The Mechanics of Dolphin Sex: All the Dirty Details You Need to Know

Perhaps the hardest thing about studying the reproductive anatomy of marine mammals using organs collected from deceased animals is that they can’t get an erection the easy way.

Re-inflating human penises postmortem is a relatively trivial feat, says Diane Kelly, a research assistant professor at the University of Massachusetts and an expert on penile inflation. Like most mammals, human penises tend to be fleshy, with plenty of vascular space for blood to flow in to stiffen the flaccid structure with turgor pressure. But whale and dolphin penises are a lot harder — quite literally.

“It’s actually a real challenge to artificially inflate cetacean penises,” she told me. Yes, the size makes it difficult – it takes a lot more saline to fill a large penis than a small one – but it’s more than that. “They have what is called a ‘fibroelastic’ penis,” she explained, meaning their penile tissue”a lot collagen, and it makes the penis, even when flaccid, very stiff and less stretchy.”

Finding a way around this difficult problem is a big part of why Dara Orbach and Patricia Brennan brought Kelly onto the project. The goal: To create the first 3D-CT scans of simulated intercourse of all species of marine mammals using real, postmortem genitalia – scans that were just like published in a paper in Proceedings of the Royal Society B.

Orbach, a postdoctoral researcher at Dalhousie University and research associate at Mount Holyoke College, had the vaginas ready. She already knew that marine mammal vaginas are much more complex than anyone else. lots of labyrinthine pockets, folds and twists, which Orbach suspects may help women control fatherhood. “But as I started dissecting more and more reproductive organs and looked at this amazing level of vaginal variability that had never been documented before, I realized that this probably somehow evolved along with the penis,” Orbach said. That meant to understand the animals’ vaginas, she needed their corresponding penises to see how they fit together during intercourse.

Orbach turned to Brennan, a genital expert at Mount Holyoke College known for her work on ducks (and their terrifying penises), and together, with a caulking gun and silicone, created models called ‘endocasts’ of vaginas from Orbach’s collection of 140 frozen marine mammal genitalia (all collected from animals that died of natural causes). Then they turned to Kelly for her penile inflation expertise.

“Most of what I’ve done is very small — armadillos, rats and mice, voles and other little things — where you just need a little syringe and a little bit of pressure and you get your erect morphology very quickly,” Kelly explained. . Cetacean dongs were “another thing altogether.”

“We’re not talking about the size of a hand — we’re talking about the size of an arm, depending on the species,” Orbach added (“We made a killer whale, which was bigger than the table”). So blowing up the members of marine mammals required creativity. After some preliminary struggles (for example, learning the hard way that plastic carboys are not pressurized), Kelly’s final design was a $35 used beer keg filled with saline and modified to allow her to pump in nitrogen gas. to achieve optimal injection pressure. “That did the trick,” she said.

Blue and green vaginal endocasts of marine mammals and their corresponding artificially inflated penises (aligned to show the penetrating parts). (Credit: modified from Figure 1 of Orbach et al. 2017)

Once pumped full of fluid, the penises were tied off and soaked in formalin to ensure they would hold their swollen shape. Then it was time to let the magic happen. “By looking at the shape of the vaginal endocasts and the penile shape, we were able to figure out which we thought would be the best possible copulation,” Orbach explained. “We then put the inflated penises in the vagina, stitched them together, dipped them in iodine so they would be stained quite well, and then did CT scans of them to see how they fit together.”

The results – thanks to radiologist Mauricio Solano – are simply dazzling.

A CT scan of an artificially inflated rocker penis (red) in a dolphin vagina. (Credit: Figure 2 from Orbach et al. 2017)

In all, they were able to simulate sexual intercourse for four species of marine mammals: harbor porpoises (phocoena phocoena), bottlenose dolphins (Tursiops truncatus), short-beaked common dolphins (Delphinus delphis), and harbor seals (Phoca vitulina) — those were the only species for which they had high-quality male and female reproductive organs (unfortunately, they didn’t have an intact killer whale vagina to mate with the larger-than-table-sized penis). They were also able to create digital 3D models of the penises and vaginas and simulate different rotations and positions to determine the deepest penetration possible.

The differences in reproductive anatomy between the species were impressive. Porpoises, despite being the smallest species in terms of body size, had the largest penises. “An erect porpoise penis goes up to its chin — or, where its chin would be, if it weren’t for a marine mammal,” Kelly said. And their vaginas are the most complex of the four, with “a whole series of spiral folds,” Orbach explained, “that just keep spinning… kind of like a corkscrew.”

But what was really fascinating was that the scans revealed how vaginal complexity could limit penile penetration. “This confirmed that there is an antagonistic coevolution,” Orbach said. That suggests the folds allow the animals to control paternity, although further analyzes will be needed to confirm that hypothesis.

When it comes down to it, we know very little about mating marine mammals, especially cetaceans. We’ve seen bottlenose dolphins recover in captivity and in the wild, but there’s no way to easily visualize what’s happening internally during copulation. We can’t just flash freeze cheating dolphins to find out where everything is during intercourse like scientists have done with small lizards.

Even courtship and mating behavior are only superficially understood. Matings have never been observed in most marine mammal species because they occur underwater and in remote locations. For the species we have seen, such as bottlenose dolphins, there are still many unanswered questions. In some places, male bottlenose dolphins form coalitions to isolate females and force mating – sometimes abducting the females for weeks – but it is not known if this is common in all pods around the world, let alone if similar behavior is common in other species. If aggressive mating systems are commonplace, it would make sense that such sexual conflicts would be reflected in the animals’ genital morphologies.

I don’t want to know why they’re grinning like that. (Credit: Hamid Elbaz)

And that seems to be what Orbach, Brennan and Kelly found, based on their copulation reconstruction data. “If the female doesn’t want to mate with a male, she may be able to subtly shift her body slightly to the left or right so that the penis isn’t at an optimal angle, meaning it gets stuck in one of these vaginal folds sooner.” “So when the sperm is ejaculated, it would have to travel a longer distance to fertilize the egg,” Orbach explained. “So subtle body positioning allows the female to determine which males are more or less likely to fertilize.”

The trio hope to look at more species, including several ungulates — distant cousins ​​of whales and dolphins. “I had the chance to dissect a hippopotamus penis a while ago, and it was amazing how much it looked like a pygmy sperm whale,” Orbach said. “I’m very curious about how the different environments have influenced penile morphology, and how much is related to a shared history, because in most animals we know that genitalia is one of the fastest evolving features.”

They are also considering using the endocasts to create biomimetic vaginas — essentially fleshlights for dolphins and other marine species — to hopefully improve artificial insemination procedures. Captive breeding facilities can help drive declining numbers of endangered or threatened species, and artificial insemination is sometimes necessary to ensure animals reproduce safely and in a way that enhances genetic diversity. “Something that would mimic a real vagina, in terms of having certain structures that would touch the penis or feel more natural, might just produce a better quality ejaculate.”

One thing is certain: the team is far from done working with large mammalian reproductive organs. “This is the first step in what will hopefully be quite a long research program,” Kelly said, smiling.

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