Search

In cannibalistic species, selection to avoid conspecifics may stem from the need to avoid being eaten or to avoid competition. Individuals may thus use conspecific cues to modulate their behavior to such threats. Yet the nature of variation for such cues remains elusive. Here, we use a half-sib/full-sib design to evaluate the contribution of (indirect) genetic or environmental effects to the behavioral response of the cannibalistic wolf spider Lycosa fasciiventris (Dufour, 1835) toward conspecific cues. Spiders showed variation in relative occupancy time, activity, and velocity on patches with or without conspecific cues, but direct genetic variance was found only for occupancy time. These three traits were correlated and could be lumped in a principal component: spiders spending more time in patches with conspecific cues moved less and more slowly in those areas. Genetic and/or environmental components of carapace width and weight loss in the social partner, which may reflect the quality and/or quantity of cues produced, were significantly correlated with this principal component, with larger partners causing focal individuals to move more slowly. Therefore, environmental and genetic trait variation in social partners may maintain trait diversity in focal individuals, even in the absence of direct genetic variation. [ABSTRACT FROM AUTHOR]

The caste fate of developing female honey bee larvae is strictly socially regulated by adult nurse workers. As a result of this social regulation, nurse-expressed genes as well as larval-expressed genes may affect caste expression and evolution. We used a novel transcriptomic approach to identify genes with putative direct and indirect effects on honey bee caste development, and we subsequently studied the relative rates of molecular evolution at these caste-associated genes. We experimentally induced the production of new queens by removing the current colony queen, and we used RNA sequencing to study the gene expression profiles of both developing larvae and their caregiving nurses before and after queen removal. By comparing the gene expression profiles of queen-destined versus worker-destined larvae as well as nurses observed feeding these two types of larvae, we identified larval and nurse genes associated with caste development. Of 950 differentially expressed genes associated with caste, 82% were expressed in larvae with putative direct effects on larval caste, and 18% were expressed in nurses with putative indirect effects on caste. Estimated selection coefficients suggest that both nurse and larval genes putatively associated with caste are rapidly evolving, especially those genes associated with worker development. Altogether, our results suggest that indirect effect genes play important roles in both the expression and evolution of socially influenced traits such as caste.

Two popular approaches for modeling social evolution, evolutionary game theory and quantitative genetics, ask complementary questions but are rarely integrated. Game theory focuses on evolutionary outcomes, with models solving for evolutionarily stable equilibria, whereas quantitative genetics provides insight into evolutionary processes, with models predicting short-term responses to selection. Here we draw parallels between evolutionary game theory and interacting phenotypes theory, which is a quantitative genetic framework for understanding social evolution. First, we show how any evolutionary game may be translated into two quantitative genetic selection gradients, nonsocial and social selection, which may be used to predict evolutionary change from a single round of the game. We show that synergistic fitness effects may alter predicted selection gradients, causing changes in magnitude and sign as the population mean evolves. Second, we show how evolutionary games involving plastic behavioral responses to partners can be modeled using indirect genetic effects, which describe how trait expression changes in response to genes in the social environment. We demonstrate that repeated social interactions in models of reciprocity generate indirect effects and conversely, that estimates of parameters from indirect genetic effect models may be used to predict the evolution of reciprocity. We argue that a pluralistic view incorporating both theoretical approaches will benefit empiricists and theorists studying social evolution. We advocate the measurement of social selection and indirect genetic effects in natural populations to test the predictions from game theory and, in turn, the use of game theory models to aid in the interpretation of quantitative genetic estimates. [ABSTRACT FROM AUTHOR]

Indirect genetic effects (IGE) occur when an individual's phenotype is influenced by genetic variation in conspecifics. Opportunities for IGE are ubiquitous, and, when present, IGE have profound implications for behavioral, evolutionary, agricultural, and biomedical genetics. Despite their importance, the empirical study of IGE lags behind the development of theory. In large part, this lag can be attributed to the fact that measuring IGE, and deconvoluting them from the direct genetic effects of an individual's own genotype, is subject to many potential pitfalls. In this Perspective, we describe current challenges that empiricists across all disciplines will encounter in measuring and understanding IGE. Using ideas and examples spanning evolutionary, agricultural, and biomedical genetics, we also describe potential solutions to these challenges, focusing on opportunities provided by recent advances in genomic, monitoring, and phenotyping technologies. We hope that this cross-disciplinary assessment will advance the goal of understanding the pervasive effects of conspecific interactions in biology. [ABSTRACT FROM AUTHOR]

