Dispersal decisions and predispersal behavior in Polistes paper wasp ‘workers’

Social experience drives the development of holistic face processing in paper wasps

Most recognition is based on identifying features, but specialization for face recognition in some taxa relies on a different mechanism, termed 'holistic processing' where facial features are bound together into a gestalt which is more than the sum of its parts. Although previous work suggests that extensive experience may be required for the development of holistic processing, we lack experiments that test how age and experience interact to influence holistic processing. Here, we test how age and experience influence the development of holistic face processing in Polistes fuscatus paper wasps. Previous work has shown that P. fuscatus use facial patterns to individually identify conspecifics and wasps use holistic processing to discriminate between conspecific faces. We tested face processing in three groups of P. fuscatus: young (1-week-old), older, experienced (2-weeks-old, normal experience), and older, inexperienced (2-weeks-old, 1 week normal social experience and 1 week social isolation). Older, experienced wasps used holistic processing to discriminate between conspecific faces. In contrast, older inexperienced wasps used featural rather than holistic mechanisms to discriminate between faces. Young wasps show some evidence of holistic face processing, but this ability was less refined than older, experienced wasps. Notably, wasps only required 2 weeks of normal experience to develop holistic processing, while previous work suggests that humans may require years of experience. Overall, P. fuscatus wasps rapidly develop holistic processing for conspecific faces. Experience rather than age facilitates the transition between featural and holistic face processing mechanisms.

Honeybee queen mandibular pheromone induces a starvation response in Drosophila melanogaster

Eusocial insect societies are defined by the reproductive division of labour, a social structure that is generally enforced by the reproductive dominant(s) or 'queen(s)'. Reproductive dominance is maintained through behavioural dominance or production of queen pheromones, or a mixture of both. Queen mandibular pheromone (QMP) is a queen pheromone produced by queen honeybees (Apis mellifera) which represses reproduction in worker honeybees. How QMP acts to repress worker reproduction, the mechanisms by which this repression is induced, and how it has evolved this activity, remain poorly understood. Surprisingly, QMP is capable of repressing reproduction in non-target arthropods. Here we show that in Drosophila melanogaster QMP treatment mimics the starvation response, disrupting reproduction. QMP exposure induces an increase in food consumption and activation of checkpoints in the ovary that reduce fecundity and depresses insulin signalling. The magnitude of these effects is indistinguishable between QMP-treated and starved individuals. As QMP triggers a starvation response in an insect diverged from honeybees, we propose that QMP originally evolved by co-opting nutrition signalling pathways to regulate reproduction.

Caste-specific storage of dopamine-related substances in the brains of four Polistes paper wasp species

How the role of dopamine differs according to the evolution of eusociality and how it is required in the flexible society of Polistes paper wasps need further clarification. In the present study, we compared the storage and usage of dopamine-related substances in brains between the castes of paper wasps. The head widths, lipid stores in the abdomen, and levels of biogenic amines in the brains were measured in newly emerged females before male emergence (workers) and after male emergence (gynes) in four Polistes species. The head widths and the lipid stores were significantly larger in gynes than workers in P. snelleni, P. rothneyi, and P. jokahamae, whereas they did not differ between castes in P. chinensis. The levels of dopamine precursors in the brains were significantly higher in gynes than workers in P. snelleni, P. chinensis, and P. rothneyi, whereas those of dopamine and its metabolites did not differ between castes in these species. In P. jokahamae, the levels of dopamine precursors and dopamine in the brains did not differ between castes, but those of a dopamine metabolite were significantly higher in gynes than workers. Thus, the caste differences in the levels of dopamine-related substances did not always match body sizes and nutritional reserves. Foundresses in P. rothneyi had significantly lower levels of dopamine precursors and higher levels of dopamine and its metabolite than newly emerged gynes. These results suggested that in several Polistes species, dopamine precursors were stored in the brain without dopamine biosynthesis at emergence, and then converted into dopamine in foundresses during colony founding. These neuroendocrinal states in Polistes species largely differed from those in eusocial bees.

Alternative Nesting Strategies of Polistine Wasps in a Subtropical Locale

Phylogenetic studies suggest that historically all paper wasps (Vespidae: Polistinae) in North America have tropical origins, but some species have adapted to survive temperate conditions. Subtropical climates, which are intermediate between temperate and tropical, allow a unique opportunity to study ancestral traits which can be retained or lost within populations, and ultimately elucidate the process of social wasp evolution. We investigated the phenology of paper wasps at study sites in subtropical Baton Rouge, USA, through nest searching and monitoring of nest parameters throughout the warm season (March-October). Across the year, two periods of nest initiation occurred: from March-May (early season nests, i.e., before the summer solstice), and from July-September (late season nests, after the solstice). We observed 240 Polistes nests from six species, of which 50.8% were initiated in early season and 49.2% in late season. In contrast, Mischocyttarus mexicanus rarely built late season nests and had longer early season colony duration than Polistes bellicosus and P. dorsalis, which built more nests in the late season than early. Across all species, late season nests had significantly shorter colony duration (~87.6 days) than early season nests (~166 days), and only P. bellicosus had fewer adults at peak population in late season nests than in early season nests. Results indicate both a bivoltine colony cycle in Polistes of subtropical climates, as well as differences in nesting strategies between genera.

