Preserving the species

- April 27, 2017

Spinner Dolphins offshore of the island of Hawaii. (SparkyLeigh photo, used under Creative Commons license)
Spinner Dolphins offshore of the island of Hawaii. (SparkyLeigh photo, used under Creative Commons license)

How do dolphins do it?

Yes, we mean “it” — sex.

For the most people, how dolphins copulate probably isn’t a topic that comes to mind often, if ever. Dara Orbach isn’t most people.

“I’m really interested in the mating strategies and behaviours of dolphins, whales and porpoises,” says Dr. Orbach, a Killam postdoctoral fellow in Biology at Dalhousie, working with Hal Whitehead's team.

After the topic piqued her interest at a marine mammal conference in 2009, she’s spent much of the past seven years studying the sexual activity of cetaceans, the class of aquatic mammals that includes species like dolphins.

This past weekend, Dr. Orbach presented her team’s findings at the American Association of Anatomists conference in Chicago. Subsequently her work has been covered by Science Magazine, National Geographic, Discovery Channel, Newsweek, the CBC and more.

Bringing it all together

Dr. Orbach and her co-authors — Patricia Brennan of Mount Holyoke College, Diane Kelly of the University of Massachusetts-Amherst, and veterinary radiologist Mauricio Solano of Tufts University — studied the physical side of dolphin intercourse.

“We wanted to understand how male and female genitalia fit together during copulation,” says Dr. Orbach.

If you think that sounds difficult to do, you’re right. To study cetacean sex, Dr. Orbach has permits that allow her team to receive and study the genitalia of marine mammals that have died of natural causes.

“Female cetaceans have unusual folds in their vaginas of unknown functions,” explains Dr. Orbach. “Male cetaceans and their closest relatives have a fibroelastic penis, which means the erectile tissue is full of collagen and resistant to bending.”

So the team created a silicone mold of the interior of the dolphin’s vagina, as well as a method to inflate the penis, then preserved it to maintain rigidity. They were then able to CT scan the penis inside the vagina to understand exactly how they fit together.

“It is important to study male and female genitalia at the same time because evolution acts on both of them together,” says Dr. Orbach.

Understanding sex, supporting conservation

Dr. Orbach’s research shows that the body positioning of cetaceans may be critical to predicting which copulations lead to fertilization success.  This research has allowed Dr. Orbach’s team to understand the role females may have in controlling paternity: by moving their bodies slightly, the male’s penis could be diverted into a position where the sperm has a longer distance to travel to fertilize the egg.
“There’s been a bias in the study of genital evolution,” says Dr. Orbach, explaining that while there has been a fair bit of research conducted on male genitalia, female reproductive morphology has not been studied to the same degree. “Females are thought to have a more passive role in controlling paternity.”

Dr. Orbach hopes that her team’s research offers insights that could be expanded to other species, and that by better understanding how animals breed, scientists and conservationists alike can help conserve and support populations of endangered species.


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