how these behaviors and dispositions may have evolved are summarized. Finally, the roles of gender relations, sexual reproduction strategies, and cooperative breeding are mentioned in relation to the theory on the evolution of egalitarianism.

Cooperative breeding, in which individuals other than the parents assist in the production of young, occurs in around 9% of birds (Cockburn, 2006). It often arises when offspring remain on their parents' territory after gaining... more

Cooperative breeding, in which individuals other than the parents assist in the production of young, occurs in around 9% of birds (Cockburn, 2006). It often arises when offspring remain on their parents' territory after gaining nutritional independence and become "helpers at the nest," assisting in rearing subsequent broods (Ligon & Burt, 2004). This helping behavior presents several potential costs, for instance, helpers sometimes forgo their own reproduction in order to help-usually gaining indirect fitness (if helping kin) but at a cost to direct fitness (Dickinson & Hatchwell, 2004). Importantly, even if no immediate opportunities

Many models have been advanced to suggest how different expressions of sociality have evolved and are maintained. However these models ignore the function of groups for the particular species in question. Here we present a new perspective... more

Many models have been advanced to suggest how different expressions of sociality have evolved and are maintained. However these models ignore the function of groups for the particular species in question. Here we present a new perspective on sociality where the function of the group takes a central role. We argue that sociality may have primarily a reproductive, protective, or foraging function, depending on whether it enhances the reproductive, protective or foraging aspect of the animal's life (sociality may serve a mixture of these functions). Different functions can potentially cause the development of the same social behaviour. By identifying which function influences a particular social behaviour we can determine how that social behaviour will change with changing conditions, and which models are most pertinent. To test our approach we examined spider sociality, which has often been seen as the poor cousin to insect sociality. By using our approach we found that the group characteristics of eusocial insects is largely governed by the reproductive function of their groups, while the group characteristics of social spiders is largely governed by the foraging function of the group. This means that models relevant to insects may not be relevant to spiders. It also explains why eusocial insects have developed a strict caste system while spider societies are more egalitarian. We also used our approach to explain the differences between different types of spider groups. For example, differences in the characteristics of colonial and kleptoparasitic groups can be explained by differences in foraging methods, while differences between colonial and cooperative spiders can be explained by the role of the reproductive function in the formation of cooperative spider groups. Although the interactions within cooperative spider colonies are largely those of a foraging society, demographic traits and colony dynamics are strongly influenced by the reproductive function. We argue that functional explanations help to understand the social structure of spider groups and therefore the evolutionary potential for speciation in social spiders.

Cooperative child care among humans, where individuals other than the biological mother (allomothers) provide care, may increase a mother’s fertility and the survivorship of her children. Although the potential benefits to the mother are... more

Cooperative child care among humans, where individuals other than the biological mother (allomothers) provide care, may increase a mother’s fertility and the survivorship of her children. Although the potential benefits to the mother are clear, the motivations for allomothers to provide care are less clear. Here, we evaluate the kin selection allomothering hypothesis using observations on Hadza hunter-gatherers collected in ten camps over 17 months. Our results indicate that related allomothers spend the largest percentage of time holding children. The higher the degree of relatedness among kin, the more time they spend holding, supporting the hypothesis of nepotism as the strongest motivation for providing allomaternal care. Unrelated helpers of all ages also provide a substantial amount of investment, which may be motivated by learning to mother, reciprocity, or coercion.

The conundrum of why subordinate individuals assist dominants at the expense of their own direct reproduction has received much theoretical and empirical attention over the last 50 years. During this time, birds and mammals have taken... more

The conundrum of why subordinate individuals assist dominants at the expense of their own direct reproduction has received much theoretical and empirical attention over the last 50 years. During this time, birds and mammals have taken centre stage as model vertebrate systems for exploring why helpers help. However, fish have great potential for enhancing our understanding of the generality and adaptiveness of helping behaviour because of the ease with which they can be experimentally manipulated under controlled laboratory and field conditions. In particular, the freshwater African cichlid, Neolamprologus pulcher, has emerged as a promising model species for investigating the evolution of cooperative breeding, with 64 papers published on this species over the past 27 years. Here we clarify current knowledge pertaining to the costs and benefits of helping in N. pulcher by critically assessing the existing empirical evidence. We then provide a comprehensive examination of the evidence pertaining to four key hypotheses for why helpers might help:

Sociality in some birds, mammals, and social insects was suggested to have evolved through the lengthening and extension of parental care behaviors to nondirect descendents. In these systems, group members care for young cooperatively... more

Sociality in some birds, mammals, and social insects was suggested to have evolved through the lengthening and extension of parental care behaviors to nondirect descendents. In these systems, group members care for young cooperatively and, thus, increase the reproductive success of the breeders and fitness of the young. Parental care behaviors, such as regurgitation feeding and matriphagy (consumption of the mother), occur in several subsocial and social spiders. However, it is not known whether females in a colony cooperate in caring for the young of other females and whether such cooperative care improves reproductive success. To answer this question, we created experimental colonies of the social spider Stegodyphus dumicola (Araneae, Eresidae), allowing only one female in a group to produce young, simulating reproductive skew occurring in nests in nature. In this paper, we show for the first time that females of S. dumicola cooperate in providing regurgitated food for young of other females and are even eaten by those young. Young raised by a group of females were larger and had greater survival than young raised only by their mother. Thus, fitness benefits from raising broods cooperatively may have favored the evolution of sociality in spiders.

