Unprecedented Study Uncovers Mammal's Unique Reproductive Behavior
New study shows that the serotine bat challenges traditional mating norms with its unique mating behavior, potentially being the first mammal to mate without penetration Intriguing discoveries about mismatched genitalia raise questions about alternative reproductive strategies
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Bats have long been the odd ones out among mammals.
The only creatures in this branch of the animal kingdom capable of powered flight, researchers have found that the serotine bat may be the first mammal known to mate without using penetration. Also known as Eptesicus serotinus, serotine bats mate by touching their genitals together, with the male bat using its penis more like an arm to move a protective membrane away from the female bat's vulva, according to a study published Monday in the journal Current Biology.
Bats possess remarkable reproductive biology that has proven challenging to research due to the nocturnal and elusive behavior of many bat species, according to study coauthor Nicolas Fasel, a bat expert at the University of Lausanne in Switzerland.
"Most of the time, you'll only see their backs against the wall, and what's really happening in front remains unseen," he explained.
A Daubenton's bat (Myotis daubentonii) in flight and hunting at night.
Johan De Meester/Universal Images Group/Getty Images
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But thanks to the dedication of a Dutch bat enthusiast who installed 18 video cameras in a church in the Netherlands containing a roosting colony of serotine bats, Fasel and his team were able to study 93 mating events in depth. Additional footage of four mating events of the same species was provided by partners at a bat rescue and rehabilitation center in Ukraine.
"We were able to observe copulation and confirm that the penis was not entering," Fasel remarked.
The video footage revealed that 50% of the recorded mating sessions lasted under 53 minutes, with one instance showing a pair of bats mating for over 12 hours. This behavior resembles a "cloacal kiss," a mating method common in various bird species. Fasel and his team's observations from the videos could potentially provide a solution to a longstanding mystery regarding the reproductive biology of this particular bat species and others in the same family.
The information on bat mating behavior could help with efforts to come up with a way to artificially inseminate endangered bat species.
Olivier Glaizot
Mismatched genitalia
The male bat's penis is seven times longer than the female's vagina, with a heart-shaped head seven times wider than the vaginal opening. This makes penetrative sex appear difficult, if not impossible, as noted by Fasel.
Teri Orr, an assistant professor at New Mexico State University specializing in bat reproductive systems, expressed astonishment at the idea of males using their genitalia as a "copulatory arm" and potentially transferring sperm like birds. Orr was not part of the study.
Orr pointed out that bats use their uropatagia (tail membranes) in various unique ways, such as acting as fishing nets and catching pups during birth. This makes them useful in many ways, but it could also be an impediment during mating, Orr said.
Spotted hyenas (Crocuta crocuta), also known as the laughing hyenaMaasai Mara National Reserve,Kenya.
Edwin Remsberg/VW Pics/Universal Images Group Editorial/Getty Images
The handling of female animals in zoology has been fundamentally flawed. "While it's true that the male of this species may use his genitalia to navigate the female's tail, there are crucial aspects that need to be addressed," she wrote in an email. "Specifically, how is the sperm transferred and what role does the female play in this process?"
Was the behavior of the serotine bat as reported in the paper truly "bizarre and unique," as stated by Alan Dixson, a biology professor at the Victoria University of Wellington in New Zealand and author of the 2021 book "Mammalian Sexuality: The Act of Mating and the Evolution of Reproduction"? According to Dixson, the researchers failed to provide adequate evidence to support their extraordinary claim, indicating that it may not be accurate.
Susanne Holtze, a senior scientist at the Leibniz Institute for Zoo and Wildlife Research in Berlin and coauthor of the study, admitted that they had not been able to conclusively demonstrate the transfer of sperm from male to female bats. She stated that this would be a major area of focus for future research, explaining, "The process of how their semen enters the female reproductive tract is still a bit of a mystery. It's possible that suction could be involved, but the exact mechanism is not fully understood."
Specializing in assisted animal reproduction, Holtze stated that the findings from the study will aid in her efforts to develop a method for artificially inseminating bats. She also noted that with over 1,000 bat species, many of which are endangered, there is currently no effective assisted reproduction strategy in place.
The study will help to inform the work of Orr's laboratory at New Mexico State University on bat reproduction, and whether their unique reproductive behavior has any relevance for understanding human infertility. "During reproduction, bats engage in various extreme behaviors, such as storing sperm and extending the duration of pregnancy," she explained.
Few bat biologists focus on the hidden behaviors of bats, with most concentrating on the more apparent and intriguing aspects of bat biology like flight and echolocation, according to Orr.
