Visual signals of individual identity in the wasp Polistes fuscatus

Age, sex, and dominance-related mushroom body plasticity in the paperwasp Mischocyttarus mastigophorus

Social Hymenoptera are important models for analyzing functional brain plasticity. These insects provide the opportunity to learn how individuals' social roles are related to flexible investment in different brain regions. We assessed how age, sex, and individual behavior influence brain development in a primitively eusocial paper wasp, Mischocyttarus mastigophorus. Previous research in other species has demonstrated experience-dependent changes in central and primary sensory centers in the brain. The mushroom body (MB) calyx is a central processing region involved in sensory integration, learning and memory and may be particularly relevant to social behavior. We extend earlier cross-sectional studies of female brain/behavior associations by measuring sex- and age-related differences in MB calyx volume, and by quantifying optic lobe and antennal lobe development. Age did predict MB development: calyx neuropils increased in volume with age. We show that MB development differs between the sexes. Males, who frequently depart to seek mating opportunities, have larger MB calyx collars (which receive optic input) than females. In contrast, females have augmented predominantly antenna-innervated MB calyx lips, which may be useful for nestmate recognition and interactions on the nest. Sex differences in MB development increased with age. After accounting for age and sex effects, social aggression was positively correlated with MB calyx volume for both sexes. We found little evidence for relationships among sex, age, or behavior and the volumes of peripheral sensory processing structures. We discuss the implications of gender- and age-related effects on brain volume in relation to male and female life history and reproductive success.

Crayfish recognize the faces of fight opponents

The capacity to associate stimuli underlies many cognitive abilities, including recognition, in humans and other animals. Vertebrates process different categories of information separately and then reassemble the distilled information for unique identification, storage and recall. Invertebrates have fewer neural networks and fewer neural processing options so study of their behavior may reveal underlying mechanisms still not fully understood for any animal. Some invertebrates form complex social colonies and are capable of visual memory–bees and wasps, for example. This ability would not be predicted in species that interact in random pairs without strong social cohesion; for example, crayfish. They have chemical memory but the extent to which they remember visual features is unknown. Here we demonstrate that the crayfish Cherax destructor is capable of visual recognition of individuals. The simplicity of their interactions allowed us to examine the behavior and some characteristics of the visual features involved. We showed that facial features are learned during face-to-face fights, that highly variable cues are used, that the type of variability is important, and that the learning is context-dependent. We also tested whether it is possible to engineer false identifications and for animals to distinguish between twin opponents.

Evolutionary biology of insect learning

Learning and memory, defined as the acquisition and retention of neuronal representations of new information, are ubiquitous among insects. Recent research indicates that a variety of insects rely extensively on learning for all major life activities including feeding, predator avoidance, aggression, social interactions, and sexual behavior. There is good evidence that individuals within an insect species exhibit genetically based variation in learning abilities and indirect evidence linking insect learning to fitness. Although insects rely on innate behavior to successfully manage many types of variation and unpredictability, learning may be superior to innate behavior when dealing with features unique to time, place, or individuals. Among insects, social learning , which can promote the rapid spread of novel behaviors, is currently known only from a few well-studied examples in social Hymenoptera. The prevalence and importance of social learning in insects are still unknown. Similarly, we know little about ecological factors that may have promoted enhanced learning abilities in insects, and whether learning has significantly contributed to speciation in insects.

Long-term memory of individual identity in ant queens

Remembering individual identities is part of our own everyday social life. Surprisingly, this ability has recently been shown in two social insects. While paper wasps recognize each other individually through their facial markings, the ant, Pachycondyla villosa, uses chemical cues. In both species, individual recognition is adaptive since it facilitates the maintenance of stable dominance hierarchies among individuals, and thus reduces the cost of conflict within these small societies. Here, we investigated individual recognition in Pachycondyla ants by quantifying the level of aggression between pairs of familiar or unfamiliar queens over time. We show that unrelated founding queens of P. villosa and Pachycondyla inversa store information on the individual identity of other queens and can retrieve it from memory after 24h of separation. Thus, we have documented for the first time that long-term memory of individual identity is present and functional in ants. This novel finding represents an advance in our understanding of the mechanism determining the evolution of cooperation among unrelated individuals.

