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Same-sex sexual behavior (SSB) is an enigma in behavioral ecology as it does not result in reproduction. Proximately, the effect of sexual signals on SSB could be distinct between signal receivers and senders. For receivers, the absence of sexual signals leads to smaller phenotypic sex differences, leading to frequent accidental SSB between receivers. Alternatively, for senders, sexual signals could help locate another sender, enhancing intentional SSB. Here, we demonstrate this link between sex pheromone signaling and the frequency of same-sex pairing in two Coptotermes termites that use the same chemical as sex pheromones but in different quantities. In termites, mating pairs engage in tandem runs, where a female emits sex pheromones to guide a male as they move together in searching a potential nest site. So, females are signal senders, and males are signal receivers for sexual communication. We found that female-female tandems were more stable in C. formosanus, whose females produce more pheromones. On the other hand, although both species did not show stable male–male tandems, males of C. gestroi , whose females produce fewer pheromones, spent more time attempting to follow another male. Thus, stronger pheromones lead to sender–sender SSB, while weaker pheromones lead to receiver–receiver SSB. The proximate mechanism of SSB is diverse according to the properties of sexual communications in heterosexual contexts. [ABSTRACT FROM AUTHOR]

Social behavior can have a major impact on the dynamics of infectious disease outbreaks. For animals that live in dense social groups, such as the eusocial insects, pathogens pose an especially large risk because frequent contacts among individuals can allow rapid spread within colonies. While there has been a large body of work examining adaptations to mitigate the spread of infectious disease within social insect colonies, there has been less work on strategies to prevent the introduction of pathogens into colonies in the first place. We develop an agent-based model to examine the effect of territorial behavior on the transmission of infectious diseases between social insect colonies. We find that by preventing the introduction of infected foreign workers into a colony, territoriality can flatten the curve of an epidemic, delaying the introduction of an infectious disease and reducing its maximum prevalence, but only for diseases with moderate to low transmissibility. Our results have implications for understanding how pathogen risk influences the evolution of territorial behavior in social insects and other highly social animals. Significance statement: Infectious disease outbreaks can impose a large fitness cost to animals that live in social groups. The frequency and pattern of contacts both within and among groups can have a large impact on the speed and extent of an epidemic. Using an individual-based model, we examined how the exclusion of foreign workers from a territory around the nest influences disease transmission between social insect colonies. We find that territoriality can protect colonies from outbreaks of low to moderately contagious pathogens by delaying the spillover from other colonies and reducing the maximum number of workers who are infected. These results suggest that the relative threat posed by infectious diseases may have played an important role in shaping the diversity of territorial behaviors seen in different social insect species. [ABSTRACT FROM AUTHOR]

Among all activities displayed by ant colonies, searching for food is essential for all individuals survival. However, many external activities are hazardous or restrictive for the entire society. Even though leaf‐cutter ants are highly successful insects, they are subject to extreme aspects of foraging, as raindrops and wind. Although recruitment and food exploitation are known to change with temperature and humidity, barometric pressure changes and how they affect ant behavior remain unknown. We aimed to determine how an increase or decrease in barometric pressure might modify foraging strategies of the leaf‐cutter ant Atta sexdens compared to steady pressure. The first modification observed in the workers behavior was the scouts greater promptness in leaving the nest when the barometric pressure decreased. Regard to the foragers, there was no difference in the number of individuals recruited for collecting leaves. However, it was cut and brought into the nest 1.5 and 2 times more leaves during the pressure drop, respectively. The reason for this foraging efficiency as a whole was ultimately the sum of the efficiency of each forager. The shifts in behavior, therefore, could be related to the indirect consequences of a pressure decrease, such as rainfall and strong winds, both strong constraints on ants on a trail. This is the first report of barometric pressure affecting the behavior of a social insect under controlled conditions. [ABSTRACT FROM AUTHOR]

Consistent among-individual differences in behavior have been described in numerous taxa. More recently, the hypothesis that such behavioral variation may also correlate to life-history traits, such as investment in current or future reproduction, has been proposed as a potential explanation for why variation is maintained among and within populations. A continual challenge in measuring the integration of these traits, or the pace-of-life syndrome (POLS), is to find a reliable and quantifiable proxy for energy allocation between reproduction and self-maintenance. Here, I address this challenge using the eusocial insects, Temnothorax ants, in a common garden experiment to directly quantify energy allocation by tracking the number of sterile workers (somatic effort) and winged reproductive ants (reproductive effort) produced across years. I use colonies collected from populations previously demonstrated to show significant differences in a risk-tolerance behavioral syndrome. I provide an empirical test of the POLS hypothesis between 2 populations of Temnothorax ants over three years. I find strong evidence for a POLS between populations and weaker, but present support for a within population POLS. More risk-tolerant populations also allocate more energy towards reproduction and grow faster across years. This study then emphasizes the value of a more holistic study of among-individual variation. Additionally, it suggests more research is needed on understanding how and why traits may correlate in some populations, but remain independent in others. [ABSTRACT FROM AUTHOR]

Social insect colonies, especially of ants, often include several egg-laying queens that are not always closely related to each other. At least in some cases, the ants seem to accept non-related queens into their colonies. Here I test whether the colony queen status (with or without a queen), genetic and geographic differences between source and recipient nests and the average relatedness of the workers in the recipient colony affect the acceptance of alien queens. I used field collected ruby ant Myrmica rubra colonies as a model system. Only the queen status significantly affected the acceptance process. Colonies without queens accepted alien queens more frequently than colonies with a queen. The nests without queens and nest fragments may act as vectors for gene flow by the movement of queens between nests, i.e., queen flow. [ABSTRACT FROM AUTHOR]

