Sculpting delicate nests from chewed-up wood pulp, Polistes fuscatus paper wasps are master architects. But the social insects have another skill that makes them appear even more similar to humans: they are capable of face recognition. In fact, the females that found new colonies learn to recognise their nestmates’ faces faster than they learn to distinguish other visual patterns. ‘Very few animals are known to have the special ability to recognize each other's faces’, says Ali Berens, from the Georgia Institute of Technology, USA, adding that the skill ‘likely evolved to reduce costly competitive interactions among nest-founding queens’. However, other paper wasp species, such as Polistes metricus, are less choosey and never learn to recognise each other visually; they simply learn to recognise patterns. Realising that the difference in the wasps’ facial recognition abilities presented the ideal opportunity to begin dissecting the essential components of wasp face recognition, Berens and her colleagues Elizabeth Tibbetts, from the University of Michigan, and Amy Toth, from Iowa State University, USA, decided to discover which genes are essential for wasp face recognition.
Tibbetts and members of her lab collected females of both species from under the eaves of local buildings as the insects founded new colonies and began constructing nests in spring. Back in the lab, they patiently trained some of the insects to recognise simple black-and-white patterns, while others had to learn to identify P. fuscatus faces from their distinctive coloured markings. Once the wasps had completed their training and their memories were secure, Tibbetts froze them and shipped the insects to Berens and Toth in Iowa, where the duo analysed the wasps’ brain gene expression patterns.
Comparing the gene expression patterns in the brains of the P. fuscatus wasps that had learned to recognise simple shapes with those of P. fuscatus that had learned to recognise faces, the team was impressed to find differences in 257 genes, including genes that are involved in neuron signalling – such as the serotonin receptor and tachykinin. However, when Berens searched the P. metricus gene expression patterns for evidence of the 257 P. fuscatus face recognition genes, none cropped up. ‘This suggests […] that there is something special about face learning – that it is not just hyper-developed visual learning, but a highly specialized learning response’, says Berens.
Having identified the genes that lie at the heart of P. fuscatus’s ability to recognise individuals, Toth is now keen to learn more about how these genes function in facial recognition. ‘We want to experimentally manipulate some of the genes that we uncovered in this study and then see whether we can make wasps forget each other or, conversely, enhance their memories of one another’, says Toth. However, it is less clear how much we will be able to learn from wasps about our own remarkable ability to distinguish between faces. ‘As wasp facial recognition evolved independently from human facial recognition, the same genes will not necessarily underpin this behavioural phenotype. However, it is not out of the realm of possibility that some of the genes might be shared’, Berens concludes.