Cuticular hydrocarbons correlate with fertility, not dominance, in a paper wasp, Polistes dominulus

Chemical Resemblance of Egg Surface Compounds and Dufour's Gland in Two Neotropical Polistinae Wasps Polistes versicolor (Olivier) and Mischocyttarus metathoracicus (de Saussure, 1854)

Chemical communication plays a major role in regulating social dynamics in social insect colonies. The most studied class of chemical compounds are the cuticular hydrocarbons (CHCs), compounds with high molecular weight that cover the insect body. CHCs are used in nestmate recognition and to signal reproductive status. Brood, in the form of larvae and eggs, is known to participate in chemical communication and social dynamics by performing hunger behaviour and inducing interaction with adults and conferring nest and maternity identity. CHCs of adults and egg surface compounds are similar in composition in social insect species. The main source of egg compounds is proposed to be Dufour's gland, an accessory reproductive gland found in several Hymenoptera females. There is still a lack of information about the level of similarity among CHCs, compounds of egg surface and Dufour's gland for several wasp species, which could provide correlational evidence about the origins of egg-marking compounds. Thus, we investigated whether egg surface compounds were more similar to CHCs or Dufour's gland secretions in two Neotropical primitively eusocial wasp species, Polistes versicolor (Olivier) and Mischocyttarus metathoracicus (de Saussure, 1854). As expected, there was a higher chemical similarity between eggs and Dufour's gland secretions in both studied species, supporting the hypothesis that this gland is the source of chemical compounds found over the eggs in these two primitively eusocial species.

Chemical signatures of egg maternity and Dufour's gland in Vespine wasps

Cuticular hydrocarbons (CHCs) are often used in the chemical communication among social insects. CHCs can be used in nestmate recognition and as queen pheromones, the latter allows the regulation of the reproductive division of labor. In the common wasp Vespula vulgaris, CHCs and egg-marking hydrocarbons are caste-specific, being hydrocarbon queen pheromones and egg maternity signals. Whether these compounds are conserved among other Vespinae wasps remains unknown. Queens, virgin queens, reproductive workers, and workers belonging to four different wasp species, Dolichovespula media, Dolichovespula saxonica, Vespa crabro, and Vespula germanica, were collected and studied. The cuticular hydrocarbons, egg surface, and Dufour's gland composition were characterized and it was found that chemical compounds are caste-specific in the four species. Quantitative and qualitative differences were detected in the cuticle, eggs, and Dufour's gland. Some specific hydrocarbons that were shown to be overproduced in the cuticle of queens were also present in higher quantities in queen-laid eggs and in their Dufour's gland. These hydrocarbons can be indicated as putative fertility signals that regulate the division of reproductive labor in these Vespine societies. Our results are in line with the literature for V. vulgaris and D. saxonica, in which hydrocarbons were shown to be conserved queen signals. This work presents correlative evidence that queen chemical compounds are found not only over the body surface of females but also in other sources, such as the Dufour's gland and eggs.

The establishment and maintenance of dominance hierarchies

Animal groups are often organized hierarchically, with dominant individuals gaining priority access to resources and reproduction over subordinate individuals. Initial dominance hierarchy formation may be influenced by multiple interacting factors, including an animal's individual attributes, conventions and self-organizing social dynamics. After establishment, hierarchies are typically maintained over the long-term because individuals save time, energy and reduce the risk of injury by recognizing and abiding by established dominance relationships. A separate set of behaviours are used to maintain dominance relationships within groups, including behaviours that stabilize ranks (punishment, threats, behavioural asymmetry), as well as signals that provide information about dominance rank (individual identity signals, signals of dominance). In this review, we describe the behaviours used to establish and maintain dominance hierarchies across different taxa and types of societies. We also review opportunities for future research including: testing how self-organizing behavioural dynamics interact with other factors to mediate dominance hierarchy formation, measuring the long-term stability of social hierarchies and the factors that disrupt hierarchy stability, incorporating phenotypic plasticity into our understanding of the behavioural dynamics of hierarchies and considering how cognition coevolves with the behaviours used to establish and maintain hierarchies. This article is part of the theme issue 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies'.

