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ABSTRACT Gray mouse lemur, Microcebus murinus, mothers either cooperatively breed plurally with kin or breed solitarily. We describe the first observations of cooperative and solitary mobbing to defend offspring by wild cooperative breeding gray mouse lemur mothers in Kirindy Forest, Western Madagascar. We observed four groups of cooperatively breeding mothers and their offspring daily between 18:00 and 04:00 from January 1 to 15, 2023. Cooperative mobbing was observed twice, and solitary mobbing by a single cooperative breeding mother was observed once. There was one Malagasy tree boa, Sanzinia madagascariensis, per mobbing event. Mothers solitarily mobbed by directly approaching within 1 m of the boa, walking and changing distance while within 1 m of the boa. In addition to the solitary mobbing behaviors, cooperatively mobbing mothers approached the boa together from the same or different directions or alternated, and they gathered around the boa. Mothers collaborated in the context of offspring defense from predators and performed different complementary tasks: mobbing while another provided alloparental care by guarding the offspring of the association, that is, babysitting. Mothers performed similar mobbing behaviors and occasionally synchronized in time or coordinate in time and in space to approach from different directions and gather around the boa. Mothers did not come in contact with the boas during mobbing but kept a distance of at least 20 cm. On two mobbing events, the boa rose up with its head facing the mobbing mothers and climbed down the tree after the mobbing. Cooperative mobbing to defend offspring likely evolved by kin selection but reciprocity and an interaction between kin selection and reciprocity cannot be ruled out, since gray mouse lemur mothers cooperatively breed with kin and basically allonurse reciprocally. [ABSTRACT FROM AUTHOR]

The central dogma of molecular biology can be conceptualised as the division of labour between templates and catalysts, where templates transmit genetic information, catalysts accelerate chemical reactions, and the information flows from templates to catalysts but not from catalysts to templates. How can template-catalyst division evolve in primordial replicating systems? A previous study has shown that even if the template-catalyst division does not provide an immediate fitness benefit, it can evolve through symmetry breaking between replicating molecules when the molecules are compartmentalised into protocells. However, cellular compartmentalisation may have been absent in primordial replicating systems. Here, we investigate whether cellular compartmentalisation is necessary for the evolution of the template-catalyst division via symmetry breaking using an individual-based model of replicators in a two-dimensional space. Our results show that replicators evolve the template-catalyst division via symmetry breaking when their diffusion constant is sufficiently high, a condition that results in low genetic relatedness between replicators. The evolution of the template-catalyst division reduces the risk of invasion by "cheaters," replicators that have no catalytic activities, encode no catalysts, but replicate to the detriment of local population growth. Our results suggest that the evolution of the template-catalyst division via symmetry breaking does not require cellular compartmentalization and is, instead, a general phenomenon in replicators with structured populations. Graphical Abstract [ABSTRACT FROM AUTHOR]

We report the first record of mutual allogrooming in free-ranging wild northern red muntjac (Muntiacus vaginalis) from dense tropical forests of Similipal Tiger Reserve, Odisha, India. This observation is similar to reciprocal allogrooming behaviour between social partners, reported only in Impala (Aepyceros melampus) in free-ranging conditions. We video-recorded cooperative allogrooming between two female (one adult and another juvenile) northern red muntjacs. Behavioural quantification suggests that although both individuals exchanged equal numbers of grooming bouts, the adult female received a greater share of grooming time and episodes, respectively. The time spent on grooming as well as the number of tongue strokes delivered were found to be negatively correlated between the two individuals. The grooming pattern could possibly be attributed to kin selection and detailed work is required to understand this behaviour in this poorly-studied primitive deer. Our record indicates the possible existence of cooperative allogrooming in other ungulates of the Order Artiodactyla. [ABSTRACT FROM AUTHOR]

Hamilton's rule provides the cornerstone for our understanding of the evolution of all forms of social behavior, from altruism to spite, across all organisms, from viruses to humans. In contrast to the standard prediction from Hamilton's rule, recent studies have suggested that altruistic helping can be favored even if it does not benefit relatives, as long as it decreases the environmentally induced variance of their reproductive success ("altruistic bet-hedging"). However, previous predictions both rely on an approximation and focus on variance-reducing helping behaviors. We derived a version of Hamilton's rule that fully captures environmental variability. This shows that decreasing (or increasing) the variance in the absolute reproductive success of relatives does not have a consistent effect--it can either favor or disfavor the evolution of helping. We then empirically quantified the effect of helping on the variance in reproductive success across 15 species of cooperatively breeding birds. We found that a) helping did not consistently decrease the variance of reproductive success and often increased it, and b) the mean benefits of helping across environments consistently outweighed other variability components of reproductive success. Altogether, our theoretical and empirical results suggest that the effects of helping on the variability components of reproductive success have not played a consistent or strong role in favoring helping. [ABSTRACT FROM AUTHOR]

Kin selection is important for understanding the evolution of social behaviour in group-living species. Yet, the role of kinship in solitary species has received little attention. We studied how kinship influences intraspecific variation in social organization and spatial structure in a predominantly solitary species, the bush Karoo rat, Otomys unisulcatus , from the Succulent Karoo semidesert of South Africa. We predicted that if social groups occur, they should consist of close kin. We further predicted that the spatial structure is not random, but that close kin live closer to each other. Over 5 years we performed trapping and focal animal observations and fitted mini-GPS dataloggers simultaneously on 125 neighbouring female bush Karoo rats to investigate how their spatial structure was influenced by kinship. Females were mainly solitary, although small social groups also occurred, all consisting of close kin, typically females, such as a mother and her adult daughter or sisters. Although females did have more nonkin than kin neighbours, kin lived closer to each other than nonkin. Daily ranges were larger in the breeding than in the nonbreeding season and overlapped more between kin than nonkin females. We conclude that kinship should be considered when studying solitary species as it might influence variation in social organization and spatial structure. • This study is the first use of mini-GPS devices in a small rodent. • Female bush Karoo rat females are mainly solitary. • Sometimes they form small groups, always consisting of close kin. • They display a kinship spatial structure. • Kinship is important to understand solitary species' social system. [ABSTRACT FROM AUTHOR]

Social behaviours are typically modelled using neighbour-modulated fitness, which focuses on individuals having their fitness altered by neighbours. However, these models are either interpreted using inclusive fitness, which focuses on individuals altering the fitness of neighbours, or not interpreted at all. This disconnect leads to interpretational mistakes and obscures the adaptive significance of behaviour. We bridge this gap by presenting a systematic methodology for constructing inclusive-fitness models. We find a behaviours inclusive-fitness effect by summing primary and secondary deviations in reproductive value. Primary deviations are the immediate result of a social interaction; for example, the cost and benefit of an altruistic act. Secondary deviations are compensatory effects that arise because the total reproductive value of the population is fixed; for example, the increased competition that follows an altruistic act. Compared to neighbour-modulated fitness methodologies, our approach is often simpler and reveals the models inclusive-fitness narrative clearly. We implement our methodology first in a homogeneous population, with supplementary examples of help under synergy, help in a viscous population and Creels paradox. We then implement our methodology in a class-structured population, where the advantages of our approach are most evident, with supplementary examples of altruism between age classes, and sex-ratio evolution.

