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Social isolation prevents the development of individual face recognition in paper wasps
Animal Behaviour 152 (2019) 71e77
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Animal Behaviour journal homepage: www.elsevier.com/locate/anbehav
Social isolation prevents the development of individual face recognition in paper wasps Elizabeth A. Tibbetts*, Erica Desjardins, Nora Kou, Laurel Wellman Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, U.S.A.
a r t i c l e i n f o Article history: Received 3 December 2018 Initial acceptance 1 February 2019 Final acceptance 6 March 2019 Available online 17 May 2019 MS. number: A18-00859R Keywords: development expertise face recognition individual recognition learning Polistes
Much work has shown that social isolation has lasting negative effects on adult social interactions, but less is known about precisely how and why isolation alters social behaviour. One way isolation may alter social behaviour is by interfering with the development of effective communication. Here, we test how social isolation influences individual recognition, a key aspect of social communication in Polistes fuscatus paper wasps. Polistes fuscatus reared in a typical social environment learn and remember the unique faces of conspecifics during social interactions. Typical P. fuscatus use individual face recognition to minimize conflict and stabilize social interactions. As wasps are adept face learners, they also readily learn to discriminate between wasp face images during training. Here, we show that social isolation had dramatic effects on recognition. We isolated wasps for 6 days after eclosion from pupation, then tested them for face recognition in social and nonsocial contexts. Isolated wasps did not learn and remember other individuals during social interactions. Furthermore, isolated wasps did not learn to discriminate between wasp face images during training. Therefore, social experience with conspecifics is essential for the development of individual recognition and face learning in paper wasps. Many aspects of wasp behaviour develop rapidly with little experience required. However, complex social interactions like individual recognition require social experience with conspecifics. © 2019 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.
Social isolation has lasting negative effects on many aspects of an animal's phenotype, including altered social interactions, slower growth, impaired learning, shorter life span and reduced immune function (Bailey & Moore, 2018; Cacioppo & Hawkey, 2009; Monaghan, 2008). One of the key behavioural consequences of social isolation is reduced social competence (Taborsky & Oliveira, 2012). That is, socially isolated animals are less able to match their behaviour to the current social environment. For example, socially isolated animals may be inappropriately aggressive across contexts, directing aggression towards competitors, mates or offspring instead of restricting aggression to competitors (Arnold & Taborsky, 2010; Gersick, Snyder-Mackler, & White, 2012; Kempes, Gulickx, van Daalen, Louwerse, & Sterck, 2008; Toth, Halasz, Mikics, Barsy, & Haller, 2008). While there is strong evidence that isolation reduces social competence, less is known about the behavioural mechanisms that link social isolation to reduced social competence. One hypothesis for why socially isolated animals have lower social competence is that they are less effective communicators.
* Correspondence: E. A. Tibbetts, Department of Ecology and Evolution, University of Michigan, 1105 N University Ave, Ann Arbor, MI, 48109, U.S.A. E-mail address: [email protected] (E. A. Tibbetts).
There is growing evidence that isolated individuals are less effective at assessing, discriminating and responding to social signals (Arnold & Taborsky, 2010; Bailey & Moore, 2018; Kempes et al., 2008). For example, female crickets that were socially isolated during development were less choosy about mates compared to females reared with conspecifics (Judge, 2010). Mice reared in isolation use different patterns of ultrasonic vocalizations during maleemale contests than mice with typical social experience (Keesom, Finton, Sell, & Hurley, 2017). However, social experience is not always required for communication; inexperienced signal receivers respond appropriately to many social signals (Maynard Smith & Harper, 2003; Searcy & Nowicki, 2005). For example, in many species, females that have not previously encountered males still assess male quality signals and use the signals to make mate choice decisions (Izzo & Tibbetts, 2012; Jennions & Petrie, 1997). Individual recognition is a type of communication that is essential for social competence in many taxa. During individual recognition, receivers learn and remember the unique phenotype of conspecifics, associate the unique phenotype with individualspecific information about the signaller and recall the information during future encounters (Tibbetts & Dale, 2007). As a result, individual recognition allows receivers to direct aggressive and
https://doi.org/10.1016/j.anbehav.2019.04.009 0003-3472/© 2019 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.
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affiliative interactions appropriately. Individual recognition mediates interactions in contexts such as territoriality, dominance interactions, cooperation, parental care and pair bonding and is found in a wide range of species, from primates to birds to insects (Johnston, 2003; Tibbetts & Dale, 2007). Thus far, little experimental work has tested how social isolation influences receiver capacity for individual recognition. A receiver's ability to learn and remember specific individuals may depend on social experience, as experience often improves performance on complex tasks that involve learning and memory (Cacioppo & Hawkey, 2009). For example, in corvid birds that store and retrieve food, young birds require extensive experience before they develop effective caching behaviour (Grodzinski & Clayton, 2010). Alternatively, receivers may not need experience to learn and remember individual conspecifics. Inexperienced receivers can assess and respond appropriately to some signals (e.g. signals of species identity, sex, strategy; Maynard Smith & Harper, 2003; Searcy & Nowicki, 2005). Polistes fuscatus wasps provide a good system to test how social isolation influences individual recognition because they have variable facial patterns that are used for individual face recognition (Tibbetts, 2002). Wasps excel at learning and remembering other individuals (Sheehan & Tibbetts, 2008). Experimental and comparative analyses indicate that learning the individual identity of conspecifics provides social benefits to nest-founding queens because individual recognition reduces aggression among queens (Sheehan & Tibbetts, 2010; Tibbetts, 2002, 2004). Wasps usually eclose from pupation onto a nest full of other wasps and gain ample social experience as they mature. However, wasps occasionally experience social isolation when they eclose onto nests that were abandoned during their pupal period. Here, we experimentally altered rearing environment to test how social isolation influences face learning and individual recognition in P. fuscatus workers. We test whether experience with P. fuscatus influences a wasp's (1) facility for learning P. fuscatus faces during training and (2) individual recognition during social interactions. We predicted that P. fuscatus reared in social isolation would be less able to learn and remember unique conspecific faces in training and social contexts than wasps reared with conspecifics.
METHODS We collected P. fuscatus individuals and their nests from areas around Ann Arbor, Michigan, U.S.A. After collection, each nest and the associated wasps were housed in individual containers under a natural day/night cycle and fed ad libitum sugar and Galleria mellonella caterpillars. Wasp larvae are stationary and have rudimentary eyes used primarily for light and motion detection (Gilbert, 1994). As a result, wasps are naïve to complex visual stimuli, social hierarchies and individual recognition when they eclose from the pupal case. Nests were checked daily for adults that eclosed from pupation. After eclosion, wasps were painted with individually distinctive marks on their thorax. Marked wasps were either returned to their natal nest or isolated with an orphaned nest (‘alone’ treatment). Wasps remained in their treatment groups for at least 6 days before being trained or used in recognition experiments. Wasps from different treatment groups were similar ages when trained (mean age ± SE: queenright: 10.5 ± 0.73; alone: 11 ± 0.68; mixed linear model comparing age across treatment groups: F1,37 ¼ 0.25, P ¼ 0.62). Polistes are considered behaviourally mature when they are 5 days old because they engage in a range of adult behaviour, including cooperative and competitive interactions with conspecifics, egg laying, flying,
hunting and navigating (Giray, Giovanetti, & West-Eberhard, 2005; Reeve, 1991; Shorter & Tibbetts, 2009).