Social Behavior, Ovary Size, and Population of Origin Influence Cuticular Hydrocarbons in the Orchid Bee Euglossa dilemma

AbstractCuticular hydrocarbons (CHCs) are waxy compounds on the surface of insects that prevent desiccation and frequently serve as chemical signals mediating social and mating behaviors. Although their function in eusocial species has been heavily investigated, little is known about the evolution of CHC-based communication in species with simpler forms of social organization lacking specialized castes. Here we investigate factors shaping CHC variation in the orchid bee Euglossa dilemma, which forms casteless social groups of two to three individuals. We first assess geographic variation, examining CHC profiles of males and females from three populations. We also consider CHC variation in the sister species, Euglossa viridissima, which occurs sympatrically with one population of E. dilemma. Next, we consider variation associated with female behavioral phases, to test the hypothesis that CHCs reflect ovary size and social dominance. We uncover a striking CHC polymorphism in E. dilemma spanning populations. In addition, we identify a separate set of CHCs that correlate with ovary size, social dominance, and expression of genes associated with social behavior, suggesting that CHCs convey reproductive and social information in E. dilemma. Together, our results reveal complex patterns of variation in which a subset of CHCs reflect the social and reproductive status of nestmates.

Hormonal modulation of reproduction and fertility signaling in polistine wasps

In social insects, it has been suggested that reproduction and the production of particular fertility-linked cuticular hydrocarbons (CHC) may be under shared juvenile hormone (JH) control, and this could have been key in predisposing such cues to later evolve into full-fledged queen pheromone signals. However, to date, only few studies have experimentally tested this "hormonal pleiotropy" hypothesis. Here, we formally test this hypothesis using data from four species of Polistine wasps, Polistes dominula, Polistes satan, Mischocyttarus metathoracicus, and Mischocyttarus cassununga, and experimental treatments with JH using the JH analogue methoprene and the anti-JH precocene. In line with reproduction being under JH control, our results show that across these four species, precocene significantly decreased ovary development when compared with both the acetone solvent-only control and the methoprene treatment. Consistent with the hormonal pleiotropy hypothesis, these effects on reproduction were further matched by subtle shifts in the CHC profiles, with univariate analyses showing that in P. dominula and P. satan the abundance of particular linear alkanes and mono-methylated alkanes were affected by ovary development and our hormonal treatments. The results indicate that in primitively eusocial wasps, and particularly in Polistes, reproduction and the production of some CHC cues are under joint JH control. We suggest that pleiotropic links between reproduction and the production of such hydrocarbon cues have been key enablers for the origin of true fertility and queen signals in more derived, advanced eusocial insects.

Strength surpasses relatedness-queen larva selection in honeybees

Nepotism was initially theoretically predicted and sometimes found to trigger the selection of specific larvae to be reared as queens in the honeybee Apis mellifera. Although the importance of selecting the next queen for a colony indicates that it should not occur at random, nepotism is increasingly considered unlikely in eusocial insect societies. Different prenatal maternal supplies of embryos have been found to impact fitness in many other species and therefore could be a possible trigger underlying the likelihood of being raised as a queen. We offered related or unrelated larvae from six colonies originating from eggs of different weights for emergency queen rearing in queenless units with worker bees from these six colonies. We showed that nurses did not significantly prefer related larvae during queen rearing, which confirms the theory that different relatedness-driven kin preferences within a colony cannot be converted into a colony-level decision. However, we found that larvae originating from heavier eggs were significantly preferred for queen breeding. Studies on other species have shown that superior maternal supply is important for later reproductive success. However, we did observe tendencies in the expected direction (e.g., queens that hatched from heavier eggs had both more ovarioles and a shorter preoviposition period). Nevertheless, our data do not allow for a significant conclusion that the selection of larvae from heavy eggs truly offers fitness advantages.