Male mice who are heterozygous for distorting and non-distorting alleles at the t -haplotype transmit the driving t -haplotype around 90% of the time—a drastic departure from Mendelian expectations. This selfish act comes at a cost. The mechanism underlying transmission distortion in this system causes severe sterility in males homozygous for the drive alleles, ultimately preventing its fixation. Curiously, many driving t -haplotypes also induce embryonic lethality in both sexes when homozygous; however, this is neither universal nor a necessity for this distortion mechanism. Charlesworth provided an adaptive explanation for the evolution of lethal t -haplotypes in a population segregating for distorting and non-distorting t alleles—if mothers compensate by replacing dead embryos with new offspring (or by transferring energy to surviving offspring), a recessive lethal can be favored because it effectively allows mothers the opportunity to trade in infertile males for potentially fertile offspring. This model, however, requires near complete reproductive compensation for the invasion of the lethal t -haplotype and produces an equilibrium frequency of lethal drivers well below what is observed in nature. We show that low levels of systemic inbreeding, which we model as brother–sister mating, allow lethal t -haplotypes to invade with much lower levels of reproductive compensation. Furthermore, inbreeding allows these lethal haplotypes to largely displace the ancestral male-sterile haplotypes. Our results show that together inbreeding and reproductive compensation move expected equilibria closer to observed haplotype frequencies in natural populations and occur under lower, potentially more reasonable, parameters. [ABSTRACT FROM AUTHOR]

Eusocial organisms typically live in colonies with one reproductive queen supported by thousands of sterile workers. It is widely believed that monogamous mating is a precondition for the evolution of eusociality. Here, we present a theoretical model that simulates a realistic scenario for the evolution of eusociality. In the model, mothers can evolve control over resource allocation to offspring, affecting offspring's body size. The offspring can evolve body-size-dependent dispersal, by which they disperse to breed or stay at the nest as helpers. We demonstrate that eusociality can evolve even if mothers are not strictly monogamous, provided that they can constrain their offspring's reproduction through manipulation. We also observe the evolution of social polymorphism with small individuals that help and larger individuals that disperse to breed. Our model unifies the traditional kin selection and maternal manipulation explanations for the evolution of eusociality and demonstrates that--contrary to current consensus belief--eusociality can evolve despite highly promiscuous mating. [ABSTRACT FROM AUTHOR]

Individuals delay natal dispersal for many reasons. There may be no place to disperse to; immediate dispersal or reproduction may be too costly; immediate dispersal may mean that the individual and their relatives miss the benefits of group living. Understanding the factors that lead to the evolution of delayed dispersal is important because delayed dispersal sets the stage for complex social groups and social behavior. Here, we study the evolution of delayed dispersal when the quality of the local environment is improved by greater numbers of individuals (e. g. , safety in numbers). We assume that individuals who delay natal dispersal also expect to delay personal reproduction. In addition, we assume that improved environmental quality benefits manifest as changes to fecundity and survival. We are interested in how do the changes in these life-history features affect delayed dispersal. We use a model that ties evolution to population dynamics. We also aim to understand the relationship between levels of delayed dispersal and the probability of establishing as an independent breeder (a population-level feature) in response to changes in life-history details. Our model emphasizes kin selection and considers a sexual organism, which allows us to study parent–offspring conflict over delayed dispersal. At evolutionary equilibrium, fecundity and survival benefits of group size or quality promote higher levels of delayed dispersal over a larger set of life histories with one exception. The exception is for benefits of increased group size or quality reaped by the individuals who delay dispersal. There, the increased benefit does not change the life histories supporting delay dispersal. Next, in contrast to previous predictions, we find that a low probability of establishing in a new location is not always associated with a higher incidence of delayed dispersal. Finally, we find that increased personal benefits of delayed dispersal exacerbate the conflict between parents and their offspring. We discuss our findings in relation to previous theoretical and empirical work, especially work related to cooperative breeding. • We study the evolution of delayed natal dispersal. • We assume delayed dispersal brings benefits to the natal group. • The number of delayed-dispersers is independent of the group quality. • Habitat saturation is not always associated with delayed dispersal. • Increased group benefits exacerbate conflict within the natal group. [ABSTRACT FROM AUTHOR]

A long-standing problem in evolutionary theory is to clarify in what sense (if any) natural selection cumulatively improves the design of organisms. Various concepts, such as fitness and inclusive fitness , have been proposed to resolve this problem. In addition, there have been attempts to replace the original problem with more tractable questions, such as whether a given gene or trait is favored by selection. Here, we ask what theoretical properties the concept fitness should possess to encapsulate the improvement criterion required to talk meaningfully about adaptive evolution. We argue that natural selection tends to shape phenotypes based on the causal properties of individuals and that this tendency is, therefore, best captured by a fitness concept that focuses on these properties. We highlight a fitness concept that meets this role under broad conditions but requires adjustments in our conceptual understanding of adaptive evolution. These adjustments combine elements of Dawkinsian gene selectionism and Egbert Leigh's "parliament of genes." [ABSTRACT FROM AUTHOR]

Behavioural and physiological resistance are key to slowing epidemic spread. We explore the evolutionary and epidemic consequences of their different costs for the evolution of tolerance that trades off with resistance. Behavioural resistance affects social cohesion, with associated group-level costs, while the cost of physiological resistance accrues only to the individual. Further, resistance, and the associated reduction in transmission, benefit susceptible hosts directly, whereas infected hosts only benefit indirectly, by reducing transmission to kin. We therefore model the coevolution of transmission-reducing resistance expressed in susceptible hosts with resistance expressed in infected hosts, as a function of kin association, and analyse the effect on population-level outcomes. Using parameter values for guppies, Poecilia reticulata, and their gyrodactylid parasites, we find that: (1) either susceptible or infected hosts should invest heavily in resistance, but not both; (2) kin association drives investment in physiological resistance more strongly than in behavioural resistance; and (3) even weak levels of kin association can favour altruistic infected hosts that invest heavily in resistance (versus selfish tolerance), eliminating parasites. Overall, our finding that weak kin association affects the coevolution of infected and susceptible investment in both behavioural and physiological resistance suggests that kin selection may affect disease dynamics across systems. [ABSTRACT FROM AUTHOR]

