Crayfish females eavesdrop on fighting males and use smell and sight to recognize the identity of the winner.

Females of many animal species select dominant males as mates but their ability to detect the male’s hierarchical status remains poorly understood. Previously, we found that females of the crayfish Procambarus clarkii eavesdrop on two fighting males before choosing the winner. Here, we asked whether eavesdropping females use vision together with smell to do so and whether their preference for the winner relies on a form of individual, rather than on status, recognition. When tested in a two-way choice paradigm, a bystander female visited the dominant first rather than the subordinate male, remained in his proximity for longer, and interacted with him more frequently. However, this happened only when she was offered the same individuals she had previously watched and smelled. This suggests that females recognize the winners as individuals and not as generic dominants, thus revealing unusual discrimination abilities in an invertebrate.