Pickett, K. M., Carpenter, J. M. & Wheeler, W. C. 2006: Systematics of Polistes (Hymenoptera: Vespidae), with a phylogenetic consideration of Hamilton's haplodiploidy hypothesis. — Ann. Zool. Fennici 43: 390–406.

A review of previously published cladistic analyses of Polistes is presented. The two most recent analyses of Polistes are shown to be largely consistent phylogenetically. Although the taxonomy implied by each differs, this difference is shown to be mostly due to taxon sampling. After the review, a phylogenetic analysis of Polistes — the most data-rich yet undertaken — is presented. The analysis includes new data and the data from previously published analyses. The differing conclusions of the previous studies are discussed in light of the new analysis. After discussing the status of subgeneric taxonomy in Polistes, the new phylogeny is used to test an important hypothesis regarding the origin of social behavior: the haplodiploidy hypothesis of Hamilton.

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Hunt, J. H. 2006: Evolution of castes in Polistes. — Ann. Zool. Fennici 43: 407–422.

A novel hypothesis for the origin of castes in Polistes has recently been proposed: the worker and gyne castes among offspring of a Polistes colony are based on the underlying ground plan of reproductive physiology that would have characterized the non-diapause and diapause generations of a bivoltine solitary vespid wasp. Here the hypothesis is reviewed in light of the dynamic nature of diapause expression in insects in general, and it is re-named the diapause ground plan hypothesis. The diapause ground plan hypothesis differs in several significant aspects from an existing hypothesis for the origin of castes — the ovarian ground plan hypothesis. Phylogenetic implications of the diapause ground plan hypothesis also are in discord with the currently accepted classification of Vespidae, and the diapause ground plan hypothesis has been challenged for its failure to address multiple levels of analysis. Each of these areas of discord is described, and key points of difference between the diapause ground plan hypothesis and competing hypotheses are identified. Strong inference — the explicit testing of a hypothesis for possible rejection — is proposed as the most efficacious route to clearer understanding of the evolution of the castes in Polistes. Specific suggestions for some strong tests of competing hypotheses are proposed.

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Sumner, S. 2006: Determining the molecular basis of sociality in insects: progress, prospects and potential in sociogenomics. — Ann. Zool. Fennici 43: 423–442.

How complex biological diversity can arise from seemingly simple strands of DNA is one of the most pertinent of questions confronting 21st century biologists. With the increasing availability and cost effectiveness of genomic techniques, there has been a rapid expansion in the taxonomic breadth of species that can now be studied at the molecular level of the genes. Consequently, behavioural ecologists are now able to examine the behaviours of their study organisms at an entirely new level. Here I review the current progress made in sociogenomics — the study of the molecular basis of sociality — with particular emphasis on what genome-level studies can reveal about social evolution. First I discuss the evolutionary interactions that occur between the genome and sociality. Next I review the current literature on how genes underlie queen and worker caste evolution: I identify 19 genes that are likely to be of importance in the evolution of caste systems across eusocial taxa; I make predictions on how gene expression patterns might orchestrate the evolution of social complexity, and make preliminary tests using the available data. Finally, I outline major questions in social evolution that can be addressed for the first time using a sociogenomic approach, highlight practical considerations in sociogenomics and discuss suitable model systems for future research on the molecular basis of sociality.

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Nonacs, P. 2006: The rise and fall of transactional skew theory in the model genus Polistes. — Ann. Zool. Fennici 43: 443–455.

Transactional Skew (TS) theory predicts that cooperative breeding associations can be adaptive for all group members as long as they properly allocate reproduction within a social contract. Polistes wasps have been the preeminent model genus for testing TS models. Most tests have focused on either the patterns of skew or on patterns of aggression between wasps, which has been assumed to set skew. However, the totality of evidence suggests that aggression (observed as darts, lunges and bites) has no connection to establishing reproductive skew. Although some patterns of reproductive skew support TS theory, most of the reproductive data are either non-supportive or inconclusive relative to the models. Of particular significance are recent findings of high skew associations between distantly or unrelated wasps when TS theory strongly predicts skew should be low. A possible evolutionary explanation for the failure of TS models is derived through a simple model. Although the TS strategy optimizes fitness, its relative advantage over a much simpler conventional rule for group formation is never greater than 3% and often less. Therefore, even small costs in evolving the cognitive mechanisms needed to form social contracts may preclude their appearance. Although TS theory may have failed in Polistes, reproductive skew is now a well-described phenomenon. Finding new viable explanations for reproductive skew and extending the theory to skews in non-reproductive contexts will maintain Polistes in its role as a model taxonomic group in the study of the evolution of social behavior.