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.

Identification of biogenic amines involved in photoperiod-dependent caste-fate determination during the adult stage in a temperate paper wasp

In the temperate paper wasp Polistes jokahamae, caste is influenced by photoperiod during the adult stage, but the mechanisms underlying the caste-fate determination system have been unclear. We measured the brain levels of monoamines and related substances in females kept isolated for two weeks under different photoperiods. Except for in the first-emerging group, the females developed ovaries under long-day conditions, whereas they stored lipids under short-day conditions. The levels of tyramine in the brain were significantly higher under long-day than under short-day conditions and positively correlated with maximum oocyte lengths. These results suggest that tyramine was produced in response to long daylength during the adult stage and associated with ovarian development, which is the principal characteristic of reproductive workers. There was also a significant positive correlation between dopamine levels in the brain and maximum oocyte length, independent of photoperiod, suggesting that dopamine is involved in reproductive function with tyramine resulting in the induction of reproductive workers. Meanwhile, higher levels of tryptophan in the brain were found in short-day conditions and positively correlated with lipid stores. However, serotonin synthesized from tryptophan and N-acetylserotonin were not associated with lipid stores without photoperiodic responses, suggesting that tryptophan is involved in the physiological changes toward gyne under short daylength, independently of serotonin signaling. In conclusion, tyramine and tryptophan are candidates for mediating photoperiod-dependent caste-fate determination in P. jokahamae: the former is involved in generating the worker caste while the latter is involved in generating the gyne caste.

Hormone-mediated dispersal and sexual maturation in males of the social paper wasp Polistes lanio

Sex-biased dispersal is common in social species, but the dispersing sex may delay emigration if associated benefits are not immediately attainable. In the social Hymenoptera (ants, some bees and wasps), newly emerged males typically disperse from the natal nest whilst most females remain as philopatric helpers. However, little information exists on the mechanisms regulating male dispersal. Furthermore, the conservation of such mechanisms across the Hymenoptera and any role of sexual maturation are also relatively unknown. Through field observations and mark-recapture, we observed that males of the social paper wasp Polistes lanio emerge from pupation sexually immature, and delay dispersal from their natal nest for up to 7 days whilst undergoing sexual maturation. Delayed dispersal may benefit males by allowing them to mature in the safety of the nest and thus be more competitive in mating. We also demonstrate that both male dispersal and maturation are associated with juvenile hormone (JH), a key regulator of insect reproductive physiology and behaviour, which also has derived functions regulating social organisation in female Hymenoptera. Males treated with methoprene (a JH analogue) dispersed earlier and possessed significantly larger accessory glands than their age-matched controls. These results highlight the wide role of JH in social hymenopteran behaviour, with parallel ancestral functions in males and females, and raise new questions on the nature of selection for sex-biased dispersal.

Individual dispersal delays in a cooperative breeder: Ecological constraints, the benefits of philopatry and the social queue for dominance

Delayed dispersal is a key step in the evolution of familial animal societies and cooperative breeding. However, no consensus has been reached on the ecological and social circumstances driving delayed dispersal. Here, we test predictions from the ecological constraints and benefits of philopatry hypotheses as well as the recently proposed dual benefits hypothesis to better understand the evolution of group-living and cooperative breeding. Furthermore, we consider how individual social circumstances within groups affect dispersal decisions. We examine 11 years of life-history information on a wild population of cooperatively breeding southern pied babblers Turdoides bicolor. We investigate the effects of ecological conditions, natal-group membership and individual social context on male and female dispersal delays, disperser survival and acquisition of dominance. Female dispersal decisions are generally unconstrained by ecological or social circumstances. In contrast, males disperse in response to relaxed ecological constraints, decreases in nepotistic tolerance or when low social rank in the queue for dominance decreases their likelihood of gaining a dominant breeding position. Early dispersal by end-of-queue males often leads to a head-of-queue subordinate position in a non-natal group, thereby increasing access to dominant breeding positions. However, males and females remaining in natal groups gain benefits of philopatry via increased survival and, for head-of-queue males, very high likelihood of acquisition of a breeding position. Overall, predictions from the dual benefits hypothesis best describe these results, while some predictions from each of the ecological constraints and benefits of philopatry hypotheses were supported. The benefits of living and working together (collective action benefits) in large stable groups are of central importance in shaping dispersal delays in southern pied babbler societies. In addition, position in the subordinate social queue for dominance is the key in determining access to reproduction, particularly for males. This research highlights the importance of considering the costs and benefits of individual social circumstances in dispersal decisions and illustrates how the dual benefits hypothesis offers new perspectives in understanding delayed dispersal.