Dominance Hierarchy, Ovarian Activity and Cuticular Hydrocarbons in the Primitively Eusocial Wasp Mischocyttarus cerberus (Vespidae, Polistinae, Mischocyttarini)

The dominance hierarchy in primitively eusocial insect societies has been shown to be mainly regulated through aggressive interactions. Females that are generally more dominant stand out and occupy the queen position, meaning that they monopolize reproduction while others perform other tasks. Chemical communication is important for maintaining social cohesion. Cuticular hydrocarbons are recognized as the main molecules responsible for mediating social interactions, especially nestmate recognition and queen signalling. Many highly eusocial groups have been studied in recent years, but primitively eusocial groups, which are key to understanding the evolution of social behavior, remain unexplored. In this study, we investigated the connection between cuticular hydrocarbons in females expressed in different social contexts in the primitively eusocial wasp Mischocyttarus cerberus. Colonies in two different ontogenetic phases, pre- and post-worker emergence, were used. We observed and categorized behavioral interactions between individual females and collected all individuals in a nest to obtain information on size, ovary activation and chemical composition. Furthermore, we conducted experiments in which the alpha (dominant) females were removed from nests to produce a new dominance hierarchy. We found that females in different hierarchical positions had small chemical difference corresponding with ovary activity. Our results support the hypothesis that cuticular hydrocarbons are associated with social context in this primitively eusocial species, with some compounds being associated with hierarchical position and ovarian activity.

The challenge hypothesis in insects

The 'challenge hypothesis' provides a predictive framework for how the social environment influences within-species variation in hormone titers. High testosterone levels are beneficial during reproduction and competition, but they also impose costs because they may suppress traits like parental care and immunity. As a result, the challenge hypothesis predicts that individuals will change their testosterone levels to match the current social environment. Although the vast majority of work on the challenge hypothesis has focused on androgens in vertebrates, there is growing evidence that insect hormones, especially juvenile hormone (JH), may respond to social stimuli in ways that parallel androgens in vertebrates. Many insects rapidly upregulate JH titers during social competition with rivals. Some insects also modulate JH titers based on contest outcomes, with winners upregulating JH and losers downregulating JH. This review will integrate work on social modulation of hormone titers in vertebrates and insects. First, we provide background on insect hormones and describe the functional parallels between androgens and JH. Second, we review evidence that insects rapidly change JH titers in response to social competition. Finally, we highlight opportunities for future work on social modulation of hormones in insects. Overall, the challenge hypothesis provides a useful conceptual framework for hypothesis-driven research in insect endocrinology. Comparing vertebrates and insects provides insight into how selection has shaped patterns of hormone responsiveness as well as the generality of hypotheses originally developed for vertebrates.

Reproductive workers insufficiently signal their reproductive ability in a paper wasp

Why workers forfeit direct reproduction is a crucial question in eusocial evolution. Worker reproduction provides an excellent opportunity to understand the mechanism of kin conflict resolution between the queen and workers. We evaluated behavioral and physiological differences among females in the paper wasp Polistes chinensis antennalis to examine why some workers reproduce under queenright conditions. Reproductive workers were old and foraged less early in the season; their cuticular hydrocarbon (CHC) profiles overlapped with those of queens but were significantly different. The distinct CHC profile of the eggs of the queen likely represented a cue for policing against those by workers. Juvenile hormone (JH) and dopamine seemed to be associated with gonadotropic function, and the JH level of reproductive workers was similar to that of the queen. The high JH level of reproductive workers likely facilitated their reproduction even under queenright conditions. Gene expression levels of the queen and reproductive workers differed only in vitellogenin. These results suggest that worker reproduction is facilitated by an increase in JH level; however, CHC is not a fertility-linked signal, but a queen-linked signal; consequently, reproductive workers without a queen-linked signal might be allowed to stay within the colony.

