Thanks to a pressurized penis inflator and genitalia flown in from across the US, an anatomist has answered a long-sought question: How do the genitals of dolphins and porpoises fit together during sex?
In a word, swimming. In a presentation at this year’s Experimental Biology meeting in Chicago, Dalhousie University postdoctoral colleague Dara Orbach showed intimate 3D scans of a variety of marine mammals. She presented scans of two species of dolphins, as well as porpoises and harbor seals, all made with genitalia collected from animals that died of natural causes.
At first glance, the intricacies of dolphin love may seem daring. But Orbach’s work is one of the first in more than a century to reanalyze the female sexual anatomy of marine mammals — in this case, dolphins and porpoises. The finds will also help scientists see how evolution shaped the organs into their current form.
“With basic anatomy, it’s often thought that we scientists have a pretty good idea about mammalian structures and their functions, but this doesn’t always turn out to be true,” said Sarah Mesnick, an ecologist at the Southwest Fisheries Science Center, part of the National Marine Fisheries. Service of the US National Oceanic and Atmospheric Administration (NOAA).
“Orbach experiences anatomy as scientists did in the Age of Discovery, gaining new insights with each dissection,” she added.
There is still a lot to discover in the field of sexual anatomy. Accurate studies of how genitals fit together have usually been limited to small insects, spiders, and lizards (although at least one MRI study has looked at humans). And science has long had a hiatus in the study of female genitalia, fueled by the relative ease of studying penises and a long-held assumption that vaginas don’t vary as much from species to species as penises. (This 99-million-year-old fossil preserves the erection of an extinct arachnid.)
However, a March 2017 study co-authored with Orbach and Mesnick shows that marine mammals’ vaginas have a stunning diversity of inner flaps and folds. For example, the common bottlenose dolphin’s vagina has a single fold; the porpoises, on the other hand, have about thirteen.
“The flaps, folds and blind alleys of the female reproductive tract can serve as a glove that must traverse a man’s sperm, or those of competing male rivals, to reach the egg,” Mesnick said in an email.
“All the evidence to date seems to indicate that sexual selection appears to drive this variation,” Orbach added. “It’s a pretty amazing system to work with.”
But to determine how evolution has shaped these folds, you need to know exactly how penises and vaginas interact. Do dolphin penises invade the cervix during sex? How do the structures on the penis match the folds? And why?
To answer these questions, Orbach went looking for reproductive tracts and asked NOAA’s National Marine Mammal Stranding Network, which responds when carcasses appear on U.S. beaches, for help. She now has about 75 tracts – cut out during carcass dissection – in storage at Mount Holyoke College, where she is a research associate. “It’s like a birthday [when] you open a smelly package,” says Orbach.
Once Orbach has matching genitals, she cleans up the tracts and then measures them exhaustively, collecting 50 types of data for a single vagina. She and her colleagues then make a silicone mold of the inside of the vagina. Separately, they inflate the penis to an erect position using a vessel of pressurized salt water, then store it in a mixture of water, methanol, and the gas formaldehyde.
The team then inserts the erect penis into a matching vagina, sews the two together and stores them in the formaldehyde mixture. Then it’s off to Tufts University’s Cummings School of Veterinary Medicine, where radiologist Mauricio Solano scans them in detail.
Finds with benefits
Orbach says her research may eventually show conservation benefits, especially when collecting sperm for artificial insemination. “Having a biomimetic (artificial but lifelike) vagina can prompt the man to produce higher quality sperm, as opposed to any other device,” she says.
It might be tempting to think that improvements to captive breeding could help Mexico’s vaquita, a harbor porpoise limited to its last 30 individuals because of illegal gillnet fishing. However, there are no vaquitas in captivity, let alone those bred in captivity. Right now, saving the last few members of the species is a much bigger concern: An emergency effort to locate, capture, and house the remaining vaquitas will begin in May, but there’s no guarantee the plan will succeed. .
“Capturing and caring for vaquitas may prove impossible, but unless we try, the species will likely disappear,” the National Marine Mammal Foundation said in a statement about the plan. (Read more about the vaquita.)
In discussing Orbach’s research, she and Mesnick emphasize its more fundamental importance to our understanding of mammalian biology.
“Across the animal kingdom, we can see and hear many aspects of mating, such as the bright colors of making love males — or their songs — and the resulting courtship rituals between the sexes. But in species with internal fertilization, there is an equally fascinating scene that goes further. than our ability to see it,” Mesnick said. “What happens in the female reproductive tract — the ultimate playing field for sexual selection — is just as important in influencing reproductive success.
“Working in this way helps people understand what it means to be a mammal and be a part of this amazing natural diversity,” she added.
Studying this diversity has been a long and difficult process, but as Orbach demonstrates, it is an appropriate – and scientifically satisfying – line of inquiry.
Editor’s Note: This story has been updated to clarify ongoing efforts to preserve the vaquita.