ZeFrank on predatory mussels and their mimicry

March 23, 2023 • 1:30 pm

This is one of my all-time favorite examples of the power of natural selection, and one I taught in my evolution class as an example of mimicry. These freshwater mussels have a load of fertilized eggs that produce larvae that feed on fish blood until they’re grown. This poses a problem: how do you get the larvae into the fish mouth, where they can latch onto the fish tissue and feed on blood in the vascularized gills?

This video shows several ways. The first is simple: the mussel latches onto a fish and then forces the larvae into the trapped fish’s mouth, the prime feeding spot for larvae (gills are loaded with blood vessels to absorb oxygen from the water). The larvae develop for a while and then drop off the fish to grow into sedentary adult mussels. This means that the mussels have to let the now-parasitized fish go so they can disperse the young.

The other way—the really amazing way—is found in Lampsilis mussels, who have evolved a brood pouch, containing the larvae, on the edge of the mantle. The brood pouch looks remarkably like a fish, and so a predatory fish approaches to nibble on the pouch. At that moment, the mussel squirts the larvae into the predator’s mouth, where they fasten onto its gills. Instead of getting a meal, the predatory fish becomes a meal, but not one that’s fatal to the fish. Still other mussels release larvae that look like worms or fly pupae and, when gobbled by hungry fish, again latch onto the fish’s blood vessels.  Still other mussels put out lures that look like fish and act like the brood pouch, squirting mussel larvae into the mouths of hungry fish.

What’s remarkable in all this is how closely the brood pouch—or the larvae—have evolved to look like food. Mimicry like this is a good way to show the power of natural selection!

7 thoughts on “ZeFrank on predatory mussels and their mimicry

  1. I enjoy these kinds of posts very much, as my background is not in science. Little science lessons- so interesting.

  2. I learned about strategies like this from malacologist the late Ruth Turner many years ago, but she didn’t have those amazing videos at her disposal! The creativity of natural selection is almost unbounded!

  3. Watching that video, I admit I was thinking “Oh, man, something Very Bad is eventually going to happen to those fish, isn’t it?” Something along the lines of the “Alien” movies. (Or tarantulas and ichneumon wasps. Or about a bajillion other simultaneously fascinating and horrifying reproductive cycles that Natural Selection has cooked up.) But no, apparently the mussel larvae just eventually detach and the fish are basically okay. Whew! Mother Nature, red in tooth and claw…but sometimes She decides to just chill out a bit.

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