When a male perceives a female: the effect of waxy components on the body surface on decision-making in the invasive pest weevil

Insects use various semiochemicals for sexual communication and mate recognition; these can therefore be used to govern the behaviours of harmful pest species, and several candidate chemicals have been explored for this purpose. For the West Indian sweet potato weevil, Euscepes postfasciatus, which is one of the most serious pests of sweet potato, no effective capture techniques, such as sex pheromone lures, exist. Toward exploring promising procedures for monitoring these weevils, we assessed the effect of secretions on the body surface on the recognition of congeners and on courtship behaviour in the weevils. Our study clearly demonstrated that weevils responded to extracts from the body surface, and the behaviour adopted by the weevils varied significantly depending on the condition of the extracts. Furthermore, we found a significantly prolonged retention time for males on glass beads covered with extracts of females based on survival analysis. These findings are, as far as we are aware, the first to show the effect of lipid components of the body surface on decision-making in these economically important pest weevils.

Rapid juvenile hormone downregulation in subordinate wasp queens facilitates stable cooperation

In many cooperatively breeding animals, subordinate group members have lower reproductive capacity than dominant group members. Theory suggests subordinates may downregulate their reproductive capacity because dominants punish subordinates who maintain high fertility. However, there is little direct experimental evidence that dominants cause physiological suppression in subordinates. Here, we experimentally test how social interactions influence subordinate reproductive hormones in Polistes dominula paper wasps. Polistes dominula queens commonly found nests in cooperative groups where the dominant queen is more fertile than the subordinate queen. In this study, we randomly assigned wasps to cooperative groups, assessed dominance behaviour during group formation, then measured levels of juvenile hormone (JH), a hormone that mediates Polistes fertility. Within three hours, lowest ranking subordinates had less JH than dominants or solitary controls, indicating that group formation caused rapid JH reduction in low-ranking subordinates. In a second experiment, we measured the behavioural consequences of experimentally increasing subordinate JH. Subordinates with high JH-titres received significantly more aggression than control subordinates or subordinates from groups where the dominant's JH was increased. These results suggest that dominants aggressively punished subordinates who attempted to maintain high fertility. Low-ranked subordinates may rapidly downregulate reproductive capacity to reduce costly social interactions with dominants. Rapid modulation of subordinate reproductive physiology may be an important adaptation to facilitate the formation of stable, cooperative groups.

Evolutionary origin of insect pheromones

Communication via chemical signals, that is, pheromones, is of pivotal importance for most insects. According to current evolutionary theory, insect pheromones originated either from extant precursor compounds being selected for information transfer or by the pheromone components exploiting a pre-existing sensory bias in the receiver. Here, we review the available experimental evidence for both hypotheses. Existing data indicate that most insect pheromones evolved from precursor compounds that were emitted as metabolic by-products or that previously had other non-communicative functions. Many studies have investigated cuticular hydrocarbons that have evolved a communicative function, although examples of pheromones exist that have arisen from defensive secretions, hormones or dietary compounds. We summarize and discuss the selective pressures shaping the pheromone during signal evolution.

Hormonal pleiotropy helps maintain queen signal honesty in a highly eusocial wasp

In insect societies, both queens and workers produce chemicals that reliably signal caste membership and reproductive status. The mechanisms that help to maintain the honesty of such queen and fertility signals, however, remain poorly studied. Here we test if queen signal honesty could be based on the shared endocrine control of queen fertility and the production of specific signals. In support of this “hormonal pleiotropy” hypothesis, we find that in the common wasp, application of methoprene (a juveline hormone analogue) caused workers to acquire a queen-like cuticular hydrocarbon profile, resulting in the overproduction of known queen pheromones as well as some compounds typically linked to worker fertility. By contrast, administration of precocene-I (a JH inhibitor) had a tendency to have the opposite effect. Furthermore, a clear gonadotropic effect of JH in queens was suggested by the fact that circulating levels of JH were ca. 2 orders of magnitude higher in queens than those in workers and virgin, non-egg-laying queens, even if methoprene or precocene treatment did not affect the ovary development of workers. Overall, these results suggest that queen signal honesty in this system is maintained by queen fertility and queen signal production being under shared endocrine control.