Background: The performance and fitness of social societies mainly depends on the efficiency of interactions between reproductive individuals and helpers. Helpers need to react to the group's requirements and to adjust their tasks accordingly, while the reproductive individual has to adjust its reproductive rate. Social insects provide a good system to study the interrelations between individual and group characteristics. In general, sterile workers focus on brood care and foraging while the queen lays eggs. Reproductive division of labor is determined by caste and not interchangeable as, e.g., in social mammals or birds. Hence, changing social and environmental conditions require a flexible response by each caste. In the ant Cardiocondyla obscurior, worker task allocation is based on age polyethism, with young workers focusing on brood care and old workers on foraging. Here, we examine how group age demography affects colony performance and fitness in colonies consisting of only old or young workers and a single old or young queen. We hypothesized that both groups will be fully functional, but that the forced task shift affects the individuals' performance. Moreover, we expected reduced worker longevity in groups with only young workers due to precocious foraging but no effect on queen longevity depending on group composition. Results: Neither the performance of queens nor that of workers declined strongly with time per se, but offspring number and weight were influenced by queen age and the interaction between queen and worker age. Individual residual life expectancy strongly depended on colony demography instead of physiological age. While worker age affected queen longevity only slightly, exposing old workers to the conditions of colony founding increased their life spans by up to 50% relative to workers that had emerged shortly before colony set-up. Conclusions: The social environment strongly affected the tempo of aging and senescence in C. obscurior, highlighting the plasticity of life expectancy in social insects. Furthermore, colonies obtained the highest reproductive output when consisting of same-aged queens and workers independent of their physiological age. However, workers appeared to be able to adjust their behavior to the colony's needs and not to suffer from agedependent restrictions. [ABSTRACT FROM AUTHOR]

One of the central tenets of life-history theory is that organisms cannot simultaneously maximize all fitness components. This results in the fundamental trade-off between reproduction and life span known from numerous animals, including humans. Social insects are a well-known exception to this rule: reproductive queens outlive nonreproductive workers. Here, we take a step forward and show that under identical social and environmental conditions the fecundity-longevity trade-off is absent also within the queen caste. A change in reproduction did not alter life expectancy, and even a strong enforced increase in reproductive efforts did not reduce residual life span. Generally, egg-laying rate and life span were positively correlated. Queens of perennial social insects thus seem to maximize at the same time two fitness parameters that are normally negatively correlated. Even though they are not immortal, they best approach a hypothetical "Darwinian demon" in the animal kingdom. [ABSTRACT FROM AUTHOR]

'Division of labor' is a misleading way to describe the organization of tasks in social insect colonies, because there is little evidence for persistent individual specialization in task. Instead, task allocation in social insects occurs through distributed processes whose advantages, such as resilience, differ from those of division of labor, which are mostly based on learning. The use of the phrase 'division of labor' persists for historical reasons, and tends to focus attention on differences among individuals in internal attributes. This focus distracts from the main questions of interest in current research, which require an understanding of how individuals interact with each other and their environments. These questions include how colony behavior is regulated, how the regulation of colony behavior develops over the lifetime of a colony, what are the sources of variation among colonies in the regulation of behavior, and how the collective regulation of colony behavior evolves. [ABSTRACT FROM AUTHOR]

The social insects serve as exemplars for social biomimicry, the search for social design inspiration from the natural world. Although their group members are individually much simpler than humans, social insect colonies provide elegant tutorials on the large-scale outcomes that can be achieved by social interactions and self-organizational processes. These range from complex physical structures built by collective effort; to exemplars of flexible work organization; to effective consensus building in group decisions. This special issue highlights examples of the lessons to be learned from the bees and ants, providing ways to think about how humans can (and in some cases should not) borrow from social insect rules of organization and their collective outcomes. [ABSTRACT FROM AUTHOR]

The spectacular morphological variation among workers of certain ant and termite species has fascinated evolutionary biologists since Darwin. In some species, environmental triggers induce larvae to develop into different phenotypes, e.g. minor or major workers (soldiers). Recently, the first soldier subcaste was discovered in a bee, the stingless bee Tetragonisca angustula. In contrast to ants, which raise their offspring by progressively feeding larvae until the pupal stage, T. angustula nurses mass provision individual brood cells after which the bees develop from egg to young workers in sealed cells on a seemingly uniform brood comb. This prompts the question of how this bee creates a morphologically variable workforce without larvae having direct contact with nursing workers. We investigated where T. angustula raises a larger soldier subcaste on its compact brood comb. Additionally, we examined whether size differences among workers could be generated by differential distribution of food by nursing workers. We found that colonies produce c. 1-6 % of soldier-sized workers, which mainly emerge from a small central area of the comb. In this area, cells are wider and a larger number of nursing bees unload larval food here before oviposition. Cell attendance levels prior to oviposition were similar across the comb and, thus, did not explain the larger food volumes found in the centre. Our results suggest that workers determine soldier production via larval food discharges and cell-building behaviour. Nutritional differences among larvae might then induce larvae into one or the other caste developmental pathway. [ABSTRACT FROM AUTHOR]

Parasite-induced alterations in host behaviour have been reported in a large number of taxa. However, some parasites are better than others to exploit the resources offered by their hosts. To date, our understanding of the extent to which some obligate parasites exploit social insect colonies is still limited. In this study, we examined parasite-mediated behavioural alterations of Polistes biglumis wasps parasitized by the obligate social parasite Polistes atrimandibularis by comparing host female-activity in parasitized and non-parasitized colonies. Host foundresses foraged more and rested less in parasitized than in non-parasitized colonies (controlling for the number of larvae in the nest, the time of day, and the day in the season). Next, we used short-term parasite removal experiments to investigate how social parasites manipulate their hosts. We found that parasitized hosts foraged more and rested less when social parasites were on the nest rather than after their removal, and we tested which kind of interactions occurred between parasites and hosts. P. atrimandibularis parasites may use mainly non-aggressive interactions (such as antennation and trophallaxis) to manipulate host activities, rather than visual, acoustic or chemical signals as other parasites do. [ABSTRACT FROM AUTHOR]

Juvenile hormone (JH) is an important regulator of development and physiology in insects. While in many insect species, including bumble bees, JH functions as gonadotropin in adults, in some highly eusocial insects its role has shifted to regulate social behavior including division of labor, dominance and aggression. Studying JH functions across social insect species is important for understanding the evolution of sociality; however, these studies have been limited because of the inability to reduce JH levels without surgically removing its glandular source, the corpora allata. Precocene is known to inhibit JH biosynthesis in several non-social insects, but has been poorly studied in social insects. Here, we tested whether precocene- I can effectively reduce JH levels in Bombus terrestris workers, and examined its effects on their physiology and behavior. Precocene-I treatment of three-worker groups decreased JH titer and ovarian activation, irrespective of the bees' dominance rank within the group, and was remedied by JH replacement therapy. Precocene-I also decreased aggressiveness and increased ester-sterility signal production; these changes were rank-dependent, and affected mainly the most reproductive and the least aggressive workers, respectively, and could not be remedied by JH replacement therapy. These results clearly confirm the role of JH as a gonadotropin and mediator of aggression in B. terrestris, and indicate that JH effects are associated with worker dominance rank. The ability to chemically reduce JH titer provides us with a non-intrusive method to probe the evolutionary changes associated with JH and the hormonal mechanisms that are associated with reproduction and behavior in social insects. [ABSTRACT FROM AUTHOR]

