Rearing conditions influence quality signals but not individual identity signals in Polistes wasps

Given the diversity of animal signals, there has been recentinterest in categorizing signals into probable functions accordingto their properties. For example, models predict that signalsof quality should be costly and condition dependent, whereassignals of individual identity should be cheap and expressedindependently of condition. Here, we test these predictionsby comparing the condition dependence of signals of individualidentity and quality in Polistes wasps. Polistes fuscatus waspshave black and yellow patterns on the face and abdomen thatsignal individual identity, whereas Polistes dominulus waspshave black and yellow facial patterns that signal aspects ofquality related to dominance. We reared both species with andwithout supplemental food and examined the facial patterns ofthe resulting offspring. As predicted, food availability didnot influence the development of identity signals in P. fuscatus.In strong contrast, P. dominulus wasps reared with supplementalfood had facial patterns that signaled higher levels of qualitythan P. dominulus reared without supplemental food. Interestingly,the identity and quality signals have different condition dependence,despite being composed of similar pigments, suggesting thatsignal function has a stronger influence on signal propertiesthan pigmentation. Because body size is often correlated withquality signal elaboration, we also tested how food supplementationinfluenced offspring size. In both species, supplemented coloniesproduced smaller offspring than nonsupplemented colonies, suggestingthat queens may invest in producing fewer, larger offspringin stressful environments.     

Individual recognition is associated with holistic face processing in Polistes paper wasps in a species-specific way

Most recognition is based on identifying features, but specialization for face recognition in primates 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. Here, we test whether individual face recognition in paper wasps also involved holistic processing using a modification of the classic part-whole test in two related paper wasp species: Polistes fuscatus, which use facial patterns to individually identify conspecifics, and Polistes dominula, which lacks individual recognition. We show that P. fuscatus use holistic processing to discriminate between P. fuscatus face images but not P. dominula face images. By contrast, P. dominula do not rely on holistic processing to discriminate between conspecific or heterospecific face images. Therefore, P. fuscatus wasps have evolved holistic face processing, but this ability is highly specific and shaped by species-specific and stimulus-specific selective pressures. Convergence towards holistic face processing in distant taxa (primates, wasps) as well as divergence among closely related taxa with different recognition behaviour (P. dominula, P. fuscatus) suggests that holistic processing may be a universal adaptive strategy to facilitate expertise in face recognition.     

The morphology of Van der Vecth's organ as a tool to measure caste dimorphism in Polistes paper wasps: a comparative approach

Given the centrality of chemical communication in social insects, there are many selective pressures acting on morpho‐functional traits that mediate chemical pheromones. On the last gastral sternite of Polistes females, there is an important exocrine surface secreting chemical pheromone, named Van der Vecht's organ. It is involved in chemical defence of the nest, in rank and nestmate recognition, preventing workers from direct reproduction. Allometric differential growth of phenotypic traits between castes of social insects is generally considered as an indication of incipient physical castes. European Polistes present different nesting strategies and reproductive choices. Here, we carry out a comparison of Van der Vecht's organ size between castes of four European Polistes to provide a general measure of dimorphism. We show that Van der Vecht's organ of Polistes dominula and Polistes nimphus foundresses shows an allometric development being enlarged with respect to workers. Otherwise, no allometries have been highlighted in the other two studied species (i.e. Polistes associus and Polistes biglumis). Therefore, our data show that neither rigid monogyny nor specific nesting habits foster the evolution of true morphological castes in primitively eusocial taxa. Thus, at least two other species of Ezuropean Polistes show real evidence of incipient morphological castes.     