Understanding the influence of social interactions on individual fitness is key to improving our predictions of phenotypic evolution. However, we often overlook the different components of selection regimes arising from interactions among organisms, including social, correlational, and indirect selection. This is due to the challenging sampling efforts required in natural populations to measure phenotypes expressed during interactions and individual fitness. Furthermore, behaviours are crucial in mediating social interactions, yet few studies have explicitly quantified these selection components on behavioural traits. In this study, we capitalize on an online multiplayer video game as a source of extensive data recording direct social interactions among prey, where prey collaborate to escape a predator in realistic ecological settings. We estimate natural and social selection and their contribution to total selection on behavioural traits mediating competition, cooperation, and predator-prey interactions. Behaviours of other prey in a group impact an individual's survival, and thus are under social selection. Depending on whether selection pressures on behaviours are synergistic or conflicting, social interactions enhance or mitigate the strength of natural selection, although natural selection remains the main driving force. Indirect selection through correlations among traits also contributed to the total selection. Thus, failing to account for the effects of social interactions and indirect selection would lead to a misestimation of the total selection acting on traits. Dissecting the contribution of each component to the total selection differential allowed us to investigate the causal mechanisms relating behaviour to fitness and quantify the importance of the behaviours of conspecifics as agents of selection. Our study emphasizes that social interactions generate complex selective regimes even in a relatively simple ecological environment., (© The Author(s) 2024. Published by Oxford University Press on behalf of the European Society of Evolutionary Biology.)

Maternal effects, or the influence of maternal environment and phenotype on offspring phenotype, may allow mothers to fine‐tune their offspring's developmental trajectory and resulting phenotype sometimes long after the offspring has reached independence. However, maternal effects on offspring phenotype do not evolve in isolation, but rather within the context of a family unit, where the separate and often conflicting evolutionary interests of mothers, fathers and offspring are all at play. While intrafamilial conflicts are routinely invoked to explain other components of reproductive strategy, remarkably little is known about how intrafamilial conflicts influence maternal effects. We argue that much of the considerable variation in the relationship between maternally derived hormones, nutrients and other compounds and the resulting offspring phenotype might be explained by the presence of conflicting selection pressures on different family members. In this review, we examine the existing literature on maternal hormone allocation as a case study for maternal effects more broadly, and explore new hypotheses that arise when we consider current findings within a framework that explicitly incorporates the different evolutionary interests of the mother, her offspring and other family members. Specifically, we hypothesise that the relationship between maternal hormone allocation and offspring phenotype depends on a mother's ability to manipulate the signals she sends to offspring, the ability of family members to be plastic in their response to those signals and the capacity for the phenotypes and strategies of various family members to interact and influence one another on both behavioural and evolutionary timescales. We also provide suggestions for experimental, comparative and theoretical work that may be instrumental in testing these hypotheses. In particular, we highlight that manipulating the level of information available to different family members may reveal important insights into when and to what extent maternal hormones influence offspring development. We conclude that the evolution of maternal hormone allocation is likely to be shaped by the conflicting fitness optima of mothers, fathers and offspring, and that the outcome of this conflict depends on the relative balance of power between family members. Extending our hypotheses to incorporate interactions between family members, as well as more complex social groups and a wider range of taxa, may provide exciting new developments in the fields of endocrinology and maternal effects. [ABSTRACT FROM AUTHOR]

The phenotypic expression and fitness consequences of behaviours that are exhibited during social interactions are especially sensitive to their local social context. This context‐dependence is expected to generate more variation in the sign and magnitude of selection on social behaviour than that experienced by static characters like morphology. Relatively few studies, however, have examined selection on behavioural traits in multiple populations.We estimated sexual selection in the wild to determine if the strength and form of selection on social phenotypes is more variable than that on morphology.We compared selection gradients on social network position, body size, and weaponry of male forked fungus beetles Bolitotherus cornutus as they influenced mating success across nine natural subpopulations.Male horn length consistently experienced positive sexual selection. However, the sign and magnitude of selection on individual measures of network centrality (strength and betweenness) differed significantly among subpopulations. Moreover, selection on social behaviours occurred at a local scale ('soft selection'), whereas selection on horn length occurred at the metapopulation scale ('hard selection').These results indicate that an individual with a given social phenotype could experience different fitness consequences depending on the network it occupies. While individuals seem to be unable to escape the fitness effects of their morphology, they may have the potential to mediate the pressures of selection on behavioural phenotypes by moving among subpopulations or altering social connections within a network. [ABSTRACT FROM AUTHOR]