Summary: Greenbeards are selfish genetic elements that make their bearers behave either altruistically towards individuals bearing similar greenbeard copies or harmfully towards individuals bearing different copies. They were first proposed by W. D. Hamilton over 50 yr ago, to illustrate that kin selection may operate at the level of single genes. Examples of greenbeards have now been reported in a wide range of taxa, but they remain undocumented in plants. In this paper, we discuss the theoretical likelihood of greenbeard existence in plants. We then question why the greenbeard concept has never been applied to plants and speculate on how hypothetical greenbeards could affect plant–plant interactions. Finally, we point to different research directions to improve our knowledge of greenbeards in plants. [ABSTRACT FROM AUTHOR]

Delayed natal dispersal is thought to have evolved in response to survival benefits of philopatry and group formation under environmental and/or demographic constraints, with kin selection subsequently promoting the emergence of cooperative breeding behaviours. We studied sociality and natal and breeding dispersal of a colour-banded population of Eastern Yellow Robin Eopsaltria australis over 10 years to better understand the evolution of facultative cooperative breeding in this long-lived, territorial songbird. Breeding group size averaged 3.08 (range 2–6) adults and 82% of helpers were males. All male young delayed dispersal to help one or both parents (82.1%), another first order relative (12.5%) or other relatives (5.4%) for between one and four years before establishing as a dominant breeder. The social relationships of female helpers was confirmed in only two instances, with the helper being the daughter of the breeding pair. Helpers significantly increased annual productivity, which averaged 1.44 (95% confidence intervals: 1.07–1.81) with no helpers and 2.04 (95% confidence intervals: 1.74–2.34) with helpers present. Male young were highly philopatric; most either inherited the natal territory or budded off a portion of the natal territory, and none dispersed more than one territory away. Most females appeared to disperse further after reaching independence to become floaters. Breeding dispersal was limited to females, who dispersed after either divorce or to avoid incest once a son inherited the territory. These results confirm that Eastern Yellow Robin helpers likely gain indirect fitness benefits from helping. [ABSTRACT FROM AUTHOR]

Prosocial punishment is a process of enforcement that promotes a partner's cooperation in a sustained relationship and is an important mechanism in the evolution of cooperative behaviour. The 'pay-to-stay' hypothesis predicts that in cooperatively breeding animals, dominant breeders punish idle subordinates (helpers) that assist breeders in offspring care to promote their cooperation. However, limited evidence demonstrates that subordinates increase helping effort in response to breeder aggression; therefore, whether breeder aggression functions as punishment remains unclear. In the laboratory, we observed idle helpers of the cooperatively breeding cichlid fish Neolamprologus savoryi and whether dominant breeders punished them. Breeders increased their aggression towards subordinates that were prevented from helping by 2 h removal from the tank, and attacked helpers subsequently increased territorial defence depending on breeder aggression level, suggesting that breeder aggression functions as punishment. No breeder aggression was observed when helpers performed pre-emptive helping behaviour prior to dominant breeder attacks. Notably, dominant breeders punished even their offspring when idle, suggesting that the helping behaviours of relatives may be facilitated by parental punishment. Our study shows that dominant group members can use punishment to elicit help from subordinates, even in nonhuman animals. • We tested whether dominant breeders punish idle helpers in Neolamprologus savoryi. • Breeders increased their aggression towards helpers prevented from helping. • The helpers that were attacked by the breeders increased territorial defence. • Pre-emptive helping by subordinates may function as pre-emptive appeasement. • Dominant breeders can use punishment to elicit help from subordinates even in fish. [ABSTRACT FROM AUTHOR]

In cooperative breeding systems, inclusive fitness theory predicts that nonbreeding helpers more closely related to the breeders should be more willing to provide costly alloparental care and thus have more impact on breeder fitness. In the red-cockaded woodpecker (Dryobates borealis), most helpers are the breeders' earlier offspring, but helpers do vary within groups in both relatedness to the breeders (some even being unrelated) and sex, and it can be difficult to parse their separate impacts on breeder fitness. Moreover, most support for inclusive fitness theory has been positive associations between relatedness and behavior rather than actual fitness consequences. We used functional linear models to evaluate the per capita effects of helpers of different relatedness on eight breeder fitness components measured for up to 41 years at three sites. In support of inclusive fitness theory, helpers more related to the breeding pair made greater contributions to six fitness components. However, male helpers made equal contributions to increasing prefledging survival regardless of relatedness. These findings suggest that both inclusive fitness benefits and other direct benefits may underlie helping behaviors in the red-cockaded woodpecker. Our results also demonstrate the application of an underused statistical approach to disentangle a complex ecological phenomenon. [ABSTRACT FROM AUTHOR]

Kin selection and direct reciprocity are two most basic mechanisms for promoting cooperation in human society. Generalizing the standard models of the multi-player Prisoner's Dilemma and the Public Goods games to allow for asymmetric cost-benefit ratios across the players, we study the effects of genetic relatedness on cooperation in the context of repeated interactions. Two sets of interrelated results are established: a set of analytical results focusing on the subgame perfect equilibrium and a set of agent-based simulation results based on an evolutionary game model. We show that in both cases increasing genetic relatedness does not always facilitate cooperation. Specifically, kinship can hinder the effectiveness of reciprocity in two ways. First, the condition for sustaining cooperation through direct reciprocity is harder to satisfy when relatedness increases in an intermediate range. Second, full cooperation is impossible to sustain for a medium-high range of relatedness values. Moreover, individuals with low cost-benefit ratios can end up with lower payoffs than their groupmates with high cost-benefit ratios. Our results point to the importance of explicitly accounting for within-population heterogeneity when studying the evolution of cooperation. [ABSTRACT FROM AUTHOR]

According to Michener's paradox, most altruistic groups in nature should be small and large groups should not exist. This is because per capita productivity is thought to decrease as groups get larger, meaning that the share of indirect fitness available to each group member declines, which favours dispersal. The empirical evidence for a decrease in per capita productivity is contradictory, however, and limited to the social Hymenoptera. I report that per capita reproductive success decreased with increasing group size across 26 cooperatively breeding bird species. Small groups comprising two or three individuals were the most common (79% of 16,101 groups), and these had the highest per capita reproductive success. This close fit between per capita reproductive success and the distribution of group sizes in nature suggests that it may indeed be difficult for large groups to evolve through indirect fitness benefits alone. [ABSTRACT FROM AUTHOR]

