This Is Not the Dolphin Kick You Learned as a Kid

The powerful muscles running across a dolphin’s back and tail stalk (called the “peduncle”) that helps it move its flukes up and down in order to propel itself are the inspiration behind what we know as the “dolphin kick,” a swimming style that simulates the dolphin’s whole-body propulsion. “In the best [human] swimmers, this [body] wave moves at about nine feet every second, about half the speed an actual dolphin performs the same motion,” writes Corey Binns at Popsci, noting that 22-Olympic medal winner Michael Phelps can ripple two waves down his entire frame at a time.

Indeed, this way of moving through water is so powerful that the governing body of swimming — Fédération Internationale de Natation (FINA) — restricted its use to the first 15 meters after the start of a race, or following a turn. Well, here’s something you didn’t learn at swim practice that FINA would probably be quick to restrict: spontaneous ejaculation.

Last month, a team of researchers detailed peduncle motion during spontaneous of ejaculation in dolphins — oh, yes, dolphins have been found to ejaculate without apparent sexual stimulation!

Researchers saw dolphins move the peduncle flukes upward, then downward before releasing a cloud of seminal fluid.

“Spontaneous ejaculation lasted 0.43 s (13 frames at (1/30 s)/frame) with the contraction of the peduncle muscle downward and dense seminal fluid being ejaculated from the tip of the penis (Figure 1A and Video S1),” researchers write in Spontaneous Ejaculation in a Wild Indo-Pacific Bottlenose Dolphin, which appeared in PLOS One. “The dolphin stretched his peduncle muscle upward and a few seconds later the remaining seminal fluid was ejaculated, lasting 0.73 s (22 frames at (1/30 s)/frame) (Figure 1B and Video S1).”

This is not the dolphin kick you learned as a kid.

Scicurious at Scientopia, covered the paper in her Weird Science column (and if you don’t follow her or read her blog, you need to do it. She has no qualms about covering sex-related papers in an open, humorous and very accessible way), writes:

Now I’m sure you must be wondering: why does this happen? It actually has to do with how ejaculation is controlled in the male mammal. This hasn’t been tested, but the hypothesis is that if the dolphin is “wired” like some mammals such as rats (and there’s no reason to believe he’s not, in this case), ejaculation is controlled at the spinal level, rather than in the brain, and controlled by the release of various chemicals. During sleepiness (which you can often detect in a dolphin due to one eye being closed, as in this case), this system would be relaxed, and spontaneous ejaculation would be more likely.

Post image from PLOS One, by Morisaka T, et al.