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.     

On status badges and quality signals in the paper wasp Polistes dominulus: body size, facial colour patterns and hierarchical rank

To establish a dominance order, social animals often rely on indicators of fighting to avoid costly aggressive encounters. In some species, individuals use colour patterns to signal their social status. Recent studies claimed that facial markings in the eusocial paper wasp Polistes dominulus are status badges that allow co-foundresses to form a linear hierarchy based on individual quality. Here, we evaluated facial patterns in natural populations of P. dominulus, in its native range, to observe whether the marks reflect overall wasp quality in different contexts. We used the same measures of clypeus patterns used by earlier studies, but did not find that they functioned as status badges. Our analyses showed no evidence that visual markers are related to: (i) size, (ii) probability of surviving winter, (iii) social rank in spring associations, or (iv) health status (assessed by the presence of strepsipteran endoparasites). Size, however, is important. Larger wasps are more likely to survive the winter and to acquire the dominant position in spring associations. Larvae infected with endoparasites become smaller adult wasps. These findings suggest that body size is a reliable quality indicator on which wasps build their social networks, and that clypeus patterning is not involved.     

Socially selected ornaments and fitness: Signals of fighting ability in paper wasps are positively associated with survival,reproductive success,and rank

Many animals have ornaments that mediate choice and competition in social and sexual contexts. Individuals with elaborate sexual ornaments typically have higher fitness than those with less elaborate ornaments, but less is known about whether socially selected ornaments are associated with fitness. Here, we test the relationship between fitness and facial patterns that are a socially selected signal of fighting ability in Polistes dominula wasps. We found wasps that signal higher fighting ability have larger nests, are more likely to survive harsh winters, and obtain higher dominance rank than wasps that signal lower fighting ability. In comparison, body weight was not associated with fitness. Larger wasps were dominant over smaller wasps, but showed no difference in nest size or survival. Overall, the positive relationship between wasp facial patterns and fitness indicates that receivers can obtain diverse information about a signaler's phenotypic quality by paying attention to socially selected ornaments. Therefore, there are surprisingly strong parallels between the information conveyed by socially and sexually selected signals. Similar fitness relationships in social and sexually selected signals may be one reason it can be difficult to distinguish the role of social versus sexual selection in ornament evolution.     

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.     

Facial Patterns are a Conventional Signal of Agonistic Ability in Polistes exclamans Paper Wasps

Some animals minimize the high costs of aggressive conflict by using conventional signals of agonistic ability to assess rivals prior to interacting. Conventional signals are more controversial than other signals of agonistic ability because they lack an inherent physical or physiological link with their bearer’s agonistic ability. Here, we test whether the variable brown facial stripes in Polistes exclamans paper wasps function as a conventional signal. Polistes exclamans were given the option of challenging or avoiding a rival with an experimentally altered facial pattern. Our results show that rival assessment is based on the facial patterns of rivals, as well as an individual’s own size, facial patterns, and nesting strategy. Individuals with larger body size and larger brown facial stripes were more likely to challenge rivals than individuals with smaller body size and smaller brown facial stripes. In addition, large individuals were more likely to challenge rivals with large brown facial stripes than small individuals, while an individual’s own body size did not influence whether or not they challenged rivals with small brown stripes. Individuals who previously nested in multiple queen groups approached rivals more rapidly than individuals who previously nested alone, suggesting that social experience also plays a role in rival assessment. Finally, rivals with small facial stripes were challenged more rapidly than those with large facial stripes. These results demonstrate that P. exclamans facial patterns function as a signal used to minimize the cost of conflict. However, individuals do not make simple decisions based on their rival’s signal alone, as an individual’s own social experience and agonistic abilities also influence rival assessment decisions.     

Sexy Faces in a Male Paper Wasp

Sexually selected signals are common in many animals, though little reported in social insects. We investigated the occurrence of male visual signals mediating the dominance relationships among males and female choice of sexual partner in the paper wasp Polistes simillimus. Males have three conspicuous, variable and sexually dimorphic traits: black pigmentation on the head, a pair of yellow abdominal spots and body size differences. By conducting behavioral assays, we found that none of the three visual traits are associated with male-male dominance relationship. However, males with higher proportion of black facial pigmentation and bigger yellow abdominal spots are more likely chosen as sexual partners. Also, after experimentally manipulating the proportion of black pigment on males'' face, we found that females may evaluate male facial coloration during the choice of a sexual partner. Thus, the black pigmentation on P. simillimus male''s head appears to play a role as a sexually selected visual signal. We suggest that sexual selection is a common force in Polistes and we highlight the importance of this group as a model for the study of visual communication in insects.     

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.     