Juvenile hormone titers, ovarian status and epicuticular hydrocarbons in gynes and workers of the paper wasp Belonogaster longitarsus

The prevailing paradigm for social wasp endocrinology is that of juvenile hormone (JH) functioning pleiotropically in potential and actual queens, where it fuels dominance behaviors, stimulates ovarian growth and/or affects the production of status-linked cuticular compounds. In colonies with annual cycles (e.g., temperate-zone species), female adults produced at the end of the summer (called gynes) are physiologically primed to hibernate. Despite the absence of egg-laying in the pre-overwintering phase, gynes engage in dominance interactions that may affect reproductive potential following hibernation. JH levels have long been inferred to be low in gynes but this has never been tested. In what is the first study to measure JH in gyne-containing colonies of a temperate paper wasp, and the first to incorporate hormone assays in Belonogaster, our results show that the JH titer positively correlates with gyne-specific traits (including oocyte length and a low frequency of foraging trips) in B. longitarsus, a South African paper wasp. Measures of dominance correlated with oocyte length, but not all dominant females possessed activated ovaries. The cuticular hydrocarbon profiles of gynes and workers were distinct, with oocyte length and JH titer showing a positive association with longer-chain methyl-branched alkanes. Nonetheless, evidence for a role of JH in dominance was inconclusive. Finally, the range of JH titers among gynes, and the positive association of JH titers with ovarian status and prospective fertility signals, makes it unlikely that the gyne phenotype is maintained by low JH levels.

Variation in Venoms of Polybia Paulista Von Ihering and Polybia Occidentalis Olivier (Hymenoptera: Vespidae), Assessed by the FTIR-PAS Technique

Wasps are able to synthesize toxic compounds known as venoms, which form a part of a mechanism to overcome prey and also to defend their colonies. Study of the compounds that constitute these substances is essential in order to understand how this defense mechanism evolved, since there is evidence that the venoms can vary both intra- and interspecifically. Some studies have used liquid and gas chromatography as a reliable technique to analyze these compounds. However, the use of Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) to analyze the variations in venom's chemical profile has been proposed recently. This study evaluated whether the FTIR-PAS technique is effective for assessing the role of environmental factors on intra- and interspecific differences in the venom of the wasps Polybia paulista Von Ihering and Polybia occidentalis Olivier by FTIR-PAS. The colonies were collected in three municipalities of Mato Grosso do Sul, Brazil, in different types of environments. The results showed that the venoms of P. paulista and P. occidentalis differed significantly in profile. In addition, the intraspecific differences in the venom's chemical profile of P. paulista are related to the type of environment where they nested, regardless of the geographical distance between the nests. The FTIR-PAS technique proved to be reliable and effective to evaluate the variations in the venom's chemical profile in social wasps.

Social insect colony as a biological regulatory system: modelling information flow in dominance networks

Social insects provide an excellent platform to investigate flow of information in regulatory systems since their successful social organization is essentially achieved by effective information transfer through complex connectivity patterns among the colony members. Network representation of such behavioural interactions offers a powerful tool for structural as well as dynamical analysis of the underlying regulatory systems. In this paper, we focus on the dominance interaction networks in the tropical social wasp Ropalidia marginata-a species where behavioural observations indicate that such interactions are principally responsible for the transfer of information between individuals about their colony needs, resulting in a regulation of their own activities. Our research reveals that the dominance networks of R. marginata are structurally similar to a class of naturally evolved information processing networks, a fact confirmed also by the predominance of a specific substructure-the 'feed-forward loop'-a key functional component in many other information transfer networks. The dynamical analysis through Boolean modelling confirms that the networks are sufficiently stable under small fluctuations and yet capable of more efficient information transfer compared to their randomized counterparts. Our results suggest the involvement of a common structural design principle in different biological regulatory systems and a possible similarity with respect to the effect of selection on the organization levels of such systems. The findings are also consistent with the hypothesis that dominance behaviour has been shaped by natural selection to co-opt the information transfer process in such social insect species, in addition to its primal function of mediation of reproductive competition in the colony.

Insect Cuticular Hydrocarbons as Dynamic Traits in Sexual Communication

Recent research has demonstrated extensive within-species variation in pheromone expression in insect species, contrary to the view that pheromones are largely invariant within species. In fact, many studies on insect cuticular hydrocarbons (CHCs) show that pheromones can be highly dynamic traits that can express significant short-term plasticity across both abiotic and social environments. It is likely that this variability in CHC expression contributes to their important role in sexual signaling and mate choice. In this review, I discuss CHC plasticity and how this might influence sexual communication. I also highlight two important avenues for future research: examining plasticity in how individuals respond to CHC signals, and testing how sexual communication varies across abiotic and social environments.

