We get a lot of information from watching other people. We read reviews, we follow links to recommended websites and we listen when our friends vouch for strangers. The opinions of strangers may even be a better guide to the things that make us happy than our own predictions. But humans aren’t the only species to make decisions based on information gleaned from our peers – even animals as supposedly simple as flies can do the same.
Frederic Mery from LEGS (the Laboratory of Evolution, Genomes and Speciation) studied the fly Drosophila melanogaster and found that females have a tendency to follow the crowd. They are more attracted to male flies if other females crowd around him.
Following the crowd makes evolutionary sense; faced with uncertainty over the best males to mate with, females could do worse than to look at who their peers find sexiest. Female fish, birds, rats and possibly even humans are influenced in this way, but this is the first time that anyone has found the same behaviour among invertebrates.
Mery created two lines of male flies – a high-quality lineage raised on a nutritious diet, and a poor-quality one that grew up on much less food. Female flies were placed in a box along with one male from either group, each housed in his own transparent container. The female couldn’t touch the males, but she could see, smell and hear him. Based on that information alone, she could tell the studs from the weaklings and spent twice as much time buzzing over the high-quality male.