Face Learning During Training Wasps were trained to differentiate between pairs of P. fuscatus face images using established methods (Appendix, Fig. A1; DesJardins & Tibbetts, 2018; Tibbetts, Pandit, & Nondorf, 2018). Face images used for training were photographs of P. fuscatus from Michigan that showed the face and antenna. Wasps were trained on one of three unique pairs of stimuli (Fig. 1). The particular image that was correct was swapped across trials. All images were printed at life size using a commercially available Sony Picture Station photo printer. During training, wasps were placed in a 2.5 4 0.7 cm wood and Plexiglas box with six identical faces glued to the inside walls. In half the bouts, the wasp was placed in a box with negative stimuli and received a mild electric shock from an electrified pad for 2 min. The electrified pad was made of antistatic conductive foam electrified by two copper wires connected to a Variac transformer. In the other half of the bouts, the wasp was placed in a similarly sized box with neutral faces and the pad was not electrified for 2 min. Between each bout, the wasp was given a 1 min break in a holding container. For example, a wasp trained to discriminate between face A and B would experience the following training. First, the wasp was placed with face A and received a shock for 2 min. The wasp was removed and given a 1 min break. Then, the wasp was placed with face B and did not receive a shock for 2 min. The wasp was removed and given a 1 min break. This process was repeated five times per wasp, so wasps saw faces A and B five times each. After training, the wasp was given a 45 min break in a holding container with food and water. Then, learning was tested by measuring whether the wasp approached the correct or incorrect stimuli over 10 trials. Testing occurred in a 3 10 0.7 cm rectangle. One end of the rectangle had the correct stimuli and the other end of the rectangle had the incorrect stimuli. The entire floor of the rectangle was electrified except the 2.25 cm closest to the correct stimuli, the ‘safety zone’. Most of the rectangle was electrified because shock motivates wasps to move. The correct choice was associated with safety to ensure learned preferences from the initial training were not extinguished during the 10-trial test.
Figure 1. Polistes fuscatus face images used for training. Pairs are shown in the same row. Faces were printed at life size (3 mm width).
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Receiving a shock while choosing a preferred stimuli can rapidly extinguish learned preferences. The centre of the rectangle had two removable, clear partitions that confined the wasp. At the beginning of each trial, the wasp was placed in the centre of the rectangle between the clear partitions, the electric shock was turned on for 5 s, both partitions were removed simultaneously, and the wasp was free to walk through the rectangle. Wasps that learned typically turned towards the correct stimuli while confined in the centre of the rectangle. When the partitions were removed, the wasp quickly walked towards the correct stimuli. A wasp was scored as making a choice when its head and thorax moved beyond the partition placed 2.5 cm from each end of the rectangle. After a wasp made a choice, it was removed from the rectangle and given a 1 min break in a holding container. The placement of the neutral and negative stimuli (right or left side) was determined randomly and changed between trials. This ensured that wasps did not associate a particular direction with correct choices. Social Individual Recognition We assessed the recognition abilities of P. fuscatus raised in isolation by staging contests between pairs of wasps with and without a prior history of social interactions (see Appendix, Fig. A2; following D'Ettorre & Heinze, 2005; Sheehan & Tibbetts, 2008; Tibbetts, Injaian, Sheehan, & Desjardins, 2018). The same method was used to illustrate that P. fuscatus workers are capable of individual recognition in social contexts (Injaian & Tibbetts, 2014). We replicated the methods from Injaian and Tibbetts (2014) as closely as possible to ensure factors unrelated to social experience did not influence experimental outcomes. Wasps were collected from the same locations in Michigan, housed in the same room, fed the same food and eclosed at the same time of year. In addition, the methods used for testing individual recognition were the same. All trials involved P. fuscatus that had been isolated since eclosion. Wasps that eclosed from the same nest were not paired. During the contests, we scored the occurrence and intensity of aggressive interactions as well as displays of nonaggressive behaviour. On the first day (day 0), we placed two unfamiliar P. fuscatus that had been isolated since eclosion in a small container (8 8 cm) and filmed their interactions. After filming, the wasps were housed together until the next day (day 1), at which point they were separated and returned to their initial solitary housing. One day later, the same two wasps were filmed interacting again (day 2). To ensure that changes in aggression between days 0 and 2 were a consequence of recognition rather than a decrease in motivation over time, we paired the wasps with other unknown social partners on the day before and after (days 1 and 3). The first half hour of all interactions was videotaped for later analysis of behaviour. We recorded the first half hour of interactions to be consistent with previous social individual recognition experiments. Wasps engage in the full range of aggressive and affiliative behaviours within 30 min of meeting a rival. We performed 17 sets of trials using 51 individuals from 39 nests. Behaviour in all videos was scored by a research assistant who was blind to experimental predictions. Cooperative and aggressive behaviours were ranked as follows: (0) nonaggressive bodily contact (partners within one body length of each other, but no darts, bites, grapples or mounts occurred); (1) dart (rapid body movement towards partner); (2) dart with open mandibles (rapid body movement towards partner with open mandibles); (3) bite (mandibles closing on body of partner); (4) grapple/mount (wrestling/ bodily contact that forces partner to accept submissive positioning). For each trial, we summed the ranks of cooperative and aggressive behaviours. We then divided the sum by the number of total
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interactions per tape to calculate an aggression index (Dreier, van Zweden, & D'Ettorre, 2007). The aggression index standardized behaviour by taking into account the number and intensity of interactions of each pair, which allowed behaviour to be compared across trials. The aggression index has been used to measure individual recognition in multiple studies (Dreier et al., 2007; Injaian & Tibbetts, 2014; Sheehan & Tibbetts, 2008, 2010). If the wasps are able to recognize and remember social partners, they should be less aggressive and have more nonaggressive contacts when they interact with a known individual (day 2) than when they interact with an individual they encounter for the first time (days 0, 1, 3). Ethical Note No permits were required for the experiments. During social individual recognition trials, wasps used ritualized aggression that does not harm conspecifics. Training involved low-level electrical shock that is aversive to wasps. However, the level of current was kept low to ensure that wasps were not harmed during training. Wasps behaved normally when they were returned to their container after the experiments. Statistical Analysis We measured learning as the total number of correct choices. We tested whether wasps learned by comparing the number of correct choices versus incorrect choices to the 50:50 random expectation with a 2 2 c2 tests. We tested whether P. fuscatus learned faces differently when reared with conspecifics or alone by comparing the number of correct choices in the two developmental environments with a mixed linear model, including nest identity to account for any possible similarity between wasps that eclosed from the same nest. Age of wasps at training was also compared across treatment groups using a mixed linear model with nest identity as a random effect. We trained 39 wasps from 20 nests, including 18 queenright wasps and 21 isolated wasps. In the social individual recognition experiment, aggression index and number of nonaggressive contacts were compared across trials using Friedman's ANOVA nonparametric analysis. The aggression index or the number of nonaggressive contacts was the dependent variable. The independent variable was trial day (day 0, 1, 2 or 3). We performed 17 sets of trials using 51 individuals from 39 nests. RESULTS Face Learning During Training Wasps reared with conspecifics learned to discriminate wasp faces better than wasps reared in isolation (F2,37 ¼ 49.1, P < 0.001; Fig. 2). In fact, P. fuscatus reared in social isolation did not learn to differentiate between pairs of P. fuscatus face images, as they chose the correct image at chance levels (c21 ¼ 0.04, P ¼ 0.84). However, P. fuscatus reared with conspecifics learned to discriminate pairs of faces. They chose the correct image significantly more often than expected by chance (c21 ¼ 21.1, P ¼ 0.001). Social Individual Recognition Polistes fuscatus reared without social contact did not learn and remember unique wasps during social interactions. Wasps were no less aggressive towards known wasps than towards unknown wasps, as aggression index did not differ across days (c23 ¼ 2.8, P ¼ 0.41; Fig. 3a). In addition, wasps had a similar number of
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Figure 2. Mean ± SE correct choices in wasps trained to discriminate pairs of P. fuscatus faces. Wasps were reared in isolation or with conspecifics. *Indicates wasps learned to discriminate face images significantly more accurately than expected by chance. Dotted line shows the 50:50 random expectation. Different lowercase letters above bars reflect significant differences (P < 0.05).
