Listen to part of a lecture in a biology class.

P: Today, we'll be talking about camouflage, how animals disguise themselves so they can sneak up on their prey or avoid getting eaten themselves. What's an example of camouflage? Anyone? Megan?

S: Lizards, right? They can change colors to blend into their habitat.

P: Some lizard species do change colors quite frequently, in fact, but not always for camouflage. One lizard species, for example, changes colors in social situations to attract a mate or intimidate a rival who's invading its territory. So what we think of as camouflage, changing colors isn't always for camouflage. It might be for communication, but I'm glad you brought this up, because camouflage, technically known as crypsis, isn't exactly straightforward. For example, crypsis isn't visual in every case. Not all animals rely on visual deception to catch prey or to avoid predation.

P: Crypsis also includes chemical camouflage, which could involve, for example, changing its scent to fool other animals. This is particularly common in aquatic environments. Why do you think that is? Alex.

S: Hmm, it's probably hard to see underwater, right? P: Exactly.

P: Many animals in aquatic environments are adapted to rely more on taste and smell than on visual signals. Let's look at an example, the pirate perch. The pirate perch is a freshwater fish found in North America. Researchers recently discovered that it might use chemical crypsis to disguise itself from its prey.

Now, that's not necessarily news. Chemical crypsis has been investigated before, and previous research has shown that there are plenty of animals that change their scent when a particular predator or prey is nearby. Many insect species, for example, use chemical crypsis to avoid detection, but this form of crypsis works against only one specific predatory species. Newer research indicates that the pirate perch might be able to chemically mask itself from a whole range of species, something that hasn't been observed before.

The pirate perch was included in a recent series of experiments involving two organisms that live near freshwater, frogs and beetles. The researchers wanted to see how the frogs and beetles responded to different species of fish, species that prey on their eggs, like the pirate perch.

So they placed various fish species in trash cans and submerged each can in its own little pool. The frogs and beetles couldn't see the fish in the trash cans, but could detect their chemical signals. So when it came to choosing a pool to lay their eggs in, the frogs and beetles avoided most of the pools because they could smell the dangerous fish. However, surprisingly, they didn't seem to have a problem with the pool containing the pirate perch and went ahead and laid their eggs there. A question, Alex?

S: Yeah, aren't there a lot of insects that mimic their surroundings visually, like imitating sticks and dead leaves so they don't stand out? Maybe the pirate perch is doing the same thing, only chemically, you know, like making itself smell like a rotting leaf. Frogs and beetles wouldn't be afraid of that.

P: Yes, that's one reasonable explanation, emitting the odor of a harmless object.

P: My guess, though, is that the pirate perch might be the only animal that does not produce any scent whatsoever.

S: You mean it was chemically invisible to the frogs and beetles?

P: Perhaps. No single study can offer definitive proof, of course, but this study certainly suggests that chemical invisibility is possible, and maybe that's what the pirate perch has achieved.