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Starks, P. T. & Fefferman, N. H. 2006: Polistes nest founding behavior: a model for the selective maintenance of alternative behavioral phenotypes. — Ann. Zool. Fennici 43: 456–467.

Here we present a novel model for the selective maintenance of alternative phenotypes. Our model is appropriate for systems where the expression of alternative tactics is both condition and frequency dependent. We use Polistes dominulus as our model system, and show how frequencies of solitary nest founding, collaborative nest founding, usurpation of defended nests, and adoption of abandoned nests are predicted to vary with changes in ecological and social conditions. To accomplish this we (1) review commonly used models that explain the selective maintenance of alternative phenotypes, (2) describe some basic life-history characteristics of Polistes wasps, (3) present a novel condition dependent mixed strategy model, (4) use this model to predict frequencies of alternative tactics under conditions of differing survivability, relatedness between co-foundresses, and reproductive skew between co-foundresses, and (5) provide future directions for refining and testing this unifying model.

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Tsuchida, K. & Suzuki, T. 2006: Conflict over sex ratio and male production in paper wasps. — Ann. Zool. Fennici 43: 468–480.

Kin selection theory has been used to generate several useful frameworks in the field of evolutionary ecology. We briefly review the research on two main theoretical predictions for sex ratio variation among colonies, and for worker policing, using a relatedness framework in paper wasps. Contrary to the studies of advanced eusocial wasps, conclusive evidence showing worker control of sex ratio has not been shown in primitively eusocial Polistes, which suggests that collective worker control is not active at the primitively eusocial stage when colony size is small. Worker control of colony investment might be facilitated in an advanced eusocial system when colony size is large. Therefore, a relatedness-based theoretical framework does not seem to be important in explaining the sex ratio variation among colonies of Polistes wasps. Worker policing, however, has been observed in monogynous and monandrous colonies of Polistes and Dolichovespula, in which relatedness benefits for workers do not exist. The observed policing behavior seems to be termed as `selfish policing'. Fertility signals and egg marking pheromones by queens are the likely proximate factors that determine the fate of workers' eggs. We also discuss the influence dominance order among workers may play in regulating worker reproduction. This is a form of decentralized regulation, which may be associated with larger colony size.

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Field, J. & Cant, M. 2006: Helping effort in primitively eusocial wasps. — Ann. Zool. Fennici 43: 481–487.

In primitively eusocial and cooperatively breeding societies, there is substantial individual variation in helping effort that is not accounted for by variation in genetic relatedness. In primitively eusocial wasps, helpers have a significant chance of inheriting breeding positions. Recent models suggest that because helpers with greater expected future fitness have more to lose, they should invest less in rearing the dominant's offspring. Observations and experiments on the paper wasp Polistes dominulus and the hover wasp Liostenogaster flavolineata support this prediction: helpers nearer to the front of the queue to inherit dominance, and helpers that stand to inherit larger, more productive groups, work less hard. These findings support the view that variation in social traits is best understood from a life-history perspective. Group augmentation effects, where greater helping effort leads to direct benefits through increased group size, seem less important in wasps. Further studies are required to understand how conflicts over helping effort are resolved in social wasps.

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Turillazzi, S. 2006: Polistes venom: a multifunctional secretion. — Ann. Zool. Fennici 43: 488–499.

Polistes venom is a complex secretion that has several functions in the social organization of a colony. The defensive function as an allomone against vertebrate and invertebrate enemies is enhanced with antimicrobial properties. Its role in chemical communication is multi-faceted as it contains both alarm and sexual pheromones, but can also have cues which are important both for nestmate and caste recognition, as well as for hibernacula marking. Research on venom chemistry is extremely important for both the establishment of specific immunotherapy for allergic patients and for the discovery of new molecules with pharmacological activity. Venom composition can also provide important characters for taxonomical and phylogenetical studies.