DISCUSSION Social isolation prevents the development of individual recognition in P. fuscatus wasps. Polistes fuscatus workers reared in a normal social environment learn and remember unique conspecifics during social interactions (Injaian & Tibbetts, 2014) and readily learn to discriminate between conspecific faces during training (Fig. 2). However, P. fuscatus wasps raised in social isolation did not individually identify other wasps during social interactions and were unable to learn P. fuscatus face images during training (Figs 2 and 3). We tested the effect of social isolation on behaviour by comparing wasps reared in isolation with those reared in a normal social environment. For face learning, isolated and social wasps were tested simultaneously. For social individual recognition, we compared new data on isolated wasps (Fig. 3) with previously published work on social wasps (Injaian & Tibbetts, 2014). The experimental conditions were replicated across social recognition experiments to ensure that extraneous factors did not influence the results. Wasps were collected from the same locations, housed in the same room, fed the same food and eclosed at the same time of year. In addition, the methods used for testing individual recognition were the same across years. As a result, it is unlikely that factors other than social isolation caused the difference in recognition between social and isolated wasps. Face training data also indicate that social experience is the key factor that caused differences in recognition between isolated and social wasps. Isolated wasps were unable to learn individual faces, while socially experienced wasps learned faces quickly and accurately (Fig. 2). Previous work has shown face training is linked to individual face recognition during social interactions. Wasps that excel at face learning during training are also capable of individual face recognition, whereas wasps that cannot learn faces during training, do not individually recognize conspecifics during social interactions (Sheehan & Tibbetts, 2010, 2011). Therefore, our results indicate that lack of social experience prevents the development of face learning and individual recognition.
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Nonaggressive contacts
nonaggressive contacts with known and unknown wasps (c23 ¼ 3.5, P ¼ 0.32; Fig. 3b). Therefore, wasps that are socially isolated do not learn and remember unique social partners.
Day (b)
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Day Figure 3. Mean ± SE (a) aggression index and (b) nonaggressive contacts per day. On days 0, 1 and 3, focal wasps interacted with individuals that they had not previously encountered. On day 2, wasps interacted with a previously encountered partner. Different lowercase letters above bars reflect significant differences (P < 0.05).
The lack of individual recognition in isolated wasps likely reduces their social competence because individual recognition is a key mediator of social interactions. Wasps use individual recognition to manage shares of reproduction, food and work in cooperative groups. Individual recognition also stabilizes dominance hierarchies and reduces conflict over ranks (Tibbetts, 2002, 2004; Tibbetts & Sheehan, 2013). As a result, conflict increases when wasps are experimentally altered to prevent individual recognition (Sheehan & Tibbetts, 2009; Tibbetts, 2002). Therefore, a lack of individual recognition may be an important behavioural mechanism linking social isolation to reduced social competence. Isolation primarily influences aggression and nonaggressive interactions with known individuals rather than altering behaviour towards both known and unknown individuals. Injaian and Tibbetts (2014) found that socially reared wasps were more aggressive and had fewer nonaggressive interactions with unknown individuals (mean aggression index ¼ 1.22 e 1.75; mean nonaggressive contacts ¼ 1.17 e 1.6) than with known individuals (mean aggression index ¼ 0.37; mean nonaggressive contacts ¼ 2.6). In comparison, in the present study, isolated wasps had similar numbers of aggressive and nonaggressive interactions with unknown individuals (mean aggression
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index ¼ 1.26 e 1.49; mean nonaggressive contacts ¼ 1.64 e 2.8) and known individuals (mean aggression index ¼ 1.34; mean nonaggressive contacts ¼ 2.0; Fig. 3). Notably, there was no behavioural difference between social and isolated wasps when wasps interacted with unknown rivals. Therefore, isolation did not cause a generalized enhancement in aggression or reduction in nonaggressive interactions. Instead, isolation prevented the development of individual recognition. This study adds to a growing body of evidence that social isolation has strong effects on adult behaviour. Across a broad range of taxa and contexts, social isolation changes how animals interact (Bailey & Moore, 2018). Isolated animals can have altered communication, difficulty integrating into social groups, altered dominance interactions and reduced ability to acquire and defend resources from conspecifics (Arnold & Taborsky, 2010; Ballen, Shine, & Olsson, 2014; Gersick et al., 2012; Kempes et al., 2008; Lesne, Cazale-Debat, Portugal, Trabalon, & Jeanson, 2016). These behavioural effects of isolation may also have significant evolutionary consequences (Bailey & Moore, 2018). For example, how and when receivers respond to signals can influence the type and direction of selection acting on signallers (Maynard Smith & Harper, 2003; Searcy & Nowicki, 2005) as well as playing a role in speciation (Verzijden et al., 2012). Therefore, an important goal of future work will be to assess how and when isolation influences communication as well as the fitness effects of altered communication across contests. Although isolation alters individual recognition in wasps, some forms of recognition do not depend on social experience. For example, female wasps do not need experience with males for sex recognition or to assess male quality with sexually selected ornaments. Male paper wasps have variable abdominal spots that females use to assess potential mates (Izzo & Tibbetts, 2012, 2015). Females who lack experience with males readily identify males and use male ornaments to discriminate between high- and low-quality mates. On the other hand, experience is important for nestmate recognition. Paper wasps learn the olfactory signatures of nestmates during a sensitive period immediately after emergence from pupation (Gamboa, Reeve, & Pfennig, 1986). Experienced wasps use odours to discriminate between nestmates and non-nestmates, but naïve wasps accept all individuals as nestmates (Singer & Espelie, 1992). Therefore, the information a signal conveys (e.g. quality, nestmate identity, species identity) may influence whether or not experience is required to accurately assess the signal. Previous experiments testing how experience influences individual recognition have focused on individual face recognition in primates. These studies indicate that experience may not be required for rudimentary individual discrimination, although experience improves recognition. Isolated monkeys reared with no exposure to faces can discriminate between different monkey face images, as isolated monkeys look longer at pictures of unfamiliar faces than at pictures of familiar faces (Sugita, 2008). This contrasts with wasps, where isolated individuals did not discriminate between unique wasps in social or nonsocial contexts (Figs 2 and 3). The wasp and monkey studies used different methods, so they are not directly comparable. Nevertheless, it is notable that isolated monkeys may be more capable of face discrimination than isolated wasps. Although naïve monkeys are capable of some face discrimination, most work on primate face recognition shows that individual face discrimination improves as primates mature and gain experience (Humphreys & Johnson, 2007; Nelson, 2001; Pascalis, de Haan, Nelson, & de Schonen, 1998). This study focused on visual communication because previous work has shown that P. fuscatus rely on visual signals alone for