The adaptive effects of inbreeding are understudied, but accumulating evidence suggests that it plays a major adaptive role in speciation, as populations with a history of inbreeding are more prone to it. Differences in inbreeding tolerance in two populations of Microtus hartingi voles were studied through a series of experiments on reproductive behaviour and partner choice. Modelling an artificial polygyny via the formation of trios composed of a brother, sister, and an unrelated female has shown an uneven attitude towards inbreeding, which was closely linked to the reproduction strategy: voles of the Rhodopean population (RP) would reproduce communally with only a moderate decrease in reproduction success, while in monogamous M. hartingi ankaraensis voles from Central Anatolia (CAP), the reproductive success dropped almost to zero due to severe social stress resulting in heavily antagonistic behaviour between females; aggression levels rose with maturation. Studies of reproduction in pairs of relatives revealed the absence of inbreeding avoidance in the polygynous population (RP) and a sharp decrease in reproduction probability in the monogamous subspecies (CAP). Olfactory three-choice behavioural tests have proven that voles do not choose the smell randomly, juveniles do not have partner preferences, and adults choose the unrelated individual's odour. RP voles prefer to mate with kin first, whereas CAP voles mate with non-kin first. The differences in reproductive strategy might have evolved due to habitat fragmentation and restriction of natal dispersal in the RP which has been isolated from the ancient Anatolian Microtus hartingi population since the Pleistocene. The adaptation to communal reproduction via kin selection resulted in increased inbreeding tolerance. [ABSTRACT FROM AUTHOR]

Much research on the evolution of altruism via kin selection, group selection, and reciprocity focuses on the role of a single locus or quantitative trait. Very few studies have explored how linked selection, or selection at loci neighboring an altruism locus, impacts the evolution of altruism. While linked selection can decrease the efficacy of selection at neighboring loci, it might have other effects including promoting selection for altruism by increasing relatedness in regions of low recombination. Here, we used population genetic simulations to study how negative selection at linked loci, or background selection, affects the evolution of altruism. When altruism occurs between full siblings, we found that background selection interfered with selection on the altruistic allele, increasing its fixation probability when the altruistic allele was disfavored and reducing its fixation when the allele was favored. In other words, background selection has the same effect on altruistic genes in family‐structured populations as it does on other, nonsocial, genes. This contrasts with prior research showing that linked selective sweeps can favor the evolution of cooperation, and we discuss possibilities for resolving these contrasting results. [ABSTRACT FROM AUTHOR]

Plants have the ability to recognize their kin neighbors, which may be a beneficial trait that increases inclusive fitness, by suppressing individual growth to support the combined growth of the group. However, the advantages of kin cooperation (known as kin selection theory), may differ across environmental gradients, with competition between related individuals potentially being detrimental under resource limitation (following niche partitioning theory). The study aimed to understand how quinoa (Chenopodium quinoa (Willd)) plants grow with kin or with non-kin under different nutrient supply rates. Plants were grown in treatments' post-germination for 70 days. Biomass accumulation, allocation to organs, and organ traits related to resource acquisition were measured at the end of the experiment. Total mass and shoot mass were greater for plants grown with kin than with non-kin across nutrient treatments. Plants grown with kin had greater root allocation than with non-kin under low and high nutrients. Allocation to leaves, specific leaf area, and average leaf mass were greater for plants grown with non-kin than kin under high-nutrient supply, but did not differ under low-nutrient supply. Allocation to stem was greater for plants grown with kin than non-kin under high-nutrient supply, but did not differ under low-nutrient supply. Specific taproot length and specific stem length were respectively positively and negatively related to increased fertility, but unrelated to kinship. Our results suggest that both niche partitioning and kin selection processes may be at play in quinoa, depending on whether soil nutrient competition is more important. Under both situations, quinoa plants always grew better with kin than non-kin regardless of soil nutrient conditions. [ABSTRACT FROM AUTHOR]

Because plumage coloration is frequently involved in sexual selection, for both male and female mate choice, birds with aberrant plumage should have fewer mating opportunities and thus lower reproductive output. Here we report an Eastern Bluebird (Sialia sialis) female with a brown phenotype that raised a brood of four chicks to fledging. The brown female and her mate were only related to their social offspring to the second degree and one of the offspring was a half‐sibling. We propose four family tree scenarios and discuss their implications (e.g., extra‐pair paternity, conspecific brood parasitism). Regardless of the tree, the brown female was able to find a mate, which may have been facilitated by the bottleneck created by the severe snowstorms in February 2021. [ABSTRACT FROM AUTHOR]

In evolutionary terms, life is about reproduction. Yet, in some species, individuals forgo their own reproduction to support the reproductive efforts of others. Social insect colonies for example, can contain up to a million workers that actively cooperate in tasks such as foraging, brood care and nest defence, but do not produce offspring. In such societies the division of labour is pronounced, and reproduction is restricted to just one or a few individuals, most notably the queen(s). This extreme eusocial organisation exists in only a few mammals, crustaceans and insects, but strikingly, it evolved independently up to nine times in the order Hymenoptera (including ants, bees and wasps). Transitions from a solitary lifestyle to an organised society can occur through natural selection when helpers obtain a fitness benefit from cooperating with kin, owing to the indirect transmission of genes through siblings. However, this process, called kin selection, is vulnerable to parasitism and opportunistic behaviours from unrelated individuals. An ability to distinguish kin from non‐kin, and to respond accordingly, could therefore critically facilitate the evolution of eusociality and the maintenance of non‐reproductive workers. The question of how the hymenopteran brain has adapted to support this function is therefore a fundamental issue in evolutionary neuroethology. Early neuroanatomical investigations proposed that social Hymenoptera have expanded integrative brain areas due to selection for increased cognitive capabilities in the context of processing social information. Later studies challenged this assumption and instead pointed to an intimate link between higher social organisation and the existence of developed sensory structures involved in recognition and communication. In particular, chemical signalling of social identity, known to be mediated through cuticular hydrocarbons (CHCs), may have evolved hand in hand with a specialised chemosensory system in Hymenoptera. Here, we compile the current knowledge on this recognition system, from emitted identity signals, to the molecular and neuronal basis of chemical detection, with particular emphasis on its evolutionary history. Finally, we ask whether the evolution of social behaviour in Hymenoptera could have driven the expansion of their complex olfactory system, or whether the early origin and conservation of an olfactory subsystem dedicated to social recognition could explain the abundance of eusocial species in this insect order. Answering this question will require further comparative studies to provide a comprehensive view on lineage‐specific adaptations in the olfactory pathway of Hymenoptera. [ABSTRACT FROM AUTHOR]

