Swingin' and clingin': The wild sex lives of barnacles

On the left: A stalked barnacle with a relaxed penis (marked with arrow); On the right: Erect barnacles releasing sperm into water. (Marjan Barazandeh et al, Proceedings of the Royal Society B)

Barnacles have the largest penises, relative to body size, in the animal kingdom, and now some are going into the record books for yet another feat: They can capture sperm directly from water.

The unique “shoot and catch” system marks a first for crustaceans, which were previously all thought to copulate in some fashion. Now we know that process is less intimate, at least for barnacles — most of which are hermaphrodites, possessing both male and female sexual organs.

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Who knew that barnacles, which many of us probably see when scraping them off of boat bottoms, had such interesting “love” lives?

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Marjan Barazandeh of the University of Alberta and colleagues made the determination after collecting common northeast Pacific, intertidal gooseneck barnacles, Pollicipes polymerus.

Using observational and chemical analysis, the scientists “confirmed that a high percentage of eggs were fertilized with sperm captured from the water. Sperm capture occurred in 100 percent of isolated individuals and, remarkably, even in 24 percent of individuals that had an adjacent partner.”

Barnacle sex then involves some individuals shooting sperm from their penises, while others capture that sperm for egg fertilization. For humans, it would sort of be like trying to get pregnant by hugging in a hot tub with other potential mates present, but without actually having sex.

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Barazandeh and team write that “these observations overturn over a century of beliefs about what barnacles can, or cannot, do in terms of sperm transfer” and “raise interesting questions about the capacity for sperm capture in other species.”

Recalling barnacles stuck on boats, remember that these animals live by gluing themselves to surfaces. That in itself would seem to pose major limitations for baby making. But clearly barnacles, or at least this particular species, have overcome the challenges.