Candidate genes for individual recognition in Polistes fuscatus paper wasps.

Few animals are known to individually recognize conspecifics, i.e. learn and recall unique individuals during subsequent encounters, and nearly all are social vertebrates. Remarkably, the social paper wasp Polistes fuscatus has recently been discovered to possess this ability, which is useful for remembering identities during competitive social interactions. We analyzed brain gene expression in staged encounters between pairs of individuals to explore potential mechanisms underlying wasps' ability to recall familiar individuals using real-time qRT-PCR. We identified four candidate genes (IP3K, IP3R, Nckx30C and Su(var)2-10) that were down-regulated in the presence of familiar individuals compared to single wasps and pairs of wasps meeting for the first time. These candidate genes are related to calcium signaling, therefore, we treated wasps with lithium chloride, a pharmacological agent that inhibits calcium signaling in neurons. This treatment decreased aggression in paper wasps, but did not affect expression of genes related to calcium signaling. The results suggest calcium signaling differences may be related to individual memory recall in wasps, and we present four promising candidate genes for future study. These data suggest genes associated with dominance behavior may be co-opted for individual recognition, but further work is needed to establish a causal association with the behavior.

Preferential phenotypic association linked with cooperation in paper wasps.

Animals can influence their social environment by preferentially associating with certain conspecifics. Such preferential association has gained increasing theoretical attention, as it may influence social evolution and population dynamics. However, relatively little empirical work has examined the occurrence of preferential association and its effects on cooperative group formation. Here, we test the factors associated with cooperative group formation in Polistes dominulus nest-founding queen wasps. P. dominulus are a good system to study preferential association, as foundresses can nest alone or in groups and group membership is flexible. We found that both social and environmental factors were associated with partner choice. First, facial patterns were associated with cooperation. Wasps with more similar facial patterns were more likely to cooperate than wasps with less similar facial patterns. This preferential phenotypic association fits the theoretical criteria for the evolution of tag-based cooperation. Season was also associated with cooperation; wasps on early-season nests were more likely to cooperate than wasps on late-season nests. High levels of aggression by nest owners during initial interactions were also correlated with lower probabilities of subsequent cooperation, suggesting that nest owners have some control over group membership. Other factors including body weight, weight similarity and nest productivity were not linked with cooperation. Overall, multiple factors influence cooperation in paper wasps, including facial pattern similarity. The occurrence of preferential phenotypic association in paper wasps is quite interesting and may influence the evolution of cooperation and population divergence in this group.

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.

Co-evolution of plumage characteristics and winter sociality in New and Old World sparrows.

Understanding the evolution of phenotypic diversity, including the stunning array of avian plumage characters, is a central goal of evolutionary biology. Here, we applied a comparative analysis to test factors associated with the origin and maintenance of black chest and throat patches, which in some taxa are referred to as 'badges-of-status'. Specifically, we tested whether the evolution of black colour patches in Old and New World sparrows is consistent with a signalling function during the nonbreeding season or breeding season. We found no positive associations between patch evolution and polygyny or summer sociality. Instead, patch evolution is significantly associated with sociality during the nonbreeding season. Additionally, unlike typical plumage characteristics under sexual selection, these patches are visible throughout the nonbreeding season. Further, the pattern of patch dimorphism uncovered in this study does not match expectations for a trait that evolved in a reproductive context. In particular, patch dimorphism is not associated with polygyny or the presence of extra-pair mating although other types of plumage dimorphism are strongly associated with nonmonogamous mating systems. Overall, patterns of patch evolution suggest that they are more strongly associated with social competition during the nonbreeding season than sexual competition during the breeding season. These results clarify why some previous work has uncovered puzzling relationships between black plumage patches and reproductive behaviour. We discuss these findings in the context of signal theory and previous work on badges-of-status.