Cooperating in the face of uncertainty: A consistent framework for understanding the evolution of cooperation

The evolution of cooperative behaviour, whereby individuals enhance the fitness of others at an apparent cost to themselves, represents one of the greatest paradoxes of evolution. Individuals that engage in such cooperative behaviour can, however, be favoured by natural selection if cooperative actions confer higher fitness than alternative actions. To understand the evolution of cooperative behaviour, the direct and indirect genetic benefits that individuals accrue in the present and future must be summed - this can be accomplished without any reference to the colorful vocabulary typically associated with studies of cooperation. When benefits are accrued indirectly through relatives or directly in the future individuals must be able to assess and enhance their probability of accruing those benefits and behave accordingly. We suggest that, in the same way that studies of kin recognition systems improved our understanding of how individuals assess and enhance their probability of accruing indirect benefits, studies of various forms of inheritance and reciprocation recognition systems will improve our understanding of how individuals assess and enhance their probability of accruing future benefits. Recognizing the parallel between studies of indirect fitness and future fitness, at multiple levels of analysis, will move us toward a simpler and more consistent framework for understanding the evolution of cooperative behaviour.

Individual recognition: it is good to be different

Individual recognition (IR) behavior has been widely studied, uncovering spectacular recognition abilities across a range of taxa and modalities. Most studies of IR focus on the recognizer (receiver). These studies typically explore whether a species is capable of IR, the cues that are used for recognition and the specializations that receivers use to facilitate recognition. However, relatively little research has explored the other half of the communication equation: the individual being recognized (signaler). Provided there is a benefit to being accurately identified, signalers are expected to actively broadcast their identity with distinctive cues. Considering the prevalence of IR, there are probably widespread benefits associated with distinctiveness. As a result, selection for traits that reveal individual identity might represent an important and underappreciated selective force contributing to the evolution and maintenance of genetic polymorphisms.

Correlation between facial pattern recognition and brain composition in paper wasps

Unique among insects, some paper wasp species recognize conspecific facial patterns during social communication. To evaluate whether specialized brain structures are involved in this task, we measured brain and brain component size in four different paper wasp species, two of which show facial pattern recognition. These behavioral abilities were not reflected by an increase in brain size or an increase in the size of the primary visual centers (medulla, lobula). Instead, wasps showing face recognition abilities had smaller olfactory centers (antennal lobes). Although no single brain compartment explains the wasps' specialized visual abilities, multi-factorial analysis of the different brain components, particularly the antennal lobe and the mushroom body sub-compartments, clearly separates those species that show facial pattern recognition from those that do not. Thus, there appears to be some neural specialization for visual communication in Polistes. However, the apparent lack of optic lobe specialization suggests that the visual processing capabilities of paper wasps might be preadapted for pattern discrimination and the ability to discriminate facial markings could require relatively small changes in their neuronal substrate.

Workers of a Polistes Paper Wasp Detect the Presence of Their Queen by Chemical Cues

Differences in long-chain hydrocarbon mixtures among reproductive and nonreproductive individuals have been often revealed in social insects. However, very few papers demonstrated that these signatures actually act as contact pheromones used by nonreproductive to recognize the presence of a related queen in the colony. Cuticular and glandular hydrocarbons of Polistes paper wasps have been extensively studied, but, until now, the perception and recognition of such cues was not demonstrated. In this paper, we show, for the first time in Vespidae, that Polistes gallicus workers distinguish nestmates from alien individuals and queens from workers by the hydrocarbon mixtures of the Van der Vecht organ secretion (VVS). We also demonstrated that stroking behavior (a peculiar behavior of Polistes by which queens probably lay VVS on the nest) acts as an inhibitor of ovarian development in workers.

Visual system of calliphorid flies: organization of optic glomeruli and their lobula complex efferents

Reconstructions of silver-stained brains revealed 27 optic glomeruli that occupy a major volume of the lateral protocerebrum. Axons from different morphological types of columnar output neurons from the lobula complex sort out to specific glomeruli. Glomeruli are partially enwrapped by glial processes and are invaded by the dendrites and terminals of local interneurons that connect different glomeruli in a manner analogous to local interneurons in the antennal lobes. Each type of columnar neuron contributes to a palisade-like ensemble that extends across the whole or a circumscribed area of the retinotopic mosaic. A second class of outputs from the lobula comprises wide-field neurons, the dendrites of which interact with planar fields or column-like patches of retinotopic inputs from the medulla. These neurons also send their axons to optic glomeruli. Dye fills demonstrate that lobula complex neurons supplying glomeruli do not generally terminate directly on descending neurons. Local interneurons and projection neurons provide integrative circuitry within and among glomeruli. As exemplified by the anterior optic tubercle, optic glomeruli can also have elaborate internal architectures. The results are discussed with respect to the identification of motion- and orientation-selective neurons at the level of the lobula and lateral protocerebrum and with respect to the evolutionary implications raised by the existence of neural arrangements serving the compound eyes, which are organized like neuropils serving segmental ganglia equipped with appendages.