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individual recognition (Tibbetts & Sheehan, 2013). Altering P. fuscatus facial patterns interferes with individual recognition (Sheehan & Tibbetts, 2009; Tibbetts, 2002; Tibbetts, Injaian, et al., 2018). Furthermore, Polistes species that lack facial pattern variation are not capable of individual recognition (Sheehan & Tibbetts, 2010). Wasps use chemical signals for communication in other contexts. Cuticular hydrocarbons are chemical signals of fertility (Izzo, Wells, Huang, & Tibbetts, 2010; Monnin, 2006) and are also used for nestmate recognition (Dani, Jones, Destri, Spencer, & Turillazzi, 2001; Izzo et al., 2010; Monnin, 2006; Singer & Espelie, 1992). There are opportunities for future work exploring how chemical and visual signals interact to influence behaviour. Overall, social experience is essential for the development of individual recognition in paper wasps. Many aspects of wasp behaviour develop rapidly and require little experience. However, isolation has strong social consequences for paper wasps because isolation prevents the development of individual recognition. Future work across diverse taxa will be useful to identify how signal responses are shaped by isolation as well as the broader evolutionary consequences of experience-dependent plasticity in communication. Acknowledgments This material is based in part upon work supported by the National Science Foundation under grant number IOS-1557564. References Arnold, C., & Taborsky, B. (2010). Social experience in early ontogeny has lasting effects on social skills in cooperatively breeding cichlids. Animal Behaviour, 79, 621e630. Bailey, N. W., & Moore, A. J. (2018). Evolutionary consequences of social isolation. Trends in Ecology & Evolution, 33, 595e607. Ballen, C., Shine, R., & Olsson, M. (2014). Effects of early social isolation on the behaviour and performance of juvenile lizards, Chamaeleo calyptratus. Animal Behaviour, 88, 1e6. Cacioppo, J. T., & Hawkey, L. C. (2009). Perceived social isolation and cognition. Trends in Cognitive Sciences, 13, 447e454. D'Ettorre, P., & Heinze, J. (2005). Individual recognition in ant queens. Current Biology, 15, 2170e2174. Dani, F. R., Jones, G. R., Destri, S., Spencer, S. H., & Turillazzi, S. (2001). Deciphering the recognition signature within the cuticular chemical profile of paper wasps. Animal Behaviour, 62, 165e171. DesJardins, N., & Tibbetts, E. A. (2018). Sex differences in face but not colour learning in Polistes fuscatus paper wasps. Animal Behaviour, 140, 1e6. Dreier, S., van Zweden, J. S., & D'Ettorre, P. (2007). Long-term memory of individual identity in ant queens. Biology Letters, 3, 459e462. Gamboa, G. J., Reeve, H. K., & Pfennig, D. W. (1986). The evolution and ontogeny of nestmate recognition in social wasps. Annual Review of Entomology, 31, 431e454. Gersick, A. S., Snyder-Mackler, N., & White, D. J. (2012). Ontogeny of social skills: social complexity improves mating and competitive strategies in male brownheaded cowbirds. Animal Behaviour, 83, 1171e1177. Gilbert, C. (1994). Form and function of stemmata in larvae of holometabolous insects. Annual Review of Entomology, 39, 323e349. Giray, T., Giovanetti, M., & West-Eberhard, M. J. (2005). Juvenile hormone, reproduction, and worker behavior in the neotropical social wasp Polistes canadensis. Proceedings of the Royal Society B: Biological Sciences, 102, 3330e3335. Grodzinski, U., & Clayton, N. S. (2010). Problems faced by food-caching corvids and the evolution of cognitive solutions. Philosophical Transactions of the Royal Society B: Biological Sciences, 365, 977e987. Humphreys, K., & Johnson, M. H. (2007). The development of 'face-space' in infancy. Visual Cognition, 15, 578e598. Injaian, A., & Tibbetts, E. A. (2014). Cognition across castes: individual recognition in worker Polistes fuscatus wasps. Animal Behaviour, 87, 91e96. Izzo, A. S., & Tibbetts, E. A. (2012). Spotting the top male: sexually selected signals in male Polistes dominulus wasps. Animal Behaviour, 83, 839e845. Izzo, A., & Tibbetts, E. A. (2015). Heightened condition dependence of a sexually selected signal in male Polistes dominulus paper wasps. Ethology, 121, 586e592. Izzo, A., Wells, M., Huang, Z., & Tibbetts, E. (2010). Cuticular hydrocarbons correlate with fertility, not dominance, in a paper wasp, Polistes dominulus. Behavioral Ecology and Sociobiology, 64, 857e864.
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Sheehan, M. J., & Tibbetts, E. A. (2011). Specialized face learning is associated with individual recognition in paper wasps. Science, 334, 1272e1275. Shorter, J. R., & Tibbetts, E. A. (2009). The effect of juvenile hormone on temporal polyethism in the paper wasp Polistes dominulus. Insectes Sociaux, 56, 7e13. Singer, T. L., & Espelie, K. E. (1992). Social wasps use nest paper hydrocarbins for nestmate recognition. Animal Behaviour, 44, 63e68. Sugita, Y. (2008). Face perception in monkeys reared with no exposure to faces. Proceedings of the Royal Society B: Biological Sciences, 105, 394e398. Taborsky, B., & Oliveira, R. F. (2012). Social competence: An evolutionary approach. Trends in Ecology & Evolution, 27, 679e688. Tibbetts, E. A. (2002). Visual signals of individual identity in the wasp Polistes fuscatus. Proceedings of the Royal Society B: Biological Sciences, 269, 1423e1428. Tibbetts, E. A. (2004). Complex social behaviour can select for variability in visual features: A case study in Polistes wasps. Proceedings of the Royal Society B: Biological Sciences, 271, 1955e1960. Tibbetts, E. A., & Dale, J. (2007). Individual recognition: It is good to be different Trends in. Ecology & Evolution, 22, 529e537. Tibbetts, E. A., Injaian, A., Sheehan, M. J., & Desjardins, N. (2018). Intraspecific variation in learning: Worker wasps are less able to learn and remember individual conspecific faces than queen wasps. American Naturalist, 191(5), 595e603. Tibbetts, E. A., Pandit, S., & Nondorf, D. (2018). Developmental plasticity and the origin of novel communication systems: Individual recognition in Polistes wasps. Evolution, 72(12), 2728e2735. Tibbetts, E. A., & Sheehan, M. J. (2013). Individual recognition and the evolution of learning and memory in Polistes paper wasps. Invertebrate Learning and Memory, 22, 561e571. Toth, M., Halasz, J., Mikics, E., Barsy, B., & Haller, J. (2008). Early social deprivation induces disturbed social communication and violent aggression in adulthood. Behavioral Neuroscience, 122, 849e854. Verzijden, M. N., ten Cate, C., Servedio, M. R., Kozak, G. M., Boughman, J. W., & Svensson, E. I. (2012). The impact of learning on sexual selection and speciation. Trends in Ecology & Evolution, 27, 511e519.