Many models have been advanced to suggest how different expressions of sociality have evolved and are maintained. However these models ignore the function of groups for the particular species in question. Here we present a new perspective... more

Many models have been advanced to suggest how different expressions of sociality have evolved and are maintained. However these models ignore the function of groups for the particular species in question. Here we present a new perspective on sociality where the function of the group takes a central role. We argue that sociality may have primarily a reproductive, protective, or foraging function, depending on whether it enhances the reproductive, protective or foraging aspect of the animal's life (sociality may serve a mixture of these functions). Different functions can potentially cause the development of the same social behaviour. By identifying which function influences a particular social behaviour we can determine how that social behaviour will change with changing conditions, and which models are most pertinent. To test our approach we examined spider sociality, which has often been seen as the poor cousin to insect sociality. By using our approach we found that the group characteristics of eusocial insects is largely governed by the reproductive function of their groups, while the group characteristics of social spiders is largely governed by the foraging function of the group. This means that models relevant to insects may not be relevant to spiders. It also explains why eusocial insects have developed a strict caste system while spider societies are more egalitarian. We also used our approach to explain the differences between different types of spider groups. For example, differences in the characteristics of colonial and kleptoparasitic groups can be explained by differences in foraging methods, while differences between colonial and cooperative spiders can be explained by the role of the reproductive function in the formation of cooperative spider groups. Although the interactions within cooperative spider colonies are largely those of a foraging society, demographic traits and colony dynamics are strongly influenced by the reproductive function. We argue that functional explanations help to understand the social structure of spider groups and therefore the evolutionary potential for speciation in social spiders.

We provide evidence for cooperative breeding in two endemic parrot species of New Caledonia, the New Caledonian Parakeet (Cyanoramphus saisseti) and the Horned Parakeet (Eunymphicus cornutus). We intensively monitored 11 breeding attempts... more

We provide evidence for cooperative breeding in two endemic parrot species of New Caledonia, the New Caledonian Parakeet (Cyanoramphus saisseti) and the Horned Parakeet (Eunymphicus cornutus). We intensively monitored 11 breeding attempts in two nests of New Caledonian Parakeets over 5 years, and noticed that two males of different size fed the female and the chicks in each nest. During one breeding attempt, the larger male guarded the female and the smaller male tried to copulate with her inside the nest. Genetic analyses showed that males shared paternity. During 17 breeding attempts in 11 Horned Parakeet nests, we observed two pairs sharing a nest on one occasion but we never saw feeding helpers.

Low birth rates in developed societies reflect women’s difficulties in combining work and motherhood. While demographic research has focused on the role of formal childcare in easing this dilemma, evolutionary theory points to the... more

Low birth rates in developed societies reflect women’s difficulties in combining work and motherhood. While demographic research has focused on the role of formal childcare in easing this dilemma, evolutionary theory points to the importance of kin. The cooperative breeding hypothesis states that the wider kin group has facilitated women’s reproduction during our evolutionary history. This mechanism has been demonstrated in pre-industrial societies, but there is no direct evidence of beneficial effects of kin’s support on parents’ reproduction in modern societies. Using three-generation longitudinal data anchored in a sample of grandparents aged 55 and over in 1992 in the Netherlands, we show that childcare support from grandparents increases the probability that parents have additional children in the next 8 to 10 years. Grandparental childcare provided to a nephew or niece of childless children did not significantly increase the probability that those children started a family. These results suggest that childcare support by grandparents can enhance their children’s reproductive success in modern societies and is an important factor in people’s fertility decisions, along with the availability of formal childcare.

Suppose that a large number of individuals are randomly matched into groups where each group plays a finite symmetric game. Individuals breed true according to their individual material payoffs, but the expected number of surviving... more

Suppose that a large number of individuals are randomly matched into groups where each group plays a finite symmetric game. Individuals breed true according to their individual material payoffs, but the expected number of surviving offspring may depend on the material payoff vector to the whole group. We show that the mean-field equation for the induced population dynamic is equivalent to the replicator dynamic for a game with payoffs derived from those in the original game. We apply this selection dynamic to a number of examples, including prisoners' dilemma games, coordination games, hawk-dove games, a prisoners' dilemma with a punishment option, and common-pool games. For each of these, we provide conditions under which our selection dynamic leads to other outcomes than those obtained under the usual replicator dynamic. By way of a revealedpreference argument, we show how our selection dynamic can explain certain stable behaviors that are consistent with individuals having social preferences.

