 So there are lots of ways to live together. For critters to live together, we are certainly not individuals. Like we have an entire, I don't know, like ecosystem of critters living on us and in us and within us and with us. And a parasite, let's just make a list of the ways to live together, live together. And perhaps it is not, perhaps it is a Freudian slip that I say love together. Because we can have parasitism and that's good for one party and bad for another party. We can have mutualism. I'm going to make my list because in a mutualistic partnership, dude, that's good for both parties. And then you have commensalism. And in this case, commensalism is good for one party and whatever, whatever for the other party. It doesn't hurt the other party, but it doesn't really help the other party. So these are ways that critters can live together. Now, we're going to focus in on the parasites because the parasites are bad for one party, but they're really good for the other party. So let's look at our walkway. This guy is a little barnacle and this barnacle infects crabs. It infects male crabs and female crabs and it goes into the crab and it produces a little crabby egg sac. It looks just like the crab's own egg sac and it takes over the crab's brain so that the crab thinks that it made its own egg sac. The little barnacle goes in and says, hey, look at that cool egg sac you made. You're so awesome. You're such a good mom taking care of that egg sac so well and the crab is like, oh yeah, look at me. Taking care of my eggs because I'm such a good mom even if it's a boy. It will take care of its eggs and that little barnacle is like, dude, this is awesome. I totally have convinced this guy to take care of my babies and that crab has had its brain taken over by the barnacle and the crab uses all of its own energy to take care of the baby barnacles and then hatch the baby barnacles and bye-bye babies come back and visit me when you have time to visit your old mom because I took care of you and the baby barnacles are like, dude, sucker, that was awesome and the mom of barnacle is thinking, man, let's do that again. That worked great. Meanwhile, the crab, no benefit for the crab because the crab spent all that energy and didn't get any of its own babies out of the mix. Kind of cold-blooded. How about this one? Okay, this is a parasitic fungus. I actually found one of these, I think, on one of the CR windows in a lecture hall. I took a picture of it because I was so excited. Okay, so this fungus infects a fly and the fungus grows into the fly's brain and takes over the fly brain. Now, just think about that. Just think about that alone. Here comes a fungus and it gets into your brain and it takes over your brain and it makes the brain say to the fly, I feel like climbing to a really high place at dusk and hanging from the really high place by my proboscis. What? Like it's a little sucker thing. And so it does. It has this parasite that makes it go, it comes up into like a tree and hang by a branch from its proboscis at dusk when the sun is going down. And then, you know what the parasite has it do? Explode. What? Are you serious? This is what it looks like. It explodes. And there are fungal spores that get spread. It explodes. So look at all those spores. And if it's high enough in the air, then the explosion spreads all those fungal spores all over the place. This is a terrible situation for the fly. The fly is a done deal. Sorry, man. But for the fungus, it's up high. All the spores get spread on the wind. This is a brilliant strategy for the fungus. How did this even happen? That's incredible. Here's another one. This is a kind of fluke that infects a snail and goes into the snail's eyes. And part of this fluke's life cycle has to take place. Part of it's in the snail, but part of it is in a bird. And so this fluke infects a snail and makes its eyes like be huge. These are normal snail eyes. Nice, subtle, you know, nothing too gaudy. The snails are pretty shy about their fashion statements. This one has been infected by flukes and it has like holy bull's eye eyeballs, really. And who can see those really well? The birds. So the bird is like, oh, look it, I see a snail. I totally am going to eat that one. Having no idea that it just ate a whole herd of parasites inside the snail. That's absolutely awesome. Now this thing looks rather boring. This is actually another fluke, but listen to this story. This is unbelievable. Okay, so this guy, that is a little fluke that infects a cow. And the cow poops out fluke eggs into its poop. And then along comes a snail that eats the eggs in the cow poop. Because, you know, there are eggs in cow poop that the snail is like, it's on the grass and I'm eating it and there's some eggs in poop around. So it eats the eggs and it now has the fluke eggs inside of it. And then the eggs hatch and the eggs produce these little wormy things. Like the babies come out and they're these little wormy things and they're irritating. And so the snail makes these slime balls and I get rid of like, oh, I'm itchy, I don't know why. And so it makes these slime balls to scrape off these little baby flukes, which it then scrapes them off onto the grass. And so now here's this lovely little slime ball but it's filled with baby flukes. You've got to be kidding me. An ant comes along and eats the slime ball. It's like, dude, this is awesome. The ant takes over the, I mean, the fluke takes over the ant brain. The ant goes and clips itself to the top of a piece of grass and who eats it. And now the fluke is inside the cow where it lays its eggs. They get dumped out in the cow doodoo and the whole thing happens again. I mean, seriously, that is absolutely phenomenal. How about this one? Oh, my gosh, and this is nothing. Like, these are just a few of my favorite parasites. This guy is a crustacean that lives in the ocean that infects fish. And it gets, the fish is like, ooh, that looks like a tasty little crustacean. Like, eats the crustacean. I mean, that thing looks like it would be tasty fish food. But then that thing is like a psychopath critter and it bites off the fish's tongue. It eats the fish's tongue and then it becomes the fish's tongue. It like hangs out inside the fish in the tongue position. The fish is like, dude, my tongue feels kind of weird, but I don't really know what happened. I'm just going to keep on doing my thing. I don't know what I did to make my tongue feel this way. It proceeds to eat all the regular food that it's going to eat. And every little bite of food, this little tongue crustacean gets a little snack and will live in there for like ages until it gets tired and maybe it dies after it makes babies or something like, wow, how awesome is that strategy? Oh, my gosh, this guy, this is a horsehair worm that infects the grasshopper, takes over its brain. Are you seeing some common themes here for parasite strategies? Takes over its brain, makes the grasshopper say, oh, I really feel like drowning myself. Who's this good for? The grasshopper drowns itself in the water. And when it dies in the water, that horsehair worm lets its eggs out in the water and then the next stage of its life cycle can take place. But it takes over the brain and causes the fish to, I mean, the grasshopper to do this really like self-destructive thing. I mean, really. And then I don't really know what this thing does. All I know is that it lives in the anal cavity of a sea cucumber. Okay, I mean, I guess it's safe in there. I suppose, you know, poop has a lot of energy in it. So I suppose that could be advantageous to just hang out there and, you know, get snacks passing by you often. I don't know. Parasites, like you could do an entire class just on parasite strategies. That is awesome. All right, my friends, have I never mind. Sex and parasites and genetic diversity all of this sets us up, number one, to tie up in a nice little bundle the whole concept of meiosis, mitosis, and heredity and gives us kind of a bouncing point to dive into some exciting work with evolution and the production, the processes that result in the genetic diversity that is so valuable. It's been lovely. One of my favorite lectures ever. I'll see you later.