Appendix
0 = Image of neutral stimulus – = Image of negatively reinforced stimulus Clear ceiling 0 Not electrified
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Figure A1. Design of the training and testing apparatus. During initial training, wasps were placed in a small box with six identical stimuli on the walls. In half of the trials, the wasp saw incorrect stimuli and the floor of the box was mildly electrified. In half of the trials, the wasp saw correct stimuli and the floor of the box was not electrified. During testing, wasps were placed in a rectangle with the correct stimuli on one end and incorrect stimuli on the other end. Learning was tested by measuring whether the wasp approached the correct or incorrect stimuli over 10 trials.
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Figure A2. Schematic illustrating the social individual recognition trials. Different coloured boxes indicate different wasps. Wasps were paired with unknown rivals on day 0, 1 and 3. Wasps were re-paired with a known rival on day 2.
Contents lists available at ScienceDirect
Animal Behaviour journal homepage: www.elsevier.com/locate/anbehav
Social isolation prevents the development of individual face recognition in paper wasps Elizabeth A. Tibbetts*, Erica Desjardins, Nora Kou, Laurel Wellman Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, U.S.A.
a r t i c l e i n f o Article history: Received 3 December 2018 Initial acceptance 1 February 2019 Final acceptance 6 March 2019 Available online 17 May 2019 MS. number: A18-00859R Keywords: development expertise face recognition individual recognition learning Polistes
Much work has shown that social isolation has lasting negative effects on adult social interactions, but less is known about precisely how and why isolation alters social behaviour. One way isolation may alter social behaviour is by interfering with the development of effective communication. Here, we test how social isolation influences individual recognition, a key aspect of social communication in Polistes fuscatus paper wasps. Polistes fuscatus reared in a typical social environment learn and remember the unique faces of conspecifics during social interactions. Typical P. fuscatus use individual face recognition to minimize conflict and stabilize social interactions. As wasps are adept face learners, they also readily learn to discriminate between wasp face images during training. Here, we show that social isolation had dramatic effects on recognition. We isolated wasps for 6 days after eclosion from pupation, then tested them for face recognition in social and nonsocial contexts. Isolated wasps did not learn and remember other individuals during social interactions. Furthermore, isolated wasps did not learn to discriminate between wasp face images during training. Therefore, social experience with conspecifics is essential for the development of individual recognition and face learning in paper wasps. Many aspects of wasp behaviour develop rapidly with little experience required. However, complex social interactions like individual recognition require social experience with conspecifics. © 2019 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.
Social isolation has lasting negative effects on many aspects of an animal's phenotype, including altered social interactions, slower growth, impaired learning, shorter life span and reduced immune function (Bailey & Moore, 2018; Cacioppo & Hawkey, 2009; Monaghan, 2008). One of the key behavioural consequences of social isolation is reduced social competence (Taborsky & Oliveira, 2012). That is, socially isolated animals are less able to match their behaviour to the current social environment. For example, socially isolated animals may be inappropriately aggressive across contexts, directing aggression towards competitors, mates or offspring instead of restricting aggression to competitors (Arnold & Taborsky, 2010; Gersick, Snyder-Mackler, & White, 2012; Kempes, Gulickx, van Daalen, Louwerse, & Sterck, 2008; Toth, Halasz, Mikics, Barsy, & Haller, 2008). While there is strong evidence that isolation reduces social competence, less is known about the behavioural mechanisms that link social isolation to reduced social competence. One hypothesis for why socially isolated animals have lower social competence is that they are less effective communicators.
* Correspondence: E. A. Tibbetts, Department of Ecology and Evolution, University of Michigan, 1105 N University Ave, Ann Arbor, MI, 48109, U.S.A. E-mail address: [email protected] (E. A. Tibbetts).
There is growing evidence that isolated individuals are less effective at assessing, discriminating and responding to social signals (Arnold & Taborsky, 2010; Bailey & Moore, 2018; Kempes et al., 2008). For example, female crickets that were socially isolated during development were less choosy about mates compared to females reared with conspecifics (Judge, 2010). Mice reared in isolation use different patterns of ultrasonic vocalizations during maleemale contests than mice with typical social experience (Keesom, Finton, Sell, & Hurley, 2017). However, social experience is not always required for communication; inexperienced signal receivers respond appropriately to many social signals (Maynard Smith & Harper, 2003; Searcy & Nowicki, 2005). For example, in many species, females that have not previously encountered males still assess male quality signals and use the signals to make mate choice decisions (Izzo & Tibbetts, 2012; Jennions & Petrie, 1997). Individual recognition is a type of communication that is essential for social competence in many taxa. During individual recognition, receivers learn and remember the unique phenotype of conspecifics, associate the unique phenotype with individualspecific information about the signaller and recall the information during future encounters (Tibbetts & Dale, 2007). As a result, individual recognition allows receivers to direct aggressive and
https://doi.org/10.1016/j.anbehav.2019.04.009 0003-3472/© 2019 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.
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affiliative interactions appropriately. Individual recognition mediates interactions in contexts such as territoriality, dominance interactions, cooperation, parental care and pair bonding and is found in a wide range of species, from primates to birds to insects (Johnston, 2003; Tibbetts & Dale, 2007). Thus far, little experimental work has tested how social isolation influences receiver capacity for individual recognition. A receiver's ability to learn and remember specific individuals may depend on social experience, as experience often improves performance on complex tasks that involve learning and memory (Cacioppo & Hawkey, 2009). For example, in corvid birds that store and retrieve food, young birds require extensive experience before they develop effective caching behaviour (Grodzinski & Clayton, 2010). Alternatively, receivers may not need experience to learn and remember individual conspecifics. Inexperienced receivers can assess and respond appropriately to some signals (e.g. signals of species identity, sex, strategy; Maynard Smith & Harper, 2003; Searcy & Nowicki, 2005). Polistes fuscatus wasps provide a good system to test how social isolation influences individual recognition because they have variable facial patterns that are used for individual face recognition (Tibbetts, 2002). Wasps excel at learning and remembering other individuals (Sheehan & Tibbetts, 2008). Experimental and comparative analyses indicate that learning the individual identity of conspecifics provides social benefits to nest-founding queens because individual recognition reduces aggression among queens (Sheehan & Tibbetts, 2010; Tibbetts, 2002, 2004). Wasps usually eclose from pupation onto a nest full of other wasps and gain ample social experience as they mature. However, wasps occasionally experience social isolation when they eclose onto nests that were abandoned during their pupal period. Here, we experimentally altered rearing environment to test how social isolation influences face learning and individual recognition in P. fuscatus workers. We test whether experience with P. fuscatus influences a wasp's (1) facility for learning P. fuscatus faces during training and (2) individual recognition during social interactions. We predicted that P. fuscatus reared in social isolation would be less able to learn and remember unique conspecific faces in training and social contexts than wasps reared with conspecifics.