Resource value and the context dependence of receiver behaviour

Many animals use signals of fighting ability to minimize the costs of competition. Theory predicts that signals must be costly to remain reliable indicators of their bearer's abilities, but many signals of fighting ability lack obvious developmental costs. Instead, receivers are thought to maintain signal accuracy by behaving aggressively towards individuals with inaccurate signals (i.e. social costs). Models predict that the evolutionary stability of social cost signals depends on receivers trusting signals in certain contexts and testing signal accuracy in other contexts. Here, I use the signals of agonistic ability in Polistes dominulus wasps to provide the first experimental evidence that receiver responses to social cost signals are context dependent. During contests over low-value resources, wasps trust signals; they avoid patches of food guarded by rivals with elaborate signals. As the value of the resource increases, wasps become more likely to test signal accuracy. In fact, receivers challenge guards regardless of their signal phenotype when the resource is sufficiently valuable. Context-dependent receiver responses are likely to be an important behavioural mechanism underlying the evolution of social costs, as context-dependent responses allow receivers to minimize the costs of conflict while also ensuring signal accuracy.     

Coevolution of visual signals and eye morphology in Polistes paper wasps

To be effective, signals must propagate through the environment and be detected by receivers. As a result, signal form evolves in response to both the constraints imposed by the transmission environment and receiver perceptual abilities. Little work has examined the extent to which signals may act as selective forces on receiver sensory systems to improve the efficacy of communication. If receivers benefit from accurate signal assessment, selection could favour sensory organs that improve discrimination of established signals. Here, we provide evidence that visual resolution coevolves with visual signals in Polistes wasps. Multiple Polistes species have variable facial patterns that function as social signals, whereas other species lack visual signals. Analysis of 19 Polistes species shows that maximum eye facet size is positively associated with both eye size and presence of visual signals. Relatively larger facets within the eye''s acute zone improve resolution of small images, such as wasp facial signals. Therefore, sensory systems may evolve to optimize signal assessment. Sensory adaptations to facilitate signal detection may represent an overlooked area of the evolution of animal communication.     

Strike Fast,Strike Hard: The Red-Throated Caracara Exploits Absconding Behavior of Social Wasps during Nest Predation

Red-throated Caracaras Ibycter americanus (Falconidae) are specialist predators of social wasps in the Neotropics. It had been proposed that these caracaras possess chemical repellents that allow them to take the brood of wasp nests without being attacked by worker wasps. To determine how caracaras exploit nests of social wasps and whether chemical repellents facilitate predation, we: (1) video recorded the birds attacking wasp nests; (2) analyzed surface extracts of the birds'' faces, feet, and feathers for potential chemical repellents; and (3) inflicted mechanical damage on wasp nests to determine the defensive behavior of wasps in response to varying levels of disturbance. During caracara predation events, two species of large-bodied wasps mounted stinging attacks on caracaras, whereas three smaller-bodied wasp species did not. The “hit-and-run” predation tactic of caracaras when they attacked nests of large and aggressive wasps reduced the risk of getting stung. Our data reveal that the predation strategy of caracaras is based on mechanical disturbance of, and damage to, target wasp nests. Caracara attacks and severe experimental disturbance of nests invariably caused wasps to abscond (abandon their nests). Two compounds in caracara foot extracts [sulcatone and iridodial] elicited electrophysiological responses from wasp antennae, and were also present in defensive secretions of sympatric arboreal-nesting Azteca ants. These compounds appear not to be wasp repellents but to be acquired coincidentally by caracaras when they perch on trees inhabited with Azteca ants. We conclude that caracara predation success does not depend on wasp repellents but relies on the absconding response that is typical of swarm-founding polistine wasps. Our study highlights the potential importance of vertebrate predators in the ecology and evolution of social wasps.     

The Role of Lateral Blue Spots in Intrasexual Relationships Between Male Iberian Rock-Lizards, Lacerta monticola

Vertebrate males often show breeding colours that may function as reliable signals of status in intrasexual competition. In many lacertid lizards, males show a conspicuous row of small but distinctive blue spots that runs along their body side on the outer margin of the belly. However, no study has examined the role of these blue spots. We first analysed in a field population of the Iberian rock lizard, Lacerta monticola, the relationships between number of blue spots and some morphological traits, which are known to be related to males’ fighting ability. The number of spots seems to be an character showing ontogenetic change as large (generally older) males showed more blue spots than small (generally younger) males. Males with a higher body condition also showed a higher number of blue spots. Thus, a higher number of blue spots may be used to signal size, age or body condition. Many contiguous blue spots would result in a visual artefact consisting of a continuous blue band, which might be a reliable size‐ or condition‐dependent signal in some social contexts. We further examined in the laboratory whether male characteristics are related to dominance status. In males with similar body size or age, those with relatively larger heads were more dominant, whereas the number of blue spots was not important. Moreover, the number of blue spots in nature was not related to relative head size. Finally, we experimentally manipulated the presence and the number of blue spots of intruding males, and examined the aggressive response of resident males. Intruder individuals manipulated to cover all their blue spots received a lower amount of aggression. However, males with different numbers of manipulated blue spots received a similar number of aggressive responses. These results suggest that, during agonistic encounters, the presence of blue spots, but not their number, may elicit aggressiveness. Thus, blue spots may serve to identify an individual as an adult male, and to enhance body size of larger males.     

