A couple of months ago, I helped out in Patricia Brennan’s lab when she made casts of dolphin vaginas. You heard me correctly. Dolphin vaginas.


Brennan is well-known among biologists for her work on sexual conflict in ducks, and on the internet for her high-speed videos of duck erection. I’ve known Brennan for years – the world of biologists who study the evolution of penises is pretty damn small. Seeking Brennan’s expertise in examining complex, three dimensional models of vaginas, Texas A&M graduate student Dara Orbach traveled all the way to Massachusetts with a crate of frozen dolphin parts. I tagged along to help with the messy, messy work that followed.

Orbach is trying to figure out how female dolphins control which males father their babies.


Like humans, females in many dolphin species mate all year round. But the ocean is big, which means it’s not easy for males to find females while they’re in the fertile part of their cycle. So when they find one, males tend to pile on in groups. When it comes to having sex, male dolphins are kind of assholes.

Dolphins use a number of different gang bang strategies to get a chance at fatherhood. Among bottlenose dolphins, two or three males may form an alliance to ride herd on a female for a few weeks, keeping her close, and away from any other potential mates. Dusky dolphins have a more free-for-all style: four or five males chase after a fertile female, each one trying to get close enough to jam his penis into her vagina during a 5-second schtup-and-run – it’s pure competition, both for the number of times a male gets close enough to copulate and the amount of sperm he can leave inside a female each time.

Male dolphins in waters around Mauritius compete to mate. Video by David Stone

Female dolphins can try to avoid the pile-ons. They can try to outswim males; they can slap them in the head with their tails; or they can roll onto their backs at the surface of the water, putting their ladybits in the air and out of reach. But it’s a limited menu for choosing who will be the father of the next baby dolphin. Orbach is trying to figure out whether female dolphins, like female ducks, can also exercise a preference for a particular male during sex.




Female ducks manage that feat with a twisted, complex vaginal canal that can shunt unwanted male attention–and sperm–into blind alleys far from their eggs. And biologists already knew that dolphin vaginas, when opened up in dissection, contained a series of muscular flaps and ridges. What we didn’t know was how those flaps and ridges were arranged in three dimensions.

There was really only one way to find out. And it involved a lot of silicone, along with several dolphin vaginas.


Genital tract of female Greenland whale. Alexander Meek, 1918

We started by setting up frames to hang the vaginal tracts inside once they were filled, weighed down with anything remotely heavy we could find in the lab space. (That’s why you’ll see a big wrench in the film above.)


We popped a cylinder of silicone and curing agent into a caulking gun, and squeezed the goo into the open end of each vagina. Casting was a two-person operation: one pushed the silicone mix out of the gun while the other massaged the outer walls of the vagina and got the casting material into all its cavities and folds. Once the vagina was completely full, we pushed a wooden popsicle stick through the center of the silicon to provide support to the mold when we pulled it out again, and left it hanging in the frame to cure.

After about 40 minutes, the silicone set. Now came the biggest challenge: removing the cast from the vagina without damaging the tissue. We couldn’t just cut it free: dolphin tissue is hard to get hold of, and Orbach needed to save what she had for other parts of her study. We squeezed, and pulled, and peeled, and squeezed, and gently rotated the tissue until the cast came free.




We were amazed at the results. What look like semi-random muscular flaps in a cut and flattened vagina are actually the framework surrounding a beautiful spiral space. This is not your standard mammalian tube.


What do the spirals mean for dolphin sex? Will they let female dolphins control where a penis goes, the way a duck vagina does? We won’t know until Orbach does her analysis. We’ll be watching her research to find out more.

[Whitehead and Mann 2002 | Silva et al. 2005 | Muller and Wrangham 2009 | Orbach et al. 2014 | Orbach et al. 2015]




Images: Greenland whale from Meek 1918; dolphin vagina cast from Diane Kelly

Top video: Patricia Brennan, research associate Teri Orr, and Dara Orbach prep casts of dolphin vaginas. As one does. Video: D. Kelly, Chris Person. Video of dolphins mating by David Stone from Vimeo


Contact the author at diane@io9.com .