METHODS We collected P. fuscatus individuals and their nests from areas around Ann Arbor, Michigan, U.S.A. After collection, each nest and the associated wasps were housed in individual containers under a natural day/night cycle and fed ad libitum sugar and Galleria mellonella caterpillars. Wasp larvae are stationary and have rudimentary eyes used primarily for light and motion detection (Gilbert, 1994). As a result, wasps are naïve to complex visual stimuli, social hierarchies and individual recognition when they eclose from the pupal case. Nests were checked daily for adults that eclosed from pupation. After eclosion, wasps were painted with individually distinctive marks on their thorax. Marked wasps were either returned to their natal nest or isolated with an orphaned nest (‘alone’ treatment). Wasps remained in their treatment groups for at least 6 days before being trained or used in recognition experiments. Wasps from different treatment groups were similar ages when trained (mean age ± SE: queenright: 10.5 ± 0.73; alone: 11 ± 0.68; mixed linear model comparing age across treatment groups: F1,37 ¼ 0.25, P ¼ 0.62). Polistes are considered behaviourally mature when they are 5 days old because they engage in a range of adult behaviour, including cooperative and competitive interactions with conspecifics, egg laying, flying,
hunting and navigating (Giray, Giovanetti, & West-Eberhard, 2005; Reeve, 1991; Shorter & Tibbetts, 2009).
Face Learning During Training Wasps were trained to differentiate between pairs of P. fuscatus face images using established methods (Appendix, Fig. A1; DesJardins & Tibbetts, 2018; Tibbetts, Pandit, & Nondorf, 2018). Face images used for training were photographs of P. fuscatus from Michigan that showed the face and antenna. Wasps were trained on one of three unique pairs of stimuli (Fig. 1). The particular image that was correct was swapped across trials. All images were printed at life size using a commercially available Sony Picture Station photo printer. During training, wasps were placed in a 2.5 4 0.7 cm wood and Plexiglas box with six identical faces glued to the inside walls. In half the bouts, the wasp was placed in a box with negative stimuli and received a mild electric shock from an electrified pad for 2 min. The electrified pad was made of antistatic conductive foam electrified by two copper wires connected to a Variac transformer. In the other half of the bouts, the wasp was placed in a similarly sized box with neutral faces and the pad was not electrified for 2 min. Between each bout, the wasp was given a 1 min break in a holding container. For example, a wasp trained to discriminate between face A and B would experience the following training. First, the wasp was placed with face A and received a shock for 2 min. The wasp was removed and given a 1 min break. Then, the wasp was placed with face B and did not receive a shock for 2 min. The wasp was removed and given a 1 min break. This process was repeated five times per wasp, so wasps saw faces A and B five times each. After training, the wasp was given a 45 min break in a holding container with food and water. Then, learning was tested by measuring whether the wasp approached the correct or incorrect stimuli over 10 trials. Testing occurred in a 3 10 0.7 cm rectangle. One end of the rectangle had the correct stimuli and the other end of the rectangle had the incorrect stimuli. The entire floor of the rectangle was electrified except the 2.25 cm closest to the correct stimuli, the ‘safety zone’. Most of the rectangle was electrified because shock motivates wasps to move. The correct choice was associated with safety to ensure learned preferences from the initial training were not extinguished during the 10-trial test.
Figure 1. Polistes fuscatus face images used for training. Pairs are shown in the same row. Faces were printed at life size (3 mm width).
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Receiving a shock while choosing a preferred stimuli can rapidly extinguish learned preferences. The centre of the rectangle had two removable, clear partitions that confined the wasp. At the beginning of each trial, the wasp was placed in the centre of the rectangle between the clear partitions, the electric shock was turned on for 5 s, both partitions were removed simultaneously, and the wasp was free to walk through the rectangle. Wasps that learned typically turned towards the correct stimuli while confined in the centre of the rectangle. When the partitions were removed, the wasp quickly walked towards the correct stimuli. A wasp was scored as making a choice when its head and thorax moved beyond the partition placed 2.5 cm from each end of the rectangle. After a wasp made a choice, it was removed from the rectangle and given a 1 min break in a holding container. The placement of the neutral and negative stimuli (right or left side) was determined randomly and changed between trials. This ensured that wasps did not associate a particular direction with correct choices. Social Individual Recognition We assessed the recognition abilities of P. fuscatus raised in isolation by staging contests between pairs of wasps with and without a prior history of social interactions (see Appendix, Fig. A2; following D'Ettorre & Heinze, 2005; Sheehan & Tibbetts, 2008; Tibbetts, Injaian, Sheehan, & Desjardins, 2018). The same method was used to illustrate that P. fuscatus workers are capable of individual recognition in social contexts (Injaian & Tibbetts, 2014). We replicated the methods from Injaian and Tibbetts (2014) as closely as possible to ensure factors unrelated to social experience did not influence experimental outcomes. Wasps were collected from the same locations in Michigan, housed in the same room, fed the same food and eclosed at the same time of year. In addition, the methods used for testing individual recognition were the same. All trials involved P. fuscatus that had been isolated since eclosion. Wasps that eclosed from the same nest were not paired. During the contests, we scored the occurrence and intensity of aggressive interactions as well as displays of nonaggressive behaviour. On the first day (day 0), we placed two unfamiliar P. fuscatus that had been isolated since eclosion in a small container (8 8 cm) and filmed their interactions. After filming, the wasps were housed together until the next day (day 1), at which point they were separated and returned to their initial solitary housing. One day later, the same two wasps were filmed interacting again (day 2). To ensure that changes in aggression between days 0 and 2 were a consequence of recognition rather than a decrease in motivation over time, we paired the wasps with other unknown social partners on the day before and after (days 1 and 3). The first half hour of all interactions was videotaped for later analysis of behaviour. We recorded the first half hour of interactions to be consistent with previous social individual recognition experiments. Wasps engage in the full range of aggressive and affiliative behaviours within 30 min of meeting a rival. We performed 17 sets of trials using 51 individuals from 39 nests. Behaviour in all videos was scored by a research assistant who was blind to experimental predictions. Cooperative and aggressive behaviours were ranked as follows: (0) nonaggressive bodily contact (partners within one body length of each other, but no darts, bites, grapples or mounts occurred); (1) dart (rapid body movement towards partner); (2) dart with open mandibles (rapid body movement towards partner with open mandibles); (3) bite (mandibles closing on body of partner); (4) grapple/mount (wrestling/ bodily contact that forces partner to accept submissive positioning). For each trial, we summed the ranks of cooperative and aggressive behaviours. We then divided the sum by the number of total