Although cuticular hydrocarbons (CHCs) have received much attention from biologists because of their important role in insect communication, few studies have addressed the chemical ecology of clonal species of eusocial insects. In this study we investigated whether and how differences in CHCs relate to the genetics and reproductive dynamics of the parthenogenetic ant Cerapachys biroi. We collected individuals of different ages and subcastes from several colonies belonging to four clonal lineages, and analyzed their cuticular chemical signature. CHCs varied according to colonies and clonal lineages in two independent data sets, and correlations were found between genetic and chemical distances between colonies. This supports the results of previous research showing that C. biroi workers discriminate between nestmates and non-nestmates, especially when they belong to different clonal lineages. In C. biroi, the production of individuals of a morphological subcaste specialized in reproduction is inversely proportional to colony-level fertility. As chemical signatures usually correlate with fertility and reproductive activity in social Hymenoptera, we asked whether CHCs could function as fertility-signaling primer pheromones determining larval subcaste fate in C. biroi. Interestingly, and contrary to findings for several other ant species, fertility and reproductive activity showed no correlation with chemical signatures, suggesting the absence of fertility related CHCs. This implies that other cues are responsible for subcaste differentiation in this species. [ABSTRACT FROM AUTHOR]

In primitively eusocial insects, air temperature is the environmental factor that primarily affects colony cycle. Several studies demonstrated interspecific differences in the adaptation of eusocial insects to local air temperature. Nevertheless, studies on intraspecific adaptations are rare. In this study, we investigate the influence of air temperature on local adaptations in behavior and colony productivity of Polistes biglumis foundresses living in warm and cold temperate zones. We hypothesized that foundresses from warm temperate zones would show a higher activity level compared to those from cold temperate zones before brood emergence, based on differences in air temperature between the two zones. After brood emergence, we expected a reduced foundress activity level in the warm climate zone, due to workers' help. In contrast, foundresses living in the cold-climate zone, which do not produce workers, were expected to remain active throughout the nesting season. We also hypothesized that colony productivity was higher in warm-climate colonies. As expected, warm-climate foundresses reduced their activity level after brood emergence and, with their relatively large number of workers, continued egg production throughout the nesting season. Further studies are necessary to assess if these intraspecific differences are attributable to phenotypic plasticity or genetic divergence. [ABSTRACT FROM AUTHOR]

Dominance rank in animal societies is correlated with changes in both reproductive physiology and behavior. In some social insects, dominance status is used to determine a reproductive division of labor, where a few colony members reproduce while most remain functionally sterile. Changes in reproduction and behavior in this context must be coordinated through crosstalk between the brain and the reproductive system. We investigated a role for biogenic amines in forming this connection in the ant Harpegnathos saltator. In this species, workers engage in an elaborate dominance tournament to establish a group of reproductive workers termed gamergates. We analyzed biogenic amine content in the brains of gamergates, insideworkers and foragers under stable colony conditions and found that gamergates had the highest levels of dopamine. Dopamine levels were also positively correlated with increased ovarian activity among gamergates. Next, we experimentally induced workers to compete in a reproductive tournament to determine how dopamine may be involved in the establishment of a new hierarchy. Dopamine levels rose in aggressive workers at the start of a tournament, while workers that were policed by their nestmates (a behavior that inhibits ovarian activity) showed a rapid decline in dopamine. In addition to dopamine, levels of serotonin and tyramine differed among castes, and these changes could contribute to differences in caste-specific behavioral patterns observed among non-reproductive workers. Overall, these results provide support that biogenic amines link changes in behavior and dominance with reproductive activity in H. saltator as well as drive differences in worker task performance. [ABSTRACT FROM AUTHOR]

Crowd behaviors can have large fitness consequences for social organisms. Here we ask if there are similarities in the crowd dynamics of organisms that differ in body size, manner of locomotion, cognitive abilities, and state of alarm. Existing models of human crowd behavior have not been tested for their generality across species and body size nor across routine and emergency movements. We explore this issue by comparing the traffic dynamics of humans and of Argentine ants ( Linepithema humile) to the predictions of our own model which was designed to simulate pedestrian movement. Some parameter values in the model were directly measured on ants but others were allometrically scaled from the human values to ant values based on the body mass difference. The model, with appropriately scaled parameters, correctly predicted two important properties of crowd behaviour for both organisms in a variety of circumstances: the flow rates and the distribution of time headways between successive ants in the escape sequence. The ability of a model of human pedestrian dynamics to predict behaviours of ant aggregations through allometric scaling of some parameter values suggests that there are fundamental features of crowd behavior that transcend the biological idiosyncrasies of the organisms involved. [ABSTRACT FROM AUTHOR]

Efficient and robust transportation networks are key to the effectiveness of many natural systems. In polydomous ant colonies, which consist of two or more spatially separated but socially connected nests, resources must be transported between nests. In this study, we analyse the network structure of the inter-nest trails formed by natural polydomous ant colonies. In contrast to previous laboratory studies, the natural colonies in our study do not form minimum spanning tree networks. Instead the networks contain extra connections, suggesting that in natural colonies, robustness may be an important factor in network construction. Spatial analysis shows that nests are randomly distributed within the colony boundary and we find nests are most likely to connect to their nearest neighbours. However, the network structure is not entirely determined by spatial associations. By showing that the networks do not minimise total trail length and are not determined only by spatial associations, the results suggest that the inter-nest networks produced by ant colonies are influenced by previously unconsidered factors. We show that the transportation networks of polydomous ant colonies balance trail costs with the construction of networks that enable efficient transportation of resources. These networks therefore provide excellent examples of effective biological transport networks which may provide insight into the design and management of transportation systems. [ABSTRACT FROM AUTHOR]

