H. Kern Reeve

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.

Estimating effective paternity number in social insects and the effective number of alleles in a population

Estimating paternity and genetic relatedness is central to many empirical and theoretical studies of social insects. The two important measures of a queens mating number are her actual number of mates and her effective number of mates. Estimating the effective number of mates is mathematically identical to the problem of estimating the effective number of alleles in population genetics, a common measure of genetic variability introduced by Kimura & Crow (1964 ). We derive a new bias‐corrected estimator of effective number of types (mates or alleles) and compare this new method to previous methods for estimating true and effective numbers of types using Monte Carlo simulations. Our simulation results suggest that the examined estimators of the true number of types have very similar statistical properties, whereas the estimators of effective number of types have quite different statistical properties. Moreover, our new proposed estimator of effective number of types is approximately unbiased, and has considerably lower variance than the original estimator. Our new method will help researchers more accurately estimate intracolony genetic relatedness of social insects, which is an important measure in understanding their ecology and social behaviour. It should also be of use in population genetic studies in which the effective number of alleles is of interest.

USING PHYLOGENIES TO TEST HYPOTHESES OF ADAPTATION: A CRITIQUE OF SOME CURRENT PROPOSALS

Investigations of the adaptive design of traits and the phylogenetic relationships of taxa have traditionally focused on very different sets of questions. Consequently, relatively few linkages have been developed between these subfields of evolutionary biology. This has recently begun to change, however, particularly with the publication of several proposed methods for using data from reconstructed phylogenies (Hennig 1966; Wiley 1981) to test hypotheses of adaptation. Two principal approaches may be distinguished. First, several statistical techniques have been devised to incorporate phylogenetic data into comparative tests of hypotheses predicting an adaptive association between two characters or between a character and an environmental variable (e.g., Ridley 1989; Felsenstein 1985a; Grafen 1992; Harvey and Pagel 1991; Pagel 1992). These techniques use information from reconstructed phylogenetic relationships in efforts to minimize the problem that characters shared among related taxa cannot be treated as statistically independent if they are shared through common ancestry rather than adaptive convergence. Second, several authors have begun using reconstructed phylogenies to directly test hypotheses of adaptive character evolution. The general procedure entails mapping characters of interest onto independently derived cladograms to assess the timing and direction of historical transitions between character states. Phylogenetic tests using this procedure have been developed to (1) determine whether a character originally spread in ancestral populations through natural selection

The emergence of a superorganism through intergroup competition.

Surveys of insect societies have revealed four key, recurring organizational trends: (i) The most elaborated cooperation occurs in groups of relatives. (ii) Cooperation is typically more elaborate in species with large colony sizes than in species with small colony sizes, the latter exhibiting greater internal reproductive conflict and lesser morphological and behavioral specialization. (iii) Within a species, per capita brood output typically declines as colony size increases. (iv). The ecological factors of resource patchiness and intergroup competition are associated with the most elaborated cooperation. Predictions of all four patterns emerge elegantly from a game-theoretic model in which within-group tug-of-wars are nested within a between-group tug-of-war. In this individual selection model, individuals are faced with the problem of how to partition their energy between investment in intercolony competition versus investment in intracolony competition, i.e., internal tugs-of-war over shares of the resources gained through intergroup competition. An individuals evolutionarily stable investment in between-group competition (i.e., within-group cooperation) versus within-group competition is shown to increase as within-group relatedness increases, to decrease as group size increases (for a fixed number of competing groups), to increase as the number of competing groups in a patch increases, and to decrease as between-group relatedness increases. Moreover, if increasing patch richness increases both the number of individuals within a group and the number of competing groups, greater overall cooperation within larger groups will be observed. The model presents a simple way of determining quantitatively how intergroup conflict will propel a society forward along a “superorganism continuum.”

Paternal inheritance of a female moth's mating preference

Females of the arctiid moth Utetheisa ornatrix mate preferentially with larger males, receiving both direct phenotypic and indirect genetic benefits. Here we demonstrate that the females mating preference is inherited through the father rather than the mother, indicating that the preference gene or genes lie mostly or exclusively on the Z sex chromosome, which is strictly paternally inherited by daughters. Furthermore, we show that the preferred male trait and the female preference for that trait are correlated, as females with larger fathers have a stronger preference for larger males. These findings are predicted by the protected invasion theory, which asserts that male homogametic sex chromosome systems (ZZ/ZW) found in lepidopterans and birds promote the evolution of exaggerated male traits through sexual selection. Specifically, the theory predicts that, because female preference alleles arising on the Z chromosome are transmitted to all sons that have the fathers attractive trait rather than to only a fraction of the sons, such alleles will experience stronger positive selection and be less vulnerable to chance loss than would autosomal alleles.

