Public versus personal information for mate copying in an invertebrate.

Organisms require information to make decisions about fitness-affecting resources, such as mates. Animals may extract "personal information" about potential mates by observing their physical characteristics or extract additional "public information" by observing their mating performance [1]. Mate copying by females [2-6] is a form of public information use that may reduce uncertainty about male quality, allowing more adaptive choices [2]. Experimental studies have produced evidence that female mate copying occurs in several species of fish [3], birds [5-7], and mammals [8], including humans [9]. We report the first evidence that a female invertebrate can exploit public information to select mates. In a first experiment, Drosophila melanogaster female prospectors increased their time in the attraction zones of poor-condition males, but not of good-condition males, after having observed them with a model female. This suggests that females appraised prospective mates by exploiting public information and did so mainly when it contrasted with personal information. In a second experiment, prospector females preferably mated with males of the color type they had previously observed copulating over males of the rejected color type, suggesting that female Drosophila can generalize socially learned information. The complexity of Drosophila decision-making suggests an unprecedented level of cognition in invertebrates. Our findings have implications for evolution given that socially learned mate preferences may lead to reproductive isolation, setting the stage for speciation [10].