Highlights: [•] Bombus terrestris foragers produce larger amounts of octyl esters compared to non-foragers. [•] Octyl esters are also known as a signal to sterility that reduces aggression. [•] Ester production is positively correlated with worker foraging efforts. [•] Foraging, potential fecundity and aggression are interlinked in B. terrestris workers. [Copyright &y& Elsevier]

Hygienic behavior in honey bees, Apis mellifera, is measured by determining the rate at which the bees uncap and remove dead sealed brood. We analyzed individual behavior of house-cleaning Africanized honey bees in order to focus on some poorly understood aspects of hygienic behavior. Two observation hives, each with approximately 3,000 individually marked bees, were used in this study. The efficiency of hygienic behavior was evaluated in hygienic and non-hygienic strains of bees using two types of combs (new and old), as well as at different periods of the day (night and day). We also recorded the age of workers that performed this task of removing dead brood. In both strains, the workers that performed tasks related to hygienic behavior were within the same age cohort; we found no influence of age on the amount of time dedicated to the task, independent of the type of comb or period of the day. The total time from perforation of the cell capping until the dead brood had been completely removed, and was significantly shorter during daytime than at night. Hygienic behavior directed towards dead brood in new combs was also significantly more efficient (faster) than for brood in old combs. The type of comb had significantly more effect than did the time of day. We conclude that the type of comb and time of day should be taken into consideration when evaluating hygienic behavior in honey bees. [ABSTRACT FROM AUTHOR]

The energetic state of an individual is a fundamental driver of its behavior. However, an individual in a eusocial group such as the honeybees is subject to the influence of both the individual and the colony energetic states. As these two states are normally coupled, it has led to the predominant view that behaviors, such as foraging, are dictated by the colony state acting through social regulatory mechanisms. Uncoupling the energetic state of an individual honeybee from its colony by feeding it with a non-nutritious sugar, we show that energetically stressed bees in a colony with full food stores do not consume this food to meet their energetic shortfall but instead compensate by first reducing their activity level and then by increasing their foraging rate. This suggests that foraging in eusocial groups is still partly under the regulatory control of the energetic state of the individual and supports the notion that regulatory mechanisms in solitary insects have been co-opted to drive altruistic behavior in eusocial insects. The observation that energetically stressed bees also experience higher mortality during foraging also suggests that energetic stress mediated by a variety of factors can be a common mechanism that underlies the recent observation of bees disappearing from their colonies. We also discuss how nutritional imbalance in a social insect individual can alter its behavior to influence colony life history. [ABSTRACT FROM AUTHOR]

Social insect colonies are attractive for many arthropods. The rare velvet ant, Mutilla europaea, visit colonies of Polistes wasps, but to date it was unclear which resources it targeted therein. Our field observations and bioassays showed that velvet ants visit the colonies of the social wasp Polistes biglumis almost undisturbed and may feed on larval wasp saliva. Chemical insignificance and resistance are the characteristics that allow velvet ants to visit unharmed wasp colonies and gain such a nutritious reward. [ABSTRACT FROM AUTHOR]

Dopamine (DA) and juvenile hormone (JH) are multifunctional regulators of behaviour in social insects, with distinct effects across species and even between different dominance positions within the same species. We examined the effects of JH on the brain dopaminergic system in honey bee males to investigate the potential relationship between JH and DA within Apis mellifera. Both DA content and the expression of three DA receptor genes ( Amdop1, Amdop2 and Amdop3) increased in the male honey bee brain from day 4 to day 8 after emergence. Treatment of 4-day-old males with a JH analogue (methoprene, JHA) enhanced brain DA levels. Brain expression of Amdop1 was also enhanced by JHA but not by a DA receptor agonist 2-amino 6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (6,7-ADTN), indicating that Amdop1 up-regulation was not mediated by increased DA receptor stimulation. Furthermore, Amdop1 expression was still enhanced when JHA was co-applied with the DA receptor antagonist cis-( Z)-flupenthixol. Expression levels of Amdop2 and Amdop3 were not altered by JHA, 6,7-ADTN or by JHA plus the DA receptor antagonist. Regulation of the brain dopaminergic system by JH, as observed in solitary species, is conserved in male honey bees but not in female honey bees and other advanced eusocial insects. [ABSTRACT FROM AUTHOR]

Social insect societies are characterized not only by a reproductive division of labor between the queen and workers but also by a specialization of workers on different tasks. However, how this variation in behavior or morphology among workers influences colony fitness is largely unknown. We investigated in the ant Temnothorax longispinosus whether aggressive and exploratory behavior and/or variation among nest mates in these behavioral traits are associated with an important fitness measure, that is, per worker offspring production. In addition, we studied how body size and variation in size among workers affect this colony fitness correlate. First, we found strong differences in worker body size, aggression, and exploration behavior among colonies. Most notably, intracolonial variance in aggression was positively correlated with per worker productivity, suggesting a selective advantage of colonies with a higher variability in worker aggression. Because ant colonies in dense patches were both more aggressive and more productive, we cannot exclude the possibility that higher productivity and greater variability in aggression could both be results of good habitat quality and not causal influences on one another. This study suggests that social insect societies with stronger behavioral variation among nest members, and possibly a more efficient task allocation, are more productive in the field. [ABSTRACT FROM PUBLISHER]

Slave-making ants reduce the fitness of surrounding host colonies through regular raids, causing the loss of brood and frequently queen and worker death. Consequently, hosts developed defenses against slave raids such as specific recognition and aggression toward social parasites, and indeed, we show that host ants react more aggressively toward slavemakers than toward nonparasitic competitors. Permanent behavioral defenses can be costly, and if social parasite impact varies in time and space, inducible defenses, which are only expressed after slavemaker detection, can be adaptive. We demonstrate for the first time an induced defense against slave-making ants: Cues from the slavemaker Protomognathus americanus caused an unspecific but long-lasting behavioral response in Temnothorax host ants. A 5-min within-nest encounter with a dead slavemaker raised the aggression level in T. longispinosus host colonies. Contrarily, encounters with nonparasitic competitors did not elicit aggressive responses toward non-nestmates. Increased aggression can be adaptive if a slavemaker encounter reliably indicates a forthcoming attack and if aggression increases postraid survival. Host aggression was elevated over 3 days, showing the ability of host ants to remember parasite encounters. The response disappeared after 2 weeks, possibly because by then the benefits of increased aggression counterbalance potential costs associated with it. [ABSTRACT FROM PUBLISHER]

