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Social recognition represents the foundation of social living. To what extent social recognition is hard-wired by early-life experience or flexible and influenced by social context of later life stages is a crucial question in animal behaviour studies. Social insects have represented classic models to investigate the subject, and the acknowledged idea is that relevant information to create the referent template for nest-mate recognition (NMR) is usually acquired during an early sensitive period in adult life. Experimental evidence, however, highlighted that other processes may also be at work in creating the template and that such a template may be updated during adult life according to social requirements. However, currently, we lack an ad hoc experiment testing the alternative hypotheses at the basis of NMR ontogeny in social insects. Thus, to investigate the mechanisms underlying the ontogeny of NMR in Polistes wasps, a model genus in recognition studies, and their different role in determining recognition abilities, we subjected Polistes dominula workers to different olfactory experiences in different phases of their life before inserting theminto the social environment of a novel colony and testing them in recognition bioassays. Our results show that workers develop their NMR abilities based on their social context rather than through pre-imaginal and early learning or self-referencing. Our study demonstrates that the social context represents the major component shaping recognition abilities in a social wasp, therefore shedding new light on the ontogeny of recognition in paper wasps and prompting the reader to rethink about the traditional knowledge at the basis of the recognition in social insects. [ABSTRACT FROM AUTHOR]

Differences in male and female phenotypes are often the results of sexual selection. Over the years, a vast number of studies investigated how and why the 2 sexes differ in their physical appearance, reaching the conclusion that peculiar visual traits, signals, or ornaments usually evolve under the pressure of sexual selection to mediate intrasexual competition and mate choice. In social contexts, however, males and females can hold different roles and social interactions may depend on the individual gender. The female-dominated hymenopteran societies represent a fascinating scenario to investigate recognition and communication among individuals of different genders outside a common sexual selection framework because sterile female workers typically do not mate and are not attracted to males. Here, we used laboratory bioassays (lure presentation experiments) to evaluate the ability of Polistes dominula workers to discriminate between individuals of the 2 genders, investigating the relevance of the chemical and visual cues potentially involved in such process. Our results showed that P. dominula workers are able to discriminate between the sexes and visual cues rather than chemical ones are responsible for such discrimination. [ABSTRACT FROM AUTHOR]

Contrasting phenotypes arise from similar genomes through a combination of losses, gains, co-option and modifications of inherited genomic material. Understanding the molecular basis of this phenotypic diversity is a fundamental challenge in modern evolutionary biology. Comparisons of the genes and their expression patterns underlying traits in closely related species offer an unrivaled opportunity to evaluate the extent to which genomic material is reorganized to produce novel traits. Advances in molecular methods now allow us to dissect the molecular machinery underlying phenotypic diversity in almost any organism, from single-celled entities to the most complex vertebrates. Here we discuss how comparisons of social parasites and their free-living hosts may provide unique insights into the molecular basis of phenotypic evolution. Social parasites evolve from a eusocial ancestor and are specialized to exploit the socially acquired resources of their closely-related eusocial host. Molecular comparisons of such species pairs can reveal how genomic material is re-organized in the loss of ancestral traits (i.e., of free-living traits in the parasites) and the gain of new ones (i.e., specialist traits required for a parasitic lifestyle). We define hypotheses on the molecular basis of phenotypes in the evolution of social parasitism and discuss their wider application in our understanding of the molecular basis of phenotypic diversity within the theoretical framework of phenotypic plasticity and shifting reaction norms. Currently there are no data available to test these hypotheses, and so we also provide some proof of concept data using the paper wasp social parasite/host system (Polistes sulcifer-Polistes dominula). This conceptual framework and first empirical data provide a spring-board for directing future genomic analyses on exploiting social parasites as a route to understanding the evolution of phenotypic specialization. [ABSTRACT FROM AUTHOR]

