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Animal Behaviour 78 (2009) 1027–1028

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Animal Behaviour

journal homepage: www.elsevier .com/locate/anbehav

In Focus

Featured Articles in This Month’s Animal Behaviour

Piggy in the Mirror

Miss Piggy was a high-maintenance Muppet. She knew whata mirror was for and she wasn’t afraid to use one. Until now, thequestion of whether Miss Piggy’s real-life brethren can make useof mirrors had not been considered but, in this month’s issue,Donald Broom and colleagues Hilana Sena and Kiera Moynihantake up the challenge (pp. 1037–1041).

The first question to ask, of course, is: why would we want toknow whether pigs can use mirrors? One reason is that it gives ussome insight into their cognitive capacities. The ability to discrimi-nate mirror images, learn that what is in the mirror is on the sameside as the observer (rather than behind the mirror itself) and torecognize the contingency between one’s own movements andthose of the mirror image are all skills that we take for granted,but they are indicative of quite sophisticated learning abilities. Ofcourse, being able to monitor its movements using a mirror doesn’tmean that an animal actually recognizes itself or has any self-aware-ness, and so mirror tests shouldn’t be overinterpreted. They do,however, provide us with a neat means to investigate whether,once they have learned how mirrors work, animals can use themas a source of information about themselves and other objects intheir environment. Studies of brainy, highly sociable animals suchas magpies, elephants, dolphins, monkeys, apes, young human chil-dren and Alex, the famous African grey parrot, have all shown thatthey can use a mirror to retrieve objects or remove marks on theirbody. Given that pigs are also sociable and behaviourally flexible,it is plausible that they could also learn to use a mirror appropriately.

To test whether this was the case, Broom and colleaguesexposed one set of young pigs (4–6 weeks old) to a mirror byplacing it in their home pen and leaving it there for 24 h. Initially,the pigs approached the mirror until their snouts touched it, andsome then looked behind it. Like other animals that have beentested in this way, one pig responded to its mirror image as thoughit were another animal; it broke the mirror suggesting it was tryingto attack its image. Following these initial responses, the pigsmoved around in front of the mirror, orienting towards it and look-ing at themselves from different angles. These kinds of movementssuggest that the pigs were correlating the movements of their bodywith the visual stimulus they were receiving from the mirror, andso learning the contingency between the two. The pigs spent about20 min inspecting themselves and then they gradually began tolose interest.

Once the pigs were mirror experienced, they were given the taskof finding food using a mirror. Their performance was comparedwith that of another set of naı̈ve pigs that had never seen a mirror.

0003-3472/$38.00 � 2009 The Association for the Study of Animal Behaviour. Publishedoi:10.1016/j.anbehav.2009.09.020

The mirror-experienced pigs were placed into a new test areawhere they were exposed to a mirror for 5 h. Following this, theywere released into a test room with a food bowl that could onlybe seen via a mirror (a fan was positioned over the food so thatthe odour was dispersed throughout the room preventing thepigs from using smell as a cue). Seven of the eight mirror-experi-enced pigs looked into the mirror, turned away from it, movedaround the end of the barrier and went directly to the food, takingan average of around 25 s after their initial release. In contrast,the mirror-naı̈ve pigs moved towards the reflection of the foodbowl in the mirror and then moved behind it, so failing to findthe food bowl.

These results suggest not only that pigs learn the contingencybetween their own movements and their image in the mirror, butthat their knowledge incorporates the layout of the environmentas well, so that they can locate objects in space. Broom andcolleagues suggest that a mirror could therefore be used as a cheapand useful enrichment device increasing pigs’ welfare by present-ing them with a more challenging route to finding food. Just asimportantly, they also suggest that these findings may, on theirown, lead to better treatment for pigs; the pigs’ ability to makeuse of the mirrors suggests that their awareness of the environmentmay be more sophisticated than suspected previously.

Louise BarrettExecutive Editor

Are All Workers Equal?

Workers in social insect colonies lose their ability to reproducedirectly by laying eggs, but in primitively eusocial colonies, workersmay be ‘totipotent’, meaning that they retain the ability to performas queens. The intriguing hypothesis of worker totipotency ina primitively eusocial bee, Megalopta genalis, is tested by AdamSmith and his colleagues Karen Kapheim, Sean O’Donnell and BillWcislo in this issue (pp. 1043–1050).

Species such as M. genalis (Fig. 1) stand at the evolutionary cuspbetween solitary life and eusociality. In primitively eusocial beesand wasps, workers have the same general appearance as queens.In fact, it is possible that all colony members are totipotent,meaning that all females are equipped to be either a queen ora worker. This contrasts with highly eusocial species, such as thehoneybee, in which worker morphology precludes workers takingon the role of the queen, and vice versa.

A major factor that could affect totipotency is worker size. Inmany primitively eusocial species, workers are smaller than thequeen, and this has led some investigators to postulate that small

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Figure 1. A female Megalopta genalis in a nest within a stick. The side of the stick hasbeen broken away to reveal the hollowed-out core that serves as the nesting cavity.Photo: Adam Smith.

In Focus / Animal Behaviour 78 (2009) 1027–10281028

workers are reproductively limited. If a bee’s own potential forreproduction is low, then the relative benefits of becoming a workerare much higher.

Even though the hypothesis of totipotency of workers in primi-tively eusocial bees and wasps has been around for years, tests havebeen rare and inconclusive. The obvious routes to testing whetherworkers retain reproductive abilities are removal of queens ortaking workers and establishing them in their own nests. Eitherapproach gives a worker the opportunity to express queen-likereproductive capacities, but usually the practical barriers tocarrying out the tests have been insurmountable.

Because it is facultatively eusocial, M. genalis is a particularlyinteresting subject for consideration of totipotency and the overallquestion of the divide between solitary and eusocial life. This beespecies makes small nests in rotting branches and vines, and isoften solitary (perhaps a third to a half of the nests); solitary orsocial behaviour are true alternatives, and not different points ona developmental trajectory. Eusocial nests contain a queen andfrom one to a few workers. (This genus gets its name from thebees’ large eyes; flight activity is crepuscular or nocturnal, makingMegalopta unusual among bees).

Smith and his colleagues, working at the Smithsonian TropicalResearch Institute on Barro Colorado Island in the Republic ofPanama, performed both manipulations with colonies of M. genalis,removing the queen from a number of colonies and establishingnewly emerged females alone in other nests. They also collectedbees from solitary nests and eusocial colonies in the field forcomparison with the manipulated bees.

The study revealed two key findings. First, removal of the queendisinhibited workers from developing eggs in their ovaries andbecoming queenlike in their behaviour. This suggests that queen–worker dominance is an important element of social behaviour inthis species. Second, when the bees were given a nest of their

own they showed equal reproductive capacity, regardless of theirbody size.

Smith and his colleagues establish that M. genalis females are,indeed, totipotent. Queens may limit food given to their daughters;this could have the effect of making them easier to dominatephysically, but smaller daughters still have the potential to repro-duce on their own. Knowing that workers are totipotent allowsus to portray more accurately the evolutionary trade-offs betweensolitary and eusocial life.

Michael BreedExecutive Editor