Queens of the honey bee, Apis mellifera (L.), exhibit extreme polyandry, mating with up to 45 different males (drones). This increases the genetic diversity of their colonies, and consequently their fitness. After copulation, drones leave a mating sign in the genital opening of the queen which has been shown to promote additional mating of the queen. On one hand, this signing behavior is beneficial for the drone because it increases the genetic diversity of the resulting colony that is to perpetuate his genes. On the other hand, it decreases the proportion of the drone's personal offspring among colony members which is reducing drone fitness. We analyze the adaptiveness and evolutionary stability of this drone's behavior with a game-theoretical model. We find that theoretically both the strategy of leaving a mating sign and the strategy of not leaving a mating sign can be evolutionary stable, depending on natural parameters. However, the signing strategy is not favored for most scenarios, including the cases that are biologically plausible in reference to empirical data. We conclude that leaving a sign is not in the interest of the drone unless it serves biological functions other than increasing subsequent queen mating chances. Nevertheless, our analysis can also explain the prevalence of such a behavior of honey bee drones by a very low evolutionary pressure for an invasion of the nonsigning strategy. [ABSTRACT FROM AUTHOR]

Collective decision making in the social insects often proceeds via feedback cycles based on positive signaling. Negative signals have, however, been found in a few contexts in which costs exist for paying attention to no longer useful information. Here we incorporate new research on the specificity and context of the negative stop signal into an agent based model of honey bee foraging to explore the adaptive basis of negative signaling in the dance language. Our work suggests that the stop signal, by acting as a counterbalance to the waggle dance, allows colonies to rapidly shut down attacks on other colonies. This could be a key adaptation, as the costs of attacking a colony strong enough to defend itself are significant. [ABSTRACT FROM AUTHOR]

The ecological success of the social insects depends on their ability to work with a unity of purpose. Task partitioning, breaking a task into subtasks performed by different individuals, is a key adaptation requiring group-level coordination of action. This study explores the communication processes that underlie task partitioning, focusing on the contrasting roles played by signals and cues. A fundamental problem of task partitioning is maintaining equal work outputs between the groups involved. Honey bees clearly use 2 mechanisms, and possibly a third, to achieve this goal. First, colonies make preemptive changes to their labor allocation by sending signals that are predictive of future work needs. Second, colonies are able to take measures to recalibrate the number of workers assigned to groups after unpredictable changes in work demand. Finally, colonies may be able to fine-tune the number of workers in task groups by modulating the activity rate of workers in time with changes in work demand. Based on this review of task partitioning, it is argued that signals are preferable to cues in some instances because they can be actively targeted to their recipients, as opposed to cues, which are passive sources of information. Furthermore, a recipient's behavioral state (active or inactive) does not affect their ability to receive signals, whereas it can for many cues. The results of this study should be broadly applicable, as wasp, bee, ant, and termite societies face similar problems and because data suggest that other social insects use similar communication mechanisms to bees. [ABSTRACT FROM PUBLISHER]

Recognition systems involve 3 components: an expression component, a perception component, and an action or response component. Disentangling the perception component from the action component can be difficult, as the absence of a discriminatory response may result from either a difference in perception or action. Social insects generally defend their colony against intruding conspecifics and provide a useful model for exploring recognition systems. However, whether differences in behavior at the colony or individual level result from the perception or action component of the recognition system is largely unknown. Furthermore, variation at the individual level has remained largely unexplored because research on social insects often focuses on the colony rather than on the individual. Using some novel behavioral bioassays, we here show that variation in the aggressive behavior of individual weaver ants (Oecophylla smaragdina L.) arises more from the identity of the recipient than of the intruder and, contrary to previous findings, that this often results from perceptual differences. We suggest that recognition in weaver ants may involve a template based on the individual’s odor prior to intermingling with other odors rather than on a common odor. We also argue that a common odor might be more important for the survival of the colony than a shared template. Conversely, possessing a range of templates may provide a colony with additional fitness benefits. By focusing on the differences among individual workers within colonies, this study reveals complexities in nest mate recognition that might otherwise have gone unnoticed. [ABSTRACT FROM PUBLISHER]

Our understanding of insect societies is rapidly expanding due to an emphasis on integrative approaches. Emerging tools enabling the molecular dissection of social behavior, together with novel hypotheses for the evolution of eusociality, are emblematic of this progress. However, an obstacle to a truly inlegrative approach remains, as social physiology--the basis of group-level coordination--has generally been neglected by geneticists. In this paper, we begin a synthesis of these fields by first reviewing three classes of social insect organization that mark major transitions in increasing social complexity. We then develop an expansion of the superorganism concept in order to place eusociality into a broad evolutionary context, and we also interpret current molecular and genetic work on the evolution of eusociality. The groundplan hypothesis proposes that eusociality arose via simple, changes in the regulation of ancestral gene sets affecting reproductive physiology and behavior, and we argue that this hypothesis is explanatory for the evolution of division of labor (social anatomy) but not for the regulatory systems that ensure group-level coordination of action (social physiology), which we propose is dependent on previously unrelated trails that are brought together into novel genetic networks. We conclude with a review of recent work in sociogenomics that supports our hypotheses. [ABSTRACT FROM AUTHOR]

In social insects, workers trade personal reproduction for indirect fitness returns from helping their mother rear collateral kin. Colony membership is generally used as a proxy for kin discrimination, but the question remains whether recognition allows workers to discriminate between kin and nonkin regardless of colony affiliation. We investigated whether workers of the ant Formica fusca can identify their mother when fostered with their mother, their sisters, a hetero-colonial queen or hetero-colonial workers. We found that workers always displayed less aggression towards both their mother and their foster queen, as compared to an unfamiliar hetero-colonial queen. In support of this finding, workers maintain their colony hydrocarbon profile regardless of foster regime, yet show modifications when exposed to different environments. This indicates that recognition entails environmental and genetic components, which allow both discrimination of kin in the absence of prior contact and learning of recognition cues based on group membership. [ABSTRACT FROM AUTHOR]

