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It's not obvious what [bioluminescence] is for. In some groups it is, like the anglerfish: they're obviously primarily using it to attract prey. All the animals are attracted to the light. They're also probably using it for attracting mates. The male's a little tiny parasite, and will hunt out the female and actually attach—some species permanently, some semipermanently—and her blood will start passing through the male. On the ones that permanently attach, the [males] lose their brains; they lose most of their nerves. And the females can have eight or nine of these attached.
Bioluminescence is all over the place. Some [fish] have bacteria that live in their body that glow, rather than them actually producing the chemicals themselves. And then some fish will let out a bioluminescent glowy ink. And so what they do is like, they're about to be eaten, they squirt it out, and then everyone's like, "Ahh, light!," and then goes after it. Those are called tubeshoulders. They're completely hideous fish otherwise.
What's cool about the toadfishes that are bioluminescent is that they don't produce any of the chemicals themselves and they don't use bacteria. So they eat a little tiny bioluminescent shrimp that lives in the ocean and they take all of its chemicals, put them in their leg organs, and then use that. The toadfish are from Washington State down to Mexico, and somewhere around Oregon the little shrimp thing, which is an ostracod, disappears. So when you go farther north than that the [toad fishes] don't actually bioluminesce.
There's dinoflagellates, which are these glowy little creatures that are kind of like plants, kind of like animals: they photosynthesize but they swim around and live in the ocean. And when you disturb them they glow. And the reason for this is that if something were to eat them, they would glow, and then that thing would get eaten and so it's sort of this defense mechanism. We're thinking about having docents being able to have these, because you can shake them and they glow, it's like a really remarkable glow. Most bioluminescent things glow just a little bit, but some of these actually, it's really startling.
Fluorescence is like the way you go under a black light and a Grateful Dead poster glows. It takes in one light and reflects out a slightly different light, so that's why blacklight is a deep blue and it lets out a green or orange. Luminescence is glowing by itself, and neither of those is phosphorescence, which stores up the energy, like a glow-in-the-dark stone, and releases it over time. We just recently found out that fishes fluoresce, so there's some of that in the exhibit.
We know that a bunch of shallow-water fishes are biofluorescent, and this is actually kinda cool. You can be looking at some eel or something that's hard for us to tell apart with natural light. You know, we'll say, "DNA says this thing and this thing are different species, but I can't tell them apart at all." But fish don't see the same things we see. It turns out that there will be different red and green bands on these things, under fluorescent light, and you can tell them apart completely. What we're finding so far is that oceanic fishes fluoresce. We have yet to find a freshwater fish that fluoresces. So it might be something they're picking up from their diet or environment.
We don't know if any deep sea fishes, with one exception that we've tested, are fluorescent. It wouldn't make any sense necessarily, because why would you fluoresce a thousand meters down if there's no light hitting you to release the other light? But you might still do it, because your ancestors did. That's what's so weird about evolution, is it's like an appendix. They're still holding onto these things just because they have to.
On land, you'll find things like scorpions will glow blue. That's actually how we collect scorpions, you shine a black-light flashlight and you'll see them. It's startling. They're so blue. And we've found that small-mammal urine glows when it's fresh, and that owls can see fluorescent light, and then they can track those mammals. I mean, all the insanity of the world with these arms races—that's why this stuff is so cool to me.
"Creatures of Light" runs through Jan 5, 2014, at the Field Museum.
Read part two of the conversation.