Honeybee (Apis mellifera) vision can discriminate between and recognise images of human faces

Recognising individuals using facial cues is an important ability. There is evidence that the mammalian brain may have specialised neural circuitry for face recognition tasks, although some recent work questions these findings. Thus, to understand if recognising human faces does require species-specific neural processing, it is important to know if non-human animals might be able to solve this difficult spatial task. Honeybees (Apis mellifera) were tested to evaluate whether an animal with no evolutionary history for discriminating between humanoid faces may be able to learn this task. Using differential conditioning, individual bees were trained to visit target face stimuli and to avoid similar distractor stimuli from a standard face recognition test used in human psychology. Performance was evaluated in non-rewarded trials and bees discriminated the target face from a similar distractor with greater than 80% accuracy. When novel distractors were used, bees also demonstrated a high level of choices for the target face, indicating an ability for face recognition. When the stimuli were rotated by 180 degrees there was a large drop in performance, indicating a possible disruption to configural type visual processing.

Visually mediated species and neighbour recognition in fiddler crabs (Uca mjoebergi and Uca capricornis)

Mating signals are often directed at numerous senses and provide information about species identity, gender, receptiveness, individual identity and mate quality. Given the diversity of colourful body patterns in invertebrates, surprisingly few studies have examined the role of these visual signals in mate recognition. Here, we demonstrate the use of claw coloration as a species recognition signal in a fiddler crab (Uca mjoebergi). Furthermore, we show that distinct carapace colour patterns in Uca capricornis enable males to discriminate between their female neighbours and unfamiliar females. This is the first empirical evidence of the social importance of colour markings in fiddler crabs and the first example of visually mediated species and neighbour recognition in invertebrates other than insects.

Individual Recognition in Ant Queens

Personal relationships are the cornerstone of vertebrate societies, but insect societies are either too large for individual recognition, or their members were assumed to lack the necessary cognitive abilities . This paradigm has been challenged by the recent discovery that paper wasps recognize each other's unique facial color patterns . Individual recognition is advantageous when dominance hierarchies control the partitioning of work and reproduction . Here, we show that unrelated founding queens of the ant Pachycondyla villosa use chemical cues to recognize each other individually. Aggression was significantly lower in pairs of queens that had previously interacted than in pairs with similar social history but no experience with one another. Moreover, subordinates discriminated familiar and unfamiliar dominants in choice experiments in which physical contact, but not odor perception, was prevented and in tests with anaesthetized queens. The cuticular chemical profiles of queens were neither associated with dominance nor fertility and, therefore, do not represent status badges , and nestmate queens did not share a common odor. Personal recognition facilitates the maintenance of stable dominance hierarchies in these small societies. This suggests that the ability to discriminate between individual traits is selected for when it incurs net benefits for the resolution of conflict.

Evolution: Social Selection for Eccentricity

The dress code of paper wasps, like that of humans, is related to their social habits: species with a flexible nest-founding strategy have highly variable black-and-yellow markings. This color polymorphism facilitates individual recognition and might have been selected to permit complex social interactions.

A socially enforced signal of quality in a paper wasp

Organisms use signals of quality to communicate information about aspects of their relative phenotypic and genetic constitution. Badges of status are a subset of signals of quality that reveal information about an individual's size and dominance. In general, signals of quality require high and differential costs to remain honest (that is, prevent low-quality cheaters from exploiting any fitness benefits associated with communicating high quality). The theoretically required costs for badges of status remain controversial because the development (or 'production') of such signals often seems to be relatively cost-free. One important hypothesis is that such signals impose social (or 'maintenance') costs incurred through repeated agonistic interactions with other individuals. However, convincing empirical evidence for social costs remains elusive. Here we report social costs in a previously undescribed badge of status: the highly variable black facial patterns of female paper wasps, Polistes dominulus. Facial patterns strongly predict body size and social dominance. Moreover, in staged contests between pairs of unfamiliar wasps, subordinate wasps with experimentally altered facial features ('cheaters') received considerably more aggression from the dominant than did sham controls, indicating that facial patterns are signals and that dishonest signalling imposes social costs.