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Dani, F. R. 2006: Cuticular lipids as semiochemicals in paper wasps and other social insects. — Ann. Zool. Fennici 43: 500–514.

Strong evidence indicates that in Polistes wasps, as in other social insects, epicuticular lipids are involved in several aspects of recognition, such as nest-, nestmate- and fertility recognition. This evidence is based both on the study of differences in composition between groups of conspecific individuals (members of different colonies; age groups; dominants and subordinates; fertile and infertile individuals), and on bioassays. The first part of this review considers the general characteristics of Polistes epicuticular hydrocarbons and summarises what is currently known about the non-hydrocarbon cuticular lipids. The second part concerns the most relevant contributions of the work on Polistes towards an understanding of the role of epicuticular hydrocarbons as semiochemicals in social insects. Four aspects, highlighted in 1993 by Howard, as future directions for the study of epicuticular hydrocarbons will be considered: (i) the need for a complete determination of epicuticular hydrocarbon structures (in particular chirality); (ii) the role of individual hydrocarbons as semiochemicals, or of classes of hydrocarbons in the epicuticular mixtures; (iii) the intraspecific variability in epicuticular lipid composition; and, (iv) current knowledge about cuticular hydrocarbon perception by insects.

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Monnin, T. 2006: Chemical recognition of reproductive status in social insects. — Ann. Zool. Fennici 43: 515–530.

Inclusive fitness theory explains how helpers reproduce indirectly via the breeders they help. The inclusive fitness helpers get depends on their relatedness to the breeder(s), colony productivity and fertility of the breeder(s). It is therefore critical for workers to assess breeder fertility. There is strong evidence that, in wasps, bees and ants, the cuticular hydrocarbon (CHC) profiles of breeders are a signal of fertility. Chemical and behavioural evidence suggests that linear alkanes are not involved in communication, whereas methyl-branched alkanes and alkenes may constitute, or at least contribute to, the fertility signal. The correlation between CHCs and reproduction is well established, as well as the fact that CHCs are detected and that workers react accordingly. However, whether CHC profiles are honest is yet to be demonstrated. Hormonal and genetic studies, such as inactivating genes regulating the production of alkenes, are promising approaches to investigate the honesty of CHC profiles.

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Cervo, R. 2006: Polistes wasps and their social parasites: an overview. — Ann. Zool. Fennici 43: 531–549.

Severe brood care costs have favoured the evolution of cheaters that exploit the parental services of conspecifics or even heterospecifics in both birds and social insects. In Polistes paper wasps, three species have lost worker castes and are dependent on hosts to produce their sexuals, while other species use hosts facultatively as an alternative to caring for their own brood. This paper offers an overview of the adaptations, strategies and tricks used by Polistes social parasites to successfully enter and exploit host social systems. Moreover, it also focuses on the analogous solutions adopted by the well-known brood parasite birds, and stresses the evolutionary convergence between these two phylogenetically distant taxa. A comparative analysis of life-history patterns, as well as of phylogenetic relationships of living facultative and obligate parasitic species in Polistes wasps, has suggested a historical framework for the evolution of social parasitism in this group. As with avian brood parasites, the analysis of adaptation and counter adaptation dynamics should direct the future approach for the study of social parasitism in Polistes wasps. The Polistes parasite–host system seems a suitable candidate for a model system in coevolutionary arms race studies, just as Polistes paper wasps have been considered for many years a model organism for sociobiological studies.

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Lorenzi, M. C. 2006: The result of an arms race: the chemical strategies of Polistes social parasites. — Ann. Zool. Fennici 43: 550–563.

The ability of social insects to discriminate between nestmates and aliens on the basis of scent has been the selective pressure favoring the evolution of chemical strategies to facilitate integration into host nests by social parasites, i.e., by organisms which rely on the nests and workers of others to rear their brood. As a result of the coevolutionary arms race, obligate social parasites of Polistes wasps have evolved complex mechanisms of mimicry. Social parasites mimic host chemical signatures at the level of species, colony, and possibly rank. Social parasites possess diluted recognition cues and apply compounds to the host nests that may result in host manipulation. The origin and evolutionary pathway to host/parasite chemical similarity is discussed by making comparisons with the tactics used by facultative social parasites, and with the development of the cuticular signature in free-living species.