Maternal inheritance of mitochondrial DNA (mtDNA) was originally thought to prevent any response to selection on male phenotypic variation attributable to mtDNA, resulting in a male‐biased mtDNA mutation load ("mother's curse"). However, the theory underpinning this claim implicitly assumes that a male's mtDNA has no effect on the fitness of females he comes into contact with. If such "mitochondrially encoded indirect genetics effects" (mtIGEs) do in fact exist, and there is relatedness between the mitochondrial genomes of interacting males and females, male mtDNA‐encoded traits can undergo adaptation after all. We tested this possibility using strains of Drosophila melanogaster that differ in their mtDNA. Our experiments indicate that female fitness is influenced by the mtDNA carried by males that the females encounter, which could plausibly allow the mitochondrial genome to evolve via kin selection. We argue that mtIGEs are probably common, and that this might ameliorate or exacerbate mother's curse. [ABSTRACT FROM AUTHOR]

A fundamental part of the quantitative genetic theory deals with the partitioning of the phenotypic variance into additive genetic and environmental components. During interaction with conspecifics, the interaction partner becomes a part of the environment from the perspective of the focal individual. If the interaction effects have a genetic basis, they are called indirect genetic effects (IGEs) and can evolve along with direct genetic effects. Sexual reproduction is a classic context where potential conflict between males and females can arise from trade‐offs between current and future investments. We studied five female fecundity traits, egg length and number, egg pod length and number and latency to first egg pod, and estimated the direct and IGEs using a half‐sib breeding design in the grasshopper Chorthippus biguttulus. We found that the male IGEs were an order of magnitude lower than the direct genetic effects and were not significantly different from zero. However, there was some indication that IGEs were larger shortly after mating, consistent with the idea that IGEs fade with time after interaction. Female direct heritabilities were moderate to low. Simulation shows that the variance component estimates can appear larger with less data, calling for care when interpreting variance components estimated with low power. Our results illustrate that the contribution of male IGEs is overall low on the phenotypic variance of female fecundity traits. Thus, even in the relevant context of sexual conflict, the influence of male IGEs on the evolutionary trajectory of female reproductive traits is likely to be small. [ABSTRACT FROM AUTHOR]

The social environment is expected to have substantial effects on behavior, and as a consequence, its heritability and evolvability. We investigated these effects by exposing Australian field crickets (Teleogryllus oceanicus) to either silence or recordings of male acoustic sexual signals. We used a combined pedigree and full‐sib/half‐sib breeding design to estimate the repeatability, heritability, and evolvability of behaviors related to boldness, exploration, and activity. All behaviors measured were significantly repeatable in both social environments. Additionally, most behaviors showed significant heritabilities in the two environments. We found no difference in repeatabilities between the silent and the acoustic environment but did find significant differences in the heritabilities and evolvabilities between these environments. There was a high degree of similarity between the phenotypic covariance matrices across the two environments, while the genotypic covariance matrices were highly dissimilar. Reflecting this, we found significant genotype‐by‐environment interactions for most of the behaviors. Lastly, we found that the repeatable aspect of behavior ("personality") was significantly heritable for most behaviors, but that these heritabilities were higher in the acoustic than in the silent environment. We conclude that the social environment can have a significant impact on the heritability and evolvability of behavior, and argue that evolutionary inferences from phenotypic studies should be made with caution. [ABSTRACT FROM AUTHOR]

The environment can have a considerable impact on behaviour. The social environment is predicted to be a particularly important driver of behavioural variation and evolution through the indirect genetic effects that arise whenever individuals interact with conspecifics. We used male Australian field crickets, Teleogryllus oceanicus , to examine the effects of changes in the social environment (recorded acoustic sexual signals of other males) on the expression and consistency of boldness, activity and exploration, and their between-individual covariation. Switching from a silent environment to being exposed to male acoustic sexual signals resulted in crickets becoming less bold, active and explorative. Switching from an acoustic to a silent environment resulted in increased boldness and activity. We also looked at the effects of changes in the nonsocial environment via a physical disturbance that mimicked the presence of a potential predator (mechanical shaking). The effects of physical disturbance (and changes thereof) on behaviour were far less pronounced than the effects of changes in the social environment. Neither the repeatability of nor correlations between behaviours were affected by changes in physical disturbance. Only the average level of exploration was affected significantly when crickets were moved from an undisturbed to a disturbed environment, with crickets becoming less explorative. Although changes in the social and the nonsocial environment affected the repeatability of and correlations between some of the behaviours measured, changes in the social environment had the greater effect. We discuss the ecological and evolutionary implications of our findings and how they relate to our current understanding of social and nonsocial environmental effects on behaviour. [ABSTRACT FROM AUTHOR]