Various hypotheses have been proposed to explain factors influencing male alloparental behavior in cooperatively breeding species. Mandarin voles (Microtus mandarinus) are ideal animal models to investigate these factors because they are... more

Various hypotheses have been proposed to explain factors influencing male alloparental behavior in cooperatively breeding species. Mandarin voles (Microtus mandarinus) are ideal animal models to investigate these factors because they are highly social rodents and display biparental care and spontaneous parental care when exposed to foster pups. Here we test the idea that the sexual and paternal experience of males influences alloparental behavior toward novel pups, and that these experiences alter the expression of neuropeptide oxytocin (OT) and estrogen receptor alpha (ER␣). Alloparental behavior and OT and ER␣ expression were compared between virgin males that had no prior sexual or reproductive experience, exposed males that with prior exposure to novel pups before the test, paired males that had been housed with a female, and new fathers having their first litter with a female. Our results show that prior exposure to novel pups and prior mating and paternal experience increased male alloparental behavior toward a novel pup. This experience also increased OT expression and affected the expression of ER␣. This study reveals important initiation factors for male alloparental behavior and suggests a relationship between alloparental behavior and central OT expression in males.

Alloparental care and feeding of young is often called "cooperative breeding" and humans are increasingly described as being a cooperative breeding species. To critically evaluate whether the human offspring care system is best... more

Alloparental care and feeding of young is often called "cooperative breeding" and humans are increasingly described as being a cooperative breeding species. To critically evaluate whether the human offspring care system is best grouped with that of other cooperative breeders. (1) Review of the human system of offspring care in the light of definitions of cooperative, communal and social breeding; (2) re-analysis of human lifetime reproductive effort. Human reproduction and offspring care are distinct from other species because alloparental behaviour is defined culturally rather than by genetic kinship alone. This system allows local flexibility in provisioning strategies and ensures that care and resources often flow between unrelated individuals. This review proposes the term "biocultural reproduction" to describe this unique human reproductive system. In a re-analysis of human life history data, it is estimated that the intense alloparenting typical of human so...

Of key importance for understanding cooperative societies is the way in which reproductive opportunities are distributed among group members. Traditionally, skew has been thought of as a product of intrasexual competition. However,... more

Of key importance for understanding cooperative societies is the way in which reproductive opportunities are distributed among group members. Traditionally, skew has been thought of as a product of intrasexual competition. However, cooperatively breeding species often live in mixed-sex groups, so the behaviour of one sex has the potential to influence skew in the other. We addressed the importance of inter- and intrasexual conflict in determining reproductive skew through a study of paternity sharing in the cooperatively breeding banded mongoose, Mungus mungo. Unlike banded mongoose females, where reproductive skew is low, males exhibited high skew, with 85% of paternities being assigned to the three oldest males in each group. Individual males appeared unable to monopolize reproduction because females come into oestrus in synchrony and mate multiply. Instead, older males increased their success by mate guarding the oldest, most fecund females. Our findings therefore highlight the importance of mate choice in males and reveal the behavioural differences between the sexes that generate reproductive skew. They also emphasize the considerable influence that female behaviour can have on male reproductive skew.

Evolutionary studies of human behavior have emphasized the importance of kin selection in explaining social institutions and fitness outcomes. Our relatives can nevertheless be competitors as well as sources of altruism. This is... more

Evolutionary studies of human behavior have emphasized the importance of kin selection in explaining social institutions and fitness outcomes. Our relatives can nevertheless be competitors as well as sources of altruism. This is particularly likely when there is local competition over resources, where conflict can lead to strife among nondispersing relatives, reducing or even negating the effects of relatedness on promoting altruism. Here, I present demographic data on a land-limited human population, utilizing large within-population variation in land ownership to determine the interactions between local resource competition and the benefits of kin in enhancing child survival, a key component of fitness in this population. As predicted, wealth affects the extent of kin altruism, in that paternal relatives (specifically father's brothers) appear to buffer young children from mortality much more effectively in rich than in poor households. This interaction effect is interpreted as evidence that the extent of nepotism among humans depends critically on resource availability. Further unanticipated evidence that maternal kin play a role in buffering children from mortality in situations where paternal kin control few resources speaks to the important role that specific local circumstance plays in shaping kin contributions to child welfare.

1. Dispersal is a key process governing the dynamics of socially and spatially struc-tured populations and involves three distinct stages: emigration, transience and settlement. At each stage, individuals have to make movement decisions,... more

1. Dispersal is a key process governing the dynamics of socially and spatially struc-tured populations and involves three distinct stages: emigration, transience and settlement. At each stage, individuals have to make movement decisions, which are influenced by social, environmental and individual factors. Yet, a comprehensive understanding of the drivers that influence such decisions is still lacking, particularly for the transient stage during which free-living individuals are inherently difficult to follow. 2. Social circumstances such as the likelihood of encountering conspecifics can be expected to strongly affects decision-making during dispersal, particularly in territorial species where encounters with resident conspecifics are antagonistic. Here, we analysed the movement trajectories of 47 dispersing coalitions of Kalahari meerkats Suricata suricatta through a landscape occupied by constantly monitored resident groups, while simultaneously taking into account environmental and individual characteristics. 3. We used GPS locations collected on resident groups to create a georeferenced social landscape representing the likelihood of encountering resident groups. We used a step-selection function to infer the effect of social, environmental and individual covariates on habitat selection during dispersal. Finally, we created a temporal mismatch between the social landscape and the dispersal event of interest to identify the temporal scale at which dispersers perceive the social landscape. 4. Including information about the social landscape considerably improved our representation of the dispersal trajectory compared to analyses that only accounted for environmental variables. The latter were only marginally selected or avoided by dispersers. Before leaving their natal territory, dispersers selected areas frequently used by their natal group. In contrast, after leaving their natal territory, they selectively used areas where they were less likely to encounter unrelated groups. This pattern was particularly marked in larger dispersing coalitions and when unrelated males were part of the dispersing coalition. 5. Our results suggest that, in socially and spatially structured species, dispersers gather and process social information during dispersal, and that reducing risk of aggression from unrelated resident groups outweighs benefits derived from con-specific attraction. Finally, our work underlines the intimate link between the social structure of a population and dispersal, which affect each other reciprocally.