Males are under different selective pressures than females, which results in differences in the physiology of the two sexes to maximize their fitness. In terms of immunity, males are typically considered as the 'sicker sex', where immunocompetence is reduced to favour increased reproductive output. However, male social Hymenoptera are also haploid and therefore lack allelic variation at the individual level, which can also lead to reduced immunocompetence. Over the last decade, several studies have provided evidence for a higher susceptibility to disease in males of social Hymenoptera, without clarifying whether this susceptibility was a direct consequence of their haploid condition or the result of a 'live hard, die young' overall evolutionary strategy. In the present study, we used an experimental approach of bacterial challenge to test the immune response of males and females in two species of social Hymenoptera (honey bees, Apis mellifera; paper wasps, Polistes dominula), where males show very different life-history traits. Drones benefit from colony protection for most of their life, whereas P. dominula males leave their colonies and have to survive for weeks at leks. If the haploid condition is responsible for a higher susceptibility in males, we should expect a lower immune response in males of both species compared to females. Conversely, if the immunocompetence depends on the life-history traits of males, an opposite trend is expected in males of the two species. Our results do not support the 'haploid susceptibility hypothesis' but are in accordance with the different life history of males from the two species. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114, 274-278. [ABSTRACT FROM AUTHOR]

The importance of early experience in animals’ life is unquestionable, and imprinting-like phenomena may shape important aspects of behaviour. Early learning typically occurs during a sensitive period, which restricts crucial processes of information storage to a specific developmental phase. The characteristics of the sensitive period have been largely investigated in vertebrates, because of their complexity and plasticity, both in behaviour and neurophysiology, but early learning occurs also in invertebrates. In social insects, early learning appears to influence important social behaviours such as nestmate recognition. Yet, the mechanisms underlying recognition systems are not fully understood. It is currently believed that Polistes social wasps are able to discriminate nestmates from non-nestmates following the perception of olfactory cues present on the paper of their nest, which are learned during a strict sensitive period, immediately after emergence. Here, through differential odour experience experiments, we show that workers of Polistes dominula develop correct nestmate recognition abilities soon after emergence even in absence of what have been so far considered the necessary cues (the chemicals spread on nest paper). P. dominula workers were exposed for the first four days of adult life to paper fragments from their nest, or from a foreign conspecific nest or to a neutral condition. Wasps were then transferred to their original nests where recognition abilities were tested. Our results show that wasps do not alter their recognition ability if exposed only to nest material, or in absence of nest material, during the early phase of adult life. It thus appears that the nest paper is not used as a source of recognition cues to be learned in a specific time window, although we discuss possible alternative explanations. Our study provides a novel perspective for the study of the ontogeny of nestmate recognition in Polistes wasps and in other social insects. [ABSTRACT FROM AUTHOR]

The chemical integration strategies of facultative social parasites of social insects have not received the scientific attention they deserve, even though there is considerable research being done on the strategies of obligate social parasites. We simulated intraspecific nest usurpations in the social paper wasp, Polistes biglumis, by dividing each nest into two parts and putting one half in the care of the original foundress and the other half in the care of a usurper. After 8days, we removed and killed foundresses and usurpers, and later tested the responses of naïve, sister-offspring to them. In each half-colony, the offspring were more tolerant to the female that was last on the nest, regardless of whether she was the foundress or a usurper. This suggested that usurpers had the chemical means to be tolerated by the host offspring. Comparisons between the epicuticular hydrocarbon profiles of foundresses and usurpers showed that usurpers were neither chemically insignificant nor transparent, nor were they mimetic, as obligate parasites often are. Instead, usurpers had chemical profiles richer in methyl-branched hydrocarbons than those of the foundresses. Analyses of the hydrocarbon profiles of nest paper revealed that usurpers supplemented host nests with their own hydrocarbons, a sort of nest marking. As a result, the chemical profiles of the host nests became qualitatively more similar to those of the usurpers. These chemical strategies illustrate that branched hydrocarbons play a role as semiochemicals and that facultative parasites may not all be on the main pathway to obligate parasitism. [ABSTRACT FROM AUTHOR]

