(Intro)

H: Hello and welcome to SciShow Talk Show.  It's that day on SciShow where we talk to interesting people about interesting stuff.  Today, we're talking to Toby Spribille, who I'm guessing from the contents of my table studies lichen.  Is that right?

T: That's right.  I do.

H: And do you study like, any particular places?

T: Well, I started studying lichens in Northwestern Montana.

H: Is the plural of lichen 'lichens?'

T: The plural of lichen is lichens.

H: So I already messed up.

T: Well, there's kinda this--well, you almost had me, too, right?  There's kind of this debate, is it a countable noun or is it not a countable noun?

H: Oh, okay.  Well, there's more than one lichen on the table.

T: Exactly.  Is this lichen or are these lichens?  Yeah.

H: Alright.  

T: We'll just say they're lichens.

H: And you have studied lichens in many places?

T: Yeah.  So I kinda got my start close to 20 years ago in Northwestern Montana, not terribly far from here actually, and yeah, since then I've--lichens have gotten me a lot of places.  Yeah.  I like to think that I could actually put a bumper sticker on the back of my car that said, "I am supported by lichen dollars."

H: Well, I don't think that you can't do that.  That is a thing.  Like, it is your car.  

T: Yeah, exactly.

H: And you could just go on CafePress and maybe somebody else would even buy it.

T: Exactly.

H: You'd just be the lichen salesman of the internet.  Now, tell me, explain to me what a lichen is.

T: So a lichen is really unlike--a lot of puns or half-puns here--a lichen is unlike a lot of other things that you see in nature that are of similar size and shape.  So plants are multicellular organisms.  When you yank a plant out, the whole plant dies.  Mosses, which I brought a couple examples of here, are basically tiny plants.  If you look very closely with a hand lens, you'll see that there's actually, there's little stems and leaves and so on, and they're individuals.

They're basically small versions of plants that don't have quite the same architecture to transport water and whatnot.  Lichens, by contrast, are microbial communities.  They consist of lots and lots of little microbes, which self-assemble in a self-replicating fashion.  So, this, little bits of this, can break off and start a new lichen.  You can kill parts of this lichen without killing other parts of the lichen, so it's very very different than a lot of, than like, plants or animals that are single multicellular organisms that die in one fell swoop when they die.

H: But there are other kinds of microbial communities out there.  There's, you know, bacterial plaques, there's--I don't know, like, sponges are kinda weird in that way in which we sort of refer to them as animals but they also sort of self-assemble and you can blend them up and then they reassemble in a way.

T: Exactly.

H: And so, there are these weird places where our definitions start to break down a little bit, and I feel like we talk about lichens but there's so much diversity inside of lichens that maybe we're not--

T: Sure.

H: We're not always entirely sure what we're talking about.  I am not always entirely sure what I'm talking about.

T: So maybe this would be a good juncture to introduce the word symbiosis.  

H: Okay, yes. 

T: Alright, so what is particularly interesting about this self-assembling microbial community is that it is a symbiosis, and on the inside of each and every one of these lichens are millions of tiny green photosynthesizing cells that are algal cells.  They constitute algae in the plural and they are doing their photosynthetic thing and bringing--creating sugars and providing that to the outer structure, and most of what you see on the outside when you're looking at a lichen is fungal, and this is in some sort of steady state or equilibrium that they are providing nutrients to the fungus and the fungus is providing a house for them to live in safe from predation on the outside, and this happens--

H: And structure as well.

T: --in a predictable fashion.  Exactly, yeah, structure.

H: So like, this is almost like, when--I feel like there's too much to talk about here.  When did lichens happen?  

T: When did lichens happen?  In the early fog of terrestrial life.  So--

H: 'Cause I feel like algae sort of like, you think of algae, it's gotta live in the water, but lichens are a way for algaes to live on land.

T: Yeah.  

H: I kinda think of it that way.

T: Yeah.  

H: Does that make sense?

T: That does make considerable sense.

H: Okay.

T: So we don't know nearly as much about the early forms of lichen life as we do about things that have preservable bones and other structures that were preserved as fossils, because lichens don't preserve as fossils well at all.  Basically, most of what we know about very, very, very old lichens are lichens that were preserved in amber, so they were kind of--they had sap flowing over them and then they were preserved (?~5:00), exactly.

H: So you need trees, like, before you can see lichens?