Dispersal is a fundamental process influencing evolution, social behaviour, and the long-term persistence of populations. We use both observational and genetic data to investigate dispersal, kin-clustering and intergroup relatedness in... more

Dispersal is a fundamental process influencing evolution, social behaviour, and the long-term persistence of populations. We use both observational and genetic data to investigate dispersal, kin-clustering and intergroup relatedness in the white-breasted thrasher, Ramphocinclus brachyurus , a cooperatively breeding bird that is globally endangered. Mark-resighting data suggested sex-biased dispersal, with females dispersing over greater distances while males remained philopatric. Accordingly, spatial autocorrelation analysis showed highly significant fine-scale genetic structure among males, but not among females. This fine-scale genetic structuring of the male population resulted in very high levels of relatedness between dominant males at neighbouring nests, similar to that seen within cooperative groups in many species where kin selection is cited as a cause of cooperation. By implication, between-group as well as within-group cooperation may be important, potentially creating a feedback loop in which short-distance dispersal by males leads to the formation of male kin clusters that in turn facilitate nepotistic interactions and favour further local recruitment. The strength of spatial autocorrelation, as measured by the autocorrelation coefficient, r , was approximately two to three times greater than that reported in previous studies of animals. Relatively short dispersal distances by both males and females may have a negative impact on the white-breasted thrasher's ability to colonize new areas, and may influence the long-term persistence of isolated populations. This should be taken into account when designating protected areas or selecting sites for habitat restoration.

Understanding the ultimate and proximate mechanisms that favour cooperation remains one of the greatest challenges in the biological and social sciences. A number of theoretical studies have suggested that competition between groups may... more

Understanding the ultimate and proximate mechanisms that favour cooperation remains one of the greatest challenges in the biological and social sciences. A number of theoretical studies have suggested that competition between groups may have played a key role in the evolution of cooperation within human societies, and similar ideas have been discussed for other organisms, especially cooperative breeding vertebrates. However, there is a relative lack of empirical work testing these ideas. Our experiment found, in public goods games with humans, that when groups competed with other groups for financial rewards, individuals made larger contributions within their own groups. In such situations, participants were more likely to regard their group mates as collaborators rather than competitors. Variation in contribution among individuals, either with or without intergroup competition, was positively correlated with individuals' propensity to regard group mates as collaborators. We found that the levels of both guilt and anger individuals experienced were a function of their own contributions and those of their group mates. Overall, our results are consistent with the idea that the level of cooperation can be influenced by proximate emotions, which vary with the degree of intergroup competition.

Cooperative breeding societies are defined by the presence of helpers. Defining helping behavior in cooperatively breeding mammals has been difficult because lactation limits the ability of individuals to provision non-genetic young. As a... more

Cooperative breeding societies are defined by the presence of helpers. Defining helping behavior in cooperatively breeding mammals has been difficult because lactation limits the ability of individuals to provision non-genetic young. As a consequence, ''helping'' behavior has frequently included predator and conspecific defense and thermoregulation. However, these behaviors are often associated with the benefits of group living and their expression may not warrant a species' classification as a cooperative breeder (e.g., many ungulates and pinnipeds). In this study, we examine cooperative breeding behavior in the common warthog, Phacochoerus africanus. Warthogs exhibit substantial variation in breeding strategies and females will raise their young alone or in association with other females. The size of warthog groups varies throughout the year and we investigate fission and fusion of individual breeding groups to elucidate the costs and benefits of adopting different reproductive strategies. We found that the cohesion of female groups was related to parturition suggesting that there are benefits to sociality that are related to the production and care of offspring. Additionally, we found that reproductively-aged group members will help other group members by both babysitting and adopting the group's offspring indicating active selection for cooperation. We did not witness any incidences of yearling group members exhibiting these behaviors indicating differential trade-offs to cooperation possibly related to the helper's age/experience.

