Sneaker Males - There’s Something in the Water

Two fish compete to be the baby daddy for the female ocellated wrasse, a colorful Mediterranean fish. It’s up to her ovarian fluid to decide who wins.

With skills like building nests from algae and nurturing young, the “nesting male” is the preferred choice. They grow faster, live longer, and pass on better genes. The “sneaker male” is smaller but carries a much larger load. The fast, clever, and virile sneaker waits by the nest for his opportunity. Once the female lays her eggs, he dashes in to release a cloud of sperm, and the swims away.


To counter the sneakiness, the female wrasse uses what ecologists call “cryptic female choice.” Her ovarian fluid favors the nesting male’s sperm, enhancing their speed and making them more likely to reach the eggs first. “It makes sense that you would see these kind of effects in the reproductive tract, but that it’s happening in the water is pretty amazing,” said evolutionary biologist Suzanne Alonzo of UC Santa Cruz in a news release.

This strategy isn’t a guarantee; sneaker males succeed in fertilizing about one-third of the eggs. So, who stays to care for those young? The gallant nesting males, of course.

Article by Teressa Carey

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Written by Rob Nelson

Rob is an ecologist from the University of Hawaii. He is the co-creator and director of Untamed Science. His goal is to create videos and content that are entertaining, accurate, and educational. When he's not making science content, he races whitewater kayaks and works on Stone Age Man.

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