The social environment of an animal is an especially interesting component of its environment because it can be shaped by both genetic and non-genetic variation among social partners. Indirect genetic effects ( IGEs) are those created when genetic variation in social partners contributes to variation in an individual's phenotype; a potentially common form of IGE occurs when the expression of a behavioral phenotype depends on the particular genotypic combination of interacting individuals. Although IGEs can profoundly affect individual- and group-level fitness, population dynamics, and even community structure, understanding their importance is complicated by two inherent challenges: (1) identifying individuals with genetic differences in social interactions that can contribute to IGEs and (2) characterizing natural social interactions that potentially involve IGEs. As a first step toward addressing both these challenges in the same system, we investigated social interactions involving genetically distinct male color morphs in the poeciliid fish Gambusia holbrooki under natural and laboratory conditions. Previous work indicates that melanic (M) and silver (S) males differ in social behavior and in how conspecifics respond to them, suggesting the potential for IGEs. We used a combination of live and video recording of social groups in two natural populations and in the laboratory to determine the potential for IGEs to contribute to behavioral variation in this species. We found that M males had more social partners, and especially more female social partners than did S males, in nature and in the laboratory. These results suggest that both direct and indirect genetic effects have the potential to play a role in the expression and evolution of social behavior in G. holbrooki. [ABSTRACT FROM AUTHOR]

Males of socially monogamous species can increase their siring success via within-pair and extra-pair fertilizations. In this study, we focused on the different sources of (co)variation between these siring routes, and asked how each contributes to total siring success. We quantified the fertilization routes to siring success, as well as behaviors that have been hypothesized to affect siring success, over a five-year period for a wild population of great tits Parus major. We considered siring success and its fertilization routes as 'interactive phenotypes' arising from phenotypic contributions of both members of the social pair. We show that siring success is strongly affected by the fecundity of the social (female) partner. We also demonstrate that a strong positive correlation between extra-pair fertilization success and paternity loss likely constrains the evolution of these two routes. Moreover, we show that more explorative and aggressive males had less extra-pair fertilizations, whereas more explorative females laid larger clutches. This study thus demonstrates that (co)variation in siring routes is caused by multiple factors not necessarily related to characteristics of males. We thereby highlight the importance of acknowledging the multilevel structure of male fertilization routes when studying the evolution of male mating strategies. [ABSTRACT FROM AUTHOR]

Aggregation behaviour is the tendency for animals to group together, which may have important consequences on individual fitness. We used a combination of experimental and simulation approaches to study how genetic variation and social environment interact to influence aggregation dynamics in Drosophila. To do this, we used two different natural lines of Drosophila that arise from a polymorphism in the foraging gene (rovers and sitters). We placed groups of flies in a heated arena. Flies could freely move towards one of two small, cooler refuge areas. In groups of the same strain, sitters had a greater tendency to aggregate. The observed behavioural variation was based on only two parameters: the probability of entering a refuge and the likelihood of choosing a refuge based on the number of individuals present. We then directly addressed how different strains interact by mixing rovers and sitters within a group. Aggregation behaviour of each line was strongly affected by the presence of the other strain, without changing the decision rules used by each. Individuals obeying local rules shaped complex group dynamics via a constant feedback loop between the individual and the group. This study could help to identify the circumstances under which particular group compositions may improve individual fitness through underlying aggregation mechanisms under specific environmental conditions. [ABSTRACT FROM AUTHOR]