Reproductive Status of Females in the Eusocial Wasp Polistes ferreri Saussure (Hymenoptera: Vespidae)

In the subfamily Polistinae, caste dimorphism is not pronounced and differences among females are primarily physiological and behavioral. We investigated factors that indicate the reproductive status in females of Polistes ferreri Saussure. We analyzed females from nine colonies and evaluated morphometric parameters, ovarian development, occurrence of insemination, relative age, and cuticular chemical profile. The colony females showed three kinds of ovarian development: type A, filamentous ovarioles; type B, ovarioles containing partially developed oocytes; and type C, long and well-developed ovarioles containing two or more mature oocytes. The stepwise discriminant analysis of the cuticular chemical profile showed that it was possible to distinguish the three groups of females: workers 1, workers 2, and queens. However, the stepwise discriminant analysis of the morphological differences did not show significant differences among these groups. The queens were among the older females in the colony and were always inseminated, while the age of the workers varied according to the stage of colony development.

Male mate recognition via cuticular hydrocarbons facilitates sexual isolation between sympatric leaf beetle sister species

Chemical signals in insects have been documented to play an important role in mate recognition, and divergence in chemical signals can often cause sexual isolation between closely related species or populations within species. We investigated the role of cuticular hydrocarbons (CHCs), short distance chemical signals, in male mate recognition between the two sympatric elm leaf beetles, Pyrrhalta maculicollis and Pyrrhaltaaenescens. Mating experiments demonstrated that strong sexual isolation between the two species was driven by CHCs divergence. Males preferred to mate with conspecific females with intact conspecific CHCs or conspecific CHCs reapplied after removal. Males also preferred heterospecific females that were treated with conspecific CHCs. Chemical analysis showed that the CHC profiles differ significantly between species. In P. maculicollis dimethyl-branched alkanes between C29 and C35 account for the majority of the saturated alkanes while the CHC profile of P. aenescens mostly consisted of monomethyl-branched alkanes between C22 and C29. Additionally, some compounds, such as 12,18-diMeC32, 12,18-diMeC34, are unique to P. maculicollis.

The role of juvenile hormone in dominance behavior, reproduction and cuticular pheromone signaling in the caste-flexible epiponine wasp, Synoeca surinama

BACKGROUND

The popular view on insect sociality is that of a harmonious division of labor among two morphologically distinct and functionally non-overlapping castes. But this is a highly derived state and not a prerequisite for a functional society. Rather, caste-flexibility is a central feature in many eusocial wasps, where adult females have the potential to become queens or workers, depending on the social environment. In non-swarming paper wasps (e.g., Polistes), prospective queens fight one another to assert their dominance, with losers becoming workers if they remain on the nest. This aggression is fueled by juvenile hormone (JH) and ecdysteroids, major factors involved in caste differentiation in most eusocial insects. We tested whether these hormones have conserved aggression-promoting functions in Synoeca surinama, a caste-flexible swarm-founding wasp (Epiponini) where reproductive competition is high and aggressive displays are common.

RESULTS

We observed the behavioral interactions of S. surinama females in field nests before and after we had removed the egg-laying queen(s). We measured the ovarian reproductive status, hemolymph JH and ecdysteroid titers, ovarian ecdysteroid content, and analyzed the cuticular hydrocarbon (CHC) composition of females engaged in competitive interactions in both queenright and queenless contexts. These data, in combination with hormone manipulation experiments, revealed that neither JH nor ecdysteroids are necessary for the expression of dominance behaviors in S. surinama. Instead, we show that JH likely functions as a gonadotropin and directly modifies the cuticular hydrocarbon blend of young workers to match that of a reproductive. Hemolymph ecdysteroids, in contrast, are not different between queens and workers despite great differences in ovarian ecdysteroid content.