Kin recognition is a critical element to kin cooperation, and in vertebrates, it is primarily based on associative learning. Recognition of socially unfamiliar kin occurs rarely, and it is reported only in vertebrate species where... more

Kin recognition is a critical element to kin cooperation, and in vertebrates, it is primarily based on associative learning. Recognition of socially unfamiliar kin occurs rarely, and it is reported only in vertebrate species where promiscuity prevents recognition of first-order relatives. However, it is unknown whether the recognition of socially unfamiliar kin can evolve in monogamous species. Here, we investigate whether genetic relatedness modulates aggression among group members in Siberian jays (Perisoreus infaustus). This bird species is genetically and socially monogamous and lives in groups that are formed through the retention of offspring beyond independence, and the immigration of socially unfamiliar nonbreeders. Observations on feeders showed that genetic relatedness modulated aggression of breeders towards immigrants in a graded manner, in that they chased most intensely the immigrant group members that were genetically the least related. However, cross-fostering experiments showed that breeders were equally tolerant towards their own and cross-fostered young swapped as nestlings. Thus, breeders seem to use different mechanisms to recognize socially unfamiliar individuals and own offspring. As Siberian jays show a high degree of nepotism during foraging and predator encounters, inclusive fitness benefits may play a role for the evolution of fine-scale kin recognition. More generally, our results suggest that fine-graded kin recognition can evolve independently of social familiarity, highlighting the evolutionary importance of kin recognition for social species.

While birdsong is a model system for animal communication studies, our knowledge is derived primarily from the study of only one sex and is therefore incomplete. The study of song in a role-reversed species would provide a unique... more

While birdsong is a model system for animal communication studies, our knowledge is derived primarily from the study of only one sex and is therefore incomplete. The study of song in a role-reversed species would provide a unique opportunity to study selective pressures and mechanisms specific to females, and to test the robustness of current theories in an empirically novel manner. We investigated function of female song in stripe-headed sparrows (Aimophila r. ruficauda), a Neotropical, duetting passerine, and found that during simulated territorial intrusions by a female, male or duetting pair, females: (i) sang more than males to same-sex and duet playback, (ii) played a leading singing role in all contexts, and (iii) showed a longer term song response than males. These results suggest that females sing competitively against other females, and that intrasexual selection may be greater among females than among males. This is the first songbird study to show a stronger vocal role in territory defence for females than males. Stripe-headed sparrows are group-living cooperative breeders, and preliminary data suggest that polyandry and/or resource defence may explain strong female singing behaviour. Stripe-headed sparrows may be a useful study species for expanding our knowledge of vocal communication in female animals.

In group-living carnivores, cooperative hunting may be a cause or a consequence of cooperative breeding. Harris’s Hawk (Parabuteo unicinctus), a raptor that hunts and nests in cooperative groups of 3 to 7 hawks (Mader 1975a, b; Bednarz... more

In group-living carnivores, cooperative hunting may be a cause or a consequence of cooperative breeding. Harris’s Hawk (Parabuteo unicinctus), a raptor that hunts and nests in cooperative groups of 3 to 7 hawks (Mader 1975a, b; Bednarz 1987; Dawson and Mannan 1989), provides an opportunity to examine benefits and possible causes of sociality because its cooperation is facultative and the species is relatively well studied. Attempts to demonstrate factors that promoted the evolution of cooperative breeding in Harris’s Hawks have mostly been unsuccessful. For example, the reproductive performance of groups did not differ from that of pairs (Mader 1975b, Bednarz 1987). And, for the most part, researchers did not find differences in the habitat quality or the resources available in territories occupied by groups versus pairs (Bednarz and Ligon 1988, Dawson and Mannan 1991b). How- ever, Bednarz (1988) demonstrated net energetic benefits for hunting parties of 5 or 6 hawks and proposed that cooperative hunting led to social living in Harris’s Hawk. Here, we support and extend this argument with a reinterpretation of data from the published literature, including an overlooked finding of significance. We hypothesize that one benefit of cooperative hunting is to increase success in habitats that make the prey difficult to catch (e.g., a high density of hiding places). We think that this benefit could be as important as capturing and overwhelming large prey, a benefit proposed by Bednarz (1988). We propose the “challenging habitats hypothesis” (CHH), similar to an idea proposed by Dawson (1988), as an additional or alternative explanation for the maintenance and, possibly, the evolution of cooperative hunting in Harris’s Hawk. As falconers, we developed this hypothesis after many years of hunting with single and cooperative groups of 2 to 8 Harris’s Hawks in a variety of habitats. We hope to rekindle scientific inquiry into cooperation in this species.

In this study, we investigated patterns of natural covariation between testosterone and reproductive status in a cooperatively breeding bird species, the azurewinged magpie (Cyanopica cyanus). To assess the relationship between... more

In this study, we investigated patterns of natural covariation between testosterone and reproductive status in a cooperatively breeding bird species, the azurewinged magpie (Cyanopica cyanus). To assess the relationship between testosterone and breeding behavior, we also manipulated testosterone (T) levels early in the season (before breeding started) using testosterone-filled or empty implants. Our results do not support the hypothesis that circulating testosterone levels affect the occurrence of helping behavior in the azure-winged magpie. Helping males had similar T levels to breeding males. Furthermore, experimentally augmented plasma T did not affect the likelihood of becoming either a helper or a breeder. Overall, these results are consistent with previous findings in other bird species and only give some support to the behavioral suppression hypothesis, suggesting that helping in the azure-winged magpie is a flexible behavioral option moderated in the short-term by social and ecological factors. Experimentally elevated testosterone levels, however, reduced the reproductive success of male breeders because of markedly lower levels of paternal care, had similar effects on their mates, but had the contrary effect on helpers, which raised levels of parental effort. We suggest increases in the share of paternity and in social prestige as possible explanations for these results.