Responses of domestic chicks (Gallus gallus domesticus) to multimodal aposematic signals

Many aposematic prey combine their visual warning signals withadditional signals. Together, these signals constitute a multimodalor multicomponent warning display. The additional signals arethought to increase the effects of the visual signals on predators.Olfactory signals are much emphasized, but later studies haveshown that also auditory signals like the buzzing of certaininsects might have multimodal effects. The wasp displays typicalvisual aposematic signals, black and yellow stripes, but doesalso emit a characteristic buzzing. We wanted to test if, andin what way, the visual and acoustic display of the wasp hasan aversive function on the predators. We therefore conducteda 12-trial discrimination-learning task on inexperienced chicksto study whether there are innate biases toward these signalsand how they affect the speed of avoidance learning. We alsoperformed three extinction-learning trials to study how memorablethe signals were to the chicks. We show that the visual signalsin the display of the wasp contribute to the protection frompredators but in different ways; the yellow color had an aversiveeffect on inexperienced predators, while the striped patternimproved the aversion learning. The sound did not enhance theinnate aversions but increased the aversion learning of stripesin green prey.     

Heightened Condition Dependence of a Sexually Selected Signal in Male Polistes dominulus Paper Wasps

Sexually selected signals are theoretically expected to exhibit heightened condition dependence compared to non‐signaling traits. This link to condition enables sexual signals to provide information regarding individual quality and also provides a mechanism that allows animals to develop signals that accurately reflect their abilities. Most previous work on sexual signal condition dependence has focused on signals that have clear developmental costs, while less is known about the development of other types of quality signals. Male Polistes dominulus paper wasps have yellow‐on‐black abdominal spots that are important signals during female choice and male–male competition. These signals lack obvious production costs, as males are covered in yellow and black patterns composed of the same pigments. Here, we assess signal condition dependence by testing whether larval diet has a stronger influence on the development of male spots than on the development of control traits composed of the same pigments. Males reared on ad libitum diets developed elliptical spots similar to those seen on dominant, attractive males, while males reared on restricted diets developed irregularly shaped spots similar to those seen on subordinate, unattractive males. Remarkably, the development of a control trait composed of the same yellow and black pigments was not influenced by larval diet. Therefore, sexually selected signals can be developmentally decoupled from traits comprised of the same pigments. Condition dependence of sexually selected signals is likely to be a widespread solution to the challenge of developing sexually selected signals that accurately convey information about individual quality.     

Social communication in siamangs (<Emphasis Type="Italic">Symphalangus syndactylus</Emphasis>): use of gestures and facial expressions

The current study represents the first systematic investigation of the social communication of captive siamangs (Symphalangus syndactylus). The focus was on intentional signals, including tactile and visual gestures, as well as facial expressions and actions. Fourteen individuals from different groups were observed and the signals used by individuals were recorded. Thirty-one different signals, consisting of 12 tactile gestures, 8 visual gestures, 7 actions, and 4 facial expressions, were observed, with tactile gestures and facial expressions appearing most frequently. The range of the signal repertoire increased steadily until the age of six, but declined afterwards in adults. The proportions of the different signal categories used within communicative interactions, in particular actions and facial expressions, also varied depending on age. Group differences could be traced back mainly to social factors or housing conditions. Differences in the repertoire of males and females were most obvious in the sexual context. Overall, most signals were used flexibly, with the majority performed in three or more social contexts and almost one-third of signals used in combination with other signals. Siamangs also adjusted their signals appropriately for the recipient, for example, using visual signals most often when the recipient was already attending (audience effects). These observations are discussed in the context of siamang ecology, social structure, and cognition.To see video sequences of signals described here, please go to     

The behavioral context of visual displays in common marmosets (Callithrix jacchus)