T: Yeah, and you can imagine how many different lichens were not preserved in amber because they just weren't growing in the right places.

H: Right.

T: So we don't know a whole lot, and what we know about the early dawns of lichen life is derived from DNA sequences.  What you're able to reconstruct just from DNA sequences and saying at a mutation rate of such and such, and a population size of such and such--

H: So there's a lot of divergence between different lichens.

T: Exactly.

H: And you can sort of trace back.

T: Yeah.  

H: To their common ancestor.

T: I've actually brought examples of three different groups of lichens that are as distantly related to each other, based on the fungal partner, which is what we use for making estimations of that sort, as are mammals from amphibians and from lungfish basically.  So--

H: So, like, back from the dawn of--

T: Exactly.

H: --of terrestrial vertebrates.  

T: And those are these three here.  These are as distantly related to each other as some of the main groups of vertebrae.  

H: So lichens and vertebrates happened around the same time, you think?

We think?

T: Terrestrial vertebrates--

H: Right.  Terrestrial vertebrates.

T: --more or less coincide with the considerable error bar.

H: Okay.

T: With the earliest fungal groups that split off and made lichens that we know about.  

H: So to me, no offense, lichens, they look pretty similar but they are very, very different.  Is there a way, as a trained person, you can see that difference and show it to me?

T: Not at this level, but at a microscopic level, when you start breaking things down, you can see the types of symbioses that they enter.  It's actually not just alga, it's lots of different algae that have engaged in different symbioses with different fungal strands.  They are wildly different fungal strains that at a microscopic level look different, but there are some macroscopic things that you can see right off-hand, which is why I brought a couple of these examples with me.

H: And is, uh, would you--do all lichens sort of derive from a common lichen ancestor or is this something that happened multiple times across Earth?

T: This is something that happened multiple times across Earth.  That's pretty clear, yeah.

H: That's interesting.  So when did fungi start being a thing?  Did they start on land?  Did they require plants before they existed?  I'm a little bit--

T: So, no.  So fungi, again, there's not a real good fossil record of fungi in general, which is a problem for lichens and a problem for the rest of the fungi as well, and so there's considerable uncertainty about the origin of fungi, but it's put at about a billion years ago.

H: Okay.  So they're very old.

T: Very old.  Predating terrestrial plants and predating just about anything we would recognize today as familiar life.  

H: Right. 

T: Yeah.  So, there's like, there's several big groups of fungi that split off in the mists of early time, but two of the big groups led to the things that we see now in supermarkets as the button mushroom, and these are called basidiomycetes and there's a lot of different things in this group around the button mushrooms that include things like rust fungi and a variety of different bizarre yeasts, and then there is like, the all-important piece that gives us bread and beer and other things, and that arose within this other group that split off around a billion years ago called the cup fungi, the ascomycetes, and virtually all lichens are made of fungi from this big group called the ascomycetes.  

H: Okay.

T: There's tens of thousands of species of ascomycetes and yeasts, the baker's yeast, which mostly we use for beer making, is just one of those thousands of species, and one of those groups went off, well, multiple groups have gone off and made lichen associations, symbiotic associations.  There are also wicked pathogens that have arisen that we take drugs against and fear in the form of outbreak, so all kinds of things have happened in that second half of the fungal kingdom.  

H: So, recently there was a story people talking about how some lichens are not just algae, fungi, there's a third member of the symbiosis?

T: That's right.  So, for close to 140 years, people have characterized, generalized the lichen symbiosis as a partnership between ascomycete fungus, so the second group of fungi, the cup fungi, and any number of different photosynthesizing algae, occasionally cyanobacteria can also get involved.  There's a lot of different variations on the theme.  But what was pretty constant in this paradigm, this dharma that's pretty well established is that there's always gotta be just one fungus and that's going to be an ascomycete fungus, and yeah, that's kind of where our story enters year 2016.  We're grinding up a bunch of lichens at the University of Montana, in collaboration with a couple other groups, and trying to figure out how specific chemical substances, toxic substances that are formed in this particular lichen here, actually both of these, how they are formed, and what we find, long story short, is at the end of the day we have three genomes.

Not two, we're expecting an algal genome and a fungal genome after going through these, and no matter how hard we try and how often we replicate these experiments, we have three genomes, and so that gets us really scratching our heads.  