Upon uptake of toxins, insects launch a detoxification program. This program is deployed in multiple organs and cells to raise their tolerance against the toxin. The molecular mechanisms of this program inside the insect body have been studied and understood in detail. Here, we report on a yet unexplored extra-corporeal detoxification of insecticides in Drosophila melanogaster. Wild-type D. melanogaster incubated with DDT, a contact insecticide, in a closed environment died as expected. However, incubation of a second cohort in the same environment after removal of the dead flies was not lethal. The effect was significantly lower if the flies of the two cohorts were unrelated. Incubation assays with Chlorpyrifos, another contact insecticide, yielded identical results, while incubation assays with Chlorantraniliprole, again a contact insecticide, was toxic for the second cohort of flies. A cohort of flies incubated in a DDT environment after an initial incubation of a honeybee survived treatment. Together, our data suggest that insects including Apis mellifera and D. melanogaster have the capacity to modify their proximate environment. Consequently, in their ecological niche, following individuals might be saved from intoxication thereby facilitating colonisation of an attractive site.

Abstract Background Conventional wisdom in evolutionary theory considers aging as a non-selected byproduct of natural selection. Based on this, conviction aging was regarded as an inevitable phenomenon. It was also thought that in the wild organisms tend to die from diseases, predation and other accidents before they could reach the time when senescence takes its course. Evidence has accumulated, however, that aging is not inevitable and there are organisms that show negative aging even. Furthermore, old age does play a role in the deaths of many different organisms in the wild also. The hypothesis of programmed aging posits that a limited lifespan can evolve as an adaptation (i.e., positively selected for) in its own right, partly because it can enhance evolvability by eliminating “outdated” genotypes. A major shortcoming of this idea is that non-aging sexual individuals that fail to pay the demographic cost of aging would be able to steal good genes by recombination from aging ones. Results Here, we show by a spatially explicit, individual-based simulation model that aging can positively be selected for if a sufficient degree of kin selection complements directional selection. Under such conditions, senescence enhances evolvability because the rate of aging and the rate of recombination play complementary roles. The selected aging rate is highest at zero recombination (clonal reproduction). In our model, increasing extrinsic mortality favors evolved aging by making up free space, thereby decreasing competition and increasing drift, even when selection is stabilizing and the level of aging is set by mutation-selection balance. Importantly, higher extrinsic mortality is not a substitute for evolved aging under directional selection either. Reduction of relatedness decreases the evolved level of aging; chance relatedness favors non-aging genotypes. The applicability of our results depends on empirical values of directional and kin selection in the wild. Conclusions We found that aging can positively be selected for in a spatially explicit population model when sufficiently strong directional and kin selection prevail, even if reproduction is sexual. The view that there is a conceptual link between giving up clonal reproduction and evolving an aging genotype is supported by computational results.

Plant-to-plant volatile-mediated communication and subsequent induced resistance to insect herbivores is common. Less clear is the adaptive significance of these interactions; what selective mechanisms favour plant communication and what conditions allow individuals to benefit by both emitting and responding to cues? We explored the predictions of two non-exclusive hypotheses to explain why plants might emit cues, the kin selection hypothesis (KSH) and the mutual benefit hypothesis (MBH). We examined 15 populations of sagebrush that experience a range of naturally occurring herbivory along a 300 km latitudinal transect. As predicted by the KSH, we found several uncommon chemotypes with some chemotypes occurring only within a single population. Consistent with the MBH, chemotypic diversity was negatively correlated with herbivore pressure; sites with higher levels of herbivory were associated with a few common cues broadly recognized by most individuals. These cues varied among different populations. Our results are similar to those reported for anti-predator signalling in vertebrates.

Abstract Much research on the evolution of altruism via kin selection, group selection, and reciprocity focuses on the role of a single locus or quantitative trait. Very few studies have explored how linked selection, or selection at loci neighboring an altruism locus, impacts the evolution of altruism. While linked selection can decrease the efficacy of selection at neighboring loci, it might have other effects including promoting selection for altruism by increasing relatedness in regions of low recombination. Here, we used population genetic simulations to study how negative selection at linked loci, or background selection, affects the evolution of altruism. When altruism occurs between full siblings, we found that background selection interfered with selection on the altruistic allele, increasing its fixation probability when the altruistic allele was disfavored and reducing its fixation when the allele was favored. In other words, background selection has the same effect on altruistic genes in family‐structured populations as it does on other, nonsocial, genes. This contrasts with prior research showing that linked selective sweeps can favor the evolution of cooperation, and we discuss possibilities for resolving these contrasting results.

Abstract The evolution of cooperation in microbes is a challenge to explain because microbes producing costly goods for the benefit of any strain types (cooperators) often withstand the threat of elimination by interacting with individuals that exploit these benefits without contributing (defectors). Here we developed an individual-based model to investigate whether partial privatization via the partial secretion of goods can favor cooperation in structured, surface-attaching microbial populations, biofilms. Whether partial secretion can favor cooperation in biofilms is unclear for two reasons. First, while partial privatization has been shown to foster cooperation in unstructured populations, little is known about the role of partial privatization in biofilms. Second, while limited diffusion of goods favors cooperation in biofilms because molecules are more likely to be shared with genetically-related individuals, partial secretion reduces goods that could have been directed towards genetically related individuals. Our results show that although partial secretion weakens the role that limited diffusion has on fostering cooperation, partial secretion favors cooperation in biofilms. Overall, our results provide predictions that future experiments could test to reveal contributions of relatedness and partial secretion to the social evolution of biofilms.

The evolution of cooperation depends on two crucial overarching factors: relatedness, which describes the extent to which the recipient shares genes in common with the actor; and quality, which describes the recipient's basic capacity to transmit genes into the future. While most research has focused on relatedness, there is a growing interest in understanding how quality modulates the evolution of cooperation. However, the impact of inheritance of quality on the evolution of cooperation remains largely unexplored, especially in spatially structured populations. Here, we develop a mathematical model to understand how inheritance of quality, in the form of social status, influences the evolution of helping and harming within social groups in a viscous-population setting. We find that: (1) status-reversal transmission, whereby parental and offspring status are negatively correlated, strongly inhibits the evolution of cooperation, with low-status individuals investing less in cooperation and high-status individuals being more prone to harm; (2) transmission of high status promotes offspring philopatry, with more cooperation being directed towards the higher-dispersal social class; and (3) fertility inequality and inter-generational status inheritance reduce within-group conflict. Overall, our study highlights the importance of considering different mechanisms of phenotypic inheritance, including social support, and their potential interactions in shaping animal societies. [ABSTRACT FROM AUTHOR]

