Study: The serotine bat uses its super-large penis as an arm when mating

Little is known about their mating habits serotine bat (Eptesicus serotinus) However, males of this species boast unusually large penises, much larger than the females’ vaginas. The purpose of such a huge organ has long puzzled scientists. but, recent papers A paper published in the journal Current Biology reveals that males of this species of bat use their tail sheaths as arms to push females away, rather than thrusting their massive bodies into them during mating. This increases the probability of successful insemination.

The Eurasian serotine bat can be identified by its long smoky-brown fur (light tan underbelly), large triangular ears, and unique flight pattern of flapping its wings with short glides in between. They usually roost in old buildings like churches with high gables and hollow walls, or in abandoned mines. Male bats are mostly solitary until the fall breeding season when they search for females. Females form maternal colonies in Europe around late May and remain there throughout the breeding season, usually giving birth to a single cub (cub) in late summer.

Female bats have an unusually long cervix, which is suitable for storing sperm. The male’s penis is 7 times longer than the female’s vagina, and the head is heart-shaped and 7 times wider than the female’s vaginal opening. “By chance, we observed that these bats have disproportionately long penises, and we always wondered, ‘How does that work?'” Co-author Nicholas Fassel said: of the University of Lausanne. “We thought maybe it’s the same way in dogs, where their penises become engorged and locked together after penetration, or maybe they just couldn’t get their penises inside. However, such type of mating has not been previously reported in mammals.”

To find out, Fasel et al. pored over nearly 100 videos depicting serotinous bats. red-handed. Four of these videos are from a bat rehabilitation center in Ukraine, while the rest were filmed mating in the attic of a Dutch church by an intrepid citizen scientist. Bats usually mated for less than 53 minutes on average, but one bat lasted a whopping 12.7 hours. The earliest mating event occurred in September, and the frequency peaked in October, while the earliest mating event occurred in March or April. The authors take this as evidence that both males and females can store sperm in their bodies for months.

The act itself typically begins with the male bat grabbing onto the female and biting the skin on the nape of her neck, followed by a combination of hindlimb movements and “quick probing movements for a fully erect penis.” During this early mating stage, the female made frequent social calls, but the calls stopped once the male bat successfully pressed his penis against her vulva, and she only moved intermittently thereafter. Male bats have never inserted (inserted) their penises into their vaginas, and even if they did, the head of a fully erect penis would be too large to fit through the opening anyway. did.

The authors observed that the female’s abdomen had a wet appearance after mating, suggesting the presence of semen (i.e., the male ejaculated into the female’s abdomen). Although this has been observed previously in small brown bats and nocturnal bats, Fasel et al. did not collect vaginal swabs to test for the presence of sperm, so this observation is inconclusive.

So why did serotinous bats evolve such huge reproductive organs? The authors suggest that females use their caudal membranes to avoid mating, and that males use their long, thick penises to push them away. suggests that it is possible. “The hollow structures observed on the dorsal side of the erect penis may function as suckers and support the maintenance of copulatory contact,” the authors write. “Therefore, penis size, shape, and prolonged hugging may further support sperm cell transport within the vagina and through the long cervix.”

The next step is to conduct further studies on normal penis morphology, capture the mating behavior of serotinous bats in more natural situations, and compare it with that of other bat species. “We’re trying to develop an aquarium-like ‘butt porn box’ with cameras everywhere.” Fasel said.

DOI: Current Biology, 2023. 10.1016/j.cub.2023.09.054 (About DOI).