CONCLUSIONS

The endocrine profile of S. surinama shows surprising differences from those of other caste-flexible wasps, although a rise in JH titers in replacement queens is a common theme. Extensive remodeling of hormone functions is also evident in the highly eusocial bees, which has been attributed to the evolution of morphologically defined castes. Our results show that hormones which regulate caste-plasticity can lose these roles even while caste-plasticity is preserved.

Reproductive status, endocrine physiology and chemical signaling in the Neotropical, swarm-founding eusocial wasp Polybia micans

In the evolution of caste-based societies in Hymenoptera, the classical insect hormones juvenile hormone (JH) and ecdysteroids were co-opted into new functions. Social wasps, which show all levels of sociality and lifestyles, are an ideal group in which to study such functional changes. Virtually all studies on the physiological mechanisms underlying reproductive division of labor and caste functions in wasps have been done on independent-founding paper wasps, and the majority of these studies have focused on species specially adapted for overwintering. The relatively little-studied tropical swarm-founding wasps of the Epiponini (Vespidae) are a diverse group of permanently social wasps, with some species maintaining caste flexibility well into the adult phase. We investigated the behavior, reproductive status, JH and ecdysteroid titers in hemolymph, ecdysteroid content of the ovary and cuticular hydrocarbon (CHC) profiles in the caste-monomorphic, epiponine wasp Polybia micans Ducke. We found that the JH titer was not elevated in competing queens from established multiple-queen nests, but increased in lone queens that lack direct competition. In queenless colonies, JH titer rose transiently in young potential reproductives upon challenge by nestmates, suggesting that JH may prime the ovaries for further development. Ovarian ecdysteroids were very low in workers but higher and correlated with the number of vitellogenic oocytes in the queens. Hemolymph ecdysteroid levels were low and variable in both workers and queens. Profiles of P. micans CHCs reflected caste, age and reproductive status, but were not tightly linked to either hormone. These findings show a significant divergence in hormone function in swarm-founding wasps compared with independently founding ones.

Virgin honeybee queens fail to suppress worker fertility but not fertility signalling

Queen mating status in social insects is a matter of crucial importance for workers because of its influence on the queen's productivity and consequently their fitness. Behavioural and physiological reactions of workers to the queens mating status have been studied as a proxy to mechanisms maintaining insect sociality. Here we show that unmated honeybee queens have considerably impaired capacity to trigger worker sterility and cooperative behaviour in comparison to mated (and thus more productive) queens and that under unmated queens social harmony in honeybee societies and queen's dominant position are somewhat compromised. Together with this it is shown that honeybee workers exposed to unmated queens despite being active reproductively and behaving accordingly display an impaired ability to advertise their fertility compared to queenless workers. These findings suggest that reproductive development, behavioural reactions and production of fertility signals are differentially regulated and differently influenced by the queen's presence.

The role of microgynes in the reproductive strategy of the neotropical ant Ectatomma ruidum

Miniaturized queens, microgynes, are regarded as an alternative reproductive strategy sparsely present through the ant world. The described roles of miniaturized queens include alternative short-distance dispersal morphs, an adaptation to polygyny and inquiline parasites. Some of these inquiline parasite microgynes have been described as a separate species from their host. In the poneromorph group, miniaturized queens are only reported in two Mexican populations of two Ectatomminae: Ectatomma tuberculatum, in which small queens represent an inquiline species (Ectatomma parasiticum) and Ectatomma ruidum. E. ruidum presents apparently facultative polygyny with microgynes. We used mitochondrial DNA markers and newly developed microsatellite loci to investigate the status as well as the role of microgynes in E. ruidum. We confirmed that microgynes and macrogynes are from the same species. This species is almost exclusively monogynous and monoandrous, supernumerary dealate queens of both types being actually daughters of the mother queen. An apparently polygynous nest was more often headed by a macrogyne than a microgyne. We didn't find any inbreeding or isolation by distance in the studied population, indicating that new gynes are inseminated by unrelated males and can establish a new nest far from their natal nest. However, re-adoption of daughter queens seems to be the rule and rate of microgyny appears to be linked to nest density and environmental factors.