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interactions per tape to calculate an aggression index (Dreier, van Zweden, & D'Ettorre, 2007). The aggression index standardized behaviour by taking into account the number and intensity of interactions of each pair, which allowed behaviour to be compared across trials. The aggression index has been used to measure individual recognition in multiple studies (Dreier et al., 2007; Injaian & Tibbetts, 2014; Sheehan & Tibbetts, 2008, 2010). If the wasps are able to recognize and remember social partners, they should be less aggressive and have more nonaggressive contacts when they interact with a known individual (day 2) than when they interact with an individual they encounter for the first time (days 0, 1, 3). Ethical Note No permits were required for the experiments. During social individual recognition trials, wasps used ritualized aggression that does not harm conspecifics. Training involved low-level electrical shock that is aversive to wasps. However, the level of current was kept low to ensure that wasps were not harmed during training. Wasps behaved normally when they were returned to their container after the experiments. Statistical Analysis We measured learning as the total number of correct choices. We tested whether wasps learned by comparing the number of correct choices versus incorrect choices to the 50:50 random expectation with a 2 2 c2 tests. We tested whether P. fuscatus learned faces differently when reared with conspecifics or alone by comparing the number of correct choices in the two developmental environments with a mixed linear model, including nest identity to account for any possible similarity between wasps that eclosed from the same nest. Age of wasps at training was also compared across treatment groups using a mixed linear model with nest identity as a random effect. We trained 39 wasps from 20 nests, including 18 queenright wasps and 21 isolated wasps. In the social individual recognition experiment, aggression index and number of nonaggressive contacts were compared across trials using Friedman's ANOVA nonparametric analysis. The aggression index or the number of nonaggressive contacts was the dependent variable. The independent variable was trial day (day 0, 1, 2 or 3). We performed 17 sets of trials using 51 individuals from 39 nests. RESULTS Face Learning During Training Wasps reared with conspecifics learned to discriminate wasp faces better than wasps reared in isolation (F2,37 ¼ 49.1, P < 0.001; Fig. 2). In fact, P. fuscatus reared in social isolation did not learn to differentiate between pairs of P. fuscatus face images, as they chose the correct image at chance levels (c21 ¼ 0.04, P ¼ 0.84). However, P. fuscatus reared with conspecifics learned to discriminate pairs of faces. They chose the correct image significantly more often than expected by chance (c21 ¼ 21.1, P ¼ 0.001). Social Individual Recognition Polistes fuscatus reared without social contact did not learn and remember unique wasps during social interactions. Wasps were no less aggressive towards known wasps than towards unknown wasps, as aggression index did not differ across days (c23 ¼ 2.8, P ¼ 0.41; Fig. 3a). In addition, wasps had a similar number of
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Figure 2. Mean ± SE correct choices in wasps trained to discriminate pairs of P. fuscatus faces. Wasps were reared in isolation or with conspecifics. *Indicates wasps learned to discriminate face images significantly more accurately than expected by chance. Dotted line shows the 50:50 random expectation. Different lowercase letters above bars reflect significant differences (P < 0.05).
DISCUSSION Social isolation prevents the development of individual recognition in P. fuscatus wasps. Polistes fuscatus workers reared in a normal social environment learn and remember unique conspecifics during social interactions (Injaian & Tibbetts, 2014) and readily learn to discriminate between conspecific faces during training (Fig. 2). However, P. fuscatus wasps raised in social isolation did not individually identify other wasps during social interactions and were unable to learn P. fuscatus face images during training (Figs 2 and 3). We tested the effect of social isolation on behaviour by comparing wasps reared in isolation with those reared in a normal social environment. For face learning, isolated and social wasps were tested simultaneously. For social individual recognition, we compared new data on isolated wasps (Fig. 3) with previously published work on social wasps (Injaian & Tibbetts, 2014). The experimental conditions were replicated across social recognition experiments to ensure that extraneous factors did not influence the results. Wasps were collected from the same locations, housed in the same room, fed the same food and eclosed at the same time of year. In addition, the methods used for testing individual recognition were the same across years. As a result, it is unlikely that factors other than social isolation caused the difference in recognition between social and isolated wasps. Face training data also indicate that social experience is the key factor that caused differences in recognition between isolated and social wasps. Isolated wasps were unable to learn individual faces, while socially experienced wasps learned faces quickly and accurately (Fig. 2). Previous work has shown face training is linked to individual face recognition during social interactions. Wasps that excel at face learning during training are also capable of individual face recognition, whereas wasps that cannot learn faces during training, do not individually recognize conspecifics during social interactions (Sheehan & Tibbetts, 2010, 2011). Therefore, our results indicate that lack of social experience prevents the development of face learning and individual recognition.
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Nonaggressive contacts
nonaggressive contacts with known and unknown wasps (c23 ¼ 3.5, P ¼ 0.32; Fig. 3b). Therefore, wasps that are socially isolated do not learn and remember unique social partners.
Day (b)
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Day Figure 3. Mean ± SE (a) aggression index and (b) nonaggressive contacts per day. On days 0, 1 and 3, focal wasps interacted with individuals that they had not previously encountered. On day 2, wasps interacted with a previously encountered partner. Different lowercase letters above bars reflect significant differences (P < 0.05).
The lack of individual recognition in isolated wasps likely reduces their social competence because individual recognition is a key mediator of social interactions. Wasps use individual recognition to manage shares of reproduction, food and work in cooperative groups. Individual recognition also stabilizes dominance hierarchies and reduces conflict over ranks (Tibbetts, 2002, 2004; Tibbetts & Sheehan, 2013). As a result, conflict increases when wasps are experimentally altered to prevent individual recognition (Sheehan & Tibbetts, 2009; Tibbetts, 2002). Therefore, a lack of individual recognition may be an important behavioural mechanism linking social isolation to reduced social competence. Isolation primarily influences aggression and nonaggressive interactions with known individuals rather than altering behaviour towards both known and unknown individuals. Injaian and Tibbetts (2014) found that socially reared wasps were more aggressive and had fewer nonaggressive interactions with unknown individuals (mean aggression index ¼ 1.22 e 1.75; mean nonaggressive contacts ¼ 1.17 e 1.6) than with known individuals (mean aggression index ¼ 0.37; mean nonaggressive contacts ¼ 2.6). In comparison, in the present study, isolated wasps had similar numbers of aggressive and nonaggressive interactions with unknown individuals (mean aggression