Why Animals Lie: How Dishonesty and Belief Can Coexist in a Signaling System

We develop and apply a simple model for animal communication in which signalers can use a nontrivial frequency of deception without causing listeners to completely lose belief. This common feature of animal communication has been difficult to explain as a stable adaptive outcome of the options and payoffs intrinsic to signaling interactions. Our theory is based on two realistic assumptions. (1) Signals are “overheard” by several listeners or listener types with different payoffs. The signaler may then benefit from using incomplete honesty to elicit different responses from different listener types, such as attracting potential mates while simultaneously deterring competitors. (2) Signaler and listener strategies change dynamically in response to current payoffs for different behaviors. The dynamic equations can be interpreted as describing learning and behavior change by individuals or evolution across generations. We explain how our dynamic model differs from other solution concepts from classical and evolutionary game theory and how it relates to general models for frequency‐dependent phenotype dynamics. We illustrate the theory with several applications where deceptive signaling occurs readily in our framework, including bluffing competitors for potential mates or territories. We suggest future theoretical directions to make the models more general and propose some possible experimental tests.

Comparison of Brain Volumes between Single and Multiple Foundresses in the Paper Wasp Polistes dominulus

Queens of the paper wasp Polistes dominulus have the option to found nests in spring alone or together with other queens. In the latter case a dominance hierarchy is established among the cofoundresses with the dominant wasp getting the major share of the reproductive output of the nest. The different reproductive strategies of an individual wasp will necessitate different behaviors. We measured the volumes of brain structures as a potential indicator of differential use and elaboration of a number of brain structures. We found a significant increase in the volume of the antennal lobe in members of multiple foundress associations in comparison to single foundresses. The volume of the collar, a substructure of the calyx of the mushroom body, was also significantly larger, especially in the dominant queen of a foundress association. No significant differences between dominant or subordinate wasps in regard to volume of the measured brain substructures were found.

Relatedness Asymmetry and Reproductive Sharing in Animal Societies

We have shown (Reeve and Keller 1995) that reproduction i social groups is generally shared more equally in sister-sister groups than in mother-daughter associations, and we proposed a model based on the relatedness asymmetry between group members to account for this pattern. Emlen (1996) endorses our model but raises the possibilities that the model might not apply to several types of vertebrate familial societies, that the well-documented dominance of parents over offspring confounds the prediction of our model, and that greater skews in mother-daughter associations may reflect greater avoidance of incestuous mating in these associations. Below we consider these points in turn. Our model examines the consequences of females having asymmetric relatedness to each others offspring (as will arise in mother-daughter associations) in the simple case in which females have a single mate. However, as Emlen points out, extrapair fertilization is common in vertebrates, with the effect of decreasing the relatedness among siblings. If a fraction f of the brood is sired by another male (unrelated to the parental male or female), the average relatedness between siblings is

Familiarity breeds cooperation

Many theoretical models have been developed to study the conditions under which unrelated individuals should cooperate or not cooperate. But such behaviour is rarely ‘all or nothing’, and new mathematical models allow the optimal level of cooperation to be determined.

The Puzzle of Partial Resource Use by a Parasitoid Wasp

When there is conspicuous underexploitation of a limited resource, it is worth asking, what mechanisms allow presumably valuable resources to be left unused? Evolutionary biologists have generated a wide variety of hypotheses to explain this, ranging from interdemic group selection to selfishly prudent individual restraint. We consider a situation in which, despite high intraspecific competition, individuals leave most of a key resource unexploited. The parasitic wasp that does this finds virtually all host egg clusters in a landscape but parasitizes only about a third of the eggs in each and then leaves a deterrent mark around the cluster. We first test—and reject—a series of system-specific simple constraints that might limit full host exploitation, such as asynchronous maturation of host eggs. We then consider classical hypotheses for the evolution of restraint. Prudent predation and bet-hedging fail as explanations because the wasp lives as a large, well-mixed population. Additionally, we find no individual benefits to the parasitoid of developing in a sparsely parasitized host nest. However, an optimal foraging model, including empirically measured costs of superparasitism and hyperparasitism, can explain through individual selection both the consistently low rate of parasitism and deterrent marking.