Parental care, a central component of reproduction in a wide range of animal species, often involves elaborate behavioural interactions between parents and their offspring. Due to the reciprocal nature of these interactions, it has been hypothesized that parental and offspring behaviours (e.g. parental food provisioning and offspring begging) are not only target but also agent of selection. These traits are therefore expected to co-evolve, ultimately leading to co-adaptation of parent and offspring behaviours within families. However, empirical data on such parent-offspring co-adaptation are limited, particularly for wild populations. Furthermore, mean levels of behaviour (as measured in previous studies) may not adequately describe the dynamic nature of the reciprocal interplay between parents and their offspring, and instead rather the behavioural reaction norms for provisioning and begging may be co-adapted., We applied a large-scale cross-fostering study over 3 consecutive breeding seasons to investigate whether provisioning behaviour of wild blue tit ( Cyanistes caeruleus) parents covaries with the begging behaviour of their genetic, cross-fostered offspring. We simultaneously analysed parent and offspring behaviours, both as static traits (mean levels) and behavioural reaction norms (offspring begging as a function of food deprivation and parental provisioning as a function of short-term experimental changes in brood size)., Neither maternal nor paternal provisioning rates covaried with the begging intensity of their genetic offspring when analysed as mean levels of behaviour. However, the slopes of the reaction norms for provisioning and begging were negatively correlated between male, but not female, parents and their genetic offspring. Thus, fathers that change their provisioning rate strongly with brood size sire offspring whose level of begging only weakly increases with hunger, and vice versa., The observed covariation suggests the existence of sex-specific optima for parent-offspring trait combinations. Thus, our study not only highlights the importance of a behavioural reaction norm approach when investigating parent-offspring interactions, but also stresses the relevance of considering parents as separate units, at least for biparental species. [ABSTRACT FROM AUTHOR]

Parents of many species provision their young, and the extent of parental provisioning constitutes a major component of the offspring's social environment. Thus, a change in parental provisioning can alter selection on offspring, resulting in the coevolution of parental and offspring traits. Although this reasoning is central to our evolutionary understanding of family life, there is little direct evidence that selection by parents causes evolutionary change in their offspring. Here we use experimental evolution to examine how populations of burying beetles adapt to a change in posthatching parental provisioning. We measured the performance of larvae descended from lab populations that had been maintained with and without posthatching parental care (Full Care and No Care populations). We found that adaptation to the absence of posthatching care led to rapid and consistent changes in larval survival in the absence of care. Specifically, larvae from No Care populations had higher survival in the absence of care than larvae from Full Care populations. Other measures of larval performance, such as the ability of larvae to consume a breeding carcass and larval mass at dispersal, did not differ between the Full Care and No Care populations. Nevertheless, our results show that populations can adapt rapidly to a change in the extent of parental care and that experimental evolution can be used to study such adaptation. [ABSTRACT FROM AUTHOR]

Behavioural ecologists increasingly study behavioural variation within and among individuals in conjunction, thereby integrating research on phenotypic plasticity and animal personality within a single adaptive framework. Interactions between individuals (cf. social environments) constitute a major causative factor of behavioural variation at both of these hierarchical levels. Social interactions give rise to complex ‘interactive phenotypes’ and group-level emergent properties. This type of phenotype has intriguing evolutionary implications, warranting a cohesive framework for its study. We detail here how a reaction-norm framework might be applied to usefully integrate social environment theory developed in behavioural ecology and quantitative genetics. The proposed emergent framework facilitates firm integration of social environments in adaptive research on phenotypic characters that vary within and among individuals. [ABSTRACT FROM AUTHOR]

Males can through their behavior (e.g., courtship feeding) exert an indirect effect on their partner's reproductive traits, such as the seasonal timing and size of her clutch. Evidence for such indirect (male) effect on reproduction is starting to accumulate. We quantify female and male effects on reproduction in the tawny owl Strix aluco using a hierarchical mixed model on data collected in 1978-2013. We find that differences between males explain 7 % of the phenotypic variance in laying date (females 5 %). In contrast, females have a clear (11 %) effect on clutch size, whereas males have no effect. Based on multivariate hierarchical modeling, we find an individual-level correlation between the male-specific effect on laying date and his body mass (but not his plumage color or wing length). Heavy males may be able to affect their partner's seasonal timing of laying because of an advantage in providing courtship feeding prior to reproduction. Our findings illustrate that males can be an important determinant of variation in reproduction and that multivariate mixed models present a general approach to pinpoint which individual characteristics could be associated with such indirect effects. [ABSTRACT FROM AUTHOR]

The social complexity that characterizes the eusocial insects strongly affects all aspects of social insect life, including the molecular and evolutionary genetic basis of social insect traits. Quantitative genetic theory and empirical approaches have been developed over the past 60 years specifically to study the genetic implications of social interactions. Surprisingly, given the obvious biological importance of social interactions in social insects, this research tradition has been and continues to be widely overlooked throughout the social insect literature, including in recent sociogenomic studies focused on understanding the molecular underpinnings of social life. Instead, the overwhelming majority of social insect genetic research has relied on conventional genetic approaches developed for solitary organisms focused on the one-to-one association of an individual's genes to its own traits. I survey social insect studies that conclusively demonstrate the importance of indirect genetic effects (IGEs), which arise from social interactions, for social insect trait expression and evolution. I explain why these genetically based social effects are expected to be ubiquitous in social insects and I explain the relevance of the IGE framework, originally developed within quantitative genetics, for molecular genetic studies of social insect traits such as behaviour and caste. I discuss the problems of ignoring IGEs and relying solely on conventional direct genetic effect approaches. Finally, I discuss the strong potential of using the IGE approach and other more systems-level-focused approaches to complement conventional reductionist approaches in elucidating the genetic basis of social insect trait expression and evolution. [ABSTRACT FROM AUTHOR]