H: Mhmm.  And so are you still scratching your head or do you have answers?

T: We have a couple answers now that have moved us to the next level and one of, sort of the central theme to the new discovery is that anywhere we have this toxic susbstance, we have tiny, tiny yeast cells that belong to this first group of fungi, the (?~10:44), and they seem to be a constant presence in these lichens and they've been overlooked for 140 years, as I was saying, so anytime--

H: But microscopically you're not gonna see this?  Like under a microscope?

T: Microscopically, they're really hard to see.  Super hard to see.  So we had to develop special techniques of ribosome labeling to actually do it at a subcellular level to get these cells to glow, to light up, and tell us who they are based on their DNA.

H: So explain that to me, because that sounds fascinating.

T: Yeah, so basically, when you take one of these lichens and you make a slice and put a tiny piece of it on a microscope slide, you get to see a whole bunch of filaments that belong to fungus, and then you see some green blobs that look like algae because they've got the chlorophyll in them so they're, you know, you can kind of make that difference.  It looks like two things.  But when you ground those up over and over again and you find that there are three genomes and two of them are fungal, it's really difficult to tell the difference between some of the filament stuff that you see on the slide and what else could be on there.  How would you know which is which?  So what we did is we had the DNA sequences behind the ribosomes, the machinery that goes and has--translates messenger RNA to--into proteins, and what we did is we unfurled these ribosomal sequences and we looked at what portions of these sequences are characteristic for the cup fungus and which portions are characteristic for the (?~12:29) fungus, and mutually exclusive, and we developed little probes that have the reverse sequence so that they would attach to these sets of DNA sequences and "hybridize" with them.  

So they would actually, like, dock and attach, and the ends of these little probes are little (?~12:47), little additional molecules that have been added that light up when excited with the particular wavelength.  

H: So and now you can see that there is that thing and where like its filaments are in both of these fungus?  Both of these lichen that are on this particular branch?

T: Right.

H: And so like, does that mean it's probably much more common than we think it is?  They could be on one branch together and look quite different?

T: Yeah, so a couple things surprised us.  One was, and we found this out fairly early in the study, is that each lichen appears to have its own "secondary fungus" or yeast.  So this one has a separate one than this one, and these two have a separate one from the others on the table, and we sort of expanded--

H: So are you saying that all lichens have this third--?

T: That's an interesting point.  So, going back to the point about early lichen evolution and how these many groups broke off and then I kind of compared them to, you know, (?~13:47) group broke off around the same time as the dinosaur avian group broke off and then a group broke off about the same time that marsupials split from (?~13:55) and other things.  The same goes for lichens, and there's one group of lichens that is more successful than all the others, and it arose around the same time as the early mammals, and that includes these, and we call them the parmelioid macrolichens, and within the parmelioid macrolichens, virtually all species that we've looked at have this additional fungus, and so we think that these parmelioid lichens may be somehow involved in another type of symbiosis with these yeasts that may have made them, for all we know, we can't rule this out at this point, maybe had a hand in making them very successful.

H: Right.

T: But we can't say the same for some of these other lichens that--these are kind of--this is kind of the dinosaur lichen, this is like the amphibian lichen, and this is another example of a parmelioid lichen.  So, the parmelioid macrolichens can be really different in form and shape and color, but they belong to this really successful modern large group that's on every terrestrial habitat on the planet, basically, every continent, and then these things, they've got other things going on.  This is research for another day.  

H: Well, that's fascinating.  This is very cool.  That was big news, so congrats on working on that project.  I'm not gonna try to remember the names of the different lichens--parmelioid?

T: Parmelioid, that was right.  Really spot on.

H: Yes.  

T: We need to popularize these obscure names.  I mean, if people can say archaeopteryx, then they can say parmelioid.  

H: 'cause you know little kids, they're gonna get super obsessed with this guy.  It's just as exciting as a dinosaur.  

T: Exactly.  This is just as exciting as a dinosaur.  I mean, this is--

H: I mean, basically, like, it is as old as a dinosaur when it, you know, split off.

T: Or older.  Yeah, this is a really interesting lichen because it's so different from so many other lichens and it--it arose separately from other lichens as well, so all of these things, they have their particular means of attachment.  This thing is called an umbilicate lichen, because it's got something like an umbilicus or belly button, and it's attached by a single strong holdfast.  This particular individual may be hundreds of years old.  They're very, very slow growing, and they just are attached to rocks like that.

