This Parasitic Mussel Pretends to Be a Fish

When you think about shellfish, “devious” is probably not the first word that comes to mind. That is, unless you’ve met the parasitic mussel Lampsilis, the trickiest thing on two shells. To attract their hosts, Lampsilis wiggles a fish-shaped lure. When a would-be predator strikes, a pouch inside the lure bursts, releasing a swarm of parasitic larvae into the big fish’s face.

The genus Lampsilis is home to more than 20 species of freshwater mussels, all with a proclivity for fraud. Their delightful common names (Waccamaw fatmucket, lined pocketbook, Alabama lamp naiad) don’t really capture the sophistication of the mussels’ snare.

The scheme starts, as so many do, with sex. During mating season, male mussels spew their sperm into the water column. Because mussels are filter feeders, the sperm-water is sucked in by nearby females. Once their eggs have been fertilized, the females transfer them into a special brood pouch. Soon, the eggs will morph into a special type of parasitic larvae called glochidia. 

Little teeny mussels!

Those itty-bitty shells are not just for show. The larvae are going to need them for what comes next.

Once her larvae have reached the glochidia stage, a female Lampsilis mussel goes into total Decepticon mode. She pushes two flaps of her mantle together to form an extremely convincing fish decoy. Inside that decoy, like a terrifying crunchy center, is the brood pouch full of glochidia.

As soon a potential host approaches, the female mussel starts wiggling her faux fish. And it’s not just any old fish; each Lampsilis lure is customized to imitate the prey of nearby host fish. Unlike real prey, the decoy doesn’t swim away, which makes it especially irresistible. It’s just sitting there!

So the big fish bites, and then things get kind of gross. The bite punctures the brood pouch and releases a cloud of glochidia.

The little larvae make their way into the fish’s gills, where they clamp on with their tiny shells. Then they dig in and start growing.

The host fish’s body is understandably not okay with this. Its immune system fights back, enclosing each larva in a cyst. But like tiny honey badgers, the larvae don’t care.

They’ll ride the big fish train until they morph into the next growth phase. Sometimes that’s 10 days, and sometimes it takes months. When the time is right, the mini shellfish pop out of their flesh prisons and sink onto the riverbed, where they’ll live out the rest of their lives. In most cases, the host fish simply swims away, suspiciously lighter than it was a few minutes ago. 

Why do this? Two reasons: defense and dispersal. Once it gets past its host’s immune system, a baby mussel buried in the gills of a bass is pretty safe. And unlike their parents, Lampsilis larvae are cruising. The bass bus will take them to places their parents have only dreamed of.

For simple animals, Lampsilis mussels rely on a pretty complicated scheme. Fortunately for them, it works; unfortunately, fish fraud may not be enough to save them. “Freshwater mussels are the most, or among the most, imperiled group of freshwater organisms in North America, and some cases you could argue in the world,” Lampsilis expert Bernard Sietman told WIRED.

To preserve the mussels’ majestic weirdness, fish and wildlife agencies have begun rearing mussel larvae in laboratories and releasing them into their river habitats. That’s right: Even humans have started to do the mussels’ bidding.

There May Be an Ancient Reason Why Your Dog Eats Poop

Dogs aren't known for their picky taste in food, but some pups go beyond the normal trash hunting and start rooting around in poop, whether it be their own or a friend's. Just why dogs exhibit this behavior is a scientific mystery. Only some dogs do it, and researchers aren't quite sure where the impulse comes from. But if your dog is a poop eater, it's nearly impossible to steer them away from their favorite feces.

A new study in the journal Veterinary Medicine and Science, spotted by The Washington Post, presents a new theory for what scientists call "canine conspecific coprophagy," or dogs eating dog poop.

In online surveys about domestic dogs' poop-eating habits completed by thousands of pet owners, the researchers found no link between eating poop and a dog's sex, house training, compulsive behavior, or the style of mothering they received as puppies. However, they did find one common link between the poop eaters. Most tended to eat only poop that was less than two days old. According to their data, 85 percent of poop-eaters only go for the fresh stuff.

That timeline is important because it tracks with the lifespan of parasites. And this led the researchers to the following hypothesis: that eating poop is a holdover behavior from domestic dogs' ancestors, who may have had a decent reason to tuck into their friends' poop.

Since their poop has a high chance of containing intestinal parasites, wolves poop far from their dens. But if a sick wolf doesn't quite make it out of the den in time, they might do their business too close to home. A healthier wolf might eat this poop, but the parasite eggs wouldn't have hatched within the first day or two of the feces being dropped. Thus, the healthy wolf would carry the risk of infection away from the den, depositing the eggs they had consumed away in their own, subsequent bowel movements at an appropriate distance before the eggs had the chance to hatch into larvae and transmit the parasite to the pack.

Domestic dogs may just be enacting this behavior instinctively—only for them, there isn't as much danger of them picking up a parasite at home. However, the theory isn't foolproof. The surveys also found that so-called "greedy eaters" were more likely to eat feces than dogs who aren't quite so intense about food. So yes, it could still be about a poop-loving palate.

But really, it's much more pleasant to think about the behavior as a parasite-protection measure than our best pals foraging for a delicious fecal snack. 

[h/t The Washington Post]

Big Questions
What Makes a Cat's Tail Puff Up When It's Scared?

Cats wear their emotions on their tails, not their sleeves. They tap their fluffy rear appendages during relaxing naps, thrash them while tense, and hold them stiff and aloft when they’re feeling aggressive, among other behaviors. And in some scary situations (like, say, being surprised by a cucumber), a cat’s tail will actually expand, puffing up to nearly twice its volume as its owner hisses, arches its back, and flattens its ears. What does a super-sized tail signify, and how does it occur naturally without help from hairspray?

Cats with puffed tails are “basically trying to make themselves look as big as possible, and that’s because they detect a threat in the environment," Dr. Mikel Delgado, a certified cat behavior consultant who studied animal behavior and human-pet relationships as a PhD student at the University of California, Berkeley, tells Mental Floss. The “threat” in question can be as major as an approaching dog or as minor as an unexpected noise. Even if a cat isn't technically in any real danger, it's still biologically wired to spring to the offensive at a moment’s notice, as it's "not quite at the top of the food chain,” Delgado says. And a big tail is reflexive feline body language for “I’m big and scary, and you wouldn't want to mess with me,” she adds.

A cat’s tail puffs when muscles in its skin (where the hair base is) contract in response to hormone signals from the stress/fight or flight system, or sympathetic nervous system. Occasionally, the hairs on a cat’s back will also puff up along with the tail. That said, not all cats swell up when a startling situation strikes. “I’ve seen some cats that seem unflappable, and they never get poofed up,” Delgado says. “My cats get puffed up pretty easily.”

In addition to cats, other animals also experience piloerection, as this phenomenon is technically called. For example, “some birds puff up when they're encountering an enemy or a threat,” Delgado says. “I think it is a universal response among animals to try to get themselves out of a [potentially dangerous] situation. Really, the idea is that you don't have to fight because if you fight, you might lose an ear or you might get an injury that could be fatal. For most animals, they’re trying to figure out how to scare another animal off without actually going fisticuffs.” In other words, hiss softly, but carry a big tail.


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