Mutual assessment via visual status signals in Polistes dominulus wasps

Many animals use signals to assess the fighting ability of rivals and reduce the cost of aggressive competition. However, little is known about how an individual''s own quality influences their signal assessment decisions. Polistes dominulus wasps have visual signals of fighting ability that provide a good model for testing the dynamics of rival choice. We found that rival assessment behaviour was influenced by the advertised quality of the individual, their rivals, and the interaction between individual and rival quality. Individuals of high advertised quality were more likely to challenge rivals and individuals of low advertised quality were more likely to be challenged. However, when choosing among two rivals with different advertised quality, individuals did not simply choose the lower quality rival. Instead, they only preferred the lower quality rival when there was a small difference between their own advertised quality and that of their rivals. Individuals were not choosy when both rivals advertised relatively high or relatively low quality. Therefore, although P. dominulus facial patterns function as conventional signals of fighting ability that provide valuable information about their bearer''s behavioural strategy, there is substantial variation in signal responses based on the relative intensity of the senders'' and receivers'' signals.     

Geographic variation in the status signals of Polistes dominulus paper wasps

Understanding intraspecific geographic variation in animal signals poses a challenging evolutionary problem. Studies addressing geographic variation typically focus on signals used in mate-choice, however, geographic variation in intrasexual signals involved in competition is also known to occur. In Polistes dominulus paper wasps, females have black facial spots that signal dominance: individuals wasps with more complex 'broken' facial patterns are better fighters and are avoided by rivals. Recent work suggests there is dramatic geographic variation in these visual signals of quality, though this variation has not been explicitly described or quantified. Here, we analyze variation in P. dominulus signals across six populations and explore how environmental conditions may account for this variation. Overall, we found substantial variation in facial pattern brokenness across populations and castes. Workers have less broken facial patterns than gynes and queens, which have similar facial patterns. Strepsipteran parasitism, body size and temperature are all correlated with the facial pattern variation, suggesting that developmental plasticity likely plays a key role in this variation. First, the extent of parasitism varies across populations and parasitized individuals have lower facial pattern brokenness than unparasitized individuals. Second, there is substantial variation in body size across populations and a weak but significant relationship between facial pattern brokenness and body size. Wasps from populations with smaller body size (e.g. Italy) tend to have less broken facial patterns than wasps from populations with larger body size (e.g. New York, USA). Third, there is an apparent association between facial patterns and climate, with wasp from cooler locations tending to have higher facial pattern brokenness than wasps from warmer locations. Additional experimental work testing the causes and consequences of facial pattern variation will be important, as geographic variation in signals has important consequences for the evolution of communication systems and social behavior.     

Visual signals of status and rival assessment in Polistes dominulus paper wasps

Aggressive competition is an important aspect of social interactions, but conflict can be costly. Some animals are thought to minimize the costs of conflict by using conventional signals of agonistic ability (i.e. badges of status) to assess rivals. Although putative badges have been found in a range of taxa, little research has tested whether individuals use badges to assess potential rivals before they engage in aggressive contests. Here, choice trials were used to test how the variable black facial patterns in Polistes dominulus wasps are used during rival assessment. Focal wasps were given access to two patches of food, each guarded by a wasp whose facial pattern had been experimentally altered. Wasps chose food patches based on the facial pattern of the guard, preferring to challenge guards with facial patterns indicating a low level of quality, while avoiding guards with facial patterns indicating a high level of quality. Therefore, status badges play an important role during rival assessment; paper wasps use facial patterns alone to quickly assess the agonistic abilities of strangers.     

Evolution of acoustic and visual signals in Asian barbets

The study of animal communication systems is an important step towards gaining greater understanding of the processes influencing diversification because signals often play an important role in mate choice and can lead to reproductive isolation. Signal evolution can be influenced by a diversity of factors such as biophysical constraints on the emitter, the signalling environment, or selection to avoid heterospecific matings. Furthermore, because signals can be costly to produce, trade‐offs may exist between different types of signals. Here, we apply phylogenetic comparative analyses to study the evolution of acoustic and visual signals in Asian barbets, a clade of non‐Passerine, forest‐dependent birds. Our results suggest that evolution of acoustic and visual signals in barbets is influenced by diverse factors, such as morphology and signalling environment, suggesting a potential effect of sensory drive. We found no trade‐offs between visual and acoustic signals. Quite to the contrary, more colourful species sing significantly longer songs. Song characteristics presented distinct patterns of evolution. Song frequency diverged early on and the rate of evolution of this trait appears to be constrained by body size. On the other hand, characteristics associated with length of the song presented evidence for more recent divergence. Finally, our results indicate that there is a spatial component to the evolution of visual signals, and that visual signals are more divergent between closely related taxa than acoustic signals. Hence, visual signals in these species could play a role in speciation or reinforcement of reproductive isolation following secondary contacts.     