Behavioural variation is essential for animals to adapt to different social and environmental conditions. The Kinship Theory of Intragenomic Conflict (KTIC) predicts that parent‐specific alleles can support different behavioural strategies to maximize allele fitness. Previous studies, including in honey bees (Apis mellifera), supported predictions of the KTIC for parent‐specific alleles to promote selfish behaviour. Here, we test the KTIC prediction that for altruism‐promoting genes (i.e. those that promote behaviours that support the reproductive fitness of kin), the allele with the higher altruism optimum should be selected to be expressed while the other is silenced. In honey bee colonies, workers act altruistically when tending to the queen by performing a 'retinue' behaviour, distributing the queen's mandibular pheromone (QMP) throughout the hive. Workers exposed to QMP do not activate their ovaries, ensuring they care for the queen's brood instead of competing to lay unfertilized eggs. Due to the haplodiploid genetics of honey bees, the KTIC predicts that response to QMP is favoured by the maternal genome. We report evidence for parent‐of‐origin effects on the retinue response behaviour, ovarian development and gene expression in brains of worker honey bees exposed to QMP, consistent with the KTIC. Additionally, we show enrichment for genes with parent‐of‐origin expression bias within gene regulatory networks associated with variation in bees' response to QMP. Our study demonstrates that intragenomic conflict can shape diverse social behaviours and influence expression patterns of single genes as well as gene networks. [ABSTRACT FROM AUTHOR]

Social animals, and ants, in particular, exhibit a range of cooperative behaviors. One such behavior is the rescue of group members, which cannot return to the nest by themselves. However, if several group members need to be rescued, how do ants prioritize whom to save first? Furthermore, when food is offered in parallel, do ants prioritize feeding over rescuing? We studied the rescue behavior of the desert ant Cataglyphis niger. Workers invest more time in rescuing pupae than adult workers, perhaps because the value of brood is higher than that of older workers serving as foragers. Specific rescue behaviors, pulling the trapped individual or digging around it, differed when directed toward adults or pupae: rescuing workers more often pulled pupae whereas they dug more around trapped adults. Rescuing workers did not prioritize living individuals over dead ones or intact workers over injured ones indicating that trapped individuals were recognized chemically rather than by their morphology or behavior. Finally, workers prioritized foraging over rescuing, perhaps because fewer workers specialize in rescue behavior than in foraging. Our analysis indeed revealed that fewer workers both foraged and rescued trapped workers than expected by chance. In conclusion, ants that rescue others exhibit a complex set of behaviors, with varying attention and specific behaviors targeted at different individuals, perhaps according to the colony's needs. Our study is important for emphasizing a relatively neglected aspect of sociality (rescue of group members) and demonstrates that the attentions of rescues differ based on the trapped nestmate's life stage. [ABSTRACT FROM AUTHOR]

The article explores the concept of "sociovirology" and its application in studying the evolution of virus life-history traits. It emphasizes the social nature of viruses and the importance of understanding their interactions with hosts. The article discusses the challenges of measuring virus fitness in a social context and the role of relatedness in shaping selective pressures on virus populations. It also suggests that evolutionary epidemiology and multiple infection theory can provide useful frameworks for studying virus evolution. The article raises questions about the appropriateness of the term "sociovirology" and highlights the need for a formal definition of fitness in this context. [Extracted from the article]

In cooperatively breeding birds, why do some individuals breed independently but others have to help at home? This question has been rarely addressed despite its fundamental importance for understanding the evolution of social cooperation.We address it using 15 years of data from Tibetan ground tits Pseudopodoces humilis where helpers consist of younger males. Since whether younger males successfully breed depends critically on their chances to occupy territories nearby home, our analytic strategy is to identify the determinants of individual differences in gaining territory ownership among these ready‐to‐breed males.Across widowed, last‐year helper and yearling males, an age advantage was evident in inheriting resident territories, occupying adjacent vacancies and budding off part of adjacent territories, which left some last‐year helpers and most yearling males to take the latter two routes. These males were more likely to acquire a territory if they were genetically related to the previous or current territory owners; otherwise they remained on natal territories as helpers. The relatedness effect can arise from the prior residence advantage established in the preceding winter when younger males followed their parents to perform kin‐directed off‐territory forays.Our research highlights the key role of local kinship in determining younger males' territory acquisition and thus their fate in terms of independent reproduction versus help. This finding provides insight into the formation of kin‐based, facultative cooperative societies prevailing among vertebrates. [ABSTRACT FROM AUTHOR]

Background: Conventional wisdom in evolutionary theory considers aging as a non-selected byproduct of natural selection. Based on this, conviction aging was regarded as an inevitable phenomenon. It was also thought that in the wild organisms tend to die from diseases, predation and other accidents before they could reach the time when senescence takes its course. Evidence has accumulated, however, that aging is not inevitable and there are organisms that show negative aging even. Furthermore, old age does play a role in the deaths of many different organisms in the wild also. The hypothesis of programmed aging posits that a limited lifespan can evolve as an adaptation (i.e., positively selected for) in its own right, partly because it can enhance evolvability by eliminating "outdated" genotypes. A major shortcoming of this idea is that non-aging sexual individuals that fail to pay the demographic cost of aging would be able to steal good genes by recombination from aging ones. Results: Here, we show by a spatially explicit, individual-based simulation model that aging can positively be selected for if a sufficient degree of kin selection complements directional selection. Under such conditions, senescence enhances evolvability because the rate of aging and the rate of recombination play complementary roles. The selected aging rate is highest at zero recombination (clonal reproduction). In our model, increasing extrinsic mortality favors evolved aging by making up free space, thereby decreasing competition and increasing drift, even when selection is stabilizing and the level of aging is set by mutation-selection balance. Importantly, higher extrinsic mortality is not a substitute for evolved aging under directional selection either. Reduction of relatedness decreases the evolved level of aging; chance relatedness favors non-aging genotypes. The applicability of our results depends on empirical values of directional and kin selection in the wild. Conclusions: We found that aging can positively be selected for in a spatially explicit population model when sufficiently strong directional and kin selection prevail, even if reproduction is sexual. The view that there is a conceptual link between giving up clonal reproduction and evolving an aging genotype is supported by computational results. [ABSTRACT FROM AUTHOR]

