Food, culture and sociality in Drosophila

with naïve " observers " with two fresh, flavored media (without quinine). In the critical test phase, demonstrators and observers were exposed separately to the two flavored media. Social transmission occurred if the oviposition choices of observers mirrored that of demonstrators. Using this methodology, Battesti et al. (2012) first showed that observer flies relied heavily on social information and acquired oviposition preferences from demonstrators , even if they had the opportunity to sample the two equally suitable media during the transmission phase, thus confirming previous observations in this species (Sarin and Dukas, 2009). The authors next investigated the mechanisms of social transmission and showed that social learning did not occur when observers were exposed to social cues only (freshly laid eggs and aggregation phero-mone) on one of the two media. Social transmission, however, always occurred when observers interacted directly with demonstrators, even if the media were unflavored. Although the precise mechanism of social learning remains an open A commentary on Spread of social information and dynamics of social transmission within Drosophila groups by Battesti Communication with and learning from others are key features of social life. We humans rely extensively on the advice of others before making important decisions. Social insects too, such as bees and ants, use social information to learn about foraging opportunities and engage in collective tasks (Dussutour and Simpson, 2009; Seeley et al., 2012). Growing interest into the learning abilities of small-brained animals has revealed that social learning in insects is more diverse and more common than previously thought (Leadbeater and Chittka, 2007), thus offering new opportunities for comparative analyses of the role of cognition in the regulation of social behavior across a rich spectrum of social forms. Recently, the fruit fly Drosophila melanogaster (Figure 1A) has emerged as a key species for studying social learning in simple insect groups (Mery et al., 2009; Sarin and Dukas, 2009). Flies aggregate on food resources, where they feed, reproduce, lay eggs, and glean information from each other. Writing in a recent issue of Current Biology, Battesti et al. (2012) present evidence that Drosophila females not only use social information to select oviposition sub-strates, but also that these socially acquired preferences can propagate and stabilize within groups, a phenomenon resembling cultural transmission of knowledge in vertebrates (Laland, 2008). The authors used a three-step experimental paradigm (Figure 1B). A group of flies was first trained to associate an aversive gustatory cue (quinine) with an artificial flavor (banana or strawberry) characterizing one of two standard ovipo-sition media (agar and sugar). These conditioned " demonstrators " were then caged question, presumably, it can be explained by relatively simple associative learning processes occurring during physical contacts between observer and demonstrator flies through the perception of the olfactory cues (banana or strawberry flavors) carried by the demonstrators. Such mechanism, for instance, underpins social transmission of food preferences in rats (Galef et al., 1985). In a third set of experiments, Battesti et al. (2012) have gone a step further into the understanding of how flies balance their use of social and personal information. By exposing observers to the two flavored media at the different phases of the experimental paradigm they demonstrated that the socially acquired preference vanished if observers were allowed to acquire personal information after the transmission phase. Considering the short lifespan of Drosophila (Lee et al., 2008), rapidly adopting the behavior of the majority may provide naïve flies with cues to choices that are locally adaptive and prevent costly trial and error. However, if information about resources is abundant and not costly to

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