This study examined the reproductive status of mothers and daughters to determine if parent-eldest daughter interactions would influence the daughter's fertility in the cooperatively breeding common marmoset, Callithrix jacchus. Twice... more

This study examined the reproductive status of mothers and daughters to determine if parent-eldest daughter interactions would influence the daughter's fertility in the cooperatively breeding common marmoset, Callithrix jacchus. Twice weekly fecal samples were collected for hormonal analyses from seven daughters and their mothers and analyzed for cortisol, estradiol, and progesterone by EIA. Behavioral data were collected three times weekly while the daughters were under three conditions: natal family, after removing from the family and paring with a novel male, and after removing from the paired condition and placed back with the family (renatal). Under the natal condition, five of the seven daughters exhibited ovarian cycles while their mother was pregnant or displaying ovarian cycling. The five cycling daughters spent significantly more time initiating affilative behaviors with their mothers than with their fathers and showed significant changes in their behavior over the length of the ovarian cycle. However, aggression, submission, and sexual behaviors were very low for daughters in the natal phase. No differences between cortisol levels were found for a daughter and her mother. Cortisol levels showed a significant and sustained increase upon pairing within the first 20 days. All females but one cycled while paired. Six of the seven females were accepted back into the family after pairing and five of the seven females were ovulating. These results suggest that marmoset daughters are not necessarily reproductively suppressed while living with the family. Additionally, these data suggest that female marmosets that leave their family to explore mating opportunities with other groups may return to their family without repro-ductive or aggressive consequences. © 2002 Elsevier Science (USA)

Resumen. Estudiamos la biología reproductiva de Leptopoecile sophiae en la zona alpina del sur de Tíbet, entre los 4110 m y los 4780 m de elevación. Esta especie es la que comienza a criar más temprano entre los paserinos, iniciando la... more

Resumen. Estudiamos la biología reproductiva de Leptopoecile sophiae en la zona alpina del sur de Tíbet, entre los 4110 m y los 4780 m de elevación. Esta especie es la que comienza a criar más temprano entre los paserinos, iniciando la puesta de huevos a principios de abril y terminando a fines de junio. Localizamos sus nidos con forma de cúpula sobre 13 especies de arbustos a una altura promedio de 0.9 m (rango 0.2-2.5 m) por encima del suelo. El tamaño de la puesta promedió 4.7 (rango 4-6) huevos, disminuyendo a lo largo de la estación. El tamaño de la nidada fue 4.3 (rango 2-6) al momento de la eclosión y 3.8 (rango 1-5) al momento de emplumamiento. La incubación duró 20.5 (rango BREEDINg BIOLOgy Of ThE WhITE-BROWED TIT-WARBLER (LepTopoeCiLe Sophiae) IN ALPINE ShRUBS, SOUThERN TIBET Biología Reproductiva de Leptopoecile sophiae en Arbustos Alpinos del Sur de Tíbet abstract. We studied the breeding ecology of the Whitebrowed Tit-Warbler (Leptopoecile sophiae) in the alpine zone of southern Tibet, elevations 4110-4780 m. The earliest breeder among local passerines, the species initiated egg-laying in early April and ended by late July. We located its domed nests in 13 species of shrubs at an average height of 0.9 m (range 0.2-2.5 m) above the ground. Clutch size averaged 4.7 (range 4-6) eggs, declining through the season. Brood size was 4.3 (range 2-6) at hatching and 3.8 (range 1-5) at fledging. Incubation lasted 20.5 (range 16-23) days, and nestlings fledged at 17.5 (range 14-21) days of age, when they were 4% above the adult weight. Of the nests we observed 66% fledged at least one young. Most pairs were monogamous, and both sexes shared all nesting duties. We noted two females attending a single nest, with a brood of normal size, and egg dumping by an additional female. At the population level, the sex ratio of offspring, determined by sexual differences in plumage of nestlings older than 6 days, did not deviate from equality. Birds breeding late in the season, however, tended to raise more females.

We examined the influence of helpers on reproductive success in the apostlebird using data gathered over three breeding seasons (116 nests, 34 breeding groups). Initially, annual productivity and individual components of reproductive... more

