Environmental and genetic influences on queen and worker body size in the social wasp Vespula maculifrons

Many social insects exhibit morphologically distinct worker and queen castes that perform different functions. These functional differences may generate unique selection regimes operating on body size. For example, queens may be under directional selection for large body size, whereas directional selection on worker body size may be limited. Such contrasting selection pressures may differentially affect levels of genetic variation associated with size variation in the two castes. This study sought to determine if genetic effects underlying phenotypic differences varied between the worker and queen castes of the social wasp Vespula maculifrons. We predicted that directional selection would remove genetic variation associated with size differences in the queen caste, whereas a lack of directional selection would tend to maintain genetic variation associated with size differences in the worker caste. We thus (1) calculated broad and narrow sense heritabilities for several morphological traits, (2) examined whether some paternal genotypes produced more morphologically diverse offspring than others, and (3) determined whether trait size variation was associated with genetic variation within colonies. We found that few morphological traits were significantly heritable, indicating that little genetic variance for those traits existed within our study population. We also found that some patrilines produced more morphologically variable offspring than others, suggesting a role of genotype in phenotypic plasticity. And finally, no significant correlations between genetic diversity arising from multiple mating by queens within colonies and trait variation in either caste were found. Overall, our findings indicate a weak effect of genotype on both worker and queen body size variation and are suggestive of a large environmental influence on morphological trait size. Moreover, our results do not indicate that levels of genetic variation underlying size variation differ substantially between castes in this species.     

Workers of a polistes paper wasp detect the presence of their queen by chemical cues

Differences in long-chain hydrocarbon mixtures among reproductive and nonreproductive individuals have been often revealed in social insects. However, very few papers demonstrated that these signatures actually act as contact pheromones used by nonreproductive to recognize the presence of a related queen in the colony. Cuticular and glandular hydrocarbons of Polistes paper wasps have been extensively studied, but, until now, the perception and recognition of such cues was not demonstrated. In this paper, we show, for the first time in Vespidae, that Polistes gallicus workers distinguish nestmates from alien individuals and queens from workers by the hydrocarbon mixtures of the Van der Vecht organ secretion (VVS). We also demonstrated that stroking behavior (a peculiar behavior of Polistes by which queens probably lay VVS on the nest) acts as an inhibitor of ovarian development in workers.     

The reproductive division of labour but not worker age affects spatial sorting within the nest in a paper wasp

Insectes Sociaux - Spatial behaviour of colony members within a nest represents an essential aspect of colony organization. However, little attention has been devoted to the study of this aspect in...     

Visual prey discrimination of queen and worker ants by a generalist lizard

Laboratory experiments were conducted to test the hypothesis that widelyforaging generalist lizard,Eumeces okadae, visually discriminates palatable queen ants from unpalatable worker ants. The workers ofCamponotus japonicus andLasius niger were rejected on sight, while the queens of both species were eaten with little prior chemical examination by tongue flicks or licks. Comparison of the lizards' responses towards the workers and wingless queens of similar size indicated that neither body size nor presence or absence of wings accounted for difference in responses toward the 2 ant castes. The lizards probably discriminated different ant castes by body proportions.     

Age dependency of worker bee response to queen pheromone in a four-armed olfactometer

Summary Behavioral responses of differently aged worker beesApis mellifera to a queen pheromonal extract were analysed. The bees were tested individually in a four-armed olfactometer, one arm being scented with the pheromonal extract. This extract was prepared from heads of 14–17-day-old unmated queens. Among the components of the blend, 470 g 9-keto-2-(E)-decenoic acid, 200 g 9-hydroxy-2-(E)-decenoic acid and 5 gp-hydroxybenzoic acid methyl ester per queen equivalent were dosed. An age dependency in the worker bees' olfactory response to the components of the queen extract was shown, the strongest response occurring below the age of 5 days.     