Selection for individual recognition and the evolution of polymorphic identity signals in Polistes paper wasps

Individual recognition (IR) requires individuals to uniquely identify their social partners based on phenotypic variation. Because IR is so specific, distinctive phenotypes that stand out from the crowd facilitate efficient recognition. Over time, the benefits of unique appearances are predicted to produce a correlation between IR and phenotypic variation. Here, we test whether there is an association between elevated phenotypic polymorphism and IR in paper wasps. Previous work has shown that Polistes fuscatus use variable colour patterns for IR. We test whether two less variable wasp species, Polistes dominulus and Polistes metricus, are capable of IR. As predicted, neither species is capable of IR, suggesting that highly variable colour patterns are confined to Polistes species with IR. This association suggests that elevated phenotypic variation in taxa with IR may be the result of selection for identity signals rather than neutral processes. Given that IR is widespread among social taxa, selection for identity signalling may be an underappreciated mechanism for the origin and maintenance of polymorphism.     

The look of royalty: visual and odour signals of reproductive status in a paper wasp

Reproductive conflicts within animal societies occur when all females can potentially reproduce. In social insects, these conflicts are regulated largely by behaviour and chemical signalling. There is evidence that presence of signals, which provide direct information about the quality of the reproductive females would increase the fitness of all parties. In this study, we present an association between visual and chemical signals in the paper wasp Polistes satan. Our results showed that in nest-founding phase colonies, variation of visual signals is linked to relative fertility, while chemical signals are related to dominance status. In addition, experiments revealed that higher hierarchical positions were occupied by subordinates with distinct proportions of cuticular hydrocarbons and distinct visual marks. Therefore, these wasps present cues that convey reliable information of their reproductive status.     

The comparative biology of two sympatric paper wasps in Michigan,the native <Emphasis Type="Italic">Polistes fuscatus</Emphasis> and the invasive <Emphasis Type="Italic">Polistes dominulus</Emphasis> (Hymenoptera,Vespidae)

Summary The biology of the invasive Polistes dominulus and the native P. fuscatus was compared at a field site in Rochester, Michigan over a two-year period. Colonies nesting semi-naturally in plywood nestboxes were studied using videography, extensive surveys, and colony-specific marking of gynes.Both single- and multiple-foundress colonies of P. dominulus were significantly more productive than comparable colonies of P. fuscatus. The disparity in productivity was significantly more pronounced in single-foundress colonies than in multiple-foundress colonies. P. dominulus had significantly shorter larval and pupal development times than P. fuscatus, which allowed P. dominulus to produce its first workers about a week earlier than P. fuscatus. P. dominulus had a number of additional advantages over P. fuscatus that contributed to its productivity including (1) significantly less parasitism by Strepsiptera, (2) significantly greater probability of renesting after predation by raccoons, (3) significantly lower usurpation pressures, and (4) possibly longer foraging days . The recovery of colony-marked foundresses indicated that gynes of P. dominulus suffered significantly greater mortality than gynes of P. fuscatus during winter diapause and that foundresses of both species were equally, strongly philopatric.P. dominulus is likely replacing P. fuscatus in many areas of southeastern Michigan via indirect or exploitative competition. The two species may be competing for nest sites.Received 7 July 2003; revised 10 October 2003; accepted 3 November 2003.     

Intra‐specific body size variation in Polistes paper wasps as a response to social parasite pressure

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.     