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index ¼ 1.26 e 1.49; mean nonaggressive contacts ¼ 1.64 e 2.8) and known individuals (mean aggression index ¼ 1.34; mean nonaggressive contacts ¼ 2.0; Fig. 3). Notably, there was no behavioural difference between social and isolated wasps when wasps interacted with unknown rivals. Therefore, isolation did not cause a generalized enhancement in aggression or reduction in nonaggressive interactions. Instead, isolation prevented the development of individual recognition. This study adds to a growing body of evidence that social isolation has strong effects on adult behaviour. Across a broad range of taxa and contexts, social isolation changes how animals interact (Bailey & Moore, 2018). Isolated animals can have altered communication, difficulty integrating into social groups, altered dominance interactions and reduced ability to acquire and defend resources from conspecifics (Arnold & Taborsky, 2010; Ballen, Shine, & Olsson, 2014; Gersick et al., 2012; Kempes et al., 2008; Lesne, Cazale-Debat, Portugal, Trabalon, & Jeanson, 2016). These behavioural effects of isolation may also have significant evolutionary consequences (Bailey & Moore, 2018). For example, how and when receivers respond to signals can influence the type and direction of selection acting on signallers (Maynard Smith & Harper, 2003; Searcy & Nowicki, 2005) as well as playing a role in speciation (Verzijden et al., 2012). Therefore, an important goal of future work will be to assess how and when isolation influences communication as well as the fitness effects of altered communication across contests. Although isolation alters individual recognition in wasps, some forms of recognition do not depend on social experience. For example, female wasps do not need experience with males for sex recognition or to assess male quality with sexually selected ornaments. Male paper wasps have variable abdominal spots that females use to assess potential mates (Izzo & Tibbetts, 2012, 2015). Females who lack experience with males readily identify males and use male ornaments to discriminate between high- and low-quality mates. On the other hand, experience is important for nestmate recognition. Paper wasps learn the olfactory signatures of nestmates during a sensitive period immediately after emergence from pupation (Gamboa, Reeve, & Pfennig, 1986). Experienced wasps use odours to discriminate between nestmates and non-nestmates, but naïve wasps accept all individuals as nestmates (Singer & Espelie, 1992). Therefore, the information a signal conveys (e.g. quality, nestmate identity, species identity) may influence whether or not experience is required to accurately assess the signal. Previous experiments testing how experience influences individual recognition have focused on individual face recognition in primates. These studies indicate that experience may not be required for rudimentary individual discrimination, although experience improves recognition. Isolated monkeys reared with no exposure to faces can discriminate between different monkey face images, as isolated monkeys look longer at pictures of unfamiliar faces than at pictures of familiar faces (Sugita, 2008). This contrasts with wasps, where isolated individuals did not discriminate between unique wasps in social or nonsocial contexts (Figs 2 and 3). The wasp and monkey studies used different methods, so they are not directly comparable. Nevertheless, it is notable that isolated monkeys may be more capable of face discrimination than isolated wasps. Although naïve monkeys are capable of some face discrimination, most work on primate face recognition shows that individual face discrimination improves as primates mature and gain experience (Humphreys & Johnson, 2007; Nelson, 2001; Pascalis, de Haan, Nelson, & de Schonen, 1998). This study focused on visual communication because previous work has shown that P. fuscatus rely on visual signals alone for
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individual recognition (Tibbetts & Sheehan, 2013). Altering P. fuscatus facial patterns interferes with individual recognition (Sheehan & Tibbetts, 2009; Tibbetts, 2002; Tibbetts, Injaian, et al., 2018). Furthermore, Polistes species that lack facial pattern variation are not capable of individual recognition (Sheehan & Tibbetts, 2010). Wasps use chemical signals for communication in other contexts. Cuticular hydrocarbons are chemical signals of fertility (Izzo, Wells, Huang, & Tibbetts, 2010; Monnin, 2006) and are also used for nestmate recognition (Dani, Jones, Destri, Spencer, & Turillazzi, 2001; Izzo et al., 2010; Monnin, 2006; Singer & Espelie, 1992). There are opportunities for future work exploring how chemical and visual signals interact to influence behaviour. Overall, social experience is essential for the development of individual recognition in paper wasps. Many aspects of wasp behaviour develop rapidly and require little experience. However, isolation has strong social consequences for paper wasps because isolation prevents the development of individual recognition. Future work across diverse taxa will be useful to identify how signal responses are shaped by isolation as well as the broader evolutionary consequences of experience-dependent plasticity in communication. Acknowledgments This material is based in part upon work supported by the National Science Foundation under grant number IOS-1557564. References Arnold, C., & Taborsky, B. (2010). Social experience in early ontogeny has lasting effects on social skills in cooperatively breeding cichlids. Animal Behaviour, 79, 621e630. Bailey, N. W., & Moore, A. J. (2018). Evolutionary consequences of social isolation. Trends in Ecology & Evolution, 33, 595e607. Ballen, C., Shine, R., & Olsson, M. (2014). Effects of early social isolation on the behaviour and performance of juvenile lizards, Chamaeleo calyptratus. Animal Behaviour, 88, 1e6. Cacioppo, J. T., & Hawkey, L. C. (2009). Perceived social isolation and cognition. Trends in Cognitive Sciences, 13, 447e454. D'Ettorre, P., & Heinze, J. (2005). Individual recognition in ant queens. Current Biology, 15, 2170e2174. Dani, F. R., Jones, G. R., Destri, S., Spencer, S. H., & Turillazzi, S. (2001). Deciphering the recognition signature within the cuticular chemical profile of paper wasps. Animal Behaviour, 62, 165e171. DesJardins, N., & Tibbetts, E. A. (2018). Sex differences in face but not colour learning in Polistes fuscatus paper wasps. Animal Behaviour, 140, 1e6. Dreier, S., van Zweden, J. S., & D'Ettorre, P. (2007). Long-term memory of individual identity in ant queens. Biology Letters, 3, 459e462. Gamboa, G. J., Reeve, H. K., & Pfennig, D. W. (1986). The evolution and ontogeny of nestmate recognition in social wasps. Annual Review of Entomology, 31, 431e454. Gersick, A. S., Snyder-Mackler, N., & White, D. J. (2012). Ontogeny of social skills: social complexity improves mating and competitive strategies in male brownheaded cowbirds. Animal Behaviour, 83, 1171e1177. Gilbert, C. (1994). Form and function of stemmata in larvae of holometabolous insects. Annual Review of Entomology, 39, 323e349. Giray, T., Giovanetti, M., & West-Eberhard, M. J. (2005). Juvenile hormone, reproduction, and worker behavior in the neotropical social wasp Polistes canadensis. Proceedings of the Royal Society B: Biological Sciences, 102, 3330e3335. Grodzinski, U., & Clayton, N. S. (2010). Problems faced by food-caching corvids and the evolution of cognitive solutions. Philosophical Transactions of the Royal Society B: Biological Sciences, 365, 977e987. Humphreys, K., & Johnson, M. H. (2007). The development of 'face-space' in infancy. Visual Cognition, 15, 578e598. Injaian, A., & Tibbetts, E. A. (2014). Cognition across castes: individual recognition in worker Polistes fuscatus wasps. Animal Behaviour, 87, 91e96. Izzo, A. S., & Tibbetts, E. A. (2012). Spotting the top male: sexually selected signals in male Polistes dominulus wasps. Animal Behaviour, 83, 839e845. Izzo, A., & Tibbetts, E. A. (2015). Heightened condition dependence of a sexually selected signal in male Polistes dominulus paper wasps. Ethology, 121, 586e592. Izzo, A., Wells, M., Huang, Z., & Tibbetts, E. (2010). Cuticular hydrocarbons correlate with fertility, not dominance, in a paper wasp, Polistes dominulus. Behavioral Ecology and Sociobiology, 64, 857e864.
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Appendix
0 = Image of neutral stimulus – = Image of negatively reinforced stimulus Clear ceiling 0 Not electrified
Clear ceiling 0
Not electrified Electrified 0
0 0
0 –
0 Clear ceiling – – Electrified
–
– –
–
Sliding doors, each containing an image of the corresponding stimulus
Figure A1. Design of the training and testing apparatus. During initial training, wasps were placed in a small box with six identical stimuli on the walls. In half of the trials, the wasp saw incorrect stimuli and the floor of the box was mildly electrified. In half of the trials, the wasp saw correct stimuli and the floor of the box was not electrified. During testing, wasps were placed in a rectangle with the correct stimuli on one end and incorrect stimuli on the other end. Learning was tested by measuring whether the wasp approached the correct or incorrect stimuli over 10 trials.
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Day 0
Day 1
Day 2
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Day 3
Figure A2. Schematic illustrating the social individual recognition trials. Different coloured boxes indicate different wasps. Wasps were paired with unknown rivals on day 0, 1 and 3. Wasps were re-paired with a known rival on day 2.