Assured fitness returns in a social wasp with no worker caste

The theory of assured fitness returns proposes that individuals nesting in groups gain fitness benefits from effort expended in brood-rearing, even if they die before the young that they have raised reach independence. These benefits, however, require that surviving nest-mates take up the task of rearing these young. It has been suggested that assured fitness returns could have favoured group nesting even at the origin of sociality (that is, in species without a dedicated worker caste). We show that experimentally orphaned brood of the apoid wasp Microstigmus nigrophthalmus continue to be provisioned by surviving adults for at least two weeks after the orphaning. This was the case for brood of both sexes. There was no evidence that naturally orphaned offspring received less food than those that still had mothers in the nest. Assured fitness returns can therefore represent a real benefit to nesting in groups, even in species without a dedicated worker caste.     

Colony fusion and worker reproduction after queen loss in army ants

Theory predicts that altruism is only evolutionarily stable if it is preferentially directed towards relatives, so that any such behaviour towards seemingly unrelated individuals requires scrutiny. Queenless army ant colonies, which have anecdotally been reported to fuse with queenright foreign colonies, are such an enigmatic case. Here we combine experimental queen removal with population genetics and cuticular chemistry analyses to show that colonies of the African army ant Dorylus molestus frequently merge with neighbouring colonies after queen loss. Merging colonies often have no direct co-ancestry, but are on average probably distantly related because of overall population viscosity. The alternative of male production by orphaned workers appears to be so inefficient that residual inclusive fitness of orphaned workers might be maximized by indiscriminately merging with neighbouring colonies to increase their reproductive success. We show that worker chemical recognition profiles remain similar after queen loss, but rapidly change into a mixed colony Gestalt odour after fusion, consistent with indiscriminate acceptance of alien workers that are no longer aggressive. We hypothesize that colony fusion after queen loss might be more widespread, especially in spatially structured populations of social insects where worker reproduction is not profitable.     

Regulation of worker activity in a primitively eusocial wasp, Ropalidia marginata

Ropalidia marginala, a tropical, primitively eusocial, polistinewasp, is unusual in that the queen (the sole egg-layer) is neitherthe most behaviorally dominant nor the most active individualin the colony. The queen by herself rarely ever initiates interactionstoward her nest mates or unloads returning foragers. There arealways a few workers in the colony who are more dominant andactive than the queen. Absence of the queen from her colonydoes not affect colony maintenance activities such as foragingor brood care, but it always results in one individual becomingvery aggressive and dominant. The dominant worker becomes thenext queen if the original queen does not return. The queendoes not appear to play any significant role in colony activityregulation. Instead, colony activities appear to be regulatedby several mechanisms including dominance behavior toward foragers,feeding of larvae, and the unloading of returning foragers,all mediated by workers themselves. Regulation of colony maintenanceappears to be based on direct evaluation of the needs of thecolony by the workers themselves. The queen however has perfectreproductive control over all workers; workers never lay eggsin the presence of the queen. It appears therefore that themechanisms involved in regulation of worker activity and workerreproduction are separate in R marginata. These findings contrastwith other primitively eusocial species where the queen actsas a "central pacemaker" and controls both worker activity andworker reproduction.     

Identification of an ant queen pheromone regulating worker sterility

The selective forces that shape and maintain eusocial societies are an enduring puzzle in evolutionary biology. Ordinarily sterile workers can usually reproduce given the right conditions, so the factors regulating reproductive division of labour may provide insight into why eusociality has persisted over evolutionary time. Queen-produced pheromones that affect worker reproduction have been implicated in diverse taxa, including ants, termites, wasps and possibly mole rats, but to date have only been definitively identified in the honeybee. Using the black garden ant Lasius niger, we isolate the first sterility-regulating ant queen pheromone. The pheromone is a cuticular hydrocarbon that comprises the majority of the chemical profile of queens and their eggs, and also affects worker behaviour, by reducing aggression towards objects bearing the pheromone. We further show that the pheromone elicits a strong response in worker antennae and that its production by queens is selectively reduced following an immune challenge. These results suggest that the pheromone has a central role in colony organization and support the hypothesis that worker sterility represents altruistic self-restraint in response to an honest quality signal.     