A latitudinal gradient in intensity of applying ant-repellent substance to the nest petiole in paper wasps (Hymenoptera: Vespidae)

Summary Observations on pre-emergence, single-foundress colonies of Japanese paper wasps (Polistes) revealed that there was a latitudinal gradient in intensity of application of an ant-repellent substance (secreted by the metasomal sternum VI glands) to the nest petiole. Thus the lower the latitude, the more frequently a foundress rubbed ant repellent onto the nest petiole. Estimation of potential ant predation on wasp brood using bait traps showed that there was a positive correlation between the frequency of rubbing and potential predation pressure from ants which are guided predominantly by substrate cues for foraging. There was also a latitudinal gradient in the degree of temporal association of rubbing behavior with foraging: the lower the latitude, the more closely foundress departure from the nest was associated with rubbing. Enlargement of the nest petiole by applying oral secretion potentially obliterated previous coats of ant repellent; however, this behavior was not always followed by rubbing behavior. The ant-repellent chemical barrier around the nest petiole may have evolved in tropical regions of the world as a defense against ant predation on wasp brood. I argue that as ant predation pressure diminishes towards the cooler regions, so does selection maintaining the behavioral sequence where foundress departure from the nest is preceded by rubbing behavior.     

Conspicuousness of Dickerson's collared lizard (Crotaphytus dickersonae) through the eyes of conspecifics and predators

Selection should favour coloration in organisms that is more conspicuous to their own visual system than to those of their predators or prey. We tested this prediction in Dickerson's collared lizard ( Crotaphytus dickersonae ), a sexually dichromatic desert reptile that preys on insects and smaller lizard species, and which in turn is prey for birds and snakes. We modelled the spectral sensitivities of the lizards and their avian and snake predators, and compared the conspicuousness of the lizards' entire colour patterns with each class of viewers. Almost all comparisons involving females strongly supported our prediction for greater chromatic and brightness conspicuousness against local terrestrial visual backgrounds to their own modelled visual system than to those of avian and snake predators. Males, in contrast, exhibited far fewer cases of greater conspicuousness to their own visual system than to those of their predators. Our own perception of spectral similarity between blue C. dickersonae males and a local nonterrestrial visual background (i.e. the Sea of Cortéz) prompted a further investigation. We compared sea (and sky) radiance with dorsum radiance of C. dickersonae males and with males from two distantly-related Crotaphytus collaris populations in which males possess blue bodies. In all three visual models, C. dickersonae males exhibited significantly lower chromatic contrast with the sea (and sky) than did their noncoastal, blue-bodied congeners. Among potential explanations, the blue body coloration that is unique to male C. dickersonae may offset, if only slightly, the cost of visibility to predators (and to prey) through reduced contrast against the extensive, local, nonterrestrial blue backgrounds of the sea and sky.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 749–765.     

Specialized visual learning of facial signals of quality in the paper wasp,Polistes dominula

Some primates and one species of paper wasp recognize faces using specific processing strategies to extract individual identity information from conspecific faces. Explanations for the evolution of face specialization typically focus on the complexity associated with individual recognition because all currently identified species with face specialization use faces for individual recognition. In the present study, we show an independent evolution of face specialization in a paper wasp species with facial patterns that signal quality rather than individual identity. Quality signals are simpler to process than individual identity signals because quality signals do not require simultaneous integration across multiple stimuli or learning and memory. Therefore, the results of the present study suggest that the complexity of processing may not be the key factor favouring the evolution of specialization. Instead, the predictable location of socially important signals relative to other anatomical features may allow easy categorization of features, thereby favouring specialized visual processing. Given that visual quality signals are found in many taxa, specific‐processing mechanisms for social signals may be widespread. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 992–997.     

Strategies of social wasps for thermal homeostasis in light paper nests

1. With the derived free-run temperature of light paper nests the influence of the thermal capacity of the nest or the nest site, respectively, on thermal homeostasis is quantified.

2. Gravimetric information from the continuous investigation of the nest weight coupled with temperature and humidity measurement allows the correlation of the colonies’ foraging behavior with their heat production inside the nest.

3. Wasps (Vespa crabro) do not regulate their nest environment towards a specific and constant temperature but rather build nests adapted to their foraging behavior and general energy budget.