Complex social behaviour can select for variability in visual features: a case study in Polistes wasps

The ability to recognize individuals is common in animals; however, we know little about why the phenotypic variability necessary for individual recognition has evolved in some animals but not others. One possibility is that natural selection favours variability in some social contexts but not in others. Polistes fuscatus wasps have variable facial and abdominal markings used for individual recognition within their complex societies. Here, I explore whether social behaviour can select for variability by examining the relationship between social behaviour and variability in visual features (marking variability) across social wasp taxa. Analysis using a concentrated changes test demonstrates that marking variability is significantly associated with nesting strategy. Species with flexible nest-founding strategies have highly variable markings, whereas species without flexible nest-founding strategies have low marking variability. These results suggest that: (i) individual recognition may be widespread in the social wasps, and (ii) natural selection may play a role in the origin and maintenance of the variable distinctive markings. Theoretical and empirical evidence suggests that species with flexible nesting strategies have reproductive transactions, a type of complex social behaviour predicted to require individual recognition. Therefore, the reproductive transactions of flexible species may select for highly variable individuals who are easy to identify as individuals. Further, selection for distinctiveness may provide an alternative explanation for the evolution of phenotypic diversity.

Informational constraints on optimal sex allocation in ants

Workers of the ant Formica truncorum specialize in rearing females or males depending on the number of fathers of a colony. These split sex ratios increase inclusive fitness, but it has remained unknown how workers assess the number of patrilines in their colonies and to what extent their reproductive decisions are constrained by lack of information. By analysis of the quantitative variation in cuticular hydrocarbon profiles of workers of multiply mated queens, we show that the heritable component of recognition cues is low and that the extent of sex ratio biasing toward males is correlated with patriline differences in hydrocarbon profiles. Workers are thus able to capitalize on colony-level relatedness asymmetry, but their inclusive fitness is constrained by uninformative recognition cues. These results are consistent with the hypothesis that the occasional expression of nepotistic phenotypes favoring full-sisters over half-sisters maintains selection against informative recognition cues. We evaluate how inclusive fitness theory may be used to predict the number and kind of recognition cues in insect societies of a specific relatedness structure.

Nestling recognition via direct cues by parental male bluegill sunfish ( Lepomis macrochirus)

Parental care can be costly to a parent in terms of both time and energy invested in the young. In species with cuckoldry or brood parasitism not all of the young under a parent's care are necessarily offspring. In such cases, distinguishing between kin and non-kin, and investing only in the former (nepotism), can be advantageous. Bluegill sunfish ( Lepomis macrochirus) are characterized by paternal care and cuckoldry, and care-providing males appear to show nepotistic behaviours. Here, we investigated nestling recognition in bluegill, determining whether parental males can differentiate between young from their own nest (familiar and related) and young from non-neighbouring nests (unfamiliar and unrelated) using (1) visual and chemical cues, and (2) chemical cues only. In the first experiment, wild-caught parental males were presented with samples of eggs or fry (newly hatched eggs) collected from their own nest or a foreign nest and placed on opposite sides of an aquarium. The time these parental males spent associating with each sample, and their "pecking" behaviours (indicating cannibalism), were recorded. Parental males showed no preference between eggs from their own nest and eggs from a non-neighbouring nest, but they preferred to associate with fry from their own nest over foreign fry. There also was a positive relationship between male body size and the time spent associated with fry from their own nest. Parental males pecked at foreign fry more than 5 times as often as fry from their own nest, though this difference was not statistically significant. In the second experiment, fry that were collected from the nest of a wild-caught parental male or a non-neighbouring nest were placed in different containers and the water from each was dripped into opposite ends of an aquarium. The time the male spent on each side was recorded. In this case, parental males spent more time near the source of water conditioned by unrelated fry, but there was a positive relationship between male condition (fat reserves) and the time he spent near the source of water conditioned by fry from his own nest. Results confirm that chemicals cue nestling recognition by parental male bluegill.