We examined the influence of helpers on reproductive success in the apostlebird using data gathered over three breeding seasons (116 nests, 34 breeding groups). Initially, annual productivity and individual components of reproductive success were examined in relation to group size (two to 17 birds). The effect of helping per se was then examined in a reduced data set by comparing (a) the predictive power of group size and actual helper numbers, and/or (b) the productivity of groups that changed in size between nests or seasons. 2. Group size was positively and linearly related to annual fledgling production and the number of offspring that survived to the following season. This was attributed to the presence of helpers, as the number of birds that fed nestlings, but not group size, was significantly related to annual fledging success. Neither group size nor helper number influenced fledgling survival over the subsequent winter. 3. The probability of re-nesting after a successful first brood increased with group size. Among double-brooded groups, the interval between nests was inversely related to group size. 4. Clutch size increased linearly with group size among groups with two to five birds, but was not related to group size among larger groups. A matched comparison of groups that changed size between years further suggests that clutch size was facultatively adjusted to group size, a phenomenon rarely reported in species with non-breeding helpers. 5. Hatching success was not related to group size or the number of birds participating in incubation. 6. The number of birds provisioning the brood was a better predictor of feeding rate per chick than group size, and was significantly and inversely related to the incidence of nestling starvation. However, there was no relationship between group size and fledgling body mass. 7. Fledging success per brood increased linearly among groups with three to five members. The only case of pair-breeding was unsuccessful, suggesting that this species is one of only a few birds that may be obligately cooperative. 8. We found no evidence that helpers influenced the likelihood of nest predation, or the probability of group members surviving to the following season.

Investment strategies in cooperative societies are often complex but should reflect individual variation in the costs and benefits of providing care. We examined the contributions to incubation and nestling provisioning by individual... more

Investment strategies in cooperative societies are often complex but should reflect individual variation in the costs and benefits of providing care. We examined the contributions to incubation and nestling provisioning by individual members of 16 groups of the cooperatively breeding apostlebird, Struthidea cinerea. Contributions varied in relation to the age, sex and breeding status of the carer, and with group size. Yearlings were less likely to help than older birds, and, when they did, spent less time incubating and fed the brood less often. Among adults (!2 years old), male helpers incubated less than breeders or female helpers. Mothers spent more time incubating than female helpers, and both incubated less when in larger groups. Mean incubation effort did not differ between fathers and male helpers, or between the sexes. Neither paternal nor male helper incubation effort was related to group size. There was no difference between adult categories in the likelihood of brood provisioning. However, male helpers provisioned at a higher rate than both female helpers and breeders. Overall, individual provisioning rates were lower in larger groups, although feeding rate per nestling increased, indicating partial adjustment to the increase in available help. Mothers and female helpers, and to some extent fathers, provisioned less when in larger groups. Because indirect benefits accruing to the sexes are expected to be similar, these observations suggest that brood provisioning may confer greater direct benefits to males than females.

In cooperatively breeding birds, breeders can adjust their parental care investment without affecting nestling survival probability and save energy to invest in other activities, such as feeding, mating or territory defense. Furthermore,... more

In cooperatively breeding birds, breeders can adjust their parental care investment without affecting nestling survival probability and save energy to invest in other activities, such as feeding, mating or territory defense. Furthermore, helpers at the nest can improve nestling nutrition and hence the reproductive performance of the breeding pair. We determined the influence of helpers on nestling feeding effort and reproductive success of breeders in the neotropical White-banded Tanager (Neothraupis fasciata). We monitored nests during the breeding seasons of 2006 and 2007 in central Brazil. Males showed a compensatory reduction of their food delivery rate in the presence of helpers, whereas females exhibited the same parental effort regardless of having helpers. Total food delivery rate was higher for nests with helpers, but there was no effect of helpers on reproductive performance of breeders (clutch size, hatching rate, fledgling productivity and reproductive success). Our results indicate that cooperative breeding in the White-banded Tanager appears to be important for males to reduce their parental care effort and, hence, invest in their survival or future reproductive attempts. Bei kooperativ brütenden Vögeln können Brüter ihren Brutpflegeaufwand anpassen, ohne dass dies die Überlebenswahrscheinlichkeit der Nestlinge beeinträchtigt, und Energie sparen, die dann in andere Aktivitäten, wie Nahrungsaufnahme, Paarung oder Revierverteidigung, investiert werden kann. Außerdem können Helfer am Nest die Ernährung der Nestlinge und somit die Fortpflanzungsleistung des Brutpaares verbessern. Wir haben ermittelt, wie sich Helfer auf den Nestlings-Fütterungsaufwand und den Fortpflanzungserfolg von brütenden neotropischen Flügelbindentangaren (Neothraupis fasciata) auswirken. Wir haben Nester während der Brutsaisons 2006 und 2007 in Zentralbrasilien überwacht. Männchen zeigten eine kompensatorische Reduktion ihrer Fütterungsrate in Anwesenheit von Helfern, während Weibchen denselben Elternaufwand zeigten, unabhängig davon, ob sie Helfer hatten oder nicht. Die Gesamtfütterungsrate war für Nester mit Helfern höher, doch Helfer hatten keinen Einfluss auf die Fortpflanzungsleistung von Brütern (Gelegegröße, Schlupfrate, Flügglingsproduktion und Fortpflanzungserfolg). Unsere Ergebnisse deuten darauf hin, dass kooperatives Brüten bei Flügelbindentangaren für Männchen wichtig zu sein scheint, um ihren Brutpflegeaufwand zu reduzieren und folglich in ihr Überleben oder weitere Fortpflanzungsversuche zu investieren.

