Tests of reproductive-skew models in social insects.

Reproductive-skew theory can be broadly divided into transactional models, in which reproduction is shared among group members in return for some fitness benefit, and tug-of-war models, in which reproductive sharing arises solely from an inability of each group member to fully control the others. For small-colony social insects in which complete reproductive control by a single individual is plausible, transactional-concession models account, better than any other existing model, for observed relationships between each of the dependent variables of skew, changes in reproductive partitioning over time, group size, and within-group aggression, and each of the predictor variables of genetic relatedness, ecological constraints on solitary breeding, and benefits of group living. An extension of transactional-concession models via the "workers-as-a-collective-dominant" model potentially offers new insights into some of the most striking reproductive patterns in large-colony eusocial Hymenopteran species, from the loss of worker capacity to produce female offspring to patterns of skew and aggression in polygynous societies

The eusociality continuum

Eusocial societies are traditionally characterized by a reproductive division of labor, an overlap of generations, and cooperative care of the breeders' young. Eusociality was once thought to occur only in termites, ants, and some bee and wasp species, but striking evolutionary convergences have recently become apparent between the societies of these insects and those of cooperatively breeding birds and mammals. These parallels have blurred distinctions between cooperative breeding and eusociality, leading to calls for either drastically restricting or expanding wage of these terms. We favor the latter approach. Cooperative breeding and eusociality are not discrete phenomena, but rather form a continuum of fundamentally similar social systems whose main differences lie in the distribution of lifetime reproductive success among group members. Therefore we propose to array vertebrate and invertebrate cooperative breeders along a common axis, representing a standardized measure of reproductive variance, and to drop such (loaded) terms as ''primitive'' and ''advanced'' eusociality. The terminology we propose unites all occurrences of alloparental helping of kin under a single theoretical umbrella (e.g., Hamilton's rule). Thus, cooperatively breeding vertebrates can be regarded as eusocial, just as eusocial inverbrates are cooperative breeders. We believe this integrated approach will foster potentially revealing cross-taxon comparisons, which are essential to understanding social evolution in birds, mammals, and in sects

The evolution of cooperation and altruism--a general framework and a classification of models.

One of the enduring puzzles in biology and the social sciences is the origin and persistence of intraspecific cooperation and altruism in humans and other species. Hundreds of theoretical models have been proposed and there is much confusion about the relationship between these models. To clarify the situation, we developed a synthetic conceptual framework that delineates the conditions necessary for the evolution of altruism and cooperation. We show that at least one of the four following conditions needs to be fulfilled: direct benefits to the focal individual performing a cooperative act; direct or indirect information allowing a better than random guess about whether a given individual will behave cooperatively in repeated reciprocal interactions; preferential interactions between related individuals; and genetic correlation between genes coding for altruism and phenotypic traits that can be identified. When one or more of these conditions are met, altruism or cooperation can evolve if the cost-to-benefit ratio of altruistic and cooperative acts is greater than a threshold value. The cost-to-benefit ratio can be altered by coercion, punishment and policing which therefore act as mechanisms facilitating the evolution of altruism and cooperation. All the models proposed so far are explicitly or implicitly built on these general principles, allowing us to classify them into four general categories