Background Identifying the sources of variation in mating interactions between males and females is important because this variation influences the strength and/or the direction of sexual selection that populations experience. While the origins and effects of variation in male attractiveness and ornamentation have received much scrutiny, the causes and consequences of intraspecific variation in females have been relatively overlooked. We used cytogenetic cloning techniques developed for Drosophila melanogaster to create "hemiclonal" males and females with whom we directly observed sexual interaction between individuals of different known genetic backgrounds and measured subsequent reproductive outcomes. Using this approach, we were able to quantify the genetic contribution of each mate to the observed phenotypic variation in biologically important traits including mating speed, copulation duration, and subsequent offspring production, as well as measure the magnitude and direction of intersexual genetic correlation between female choosiness and male attractiveness. Results We found significant additive genetic variation contributing to mating speed that can be attributed to male genetic identity, female genetic identity, but not their interaction. Furthermore we found that phenotypic variation in copulation duration had a significant male-associated genetic component. Female genetic identity and the interaction between male and female genetic identity accounted for a substantial amount of the observed phenotypic variation in egg size. Although previous research predicts a trade-off between egg size and fecundity, this was not evident in our results. We found a strong negative genetic correlation between female choosiness and male attractiveness, a result that suggests a potentially important role for sexually antagonistic alleles in sexual selection processes in our population. Conclusion These results further our understanding of sexual selection because they identify that genetic identity plays a significant role in phenotypic variation in female behaviour and fecundity. This variation may be potentially due to ongoing sexual conflict found between the sexes for interacting phenotypes. Our unexpected observation of a negative correlation between female choosiness and male attractiveness highlights the need for more explicit theoretical models of genetic covariance to investigate the coevolution of female choosiness and male attractiveness. [ABSTRACT FROM AUTHOR]

Cooperation is assumed to benefit groups at cost to individuals, but comparisons of cooperative and solitary ant queens show that payoffs depend on who is in the group. Groups of cooperative queens coordinate to produce workers more efficiently, while normally solitary queens escalate aggression leading to their higher mortality. Importantly, solitary queens do not outcompete cooperative queens in mixed pairs, meaning populations with both strategies could co-exist at the transition to cooperative sociality.Social dynamics, the emergent effects of interactions within structured groups, play a key role in shaping social phenotypes and fitness. We examined the potential positive and negative effects of social dynamics in simple groups, by creating social groups of harvester ant queens with 2 alternate nest-founding strategies, solitary versus cooperative. We compared social interactions, survival, and nest productivity of pairs containing queens from the cooperative founding population, the normally solitary founding population, or mixed pairs of the 2 types. Expressed social phenotypes of queens in pairs depended strongly on the lineage of the other queen. Two behaviors, aggression and brood care, showed simple social dynamical effects. Aggression escalated in pairs of normally solitary queens, whereas queens in cooperative pairs coordinated brood output, leading to more efficient worker production. These dynamics had context-based fitness consequences, such that cooperative queens gained a survival advantage in cooperative pairs, but neither type of queen experienced an advantage or disadvantage in “mixed” associations. The interplay between social dynamics and fitness in these associations provides an empirical example of social selection. It captures a likely scenario of the transition to and the early evolution of cooperative living, in which cooperative individuals interact with solitary individuals who lack a priori strategies for cooperation or cheating. [ABSTRACT FROM PUBLISHER]

Mate choice often depends on the properties of both sexes, such as the preference and responsiveness of the female and the sexual display traits of the male. Quantitative genetic studies, however, traditionally explore the outcome of an interaction between males and females based solely on the genotype of one sex, treating the other sex as a source of environmental variance. Here, we use a half-sib breeding design in the field cricket, Teleogryllus commodus, to estimate the additive genetic contribution of both partners to three steps of the mate choice process: the time taken to mate; the duration of spermatophore attachment; and the intensity of mate guarding. Rather than each sex contributing equally to the interactions, we found that genetic variation for latency to mate and spermatophore attachment was sex-specific, and in the case of mate-guarding intensity, largely absent. For a given interaction, genetic variation in one sex also appears to be largely independent of the other, and is also uncorrelated with the other traits. We discuss how pre- and postcopulatory interactions have the potential to evolve as an interacting phenotype, but that any coevolution between these traits, due to sexual selection or sexual conflict, may be limited. [ABSTRACT FROM AUTHOR]