Social behaviours are typically modelled using neighbour-modulated fitness, which focuses on individuals having their fitness altered by neighbours. However, these models are either interpreted using inclusive fitness, which focuses on individuals altering the fitness of neighbours, or not interpreted at all. This disconnect leads to interpretational mistakes and obscures the adaptive significance of behaviour. We bridge this gap by presenting a systematic methodology for constructing inclusive-fitness models. We find a behaviour's 'inclusive-fitness effect' by summing primary and secondary deviations in reproductive value. Primary deviations are the immediate result of a social interaction; for example, the cost and benefit of an altruistic act. Secondary deviations are compensatory effects that arise because the total reproductive value of the population is fixed; for example, the increased competition that follows an altruistic act. Compared to neighbour-modulated fitness methodologies, our approach is often simpler and reveals the model's inclusive-fitness narrative clearly. We implement our methodology first in a homogeneous population, with supplementary examples of help under synergy, help in a viscous population and Creel's paradox. We then implement our methodology in a class-structured population, where the advantages of our approach are most evident, with supplementary examples of altruism between age classes, and sex-ratio evolution. [ABSTRACT FROM AUTHOR]

Laboratory experiments have suggested that bacteria perform a range of cooperative behaviors, which are favored because they are directed toward relatives (kin selection). However, there is a lack of evidence for cooperation and kin selection in natural bacterial populations. Molecular population genetics offers a promising method to study natural populations because the theory predicts that kin selection will lead to relaxed selection, which will result in increased polymorphism and divergence at cooperative genes. Examining a natural population of Bacillus subtilis, we found consistent evidence that putatively cooperative traits have higher polymorphism and greater divergence than putatively private traits expressed at the same rate. In addition, we were able to eliminate alternative explanations for these patterns and found more deleterious mutations in genes controlling putatively cooperative traits. Overall, our results suggest that cooperation is favored by kin selection, with an average relatedness of r = .79 between interacting individuals. [ABSTRACT FROM AUTHOR]

A basic mechanism of kin selection is limited dispersal, whereby individuals remain close to their place of origin such that even indiscriminate social interaction tends to modify the fitness of genealogical kin. Accordingly, the causes and consequences of dispersal have received an enormous amount of attention in the social evolution literature. This work has focused on dispersal of individuals in space, yet similar logic should apply to dispersal of individuals in time (e.g. dormancy). We investigate how kin selection drives the evolution of dormancy and how dormancy modulates the evolution of altruism. We recover dormancy analogues of key results that have previously been given for dispersal, showing that: (1) kin selection favours dormancy as a means of relaxing competition between relatives; (2) when individuals may adjust their dormancy behaviour to local density, they are favoured to do so, resulting in greater dormancy in high-density neighbourhoods and a concomitant 'constant non-dormant principle'; (3) when dormancy is constrained to be independent of density, there is no relationship between the rate of dormancy and the evolutionary potential for altruism; and (4) when dormancy is able to evolve in a density-dependent manner, a greater potential for altruism is expected in populations with lower dormancy. [ABSTRACT FROM AUTHOR]

Abstract Background Kin and multilevel selection provide explanations for the existence of altruism based on traits or processes that enhance the inclusive fitness of an altruist individual. Kin selection is often based on individual-level traits, such as the ability to recognize other altruists, whereas multilevel selection requires a metapopulation structure and dispersal process. These theories are unified by the general principle that altruism can be fixed by positive selection provided the benefit of altruism is preferentially conferred to other altruists. Here we take a different explanatory approach based on the recently proposed concept of an “ecological scaffold”. We demonstrate that ecological conditions consisting of a patchy nutrient supply that generates a metapopulation structure, episodic mixing of groups, and severe nutrient limitation, can support or “scaffold” the evolution of altruism in a population of microbes by amplifying drift. This contrasts with recent papers in which the ecological scaffold was shown to support selective processes and demonstrates the power of scaffolding even in the absence of selection. Results Using computer simulations motivated by a simple theoretical model, we show that, although an altruistic mutant can be fixed within a single population of non-altruists by drift when nutrients are severely limited, the resulting altruistic population remains vulnerable to non-altruistic mutants. We then show how the imposition of the “ecological scaffold” onto a population of non-altruists alters the balance between selection and drift in a way that supports the fixation and subsequent persistence of altruism despite the possibility of invasion by non-altruists. Conclusions The fixation of an altruistic mutant by drift is possible when supported by ecological conditions that impose a metapopulation structure, episodic mixing of groups, and severe nutrient limitation. This is significant because it offers an alternative explanation for the evolution of altruism based on drift rather than selection. Given the ubiquity of low-nutrient “oligotrophic” environments in which microbes exist (e.g., the open ocean, deep subsurface soils, or under the polar ice caps) our results suggest that altruistic and cooperative behaviors may be highly prevalent among microbial populations.

Cooperatively breeding species vary widely in degree of social complexity, and disentangling relationships among group members can reveal the costs and benefits of cooperation. Here, we describe the social system of the cooperatively breeding Variegated Fairywren (Malurus lamberti) and explore how social complexity and group dynamics may affect cooperation and conflict. We used a combination of field-based population monitoring and detailed social association observations to determine group membership annually across four breeding seasons (2014–2017) and used a ddRAD-seq genotyping method to determine genetic relationships within social groups. Social groups ranged in size from two to eight individuals and nearly half of all social groups had multiple adult individuals of both sexes. Approximately half of all groups exhibited plural breeding, in which multiple females within the same social group nested individually in the same territory. Genetic relationships were diverse among social groups due to high rates of extra-pair paternity and immigration, with most groups containing close relatives and non-relatives of each sex. Notably, although related females were often present within a social group, co-breeding females in the same social group were never closely related to each other. Given the extensive variation in relatedness among group members, cooperation in the Variegated Fairywren is likely maintained by a combination of direct and indirect fitness benefits. [ABSTRACT FROM AUTHOR]

Group-living animals are faced with the challenge of sharing space and local resources amongst group members who may be either relatives or non-relatives. Individuals may reduce the inclusive fitness costs they incur from competing with relatives by either reducing their levels of aggression toward kin, or by maintaining physical separation between kin. In this field study, we used the group-living cichlid Neolamprologus multifasciatus to examine whether within-group aggression is reduced among group members that are kin, and whether kin occupy different regions of their group's territory to reduce kin competition over space and local resources. We determined the kinship relationships among cohabiting adults via microsatellite genotyping and then combined these with spatial and behavioral analyses of groups in the wild. We found that aggressive contests between group members declined in frequency with spatial separation between their shelters. Female kin did not engage in aggressive contests with one another, whereas non-kin females did, despite the fact these females lived at similar distances from one another on their groups' territories. Contests within male–male and male–female dyads did not clearly correlate with kinship. Non-kin male-male and male–female dyads lived at more variable distances from one another on their territories than their corresponding kin dyads. Together, our study indicates that contests among group members can be mediated by relatedness in a sex-dependent manner. We also suggest that spatial relationships can play an important role in determining the extent to which group members compete with one another. [ABSTRACT FROM AUTHOR]