In order to understand how the apparent freedom of individual movements can concur with social order in a colony, we investigated spatial relationships between foundresses, workers and immature brood in a paper wasp. This is the first time an ecological analytical approach (home range analysis) has been employed to describe small scale spatial use in a social context. In this study, home range was not used in its strictly ecological sense, but rather applied to the comb. Our results show that the positions individual wasps assumed on Polistes dominulus combs are spatially structured. Workers and foundresses do not occupy the comb in random distribution, but rather follow predictable spatial patterns. Each active wasp has its own spatial fidelity area, at least over a 1 d observation period, spending the majority of its time within a very small area averaging approx. 12% of the comb but occasionally it may cover an area of up to 50% of the comb surface. Dominant females occupied a significantly smaller area that either subordinate foundresses or workers. Areas patrolled by workers varied in shape and size, with no relation to time spent on the comb, wasp density or position of immature brood. All the wasps clumped around the dominant female, who proved to be the only individual affected by cell content. Nevertheless, although the wasps tended to clump together, average superimposition rates among nest-mates was very low (higher in workers than foundresses), suggesting that the wasps limit each other’s individual spaces. [ABSTRACT FROM AUTHOR]

1. Like avian brood parasites, obligate insect social parasites exploit the parental care of a host species to rear their brood, causing an evident loss of host reproductive success. This fitness cost imposes selective pressure on the host to reduce the parasite effect. A possible outcome of an evolutionary arms race is the selection of host morphological counter-adaptations to resist parasite attacks. 2. We studied host–parasite pairs of Polistes wasps in which the fighting equipment of the parasite's body allows it to enter the host colony. 3. We searched for host morphological traits related to fighting ability that could be considered counter-adaptations. As a host–parasite co-evolutionary arms race can only occur where the two lineages co-exist, we compared morphological traits of hosts belonging to populations with or without parasite pressure. We report that host foundresses belonging to populations under strong parasite pressure have a larger body size than those belonging to populations without parasite pressure. 4. Behavioural experiments carried out to test if an increase in host body size is useful to oppose parasite usurpation show that large body size foundresses exhibit a greater ability of nest defence. [ABSTRACT FROM AUTHOR]

In animals, restlessness is a strategy to fulfil a goal within a narrow seasonal window when ecological and physiological constraints require the performance of certain fundamental events. Although restlessness can be expected in parasitic species that have their biological cycle similar to that of the host, no ‘urge to parasitize’ has thus far been demonstrated in any host-parasite pair. The paper wasp, Polistes sulcifer, is a social parasite that has lost the nest-building ability and marked by the absence of the worker caste; it depends on a congeneric host species to reproduce. Host colony usurpation is successful when it occurs in a well-defined seasonal window. The short time available for host-nest usurpation might lead to parasite restlessness that overlaps this period. Under controlled laboratory conditions, we demonstrated that the parasite females exhibit ‘usurpation restlessness’ during the period in which field usurpations occur. Additional experiments showed that both this period and laboratory temperature influence the parasite’s ‘urge to usurp’. [ABSTRACT FROM AUTHOR]

Polistes foundresses can behave as facultative social parasites when, instead of founding their own nest, they usurp colonies of the same or a different species and temporary use the host workforce to raise their own brood. Conspecific usurpation appears to be common among Polistes wasps, but nothing is known about the mechanisms that these facultative social parasites use to have themselves accepted within usurped colonies. Using behavioural tests, we studied the chemical strategies employed by females of Polistes nimphus when they behave as facultative social parasites in colonies of the same or of a different species. We hypothesized that usurpers would mark host nests with their own odours and/or acquire host nest odours in order to camouflage their real identity from host workers. Our results indicated that P. nimphus usurpers used different chemical strategies depending on host nest species: they acquired conspecific host odours but marked heterospecific host combs with their own odours. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 505–512. [ABSTRACT FROM AUTHOR]