Lack of conflict during queen production in the social wasp Vespula maculifrons

Social insects display extreme cooperative and helping behaviours. However, social insect colonies are also arenas of intense competitive interactions. One particularly important matter over which colony members may compete centres on the development of sexual offspring. Specifically, colony members may engage in selfish behaviours leading to reproductive competition, whereby individuals either strive to develop as sexuals or assist kin so that close relatives emerge as new reproductives. We investigated whether reproductive competition occurred in the polyandrous social wasp Vespula maculifrons. We genotyped V. maculifrons workers and new queens at eight polymorphic microsatellite loci to determine if larvae of particular genotypes were reared as gynes more frequently than expected by chance. However, we found no significant evidence of reproductive competition in this species. The proportional contributions of males to workers and new queens did not vary within colonies. Moreover, male reproductive skew did not differ between workers and new queens. Finally, novel statistical techniques uncovered no evidence of patriline reversal, the phenomenon whereby males that contribute little to worker production contribute substantially to new queen production. Consequently, we conclude that individual level selection operating to increase the frequency of selfish behaviours that would lead to reproductive competition has been nullified by colony-level selection acting to maintain colony efficiency and cooperation.     

Insurance-based advantages for subordinate co-foundresses in a temperate paper wasp

Recent explanations for the evolution of eusociality, focusing more on costs and benefits than relatedness, are largely untested. We validate one such model by showing that helpers in foundress groups of the paper wasp Polistes dominulus benefit from an insurance-based mechanism known as Assured Fitness Returns (AFRs). Experimental helper removals left remaining group members with more offspring than they would normally rear. Reduced groups succeeded in preserving the dead helpers' investment by rearing these extra offspring, even when helper removals occurred long before worker emergence. While helpers clearly gained from AFRs, offspring of lone foundresses failed after foundress death, so that AFRs represent a true advantage for helpers. Smaller, less valuable offspring were probably sacrificed to feed larger offspring, but reduced groups did not preferentially attract joiners or increase their foraging effort to compensate for their smaller workforce. We failed to detect a second insurance-based advantage, Survivorship Insurance, in which larger groups are less likely to fail than smaller groups. We suggest that through their use of small offspring as a food store to cope with temporary shortages, wasps may be less susceptible than vertebrates to offspring failure following the death of group members.     

The influence of queen age and quality during queen replacement in honeybee colonies

Honeybee, Apis mellifera, colonies replace their queens by constructing many queen cells and then eliminating supernumerary queens until only one remains. The ages of the queens and the variation in their reproductive potential are important factors in the outcome of such events. Selection would favour colonies that requeen as quickly as possible to minimize the brood hiatus, therefore selecting for queens reared from older larvae. Conversely, reproductive potential (queen 'quality') is maximized by rearing queens from younger larvae. This potential trade-off was tested during two phases of queen replacement, namely queen rearing and polygyny reduction. Our results suggest that queen age is a significant element during both queen rearing and polygyny reduction, whereas queen quality, at least to the magnitude tested in this experiment, has little impact on the outcome of either process. The rate of queen replacement therefore appears to be an important factor in the honeybee life cycle, and further mechanisms of potential importance during this life history transition are discussed. Copyright 2000 The Association for the Study of Animal Behaviour.     

Influence of queen weight and colony origin on worker response in Solenopsis geminata

Abstract. The influence of weight and colony origin of the queen of Solenopsis geminata (F.) (Hymenoptera: Formicidae) on worker attraction is studied under laboratory conditions. In the first experiment, worker response to individual queens of different weight from the same colony is evaluated. Heavier queens are more attractive than smaller queens to their own workers. In subsequent experiments, the colony origin effect is investigated and worker response to a pair of queens of the same weight from the same or different colonies is compared. When queens are from the same colony, workers do not show a significant preference between queens. However, when queens are from a different colony, workers are significantly more attracted to their own queen than to the foreign queen. Finally, the response of workers to queens of different weight from the same or different colonies is investigated. In both cases, workers are significantly more attracted to a heavier queen than a lighter queen, even if the lighter queen is their own queen. A putative pheromonal component (E)‐6‐(1‐pentenyl)‐2H‐2‐pyranone, is not positively correlated with queen weight.     