Insect societies are well known for their high degree of cooperation, but their colonies can potentially be exploited by reproductive workers who lay unfertilized, male eggs, rather than work for the good of the colony. Recently, it has also been discovered that workers in bumblebees and Asian honeybees can succeed in entering and parasitizing unrelated colonies to produce their own male offspring. The aim of this study was to investigate whether such intraspecific worker parasitism might also occur in stingless bees, another group of highly social bees. Based on a large-scale genetic study of the species Melipona scutellaris, and the genotyping of nearly 600 males from 45 colonies, we show that ∼20% of all males are workers’ sons, but that around 80% of these had genotypes that were incompatible with them being the sons of workers of the resident queen. By tracking colonies over multiple generations, we show that these males were not produced by drifted workers, but rather by workers that were the offspring of a previous, superseded queen. This means that uniquely, workers reproductively parasitize the next-generation workforce. Our results are surprising given that most colonies were sampled many months after the previous queen had died and that workers normally only have a life expectancy of ∼30 days. It also implies that reproductive workers greatly outlive all other workers. We explain our results in the context of kin selection theory, and the fact that it pays workers more from exploiting the colony if costs are carried by less related individuals. [ABSTRACT FROM AUTHOR]

Social insects are distinguished by their extraordinary degree of cooperation and the complexity of their group organization. However, a high proportion of individuals (often >50% at any one time) in a social insect colony tend to be inactive. It has been hypothesized that larger colonies can afford such inactivity because of efficiencies gained through stronger division of labor. We quantify the degree to which colonies of different sizes exhibit division of labor, and what proportion tends to be inactive, in the ant Temnothorax albipennis. Colony size neither influenced individual specialization nor overall division of labor in this species and larger colonies did not show a higher proportion of inactive workers. Interestingly, small colonies seemed to rely more on a small number of high-performance workers: the proportion of work performed by the single most active worker is significantly higher in smaller colonies for several tasks. More research is needed to resolve when and how colony size affects collective organization and division of labor in insect colonies. [ABSTRACT FROM PUBLISHER]

Response threshold models are an important tool to model division of labor in social insects and to investigate the underlying principles of self-organization. In this article response threshold models which incorporate dynamic environments with varying demand for work and their influence on division of labor are studied. In their natural habitats, social insects are always exposed to dynamic environments, however, the effect that such environments have on response threshold models has rarely been investigated. In the course of this article it is shown that overworking and underworking, i.e. working more or less than the ideal amount, over a certain time is a colony-size dependent effect in dynamic situations. By adjusting the number of possible learning steps, which correspond to changes in the maximal threshold values relative to a colony's size, the performance of colonies in dynamic environments can be increased. A setup inspired by repeated migration behavior is also investigated. It is shown that these different learning rates affect a colony's ability to maintain an activity onset for a reappearing task. [ABSTRACT FROM AUTHOR]

Successful foraging is necessary for procurement of nutritional resources essential for an animal’s survival. Maintenance of foraging and food acquisition is dependent on the ability to balance food intake and energy expenditure. This review examines the role of cGMP-dependent protein kinase (PKG) as a regulator of foraging behaviour, food acquisition, and energy balance. The role of PKG in food-related behaviours is highly conserved among worms, flies, bees, ants, and mammals. A growing body of literature suggests that PKG plays an integral role in the component behaviours and physiologies underlying foraging behaviour. These include energy acquisition, nutrient absorption, nutrient allocation, nutrient storage, and energy use. New evidence suggests that PKG mediates both neural and physiological mechanisms underlying these processes. This review illustrates how investigating the role of PKG in energy homeostasis in a diversity of organisms can offer a broad perspective on the mechanisms mediating energy balance. La recherche de nourriture est nécessaire à l’obtention des ressources nutritionnelles essentielles à la survie d’un animal. Le maintien de la recherche et de l’acquisition de nourriture repose sur une capacité à équilibrer la prise alimentaire et la dépense énergétique. Cet article de synthèse examine le rôle de la protéine kinase dépendante du GMPc (PKG) en tant que régulateur du comportement de recherche alimentaire, d’acquisition de nourriture et d’équilibre énergétique. Le rôle de la PKG dans les comportements alimentaires est très conservé chez les vers, les mouches, les abeilles, les fourmis et les mammifères. Un corpus croissant au sein de la littérature suggère que la PKG joue un rôle intégral dans les composantes d’ordre comportemental et physiologique qui sous-tendent les comportements de recherche de nourriture. Celles-ci comprennent l’acquisition d’énergie, l’absorption de nutriments, l’allocation des nutriments, l’entreposage des nutriments et la consommation énergétique. De nouvelles évidences suggèrent que la PKG contrôle à la fois des mécanismes neuraux et physiologiques sous-tendant ces processus. Cette synthèse illustre comment l’étude du rôle de la PKG dans l’homéostasie énergétique chez divers organismes peut offrir une perspective large sur les mécanismes déterminant l’équilibre énergétique. [ABSTRACT FROM AUTHOR]

Worker insects altruistically sacrifice their own reproduction to rear nondescendant kin. This sacrifice reaches its most spectacular level in suicidal colony defense. Suicidal defense, such as when the sting of a honeybee worker embeds in a predator and then breaks off, is normally a facultative response. Here we describe the first example of preemptive self-sacrifice in nest defense. In the Brazilian ant Forelius pusillus, the nest entrance is closed at sunset. One to eight workers finish the job from the outside and, in doing so, sacrifice their lives. [ABSTRACT FROM AUTHOR]

Natural selection shaped the foraging-related processes of honeybees in such a way that a colony can react to changing environmental conditions optimally. To investigate this complex dynamic social system, we developed a multi-agent model of the nectar flow inside and outside of a honeybee colony. In a honeybee colony, a temporal caste collects nectar in the environment. These foragers bring their harvest into the colony, where they unload their nectar loads to one or more storer bees. Our model predicts that a cohort of foragers, collecting nectar from a single nectar source, is able to detect changes in quality in other food sources they have never visited, via the nectar processing system of the colony. We identified two novel pathways of forager-to-forager communication. Foragers can gain information about changes in the nectar flow in the environment via changes in their mean waiting time for unloadings and the number of experienced multiple unloadings. This way two distinct groups of foragers that forage on different nectar sources and that never communicate directly can share information via a third cohort of worker bees. We show that this noisy and loosely knotted social network allows a colony to perform collective information processing, so that a single forager has all necessary information available to be able to 'tune' its social behaviour, like dancing or dance-following. This way the net nectar gain of the colony is increased. [ABSTRACT FROM AUTHOR]