A complete understanding of male reproductive success, and thus sexual selection, often requires an insight into male success in sperm competition. Genuine conclusions on male sperm competitiveness can only be made in real competitive situations. However, statistical analyses of sperm competitiveness from fertilization success data have been shown to be problematic. Here, I first outline a comprehensive general description of the different additive and nonadditive elements relevant for the outcome of sperm competition staged between two males. Based on this description, I will highlight two main problems that are frequently encountered in experiments aiming at estimating sperm competitiveness. First, I focus on potential problems when using standardized competitors versus random mating trials, because trials with standardized competitors do not allow generalization if male-male interactions are important. Second, I illustrate the necessity to analyze data on the logit scale rather than on raw proportions, because only the logit scale allows a clean separation of additive and nonadditive effects (i.e., male × male and female × male interactions). [ABSTRACT FROM AUTHOR]

Female mating preferences are often flexible, reflecting the social environment in which they are expressed. Associated indirect genetic effects (IGEs) can affect the rate and direction of evolutionary change, but sexual selection models do not capture these dynamics. We incorporate IGEs into quantitative genetic models to explore how variation in social environments and mate choice flexibility influence Fisherian sexual selection. The importance of IGEs is that runaway sexual selection can occur in the absence of a genetic correlation between male traits and female preferences. Social influences can facilitate the initiation of the runaway process and increase the rate of trait elaboration. Incorporating costs to choice do not alter the main findings. Our model provides testable predictions: (1) genetic covariances between male traits and female preferences may not exist, (2) social flexibility in female choice will be common in populations experiencing strong sexual selection, (3) variation in social environments should be associated with rapid sexual trait divergence, and (4) secondary sexual traits will be more elaborate than previously predicted. Allowing feedback from the social environment resolves discrepancies between theoretical predictions and empirical data, such as why indirect selection on female preferences, theoretically weak, might be sufficient for preferences to become elaborated. [ABSTRACT FROM AUTHOR]

Indirect genetic effects (IGEs), which occur when phenotypic expression in one individual is influenced by genes in another conspecific individual, may have a drastic effect on evolutionary response to selection. General evolutionary models of IGEs have been developed using two distinct theoretical frameworks derived from maternal effects theory. The first framework is trait-based and focuses on how phenotypes are influenced by specific traits in a social partner, with the strength of interactions defined by the matrix Ψ. The second framework partitions total genetic variance into components representing direct effects, indirect effects, and the covariance between them, without identifying specific social traits responsible for IGEs. The latter framework has been employed more commonly by empiricists because the methods for estimating variance components are relatively straightforward. Here, we show how these two theoretical frameworks are related to each other and derive equations that can be used to translate between them. This translation leads to a generalized method that can be used to estimate Ψ via standard quantitative genetic breeding designs or pedigrees from natural populations. This method can be used in a very general set of circumstances and is widely applicable to all IGEs, including maternal effects and other interactions among relatives. [ABSTRACT FROM AUTHOR]

Theory for the evolution of social interactions based on continuous strategies often assumes for simplicity that expressed behaviours are independent of previous encounters. In reality, however, such dependencies are likely to be widespread and often strong, generating complex behavioural dynamics. To model this process and illustrate potential consequences for the evolution of behavioural interactions, we consider the behavioural dynamics of the interaction between caring parents and their demanding offspring, a prime example of long series of interdependent and highly dynamic interactions. These dynamics can be modelled using functions describing mechanisms for how parents and their offspring respond to each other in the interaction. We establish the general conditions under which the behavioural dynamics converge towards a proximate equilibrium and refer to such converging interactions as behaviourally stable strategies (BSSs). We further demonstrate that there is scope for behavioural instability under realistic conditions; that is, whenever parents and/or offspring ‘overreact’ beyond some threshold. By applying the derived condition for behavioural stability to evolutionary models of parent–offspring conflict resolution, we show by numerical simulations that evolutionarily stable strategies (ESSs) of current models are not necessarily behaviourally stable. Because behavioural instability implies that expressed levels of behaviours deviate from the ESS, behavioural stability is required for strict evolutionary stability in repeated behavioural interactions. [Copyright &y& Elsevier]