H: And you just yanked it off a rock.

T: Well, in the interests of science and education.  And it changes color dramatically when you put it in water as well, so we're gonna do that and we're gonna watch it.

H: Is it still alive then?

T: It's still alive. It was alive and happy in its habitat as late as yesterday evening.  

H: Oh.  Okay.  

T: And it's gonna do its thing.  And a lot of these things, you can kind of see, this is, we'll just call these the amphibians for today's purposes.  They're as different from these other groups of lichens as amphibians are from mammals.

H: Is it gonna be happy now?

T: So, so, we're gonna have the dry wet and this will take a minute or two and it's gonna change color dramatically and the way it changes color is going to tell you a little bit about what's on the inside of it.

H: Let's do a time lapse.

T: 'cause you're gonna see the alga is waking up now and becoming very, very happy.  So we have the dry one here, and this one's going green and this one is going another hue of grey toward green, it's no longer this kind of chalky white thing.  

H: Mhmm.  That one's turning very green.

T: They're becoming physiologically active.  They're registering the lights around us, and that's one of the cool things about lichens is unlike a lot of other organisms, they can go from dormant to active within 60 to 90 seconds, because they need to be able to capitalize on whatever little moisture or rain they get.  This is why they can live in deserts on cactus stumps.  

H: Hm.  And yeah, and basically become completely dormant for--

T: Yep.  And they can take advantage of fog rolling in off the ocean without it ever needing to rain.

H: Neat.  Well, I cannot believe how green and lush that thing looks now.  

Look at that, wow.  

T: Dormant.  Active & happy.  

H: So I suppose now we should just--we should just hang out with some kind of animal, 'cause, you know, maybe something that will try to eat some of these and maybe not.  

T: We can see how it feels about lichen.

H: We can see how it goes. 

We're back, Jessi, hi.  

J: Hi, how are you?

H: Good, how are you?

J: Good, how are you?

T: I'm also well.  

J: Good.  This is amazing.  It's just really exciting.

H: Yeah, it's pretty cool.

J: Yeah.  

H: This is Toby, this is Jessi.  It's nice to introduce you to each other.  

T: Good to see you.

H: Did you bring something for us?

J: I did, I did.  You've never met her before.  Her name is Jabba.  

H: After Jabba the Hutt.

J: Yeah, yeah.

H: Okay.

J: Can you imagine what she might look like?

H: Like a Hutt.  Like a--like a--like an adult Hutt.

J: Yeah.

H: Not a Huttling.

J: Yeah, yeah.  So let me--let me just bring her out here.  

H: Oh, you do look like a Hutt.  Like--well, I guess he was sort of a toad man.  

J: A little bit, a little bit.  I think her mouth most closely resembles him, and we didn't know whether it was male or female when we got her and then she grew up and she's a female.

H: And how do you tell?

J: Well--should I tell you what it is?  

H: Yes, sure, do that first.

J: This is an African Pixie Frog, also known as an African Bullfrog, and you can tell if they're a male or female as they mature.  They're thr--the males--don't--do not put your finger in front of her mouth.

H: Okay.

J: I'll tell you why in a second.

H: Okay.  Thanks for letting me know.

J: She--so, as they grow, the male's gonna have a very yellow throat and the female's going to have a cream colored throat, and then the female's gonna top out at about four, four and a half inches and the male's gonna get almost ten inches.

H: So you did not know what you were signing up for.

J: We didn't know what we had.  

H: A ten inch toad would not even fit in this case.

J: And I'm glad you said toad, because you're wrong.  

H: Oh my gosh.

J: Yeah.  

H: Well, it looks so slimy, why did I say toad?

J: Well, I know.  I mean, she has little bumps on her, but she's a frog, and there's a big difference between frogs--true frogs and true toads, and true frogs are going to have teeth on their upper part of their mouth, and pixie frogs are pretty intense.  They actually have three huge teeth on the bottom as well, and they're known to be quite aggressive, and if you can imagine a ten inch pixie frog in the wild, you walk up to it and you go like, whoa, that's awesome, hey, let's, you know, bug it.  No, no.  It'll bite ya.

H: Yeah.  No jokin' around.  Why does someone want one of these?  Is this a pet?

J: Um, it was a pet and they just--they didn't want her anymore.  