Revision of the West Palaearctic Polistes Latreille, with the descriptions of two species - an integrative approach using morphology and DNA barcodes (Hymenoptera, Vespidae)

The genus Polistes is revised for the West Palaearctic region based on morphology and DNA barcodes. The revision includes all known West Palaearctic species, raising the number of species in Europe to 14 and to 17 for the West Palaearctic realm. DNA barcodes were recovered from 15 species, 14 of which belong to the subgenusPolistes, and one, P.wattii, to the subgenus Gyrostoma. An integrative taxonomic approach combining morphology and molecular data (DNA barcoding) was employed to resolve longstanding taxonomic problems in this group. Two species, P.austroccidentalis van Achterberg & Neumeyer, sp. n. (= P.semenowi auctt.) from W and SW Europe and P.maroccanus Schmid-Egger, sp. n. from Morocco are described as new. Polistesbucharensis Erichson, 1849, and P.foederatus Kohl, 1898, were restored from synonymy. The following new synonyms are proposed: P.sulcifer Zimmermann, 1930, and Pseudopolistessulcifervar.similator Zirngiebl, 1955, under P.semenowi Morawitz, 1889, syn. n.; Polistesiranus Guiglia, 1976, Polistesgallicavar.ornata Weyrauch, 1938 and Polistesgallicusmuchei Gusenleitner, 1976, under P.bucharensis Erichson, 1849, syn. n.; Polistesomissusvar.ordubadensis Zirngiebl, 1955, and P.hellenicus Arens, 2011, under Polistesmongolicus du Buysson, 1911, syn. n. An illustrated key includes all species and additionally three species from the subgenera Aphanilopterus Meunier, 1888 and Gyrostoma Kirby, 1828 (including a Nearctic species recently introduced to Spain and two species occurring in Egypt, the Arabian Peninsula, and SW Asia). A phylogenetic analysis using Bayesian inference provides insights into phylogenetic relationships within the genus Polistes.

Strategic reduction of help before dispersal in a cooperative breeder

In cooperative breeders, sexually mature subordinates can either queue for chances to inherit the breeding position in their natal group, or disperse to reproduce independently. The choice of one or the other option may be flexible, as when individuals respond to attractive dispersal options, or they may reflect fixed life-history trajectories. Here, we show in a permanently marked, natural population of the cooperatively breeding cichlid fish Neolamprologus pulcher that subordinate helpers reduce investment in territory defence shortly before dispersing. Such reduction of effort is not shown by subordinates who stay and inherit the breeding position. This difference suggests that subordinates ready to leave reduce their investment in the natal territory strategically in favour of future life-history perspectives. It seems to be part of a conditional choice of the dispersal tactic, as this reduction in effort appears only shortly before dispersal, whereas philopatric and dispersing helpers do not differ in defence effort earlier in life. Hence, cooperative territory defence is state-dependent and plastic rather than a consistent part of a fixed life-history trajectory.

The effect of juvenile hormone on Polistes wasp fertility varies with cooperative behavior

Social insects provide good models for studying how and why the mechanisms that underlie reproduction vary, as there is dramatic reproductive plasticity within and between species. Here, we test how the effect of juvenile hormone (JH) on fertility covaries with cooperative behavior in workers and nest-founding queens in the primitively eusocial wasp Polistes metricus. P. metricus foundresses and workers appear morphologically similar and both are capable of reproduction, though there is variation in the extent of social cooperation and the probability of reproduction across castes. Do the endocrine mechanisms that mediate reproduction co-vary with cooperative behavior? We found dramatic differences in the effect of JH on fertility across castes. In non-cooperative nest-founding queens, all individuals responded to JH by increasing their fertility. However, in cooperative workers, the effect of JH on fertility varies with body weight; large workers increase their fertility in response to JH while small workers do not. The variation in JH response may be an adaptation to facilitate resource allocation based on the probability of independent reproduction. This work contrasts with previous studies in closely related Polistes dominulus paper wasps, in which both foundresses and workers form cooperative associations and both castes show similar, condition-dependent JH response. The variation in JH responsiveness within and between species suggests that endocrine responsiveness and the factors influencing caste differentiation are surprisingly evolutionarily labile.