Ground nesting in the paper wasp <Emphasis Type="Italic">Polistes aurifer</Emphasis> (Hymenoptera,Vespidae)

Summary Polistes paper wasp species vary in their nest site selection, with some nesting in relatively exposed areas and others in protected cavities. Locating the nest sites of cavity dwelling species in natural habitat can prove difficult, and most behavioral studies on these species are therefore conducted using human-built structures. Since Hungerford and Williams (1912) and Rau (1929) noted the location of several P. fuscatus (Fabricius) nests in rodent burrows, there have been no published accounts of ground nesting Polistes species. I report the occurrence of a large, dense cluster of P. aurifer (Saussure) nests located within cracks in the dried soil of the Santa Monica Mountains of southern California, USA.Received 8 April 2003; revised 10 October 2003; accepted 31 October 2003.     

The influence of ultraviolet reflectance differs between conspicuous aposematic signals in neotropical butterflies and poison frogs

Warning signals are often characterized by highly contrasting, distinctive, and memorable colors. Greater chromatic (hue) and achromatic (brightness) contrast have both been found to contribute to greater signal efficacy, making longwave colored signals (e.g., red and yellow), that are perceived by both chromatic and achromatic visual pathways, particularly common. Conversely, shortwave colors (e.g., blue and ultraviolet) do not contribute to luminance perception yet are also commonly found in warning signals. Our understanding of the role of UV in aposematic signals is currently incomplete as UV perception is not universal, and evidence for its utility is at best mixed. We used visual modeling to quantify how UV affects signal contrast in aposematic heliconiian butterflies and poison frogs both of which reflect UV wavelengths, occupy similar habitats, and share similar classes of predators. Previous work on butterflies has found that UV reflectance does not affect predation risk but is involved in mate choice. As the butterflies, but not the frogs, have UV‐sensitive vision, the function of UV reflectance in poison frogs is currently unknown. We found that despite showing up strongly in UV photographs, UV reflectance only appreciably affected visual contrast in the butterflies. As such, these results support the notion that although UV reflectance is associated with intraspecific communication in butterflies, it appears to be nonfunctional in frogs. Consequently, our data highlight that we should be careful when assigning a selection‐based benefit to the presence of UV reflectance.     

Distributed cognition and social brains: reductions in mushroom body investment accompanied the origins of sociality in wasps (Hymenoptera: Vespidae)

The social brain hypothesis assumes the evolution of social behaviour changes animals'' ecological environments, and predicts evolutionary shifts in social structure will be associated with changes in brain investment. Most social brain models to date assume social behaviour imposes additional cognitive challenges to animals, favouring the evolution of increased brain investment. Here, we present a modification of social brain models, which we term the distributed cognition hypothesis. Distributed cognition models assume group members can rely on social communication instead of individual cognition; these models predict reduced brain investment in social species. To test this hypothesis, we compared brain investment among 29 species of wasps (Vespidae family), including solitary species and social species with a wide range of social attributes (i.e. differences in colony size, mode of colony founding and degree of queen/worker caste differentiation). We compared species means of relative size of mushroom body (MB) calyces and the antennal to optic lobe ratio, as measures of brain investment in central processing and peripheral sensory processing, respectively. In support of distributed cognition predictions, and in contrast to patterns seen among vertebrates, MB investment decreased from solitary to social species. Among social species, differences in colony founding, colony size and caste differentiation were not associated with brain investment differences. Peripheral lobe investment did not covary with social structure. These patterns suggest the strongest changes in brain investment—a reduction in central processing brain regions—accompanied the evolutionary origins of eusociality in Vespidae.     

Hole repair and the influence of learning on nest repair in the paper wasp,Polistes fuscatus (Hymenoptera: Vespidae)

Two methods of hole repair used by the paper wasp, Polistes fuscatus,were examined and compared, and the hypothesis that nest repair behavior may improve with experience was tested. Similarly sized holes were repeatedly made in the sides of nests and the repair behavior of the nest residents was recorded. The distance of the hole from the cell mouth determined which repair method was used. In addition, both the amount of time for hole repair completion and the number of pulp loads used in making the repair decreased significantly with experience.