H: They were like, that thing has pretty big teeth.

J: So like, maybe they got bit.  Yeah, you don't wanna mess around with that.  I mean, it'll get ya good.  Big, big teeth.  The other difference between a frog and a toad is toads are gonna have really big pits behind their eyes and that's gonna be poison glands back there, and since she--she has a little bit of toxicity--

H: What.  What.  Wait, toads have been poisonous my whole life and I didn't know that?

J: Uh-huh, yeah.  Yeah, have you ever heard of the story where it's like, a dog's messing with one and they go ahh!  You know, and they've been sprayed by poison?

H: No.

J: No.  Okay.  Well, have you?

T: No, I haven't of that either.

H: I am upset that I didn't know that about toads.

J: Well, not very many of them are toxic enough to like, kill a human.  

H: Well, certainly, but even the little bit of venom.

J: It's not venom.

H: Sorry, poison.

J: It's poison, yeah, so they're not injecting, they're not biting it into you or stinging it into you.

H: Okay.  

J: It's just secreted by the poison glands--

H: They'll spray it on ya.

J: --and then they can like, shoot it out of their poison glands.

H: So it comes out of a just whole separate system.

T: And all toads can do this?

J: Toads, all but one species, I think, yeah, yeah.  

T: Huh.  Wow.

J: And then, frogs, they're a little bit toxic on their skin so they taste bad and it can make, you know, a small animal sick if they want to eat it, but um, yeah, yeah, but toads are definitely more poisonous.

H: Okay.  

J: Yeah, yeah, so she's not really poisonous.  These guys are actually eaten as a delicacy in Africa.

T: She moved when you said that.  

J: She was like, um, no.  

H: You don't like to hear about that.  But you just gotta take the skin off first?

J: Uh, I didn't research into it that much.

H: Well, I'm guessing, you know--

J: I didn't see how they prepared them.

H: Well, yeah, I just feel like, if I'm gonna prevent an animal from eating me.

J: Get in there, get in there, yeah, that feels good.

H: You are somethin' else.  

J: She's going in her little sauna.

H: Yeah, if I'm gonna prevent an animal from eating me, putting my poison on my skin is probably the place to put it, 'cause it's the first place that the animal's mouth encounters, but most foxes, for example, aren't like skinning a frog before they eat it.

J: No, and that's why they can get sick from it.  And it'll just taste bad, so yeah, yeah, yeah, so she's going to be moving around about 50% in the water and 50% on land.  

H: So I'm just gonna ask, what's the point of all of the frog?  Part of it.  So I like, I'm like, okay, so it needs eyes, it needs a mouth, it needs a head and legs.  What is all this extra stuff for?  'Cause like, 90% of this frog is just like--do you feed it too much?  Or is this what she's supposed to look like?

J: This is what she's supposed to look like.

H: Okay, I didn't--I feel bad.  I do feel really bad.

J: I feel like you're being a little judgmental.  

H: I just don't know what it's for.  I don't--

J: She--so a male is gonna be like, half-head.  So like, a male's gonna have a head like, this big, and they can eat--and then the body's gonna be like that, so it's huge.  So anything that can fit in their mouth, they'll eat.  They're carnivores, and so they eat birds and lizards and snakes and other frogs and small rodents and--I know, there's lots going on, uh-huh.

T: She just heard you recite the menu.

J: I know, mm, delicious.  So, when they get threatened by a predator, say, like a monitor lizard or something walks up and is gonna try and eat her or a turtle or something, then she's gonna puff up as much as she can so she's going to increase in size, she's gonna look quite a bit bigger, and then she's gonna do a little bit of a hiss, you know, to try and scare them off, so the big body is gonna help protect her, and these guys are actually the largest species of frog in Africa, the second largest in the world.  

The males are.  

H: Oh wow.  I'm glad you don't have a male.  I'm honestly--I mean, maybe I do--

J: It's kinda cool.  They're huge. I got to hold one once and it was just like, I don't have enough hand to hold you.

H: It's weird to think of a frog that you are like, physically afraid of.  Like, most of the time, I see a frog and I'm like, hey, buddy.

J: Yeah, exactly.

H: But if there's one that's like, it could fit my hand in its mouth--

J: And it would hurt a lot.

H: And it has big teeth.

J: A lot.  A lot.  But you wanna hear some like redeeming factors?