cGMP modulates responses to queen mandibular pheromone in worker honey bees

Responses to social cues, such as pheromones, can be modified by genotype, physiology, or environmental context. Honey bee queens produce a pheromone (queen mandibular pheromone; QMP) which regulates aspects of worker bee behavior and physiology. Forager bees are less responsive to QMP than young bees engaged in brood care, suggesting that physiological changes associated with behavioral maturation modulate response to this pheromone. Since 3′,5′-cyclic guanosine monophosphate (cGMP) is a major regulator of behavioral maturation in workers, we examined its role in modulating worker responses to QMP. Treatment with a cGMP analog resulted in significant reductions in both behavioral and physiological responses to QMP in young caged workers. Treatment significantly reduced attraction to QMP and inhibited the QMP-mediated increase in vitellogenin RNA levels in the fat bodies of worker bees. Genome-wide analysis of brain gene expression patterns demonstrated that cGMP has a larger effect on expression levels than QMP, and that QMP has specific effects in the presence of cGMP, suggesting that some responses to QMP may be dependent on an individual bees’ physiological state. Our data suggest that cGMP-mediated processes play a role in modulating responses to QMP in honey bees at the behavioral, physiological, and molecular levels.     

Social dominance molds cuticular and egg chemical blends in a paper wasp

Hamilton's theory [1] for the evolution of social behaviour predicts that helpers may renounce direct reproduction to help their more fertile kin. Intra-colony recognition among queens and helpers (subordinate queens or workers) is consequently a central issue in insect sociobiology. In social insects, cuticular hydrocarbons (CHCs) are involved in recognition, and egg-laying and non-egg-laying individuals often differ in CHC composition. These differences are assumed to be directly determined by fertility status [2,3]. In several ants and in Polistes wasps, when egg-layers disappear they are substituted by helpers, which develop their ovaries and become chemically similar to their former queens [2,3]. Sometimes helpers lay eggs in the presence of queens, which recognize and destroy the subordinates' eggs [4]. In ponerine ants, eggs often have the same chemical signature as the maternal cuticle [2]. If chemical signatures depend on fertility, egg-laying subordinates should match the queen's signature even when she is present, making egg recognition and differential oophagy impossible. In the study reported here, we experimentally separated fertility from dominance and analyzed the dynamics of hydrocarbon profiles of the cuticle of Polistes dominulus foundresses and the shell surface of their eggs. We have demonstrated that, contrary to the widely accepted view, dominance, rather than fertility, determines chemical signatures in Polistes wasps. This explains why queens can recognize their own eggs and police reproduction by subordinates if they become fertile and lay eggs.     

Colony insularity through queen control on worker social motivation in ants

We investigated the relative contribution of the queen and workers to colony nestmate recognition cues and on colony insularity in the Carpenter ant Camponotus fellah. Workers were either individually isolated, preventing contact with both queen and workers (colonial deprived, CD), kept in queenless groups, allowing only worker-worker interactions (queen deprived, QD) or in queenright (QR) groups. Two weeks post-separation QD and QR workers were amicable towards each other but both rejected their CD nestmates, which suggests that the queen does not measurably influence the colony recognition cues. By contrast, aggression between QD and QR workers from the same original colony was apparent only after six months of separation. This clearly demonstrates the power of the Gestalt and indicates that the queen is not a dominant contributor to the nestmate recognition cues in this species. Aggression between nestmates was correlated with a greater hydrocarbon (HC) profile divergence for CD than for QD and QR workers, supporting the importance of worker-worker interactions in maintaining the colony Gestalt odour. While the queen does not significantly influence nestmate recognition cues, she does influence colony insularity since within 3 days QD (queenless for six months) workers from different colony origins merged to form a single queenless colony. By contrast, the corresponding QR colonies maintained their territoriality and did not merge. The originally divergent cuticular and postpharyngeal gland HC profiles became congruent following the merger. Therefore, while workers supply and blend the recognition signal, the queen affects worker-worker interaction by reducing social motivation and tolerance of alien conspecifics.