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Beani, L. 2006: Crazy wasps: when parasites manipulate the Polistes phenotype. — Ann. Zool. Fennici 43: 564–574.

The infection of Polistes dominulus wasps by the strepsipteran Xenos vesparum provides a suitable case study for exploring parasitic manipulation. One aim of this review is to summarize the life cycle of X. vesparum: from infection of immature wasps to the "stylopization" of adults, and from its mating at summer aberrant aggregations of infected wasps to the overwintering of fertilized Xenos inside the abdomen of hibernating wasps. The second aim of this review it to highlight how this parasite manipulates the flexible phenotype of the wasp to maximize its own reproductive success.

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Tibbetts, E. A. 2006: Badges of status in worker and gyne Polistes dominulus wasps. — Ann. Zool. Fennici 43: 575–582.

Despite widespread interest in quality signals, a broad understanding of quality that incorporates information about signals used in a variety of contexts remains elusive. For example, relatively little is known about arbitrary signals of quality used during aggressive competition (badges of status). Recently, a new badge of status was found: black facial patterns in Polistes dominulus wasps. Previous work on P. dominulus facial patterns focused on queens, finding that facial patterns predict body size and social dominance. Here, I examine worker facial patterns for the first time. Worker facial patterns provide an interesting comparison with queens and help shed light on two unresolved issues: (1) Is there pre-imaginal caste bias in these primitively eusocial insects? (2) Is badge-of-status elaboration influenced by developmental environment? I show that worker and gyne (future queen) facial patterns are correlated with body size. Larger individuals have a larger proportion of their clypeus pigmented black, corroborating the relationship between body size and facial pattern found previously in queens. Independent of the size relationship, workers and gynes have different facial patterns. Gynes have the disrupted, black facial patterns that signal a high level of quality, while workers have yellow facial patterns associated with a low level of quality. The differences between worker and gyne facial patterns suggest that there is some pre-imaginal caste bias in these eusocial wasps. Workers and gynes are genetically similar but experience different developmental environments, so the differences between worker and gyne facial patterns suggests that badge development is influenced by environmental factors.

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Dapporto, L. & Palagi, E. 2006: Wasps in the shadow: Looking at the pre-hibernating clusters of Polistes dominulus. — Ann. Zool. Fennici 43: 583–594.

In some Polistes species, hibernation begins with the formation of clusters. Pre-hibernating aggregations may be evolutionarily favoured because they provide a dilution effect, better active defence from predators, and insulation from cold and/or dryness. Many authors have suggested that the pre-hibernating phase represents a socially inactive period for wasps. This paradigm strongly influenced the direction of research; in fact, most studies on Polistes behaviour focus on the nesting phase. It has been demonstrated, however, that many social interactions occur in aggregations, and that a division of labour is also present in these aggregations. Here, we evaluate the influence of cluster formation and social networks on the main aspects of wasp social behaviour, such as the consequences on kin-assortment (philopatry and tolerance level), variation in chemical recognition, division of labour, and helping behaviour.

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Liebert, A. E., Gamboa, G. J., Stamp, N. E., Curtis, T. R., Monnet, K. M., Turillazzi, S. & Starks, P. T. 2006: Genetics, behavior and ecology of a paper wasp invasion: Polistes dominulus in North America. — Ann. Zool. Fennici 43: 595–624.

Studies of social insect invasions to date have focused primarily on highly eusocial insects such as ants and yellowjacket wasps. Yet insect societies without fixed, morphological caste systems may be particularly good invaders due to their behavioral flexibility, as demonstrated by the recent invasion of the European paper wasp Polistes dominulus into North America. Here we provide a review of this ongoing invasion in terms of (1) population genetic variation in P. dominulus, and (2) comparative behavior and ecology of P. dominulus vs. the native P. fuscatus. We present new genetic evidence supporting the occurrence of multiple independent introductions of P. dominulus into the USA, confirming previous results demonstrating relatively high genetic variation in introduced populations. We also present behavioral and demographic evidence suggesting that P. dominulus is displacing the native P. fuscatus in at least part of its range, most likely due to the superior productivity and survivorship of P. dominulus colonies. We review data from comparative studies where the two species are sympatric and discuss possible mechanisms contributing to the differences between them. Finally, we discuss the ecological impacts of this invasion and the role of P. dominulus as a model organism for invasion biology.

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