Whilst the effects of inbreeding on growth and survival have been well studied, knowledge on the impact of inbreeding on the social behaviour is scarce. Animal groups are often composed of relatives, which can facilitate cooperation (due to kin selection) and improve group performance accordingly. Therefore, increased genetic relatedness in inbred kin groups could increase group performance, whilst the reduced genetic diversity could have negative effects (inbreeding depression). We compared the juvenile shoaling behaviour of inbred and outbred sibling groups in Pelvicachromis taeniatus (Boulenger 1901), a West-African cichlid fish with kin mating preferences. Activity (travelled distance), shoal density (inter-individual distance) and recovery from a disturbance (freezing time) in a novel environment were analysed using tracking software. Inbred individuals travelled shorter distances compared to outbred individuals, which may decrease conspicuousness and thus predation risk. Furthermore, inbred sibling groups recovered faster after the disturbance compared to outbred sibling groups suggesting improved coordination. In conclusion, our study revealed differences in shoaling between inbred and outbred sibling groups. The higher relatedness in inbred groups may have positive effects in the form of a reduced conspicuousness. The reduced activity may impair foraging success under natural conditions which might, however, be compensated by faster recovery from disturbances. [ABSTRACT FROM AUTHOR]

Inbreeding can result in inbreeding depression. Therefore, many species seek to avoid inbreeding. However, theory predicts that inbreeding can be beneficial. Accordingly, some species tolerate inbreeding or even prefer mating with close relatives. Evidence for active inbreeding, i.e., kin-mating preference was reported in the biparental African cichlid fish Pelvicachromis taeniatus. Related mating partners revealed better parental cooperation due to kin selection, a potential benefit of inbreeding. In this study, we investigated kin-mating preference in a genetically diverse, outbred F2-lab population of Pelvicachromis pulcher, a closely related species to P. taeniatus. Like P. taeniatus, this species shows mutual ornamentation and mate choice as well as intense biparental brood care. The F1 P. pulcher generation had revealed signs of inbreeding depression but no inbreeding avoidance. We studied mating behavior and aggression in trios consisting of a male P. pulcher, an unfamiliar sister, and an unfamiliar, unrelated female. Because the study focused on kin-mating patterns, female pairs were matched for body size and coloration. The results provide no evidence for inbreeding avoidance but rather suggest inbreeding preference. We also found no significant impact of inbreeding on offspring survival. The results suggest no inbreeding avoidance in P. pulcher; however, the strength of inbreeding preference and inbreeding depression seems to be variable. We discuss possible causes for this variation like context-dependent inbreeding depression. The number of eggs positively correlated with female body size and coloration. Furthermore, the female aggressiveness was positively correlated with female coloration indicating that coloration signal female dominance and quality. [ABSTRACT FROM AUTHOR]

Male alliances are an intriguing phenomenon in the context of reproduction since, in most taxa, males compete over an indivisible resource, female fertilization. Adult male bottlenose dolphins (Tursiops aduncus) in Shark Bay, Western Australia, form long-term, multilevel alliances to sequester estrus females. These alliances are therefore critical to male reproductive success. Yet, the long-term processes leading to the formation of such complex social bonds are still poorly understood. To identify the criteria by which male dolphins form social bonds with other males, we adopted a long-term approach by investigating the ontogeny of alliance formation. We followed the individual careers of 59 males for 14 years while they transitioned from adolescence (8-14 years of age) to adulthood (15-21 years old). Analyzing their genetic relationships and social associations in both age groups, we found that the vast majority of social bonds present in adolescence persisted through time. Male associations in early life predict alliance partners as adults. Kinship patterns explained associations during adolescence but not during adulthood. Instead, adult males associated with males of similar age. Our findings suggest that social bonds among peers, rather than kinship, play a central role in the development of adult male polyadic cooperation in dolphins.

Abstract Background Eusociality is widely considered to evolve through kin selection, where the reproductive success of an individual’s close relative is favored at the expense of its own. High genetic relatedness is thus considered a prerequisite for eusociality. While ants are textbook examples of eusocial animals, not all ants form colonies of closely related individuals. One such example is the ectatommine ant Rhytidoponera metallica, which predominantly forms queen-less colonies that have such a low intra-colony relatedness that they have been proposed to represent a transient, unstable form of eusociality. However, R. metallica is among the most abundant and widespread ants on the Australian continent. This apparent contradiction provides an example of how inclusive fitness may not by itself explain the maintenance of eusociality and raises the question of what other selective advantages maintain the eusocial lifestyle of this species. Results We provide a comprehensive portrait of the venom of R. metallica and show that the colony-wide venom consists of an exceptionally high diversity of functionally distinct toxins for an ant. These toxins have evolved under strong positive selection, which is normally expected to reduce genetic variance. Yet, R. metallica exhibits remarkable intra-colony variation, with workers sharing only a relatively small proportion of toxins in their venoms. This variation is not due to the presence of chemical castes, but has a genetic foundation that is at least in part explained by toxin allelic diversity. Conclusions Taken together, our results suggest that the toxin diversity contained in R. metallica colonies may be maintained by a form of group selection that selects for colonies that can exploit more resources and defend against a wider range of predators. We propose that increased intra-colony genetic variance resulting from low kinship may itself provide a selective advantage in the form of an expanded pharmacological venom repertoire. These findings provide an example of how group selection on adaptive phenotypes may contribute to maintaining eusociality where a prerequisite for kin selection is diminished.

Abstract Cooperatively breeding animals live longer than their solitary counterparts. This has been suggested for birds, mole rats, and social insects. A common explanation for these long lifespans is that cooperative breeding evolves more readily in long‐lived species because lower mortality reduces the rate of territory turnover and thus leads to a limitation of breeding territories. Here, we reverse this argument and show that—rather than being a cause for its evolution—long lifespans are an evolutionary consequence of cooperative breeding. In evolutionary individual‐based simulations, we show that natural selection favors a delayed onset of senescence in cooperative breeders, relative to solitary breeders, because cooperative breeders have a delayed age of first reproduction as helpers wait in a reproductive queue to obtain breeder status. Especially long lifespans evolve in cooperative breeders in which queue positions depend on the helpers’ age rank among the helpers within the breeding territory. Furthermore, we show that lower genetic relatedness among group members leads to the evolution of longer lifespans. This is because selection against higher mortality is weaker when mortality reduces competition for breeding between relatives. Our results link the evolutionary theory of ageing with kin selection theory, demonstrating that the evolution of ageing in cooperative breeders is driven by the timing of reproduction and kin structure within breeding territories.