Abstract: Workers of Reticulitermes flavipes were isolated in groups of increasing numbers to determine the in vitro rates of juvenile hormone (JH) synthesis by individual pairs of corpora allata (CA) as other castes differentiated. Only neotenic reproductives developed in groups of 12. Mean JH synthesis rates increased after 5 weeks but only a few individuals had significantly higher rates, about 0.4pmol/pair/h, which occurred at about 3 weeks before neotenics developed. Soldiers and neotenics developed in groups of 50. Mean rates increased to a peak at week 6 after isolation, but only a few individuals had rates approaching 1pmol/pair/h, which occurred at the same time after isolation as the development of pre-soldiers. JH synthesis by CA of pharate pre-soldiers and soldiers was low compared to that of pharate workers and neotenics. CA of pre-soldiers attained a peak mean rate of JH synthesis of 0.9pmol/pair/h at 6 days of age, whereas CA of soldiers attained only a peak mean rate of 0.3pmol/pair/h. These measurements of JH synthesis by individual pairs of CA suggest that the few workers destined to become pre-soldiers have 2.5-fold higher JH synthesis than the few that would develop into neotenic reproductives, and show that a cycle of synthesis accompanies the development of pre-soldiers into soldiers. [Copyright &y& Elsevier]

The advanced colonial state of eusociality has evolved in insects as a defense of nest sites within foraging distance of persistent food sources. In the Hymenoptera, the final step in the approach to eusociality is through a suite of preadaptations comprising simultaneous provisioning, fidelity to the nest, and a preexisting propensity toward dominance behavior and the selection of tasks according to opportunity. The only genetic change needed to cross the threshold to the eusocial grade is the foundress's possession of an allele that holds the foundress and her offspring to the nest. The preadaptations provide the phenotypic flexibility required for eusociality, as well as the key emergent traits arising from interactions of the group members. Group (colony-level) selection then immediately acts on both of these traits. The rarity of the origin of eusociality is evidently due to the rarity of the combination of progressive provisioning with environments of the kind that give an edge to group selection over individual direct selection, causing offspring to stay at the natal nest rather than disperse. Several lines of evidence, examined here, suggest that collateral kin selection does not play a significant role. [ABSTRACT FROM AUTHOR]

One of the most obvious characteristics of an insect society is reproductive cooperation. Yet insect colonies are vulnerable to reproductive parasitism, both by workers from their own colony and by workers from others. Little is known about the mechanisms insect societies have evolved to protect themselves from being exploited from within and outside the colony and the mechanisms that social parasites have evolved to circumvent these mechanisms. Here we showcase recently discovered cases of intraspecific parasitism by workers in eusocial bees. These discoveries overturn the widespread view that insect colonies are like fortresses populated by female eunuchs, and yield important insights into the mechanisms that normally enforce functional worker sterility. [ABSTRACT FROM AUTHOR]

In socially living animals, individuals interact through complex networks of contact that may influence the spread of disease. Whereas traditional epidemiological models typically assume no social structure, network theory suggests that an individual’s location in the network determines its risk of infection. Empirical, especially experimental, studies of disease spread on networks are lacking, however, largely due to a shortage of amenable study systems. We used automated video-tracking to quantify networks of physical contact among individuals within colonies of the social bumble bee Bombus impatiens. We explored the effects of network structure on pathogen transmission in naturally and artificially infected hives. We show for the first time that contact network structure determines the spread of a contagious pathogen ( Crithidia bombi) in social insect colonies. Differences in rates of infection among colonies resulted largely from differences in network density among hives. Within colonies, a bee’s rate of contact with infected nestmates emerged as the only significant predictor of infection risk. The activity of bees, in terms of their movement rates and division of labour (e.g., brood care, nest care, foraging), did not influence risk of infection. Our results suggest that contact networks may have an important influence on the transmission of pathogens in social insects and, possibly, other social animals. [ABSTRACT FROM AUTHOR]

A potential tragedy of the commons arises in social-insect colonies where workers are fertile if egg-laying workers decrease their contribution to other tasks. We studied worker ovary development and egg laying in relation to kin structure, colony size, and the presence of a queen in nine species (11 populations) of Formica ants. Workers were highly fertile and laid eggs in the presence of a queen in five out of the seven species where egg samples were obtained. Worker fertility correlated neither with colony size nor with kin structure, which suggests that colony-level costs and efficiency of policing precede relatedness as the most important conflict determinant. We conclude that careful quantification of the costs of worker reproduction and policing is essential for inferences about the tragedy of the commons. [ABSTRACT FROM AUTHOR]

1. Large colonies of ants are known to have a higher propensity for sexual offspring production, probably owing to their high capacity to exploit food resources. 2. The effects of food supplementation on the propensity for sexual offspring production, and whether it is linked with colony size, were investigated in an environment with poor resources (clear-cut areas). 3. Large colony size was associated with a higher propensity for sexual offspring production in food-supplemented colonies, whereas in non-supplemented control colonies an association with colony size was not found. 4. The results demonstrate that large colonies seem to have a higher capacity to exploit supplemented food. In addition, the production of sexual offspring was apparently limited by food availability in clear-cuts, especially for large colonies. [ABSTRACT FROM AUTHOR]

The aim of this paper is to consider the relationships between robots and insects. To this end, an overview is provided of the two main areas in which insects have been implicated in robotics research. First, robots have been used to provide working models of mechanisms underlying insect behaviour. Second, there are developments in robotics that have been inspired by our understanding of insect behaviour; in particular the approach of swarm robotics. In the final section of the paper, the possibility of achieving "strong swarm intelligence" is discussed. Two possible interpretations of strong swarm intelligence are raised: (1) the emergence of a group mind from a natural, or robot swarm, and (2) that behaviours could emerge from a swarm of artificial robots in the same way as they emerge from a biological swarm. Both interpretations are dismissed as being unachievable in principle. It is concluded that bio-robotic modelling and biological inspiration have made important contributions to both insect and robot research, but insects and robots remain separated by the divide between the living and the purely mechanical. [ABSTRACT FROM AUTHOR]

