Mating without intromission in a bat.

Copulatory behaviours stand as cornerstones of sexual selection, yet they remain mysterious in many species. Because of their nocturnal and elusive lifestyle, the copulatory behaviours of bats have been mostly overlooked. Several aspects of bat reproduction differ from other mammals (e.g. prolonged sperm storage, delayed development). Here, we show that in serotine bats (Eptesicus serotinus) the penis is used as a 'copulatory arm' rather than an intromittent organ, revealing a novel copulatory behaviour in mammals.