The active and coordinating capacity of defending the nest is a key feature of social insects. The present study investigates the presence of alarm pheromones in the venom of workers of the social wasp, Polistes dominulus. Laboratory experiments were performed with caged colonies of P. dominulus using a wind tunnel apparatus to test the behavioural response of workers to venom released by other workers and to venom extracts. Contrary to that previously reported for European paper wasps, the present results show that the venom is the source of alarm pheromones. Field experiments combining a visual (black target) and a chemical stimulus (venom extract) were performed to test the effect of the venom on the reaction of colonies. Wasps leave the nest, land on the visual target and attack the target significantly more once exposed to venom extract plus target than to solvent plus target. This work shows that the venom of P. dominulus workers elicits an alarm response, reduces the threshold for attack and acts as an attractant on targets. These results using P. dominulus indicate that, in both American and European species, colony defence is based on the same features, suggesting that chemical alarm is a widespread trait in the genus Polistes. [ABSTRACT FROM AUTHOR]

A recent study (Izzo et al., Behav Ecol Sociobiol 64: 857–864, ) reported that cuticular hydrocarbons (CHCs) correlate with fertility, not dominance, in the paper wasp Polistes dominulus thus contradicting the results of recent investigations which concluded that social dominance is the main determinant for CHC signatures in this species. We suggest here that different forms of dominance in the pre-nesting and post-nesting phases caused the apparently contradictory results. Thus the assumption that dominance behaviour in the pre-nesting stage is synonymous with dominance after colony foundation is incorrect. We provide standardised definitions for forms of “dominance” observed in the P. dominulus life cycle to avoid apparent discrepancies in the future among studies dealing with the same topics in different annual stages. [ABSTRACT FROM AUTHOR]

Insect social parasites have to conquer a host colony by overcoming its defensive barriers. In addition to increased fighting abilities, many social parasites evolved sophisticated sensory deception mechanisms to elude host colonies defenses by exploiting host communication channels. Recently, it has been shown that the conspicuous facial markings of a paper wasp social parasite, Polistes sulcifer , decrease the aggressiveness of host foundresses. Two main hypotheses stand as explanations of this phenomenon: visual sensory deception (i.e. the black patterning reduces host aggression by exploiting the host visual communication system) and visual quality assessment (i.e. facial markings reduce aggressiveness as they signal the increased fighting ability of parasites). Through behavioral assays and morphological measurements we tested three predictions resulting from these hypotheses and found no support either for the visual sensory deception or for the quality assessment to explain the reduction in host aggressiveness towards the parasite. Our results suggest that other discrimination processes may explain the observed phenomenon. [ABSTRACT FROM AUTHOR]

How work is organized varies in social insect colonies. Some investigators have argued that the queen plays an active role in regulating worker activity in species with small, simple colonies, but that work is self-organized in species with large, complex colonies. Here, we present data that suggest that two species of paper wasps do not fit this pattern. Polistes wasps are traditionally classified as primitively eusocial wasps, showing characteristics of simple insect societies, such as small colony sizes, lack of queen–worker dimorphism, and queen control of both reproduction and worker activity. Colony activity in Polistes is episodic; quiet periods are followed by periods of intense activity when most wasps in the colony are active. We tested whether queens in P. instabilis and P. dominulus controlled work by initiating active periods, goading workers into activity. Instead, we found that colony activity was initiated by the behaviours of workers arriving at the colony, walking across the nest face or, less commonly, antennating, leaving or gaster wagging. Queens initiated no more activity periods than the average worker. Furthermore, activity levels in colonies of P. dominulus in which the queen was removed did not differ significantly from activity levels in colonies with queens. Polistes instabilis and P. dominulus colonies showed characteristics of primitively eusocial insect societies, but also showed worker initiation of colony activity, suggesting that these two species represent examples of an intermediate level of colony organization in which queens control reproduction but do not control the organization of work. [Copyright &y& Elsevier]