A conceptual model for the origin of worker behaviour and adaptation of eusociality

In a model based on the wasp family Vespidae, the origin of worker behaviour, which constitutes the eusociality threshold, is not based on relatedness, therefore the origin of eusociality does not depend on inclusive fitness, and workers at the eusociality threshold are not altruistic. Instead, incipient workers and queens behave selfishly and are subject to direct natural selection. Beyond the eusociality threshold, relatedness enables 'soft inheritance' as the framework for initial adaptations of eusociality. At the threshold of irreversibility, queen and worker castes become fixed in advanced eusociality. Transitions from solitary to facultative, facultative to primitive, and primitive to advanced eusociality occur via exaptation, phenotypic accommodation and genetic assimilation. Multilevel selection characterizes the solitary to highly eusocial transition, but components of multilevel selection vary across levels of eusociality. Roles of behavioural flexibility and developmental plasticity in the evolutionary process equal or exceed those of genotype.

Reproductive plasticity in Polistes paper wasp workers and the evolutionary origins of sociality

Regulatory pathways in solitary species provide the raw materials for the evolution of sociality. Therefore, comparing the mechanisms that mediate reproductive plasticity in social species and their solitary ancestors can provide insight into the evolutionary origin of sociality. In many solitary insects, the effect of juvenile hormone (JH) on fertility is mediated through the fat body; individuals in good physical condition show a stronger fertility response to JH than individuals in poor physical condition. Here, we test whether a similar, condition-dependent JH response mediates fertility in workers of the primitively eusocial Polistes dominulus wasps. We test how body weight, JH, and adult nutrition influence worker ovarian development. Both JH-treatment and adult nutrition dramatically increased ovarian development. Body weight also influenced ovarian development, as large workers developed more eggs than smaller workers. Body weight and fat are strongly linked in P. dominulus workers, so these results suggest that the fat-dependent JH responsiveness common in solitary insects is conserved in social wasps. The simple, ancestral relationship between reproductive investment and physical condition may facilitate cooperation by allowing workers to adaptively allocate energy into reproduction based on their probability of successfully becoming a queen.

The condition dependence and heritability of signaling and nonsignaling color traits in paper wasps

Research on quality signal development typically focuses on signals with production costs; less is known about signals that lack production costs (conventional signals). Here, I test the condition dependence and heritability of the facial patterns that function as a conventional signal of quality in Polistes dominulus wasps. Two aspects of facial patterns are compared: (1) amount of black pigment (no signal value) and (2) disruption in the black pigment's distribution (quality signal). When colonies received the same diet, they produced offspring with similar facial patterns and both traits were heritable. However, experimental diet manipulation substantially influenced quality signal development. Wasps fed unlimited caterpillars developed more disrupted facial patterns than wasps fed a restricted diet. Further, signal heritability was obscured following the diet treatment. In contrast, the nonsignaling trait was not influenced by the diet treatment and remained heritable. Overall, the quality signal in P. dominulus is condition dependent and heritable, but its heritability may be obscured by environmental variance. The nonsignaling aspect of wasp facial patterns is not condition dependent and is more consistently heritable across environments. Therefore, the information a signal conveys may be influenced by its developmental properties rather than its honesty-ensuring cost or the pigments that constitute it.

No actual conflict over colony inheritance despite high potential conflict in the social wasp Polistes dominulus

Social insect societies are outstanding examples of cooperation and conflict. Individuals work together, yet seek to increase their inclusive fitness at each others' expense. One such conflict is over colony inheritance, when a queen inherits the colony following the death of the previous queen. Colony inheritance is common in the social wasp Polistes dominulus, and it can have dramatic fitness consequences. The subordinate inheriting the colony is often unrelated to the initial foundress (alpha) and the workers, who therefore get zero inclusive fitness. Workers are capable of mating and reproducing, so that inheritance by a subordinate rather than by a related worker is surprising. Using patterns of egg-laying and egg destruction, we show in 32 laboratory colonies that, upon the removal of alpha, workers fully accepted a subordinate as the new breeder. This new alpha monopolized reproduction to the same extent as alpha, and there was no increase in reproduction by workers and other subordinates. Why workers accept a potentially unrelated subordinate as breeder rather than a full-sister worker is unclear. They may be constrained to do so, and they may seek fitness benefits by producing males later in the season or by absconding the nest.

Mating system and genetic structure in the paper wasp (Polistes humilis)

We provide the first description of the mating system, genetic structuring and dispersal in the Australian paper wasp, Polistes humilis. Individuals were collected from 13 colonies that were within 700 m of each other at a location near Sydney, Australia. Analysis of genotypic data from four microsatellite loci provided no evidence of males siring offspring in their natal colony and heterozygote excesses within most colonies suggest that this form of outbreeding is typical in P. humilis. The same data show that queens are singly mated and that the number of queens and therefore groups of full siblings increase with colony size. Consequently, genetic variation also increases with colony size. The relationship between the number of queens and colony size in P. humilis may be indicative of a breakdown in dominance hierarchies in larger colonies or a defence against disease transmission.