Frailty and health-related quality of life in older women with breast cancer

Purpose: In older women, breast cancer and its treatment can have profound impact on their physical, mental, and social health, especially in frail patients. This study evaluated the association between frailty and long-term health-related quality of life (HRQOL) in older women undergoing breast cancer treatment. Methods: Using the Carolina Senior Registry (CSR), participants with breast cancer were contacted to complete a follow-up HRQOL questionnaire (median 4 years). Baseline Geriatric Assessment (GA) variables were used to calculate the Carolina Frailty Index (CFI) and categorize participants as robust, pre-frail, or frail. Outcomes included HRQOL domains of physical function, social roles, fatigue, depression, anxiety, pain, and sleep disturbance assessed using PROMIS® instruments. Regression modeling compared outcomes between frailty groups using adjusted mean differences (AMD). Results: Of 190 eligible patients, 63 completed follow-up HRQOL survey. Mean age was 70 years (range 65–86) and 91% were white. Based on the CFI, 49 (78%) patients were robust, 11 (18%) pre-frail, and 3 (5%) frail. After controlling for age and cancer stage, patients identified as pre-frail/frail reported worse physical function (AMD − 9.2, p < 0.001) and social roles (AMD − 7.2, p = 0.002) and more fatigue (AMD 7.6, p = 0.008), depression (AMD 5.6, p = 0.004), and sleep disturbance (AMD 6.9, p = 0.008) compared to robust patients at follow-up. Conclusions: Frailty in older women with breast cancer was associated with worse long-term HRQOL outcomes. Further research is needed to develop interventions for frail patients at-risk for reduced HRQOL

Analytical Results for Individual and Group Selection of Any Intensity

The idea of evolutionary game theory is to relate the payoff of a game to reproductive success (= fitness). An underlying assumption in most models is that fitness is a linear function of the payoff. For stochastic evolutionary dynamics in finite populations, this leads to analytical results in the limit of weak selection, where the game has a small effect on overall fitness. But this linear function makes the analysis of strong selection difficult. Here, we show that analytical results can be obtained for any intensity of selection, if fitness is defined as an exponential function of payoff. This approach also works for group selection (= multi-level selection). We discuss the difference between our approach and that of inclusive fitness theory

Partitioning of reproduction in mother-daughter versus sibling associations : a test of optimal skew theory

A critical feature of cooperative animal societies is the reproductive skew, a shorthand term for the degree to which a dominant individual monopolizes overall reproduction in the group. Our theoretical analysis of the evolutionarily stable skew in matrifilial (i.e., mother-daughter) societies, in which relatednesses to offspring are asymmetrical, predicts that reproductive skews in such societies should tend to be greater than those of semisocial societies (i.e., societies composed of individuals of the same generation, such as siblings), in which relatednesses to offspring are symmetrical. Quantitative data on reproductive skews in semisocial and matrifilial associations within the same species for 17 eusocial Hymenoptera support this prediction. Likewise, a survey of reproductive partitioning within 20 vertebrate societies demonstrates that complete reproductive monopoly is more likely to occur in matrifilial than in semisocial societies, also as predicted by the optimal skew model

Partitioning of reproduction in animal societies.

A key feature differentiating cooperative animal societies Is the apportionment of reproduction among individuals. Only recently have studies started to focus on intraspecific variability in the distribution of reproduction within animal societies, and the available data suggest that this variability might be greater than previously suspected. How can one account for intra-and interspecific variability in partitioning of reproduction? This Is one of the most intriguing problems in the study of social behaviour, and understanding the factors underlying this variability is one of the keys to understanding the properties of complex animal societies

Reproductive bribing and policing as evolutionary mechanisms for the suppression of within-group selfishness.

We show that a new, simple, and robust general mechanism for the social suppression of within-group selfishness follows from Hamilton's rule applied in a multilevel selection approach to asymmetrical, two-person groups: If it pays a group member to behave selfishly (i.e., increase its share of the group's reproduction, at the expense of group productivity), then its partner will virtually always be favored to provide a reproductive "bribe" sufficient to remove the incentive for the selfish behavior. The magnitude of the bribe will vary directly with the number of offspring (or other close kin) potentially gained by the selfish individual and inversely with both the relatedness r between the interactants and the loss in group productivity because of selfishness. This bribe principle greatly extends the scope for cooperation within groups. Reproductive bribing is more likely to be favored over social policing for dominants rather than subordinates and as intragroup relatedness increases. Finally, analysis of the difference between the group optimum for an individual's behavior and the individual's inclusive fitness optimum reveals a paradoxical feedback loop by which bribing and policing, while nullifying particular selfish acts, automatically widen the separation of individual and group optima for other behaviors (i.e., resolution of one conflict intensifies others)