Social interactions pervade all aspects of life in the social insects. Networks of interacting nestmates enable the maintenance of colony homeostasis and regulation of brood development. Artificial colony-level selection on the amount of pollen stored in honeybee colonies has produced high- and low-pollen-hoarding strains that have been used as a model system to study the genetic and physiological basis of differences in forager behavior that contribute to colony-level differences in pollen hoarding. Here we extend this model system using an interacting-phenotypes approach that explicitly studies genetic components arising from social interactions. High- and low-pollen-hoarding-strain larvae were reared in hives with high- or low-strain older larvae and high- or low-strain adult workers. The ovariole number and dry mass of focal individuals depended on interactions between the genotypes of the focal individuals and their brood and adult worker nestmates. These results show that trait expression by individual honeybee workers is modulated by the genotypic composition of the colony, indicating that individual-level phenotypes are properties of the composite "sociogenome." Thus, colony-level selection has produced strains with distinct combinations of socially interacting genes, which make up the social networks that regulate development and expressed phenotypes. [ABSTRACT FROM AUTHOR]

Sexual selection requires social interactions, particularly between the sexes. When trait expression is influenced by social interactions, such traits are called interacting phenotypes and only recently have the evolutionary consequences of interacting phenotypes been considered. Here we investigated how variation in relative fitness, or the opportunity for sexual selection, affected the evolutionary trajectories of interacting phenotypes. We used experimentally evolved populations of the naturally promiscuous Drosophila pseudoobscura, in which the numbers of potential interactions between the sexes, and therefore relative fitness, were manipulated by altering natural levels of female promiscuity. We considered two different mating interactions between the sexes: mating speed and copulation duration. We investigated the evolutionary trajectories of means and (co)variances ( P) and also the influence of genetic drift on the evolutionary response of these interactions. Our sexual selection treatments did not affect the means of either mating speed or copulation duration, but they did affect P. We found that the means of both traits differed among replicates within each selection treatment whereas the Ps did not. Changes as a consequence of genetic drift were excluded. Our results show that although variable potential strengths of sexual interactions influence the evolution of interacting phenotypes, the influence may be nonlinear. [ABSTRACT FROM AUTHOR]

Evolutionary conflict arises between reproductive partners when alternative reproductive opportunities are available. Sexual conflict can generate sexually antagonistic selection, which mediates sexual selection and intersexual coevolution. However, despite intense interest, the evolutionary implications of sexual conflict remain unresolved. We propose a novel theoretical approach to study the evolution of sexually antagonistic phenotypes based on quantitative genetics and the measure of social selection arising from male-female interactions. We consider the phenotype of one sex as both a genetically influenced evolving trait as well as the (evolving) social environment in which the phenotype of the opposite sex evolves. Several important points emerge from our analysis, including the relationship between direct selection on one sex and indirect effects through selection on the opposite sex. We suggest that the proposed approach may be a valuable tool to complement other theoretical approaches currently used to study sexual conflict. Most importantly, our approach highlights areas where additional empirical data can help clarify the role of sexual conflict in the evolutionary process. [ABSTRACT FROM AUTHOR]

Two popular approaches for modeling social evolution, evolutionary game theory and quantitative genetics, ask complementary questions but are rarely integrated. Game theory focuses on evolutionary outcomes, with models solving for evolutionarily stable equilibria, whereas quantitative genetics provides insight into evolutionary processes, with models predicting short-term responses to selection. Here we draw parallels between evolutionary game theory and interacting phenotypes theory, which is a quantitative genetic framework for understanding social evolution. First, we show how any evolutionary game may be translated into two quantitative genetic selection gradients, nonsocial and social selection, which may be used to predict evolutionary change from a single round of the game. We show that synergistic fitness effects may alter predicted selection gradients, causing changes in magnitude and sign as the population mean evolves. Second, we show how evolutionary games involving plastic behavioral responses to partners can be modeled using indirect genetic effects, which describe how trait expression changes in response to genes in the social environment. We demonstrate that repeated social interactions in models of reciprocity generate indirect effects and conversely, that estimates of parameters from indirect genetic effect models may be used to predict the evolution of reciprocity. We argue that a pluralistic view incorporating both theoretical approaches will benefit empiricists and theorists studying social evolution. We advocate the measurement of social selection and indirect genetic effects in natural populations to test the predictions from game theory and, in turn, the use of game theory models to aid in the interpretation of quantitative genetic estimates., (© The American Genetic Association. 2022. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)