H: Sure.

H: Of the dads?  The dads are actually really cool.  So the female's gonna lay the eggs in a little pond, and they're gonna live in like, a grasslands in Africa, like South-Central, they have a very wide range, down in South-Central Africa, and in the grasslands, there's like these pools and they're gonna be hanging out, like, around elephants and just hanging out in those little ponds and puddles and so, the dad has to watch the eggs, and after two days, they hatch, and then about three weeks later, the little tadpoles become little frogs so they can leave, but during this time, he has to make sure that they don't all die.  There's actually a pretty high mortality rate, about 20% of them survive, and they're gonna be eating a little bit--

H: That seems quite good to me.

J: Considering they lay 3-4000 eggs at a time.

H: Oh yeah.  Well, you only have to have like, three of them survive.

J: So I mean, I like using that analogy with kids, because they will actually, if there's not enough food around, they'll actually eat each other and then the dad, if he's like, running out of energy to keep them all alive, he'll just, like, snack on a couple and then at least a couple survive, right, but let's eat all of you.

H: It's like--he's like--

T: You were gonna mention some redeeming qualities here.  

H: Let me redeem them, and then you just like, do jumping jacks and the one who stops first, I eat.

J: These little legs, can you imagine?  Um, okay, so this is the cool thing.  If the puddle starts drying out, then he--they have really strong back legs and they'll just push their head down and they will plow through the dirt and make these little tunnels to bigger puddles and so the little tadpoles can like, swim down to a bigger puddle.

H: That's really cool.

J: It's pretty cool.

H: That's awesome.  

J: Yeah.  Yeah.  And they'll just eat anything that tries to attack 'em.

H: You build a canal.

J: Yeah.

H: You're a canal builder.

J: She doesn't.  She leaves.

H: Well, your species.  Also, even if you had, he wouldn't build canals, he'd be stuck in a box.  

H: Yeah, yeah.  So you don't want a male?

J: Um, I don't know if it's about wanting, it's just like--

H: You'd take one.  

J: Yeah, if one needed a home, yeah.  So we're happy to care for whatever we get.  

H: But you don't do a lot of handling.

J: I don't and the reason is because she's amphibian, she can soak up some toxins from us, oils and stuff like that, and also, she doesn't really like it that much.

H: Yeah.

J: So these guys, there's another really cool thing they do.  Africa has a big dry season, and they will burrow down into the ground and then they will coat themselves in a cocoon of dead cells, and it retains the moisture inside, and they can actually, they'll lose like, half of the amount of moisture when they're in this coccoon thing.  They can ride out a dry season and they can actually use the liquid from their bladder to keep themselves moist, so if you ever pick up a frog of any sort and they pee on you, that's a defense mechanism, but it's also pretty dangerous for them to expel all of their fluids, especially if the dry season is coming up.  So, I don't like to stress her out that much.  I want her nice and liquid-y.  

H: All puffed up, you seem to have got plenty of liquid right now.

J: Oh, and when they--when the wet season comes, it like, moistens up that cocoon, and it like, cracks open, and then they can (?~27:53).

H: Cool.

J: It is cool.

H: Weird.  That's weird.  

T: Takes enjoyment to a whole new level.

No, I wouldn't wanna mess with a frog like that.  

H: No, absolutely not.

J: They--and then if they start hissing at you--

T: Hissing?

J: Yeah, yeah, yeah.

T: Baring their teeth, like--

J: Oh, they look pretty funny, 'cause they (?~28:17)

H: Funny ridiculous until they're inside of your hand.

J: Until you put your hand in there, yeah.

H: Well, Jabba, thank you for visiting.

J: Yeah.  

H: Thank you for visiting, Jessi.

J: Thanks for having me.  

H: You can see more of what Jessi's up to at YouTube.com/AnimalWondersMontana.  Toby, thank you for sharing all of your beautiful lichen, and how amazingly active they are.  I didn't expect to be so excited about this.  So thanks a lot and keep doing cool research.

T: Thanks for having me.

H: And thank you, people of the internet, for watching this episode of SciShow Talk Show.  If you wanna keep getting smarter with us, you can go to YouTube.com/SciShow and subscribe.

(Outro)

Tabetha: And when a planet crosses in front of a star, then it blocks out a tiny bit of light and you can see this in this data, and this is what the planet hunter researchers--