Communication is important in social species, and may occur with the use of visual, olfactory or auditory signals. However, visual communication may be hampered in species that are arboreal have elaborate facial coloring and live in small groups. The common marmoset fits these criteria and may have limited visual communication. Nonetheless, some (contradictive) propositions concerning visual displays in the common marmoset have been made, yet quantitative data are lacking. The aim of this study was to assign a behavioral context to different visual displays using pre–post‐event‐analyses. Focal observations were conducted on 16 captive adult and sub‐adult marmosets in three different family groups. Based on behavioral elements with an unambiguous meaning, four different behavioral contexts were distinguished: aggression, fear, affiliation, and play behavior. Visual displays concerned behavior that included facial expressions, body postures, and pilo‐erection of the fur. Visual displays related to aggression, fear, and play/affiliation were consistent with the literature. We propose that the visual display “pilo‐erection tip of tail” is related to fear. Individuals receiving these fear signals showed a higher rate of affiliative behavior. This study indicates that several visual displays may provide cues or signals of particular social contexts. Since the three displays of fear elicited an affiliative response, they may communicate a request of anxiety reduction or signal an external referent. Concluding, common marmosets, despite being arboreal and living in small groups, use several visual displays to communicate with conspecifics and their facial coloration may not hamper, but actually promote the visibility of visual displays. Am. J. Primatol. 75:1084–1095, 2013. © 2013 The Authors. American Journal of Primatology Published by Wiley Periodicals, Inc.     

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.     

A novel 'sit and wait' reproductive strategy in social wasps

I present evidence indicating that a subset of spring females in the social wasp Polistes dominulus do not initiate colonies but rather ''sit and wait'' to adopt colonies initiated and abandoned by other conspecifics. These results are, to my knowledge, the first to demonstrate conclusively this alternative reproductive strategy in social wasps. Individuals engaging in the sit-and-wait strategy behave selfishly by adopting the most mature nests available; such nests will produce workers sooner than less mature nests and, consequently, are more likely to survive. The sit-and-wait reproductive strategy may safeguard an individual from early-season, foraging-related mortality as well as reduce early-season energy expenditure.     

Scaling in nests of a social wasp: a property of the social group

The numbers of brood cells in nests built by founding swarms of the Neotropical social wasp Polybia occidentalis closely correlate with the numbers of wasps in the swarms. We analyzed nests of different sizes to determine how they scale with respect to the allocation of brood cells among combs. Three patterns were evident: compared to smaller nests, larger nests have (1) more combs and (2) larger combs; and (3) among nests containing the same number of combs, the last two combs diverge in relative size as nest size increases. Taken together, these results suggest that members of a swarm somehow "know" the size of the swarm they are in. This information feeds back to individual builders, which quantitatively modulate their responses to stigmergic cues in ways that result in the nest-size-scaled allocation of brood cells among combs. The patterns also suggest that swarms fine-tune the final size of their nests by making corrections as they build.     

Social Use of Facial Expressions in Hylobatids

Non-human primates use various communicative means in interactions with others. While primate gestures are commonly considered to be intentionally and flexibly used signals, facial expressions are often referred to as inflexible, automatic expressions of affective internal states. To explore whether and how non-human primates use facial expressions in specific communicative interactions, we studied five species of small apes (gibbons) by employing a newly established Facial Action Coding System for hylobatid species (GibbonFACS). We found that, despite individuals often being in close proximity to each other, in social (as opposed to non-social contexts) the duration of facial expressions was significantly longer when gibbons were facing another individual compared to non-facing situations. Social contexts included grooming, agonistic interactions and play, whereas non-social contexts included resting and self-grooming. Additionally, gibbons used facial expressions while facing another individual more often in social contexts than non-social contexts where facial expressions were produced regardless of the attentional state of the partner. Also, facial expressions were more likely ‘responded to’ by the partner’s facial expressions when facing another individual than non-facing. Taken together, our results indicate that gibbons use their facial expressions differentially depending on the social context and are able to use them in a directed way in communicative interactions with other conspecifics.     

Manipulating the appearance of a badge of status causes changes in true badge expression

Signals of dominance and fighting ability (i.e. status signals) are found in a wide range of taxa and are used to settle disputes between competitive rivals. Most previous research has considered status-signal phenotype as an attribute of the individual; however, it is more likely that signal expression is an emergent property that also incorporates aspects of the social environment. Furthermore, because an individual''s signal phenotype is likely to influence its social interactions, the relationships between status signals, social environment and individual quality are probably much more complex than previously appreciated. Here, we explore the dynamic relationship between social interactions and signal expression in a previously undescribed status signal, the frontal shield of the pukeko (Porphyrio porphyrio melanotus: Aves). We demonstrate that frontal shield size is a strong predictor of dominance status within social groups, even after controlling for potentially confounding variables. Then, we evaluate the relationship between social interactions and signal expression by testing whether manipulating apparent shield size influences (i) dominance interactions and (ii) future signal expression. By showing that decreasing apparent shield size causes both an increase in the amount of aggression received and a decrease in an individual''s true shield size, we provide the first evidence of dynamic feedback between signal expression and social interactions. Our study provides important insight into the role of receiver-dependent (i.e. social) costs in maintaining signal honesty and demonstrates a unique approach to studying status signalling applicable to future studies on dynamic morphological signals.