The molecular mechanisms underlying complex social behaviours such as dominance are largely unknown. Studying the cooperatively breeding African cichlid Neolamprologus pulcher , we show that dominant females were similar to dominant males... more

The molecular mechanisms underlying complex social behaviours such as dominance are largely unknown. Studying the cooperatively breeding African cichlid Neolamprologus pulcher , we show that dominant females were similar to dominant males in dominance behaviour, high testosterone levels and brain arginine vasotocin expression (a neuropeptide involved in vertebrate territorial, reproductive and social behaviours) compared to subordinate helpers, but had lower levels of 11-ketotestosterone than males. Furthermore, brain gene expression profiles of dominant females were most similar to those of the males (independent of social rank). Dominant breeder females are masculinized at the molecular and hormonal level while being at the same time reproductively competent, suggesting a modular organization of molecular and endocrine functions, allowing for sex-specific regulation.

In approximately 3.2% of bird species individuals regularly forgo the opportunity to breed independently and instead breed cooperatively with other conspeci¢cs, either as non-reproductive`helpers' or as co-breeders. The traditional... more

In approximately 3.2% of bird species individuals regularly forgo the opportunity to breed independently and instead breed cooperatively with other conspeci¢cs, either as non-reproductive`helpers' or as co-breeders. The traditional explanation for cooperative breeding is that the opportunities for breeding independently are limited owing to peculiar features of the species' breeding ecology. However, it has proved remarkably di¤cult to ¢nd any common ecological correlates of cooperative breeding in birds. This di¤culty has led to the`life history hypothesis', which suggests that the common feature of cooperatively breeding birds is their great longevity, rather than any particular feature of their breeding ecology. Here, we use a comparative method to test the life history hypothesis by looking for correlations between life history variation and variation in the frequency of cooperative breeding. First, we ¢nd that cooperative breeding in birds is not randomly distributed, but concentrated in certain families, thus supporting the idea that there may be a common basis to cooperative breeding in birds. Second, increases in the level of cooperative breeding are strongly associated with decreases in annual adult mortality and modal clutch size. Third, the proportion of cooperatively breeding species per family is correlated with a low family-typical value of annual mortality, suggesting that low mortality predisposes cooperative breeding rather than vice versa. Finally, the low rate of mortality typically found in cooperatively breeding species is associated with increasing sedentariness, lower latitudes, and decreased environmental £uctuation. We suggest that low annual mortality is the key factor that predisposes avian lineages to cooperative breeding, then ecological changes, such as becoming sedentary, further slow population turnover and reduce opportunities for independent breeding. As the traditional explanation suggests, the breeding habitat of cooperatively breeding species is saturated, but this saturation is not owing to any peculiar feature of the breeding ecology of cooperative breeders. Rather, the saturation arises because the local population turnover in these species is unusually slow, as predicted by the life history hypothesis.

Allomaternal assistance, investment provided to children by caregivers other than the biological mother, occurs cross-culturally in varying degrees. Allomothering, which consists of caregiving and/or provisioning, can increase the... more

Allomaternal assistance, investment provided to children by caregivers other than the biological mother, occurs cross-culturally in varying degrees. Allomothering, which consists of caregiving and/or provisioning, can increase the survival of children and the fertility of the mother. Allomothers, who may be related or unrelated to the child, provide care because they receive either direct or indirect benefits. Fathers and grandmothers, who represent a special category of helper and consistently provide the greatest amount of high-investment allomaternal care, show a marked decrease in sex steroid hormones and sexual activity. The sexuality of the recipient mother may also be affected by the presence of allomothers, whether in the form of relatives, a nanny, a babysitter, or a play date—all options alleviate the time constraints of the mother and allow her to invest in other activities, including time for her partner.

Striped mouse breeding synchron

A variety of caregivers, including grandparents, help raise children. Among grandparents, most Western samples evidence a matrilateral (i.e., mother’s kin) bias in caregiving, and many studies show more positive impacts and stronger... more

A variety of caregivers, including grandparents, help raise children. Among grandparents, most Western samples evidence a matrilateral (i.e., mother’s kin) bias in caregiving, and many studies show more positive impacts and stronger relationships with grandmothers than grandfathers. The aim of the present study is to test competing hypotheses about a potential laterality bias and explore contrasts between grandmothers and grandfathers in a sample of urban young adult university students in Bangalore, India. A sample of 377 (252 women) relatively mobile and high socioeconomic status individuals 17 to 25 years of age completed a survey consisting of sociodemographic and grandparenting questions. Results reveal generally little evidence of either a patrilateral or matrilateral bias, though findings varied for some outcomes. As illustrations, there were no differences in residential proximity or the most recent time when a participant saw matrilateral or patrilateral grandparents, whereas maternal grandmothers were more approving of one’s choice of a life partner than were paternal grandmothers. In inductively coded responses to an open-ended item about the roles of grandparents, maternal grandmothers were more often identified as “guides” and less often deemed “non-significant” than paternal grandmothers, while paternal grandfathers were less often viewed as guardians and more often noted for their influence compared with maternal grandparents. Findings also revealed differences between grandmothers and grandfathers, such as grandmothers playing more prominent roles in community and religious festivals. Findings are interpreted within changing residential, work, education, and family dynamics in urban India as well as a primary importance on parents relative to grandparents.