Kinship among group members has long been recognized as a main factor promoting the evolution of sociality and reproductive altruism, yet some ants have an extraordinary social organization, called unicoloniality, whereby individuals mix freely among physically separated nests. This type of social organization is not only a key attribute responsible for the ecological dominance of these ants, but also an evolutionary paradox because relatedness between nestmates is effectively zero. Recently, it has been proposed that, in the Argentine ant, unicoloniality is a derived trait that evolved after its introduction into new habitats. Here we test this basic assumption by conducting a detailed genetic analysis of four native and six introduced populations with five to 15 microsatellite loci and one mitochondrial gene. In contrast to the assumption that native populations consist of family-based colonies with related individuals who are aggressive toward members of other colonies, we found that native populations also form supercolonies, and are effectively unicolonial. Moreover, just as in introduced populations, the relatedness between nestmates is not distinguishable from zero in these native range supercolonies. Genetic differentiation between native supercolonies was very high for both nuclear and mitochondrial markers, indicating extremely limited gene flow between supercolonies. The only important difference between the native and introduced populations was that supercolonies were several orders of magnitude smaller in the native range (25-500 m). This size difference has important consequences for our understanding of the evolution and stability of unicolonial structures because the relatively small size of supercolonias in the native range implies that competition can occur between supercolonies, which can act as a break on the spread of selfish mutants by eliminating supercolonies harboring them. [ABSTRACT FROM AUTHOR]

The occurrence of polygyny and polyandry in social insects has long puzzled evolutionary biologists. If cooperation requires genetic relatedness, how do we explain the occurrence and maintenance of mechanisms that reduce the degree of relatedness among colony members? A much-discussed hypothesis states that genetically diverse colonies are more resistant to parasitism than homogenous colonies because genetic diversity reduces the spread of a disease within a colony. However, as we will argue in this note, a necessary condition for the parasite hypothesis is that genetically heterogeneous colonies have a larger suite of parasites that are capable of infecting them. This implicit relationship is important because it implies that even if the cost per infection is reduced, this may not be sufficient to offset the increased rate of acquiring infections. The advantages of genetic heterogeneity as a defense against parasites thus may not be as big as commonly thought. [ABSTRACT FROM AUTHOR]

Division of labour among workers is central to the organisation and ecological success of insect societies. If there is a genetic component to worker size, morphology or task preference, an increase in colony genetic diversity arising from the presence of multiple breeders per colony might improve division of labour. We studied the genetic basis of worker size and task preference in Formica selysi, an ant species that shows natural variation in the number of mates per queen and the number of queens per colony. Worker size had a heritable component in colonies headed by a doubly mated queen ( h 2=0.26) and differed significantly among matrilines in multiple-queen colonies. However, higher levels of genetic diversity did not result in more polymorphic workers across single- or multiple-queen colonies. In addition, workers from multiple-queen colonies were consistently smaller and less polymorphic than workers from single-queen colonies. The relationship between task, body size and genetic lineage appeared to be complex. Foragers were significantly larger than brood-tenders, which may provide energetic or ergonomic advantages to the colony. Task specialisation was also often associated with genetic lineage. However, genetic lineage and body size were often correlated with task independently of each other, suggesting that the allocation of workers to tasks is modulated by multiple factors. Overall, these results indicate that an increase in colony genetic diversity does not increase worker size polymorphism but might improve colony homeostasis. [ABSTRACT FROM AUTHOR]

The genetic basis of morphological traits in social insects remains largely unexplored. This is even true for individual body size, a key life-history trait. In the social insects, the size of reproductive individuals affects dispersal decisions, so that small size in queens is often associated with reduced dispersal, and large size with long-range dispersal and independent colony founding. Worker size is connected to division of labour when workers specialize in certain tasks according to their size. In many species, variation in worker size has been shown to increase colony performance. In this study, we present the first evidence of an additive genetic component to queen size in ants, using maternal half sib analysis. We also compared intra-colony size variation in colonies with high (queen doubly mated) versus low (queen singly mated) genetic variability. We found a high and significant heritability (h2=0.51) for queen size in one of the two study years, but not in the other. Size variation among queens was greater in colonies headed by a doubly mated queen in one of the study years, but not in the other. This indicates that genetic factors can influence queen size, but that environmental factors may override these under some circumstances. The heritability for worker size was low (h2=0.09) and non-significant. Increased genetic diversity did not increase worker size variation in the colonies. Worker size appeared largely environmentally determined, potentially allowing colonies to adjust worker size ratios to current conditions. [ABSTRACT FROM AUTHOR]

Considerable attention has focused on why females of many species mate with several males. For social hymenopteran insects, efforts have primarily concentrated on determining whether multiple mating increases colony performance due to the increased genetic diversity. Most of these studies are correlative because it is difficult or impossible to experimentally mate queens in most species. Thus, the positive associations found between multiple paternity and colony fitness in some cases may not be due to direct effects of genetic diversity but could, in theory, arise from high-quality queens having more mates. Here we show that in the ant Lasius niger variation in the number of matings covaries with queen phenotype. Young queens that were heavier at the time of the mating flight were significantly more likely to mate with several males. As a result, heavier queens stored more sperm. The initial weight of queens was significantly associated with the probability of surviving mating flights during the two years of the study, with queens of intermediate weight having the highest across-year survival. Queen initial weight was also significantly and positively associated with the quantity of brood at the time of the first worker eclosion as well as colony productivity at the time of hibernation. By contrast, there was little evidence for a positive effect of the number of matings on colony performance when the effect of mate number and queen initial weight were considered simultaneously. [ABSTRACT FROM AUTHOR]

Stigmergy is a class of mechanisms that mediate animal-animal interactions. Its introduction in 1959 by Pierre-Paul Grassé made it possible to explain what had been until then considered paradoxical observations: In an insect society individuals work as if they were alone while their collective activities appear to be coordinated. In this article we describe the history of stigmergy in the context of social insects and discuss the general properties of two distinct stigmergic mechanisms: quantitative stigmergy and qualitative stigmergy. [ABSTRACT FROM AUTHOR]