 Welcome to Platypus 2, Electric Boogaloo. I am Lita Stevenson, and I'm going to talk to you about our dear friend, the platypus. Actually, that was a surprising segue to a joke that I wasn't going to make, which is that my sinister ambition here is to impress upon all of you that the platypus is the most adorable, charming, and amazing creature in the world so that it can take over cats and the internet. So let's move ahead and have a look at the little guys. So behold, the platypus. This adorable little guy is so ridiculous looking that when they were originally sent to modern scientists in Britain when they were discovered, they were dismissed as a hoax. But what all of this adorableness actually is is just a sublimely adapted creature. It's a very, very ancient mammal. It's the oldest branch of the mammalian family tree. As a matter of fact, almost unchanged fossils of these critters have been found back 166 million years. So this guy lived right alongside the dinosaurs. And so he's the only remaining member of his family, ornithorinkidae, ornithorinkus, which means flat face, flat face. And so if he's lasted this long, he must be doing something right. And how could you go wrong with that? So let's take a closer look at the little guy. I'm a perperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperperper Jumping bottom, eating burrow, digging, uh, uh, uh, uh, uh, uh, uh, uh, uh, uh, uh, platypus. So behold the platypus. You guys can send all hate mail to LitaStevensson at gmail.com because that will be in your head for days. Trust me. So here he is. So these little guys are kind of a mishmash of characteristics. So they've got this funny beaver-like body. They're actually smaller than you might imagine. The platypus is about half the size of a house cat. And they've got this very dense fur. They were originally hunted for their fur. So they've got these silly duck-like bills and, uh, they also produce milk like all mammals. But unlike most mammals you may be accustomed to, they don't have nipples. They just sort of ooze milk out of their bellies. And it sort of seeps out onto their fur and the babies lick it up. So, yeah, nice, huh? So, so we got, we got milk, we got fur, we're a mammal. But these guys also have a suite of kind of unusual reptilian characteristics. For example, they lay leathery reptile-like eggs. And they also, at least the males, produce a very, a snake-like venom out of a spur in their back leg, which causes paralyzing pain and massive swelling. So all of this kind of mix of characteristics is broken down all the way into the DNA of these animals. And that's just because they're such an ancient creature. So as old as they are, these guys actually represent a lot of the characteristics of our oldest reptiles that were like, that had mammal-like characteristics. So the oldest branch of the reptile tree that eventually led to mammals. So one of the other things that we're gonna look at, the most important for us today, is this adorable duck-like bill. So what is so important about the platypus's bill? Well, the platypus's bill has, it's a very specialized aquatic sensory organ. It's got about 100,000 very specialized receptors on it that both are sensitive to disturbances in the water and also are sensitive to electrical signals. So the platypus is one of very few mammals that is able to perform electroreception. So what is electroreception? Electroreception is the biological ability to perceive environmental electrical signals. And it's very well-preserved in fish, such as sharks, rays, and paddlefish. And as many of you undoubtedly know, there are also fish that produce and receive their own electrical signals. They have these specialized organs that shoot them out, bounce off things, receive them back. So they're sort of like electrical sonar. And recently, electroreception has been discovered in a species of dolphin and bees. So what's up with electroreception? It's most common in aquatic animals for the obvious reason that water is a better conductor for electricity than air. And in the water, vision is usually compromised over long distances. However, these guys can send signals. So it's usually a passive sense in these animals and they use it to navigate or to seek out prey. So why does our buddy the platypus care about electroreception? So you can see here in this image, when they dive into the water, they clamp down their eyes, their ears, and their nostrils. So they're functionally deaf, blind, and they can't smell. But they're perfectly successful. As we know, they're 166 million years old, so they must be doing something. And so scientists originally proposed that they might be using electrical signals to get around and to hunt prey when they looked at their bills up close and discovered that they had these kind of poor-like receptors that were sort of similar to those that you see in electric fish. So to test this, they put these cute little guys in tanks and dropped batteries in. And sure enough, when the batteries were dropped into the tanks, the platypus would seek them out and attack them. So it was demonstrated that they can perceive electrical signals in the water. So what are they looking for in their native environment? Well, like all animals, I see the pizzas before you, they are looking for food. So why are they looking for electrical signals? And what's going on in the food that they're looking for? Well, we've got little fish shrimp and aquatic invertebrates that they eat. They've got contracting muscles, they're disturbing the water. So these guys are looking for electrical signals from them. So why is that? Well, it's because muscles function via electricity. So... So... So all active muscles produce electrical signals. And when muscles are contracting, you can perceive and measure these electrical signals if you have the appropriate sensors. That's what EMG measures. So sure enough, that's exactly what happens in the water. If the animals have the right receptive systems, they can read electrical signals that are released by muscle contraction from prey items. And that's exactly the case with our platypus. When the invertebrates that they eat are swimming around, they're releasing small electrical bursts that these guys can read. So... With a stimulus of a sufficient threshold, the platypus will receive a signal at the bill in some location. And when it receives the signal at the bill, a neuron associated with the receptor will fire and the brain will receive a signal that says, yep, we've got an electrical signal and it's from this location. So in the platypus, it's unique because this is a very, very directionally sensitive system. So for example, if there's a piece of prey or an item of prey that's like up swimming up to the left, they'll perform this reflex arc that shifts their head to put the most sensitive parts of their bill in the direction of the signal. So if it's up into the left, up into the left. If it's down into the right, down into the right. And that's unique to these guys. Electric fish cannot perform that. So that gives us an idea of how they can use this ability to kind of pinpoint prey in three-dimensional space. But there's more to it than that. So in the platypus' bill, there are actually two types of receptors. We have our electoreceptors in red, like we've discussed. But there's also a second set, which are these mechanical receptors, as we kind of briefly discussed in the first place. Mechanoreceptors in the platypus are kind of unique, again. Mechanoreceptors in all animals are very, very common. These are just receptors that tell you that you're receiving some kind of signal to your skin. So like if I push on my hand, I'm activating pressure receptors in my skin that tell me I'm pushing on my hand, it's happening here, it doesn't hurt yet, if I do it harder, it will. These in the platypus are called push rod mechanoreceptors, and that's because of this kind of columnar shape that they have. Both receptors in the bills are actually only available to the platypus when they enter the water. So when the bill is submerged, they have these cells that cover them up, they open up, and they're able to actually perform. So this is kind of unusual for these guys, because other related receptors and other animals are tethered to the sides. These guys are free to rotate around their base, which means that they're even more sensitive to vibrational activity in the water. So the electroreceptors are kind of evenly distributed along the bill, or the mechanoreceptors rather, are evenly distributed along the bill. But the electroreceptors are arranged in these very, very neat, tidy red stripes that you see there. And these stripes actually correspond to the directional sensitivity of the animal. So like I said, they're directional, they have an area of sensitivity, that area of sensitivity is forward and down. So it's kind of pointing outwards. And in nature that corresponds to the animal being able to sort of sweep the substratum of the water that it lives in. So it goes down to the bottom, kind of looks around, and that's the area that's the most sensitive. So the organization of these receptors kind of follows along that. So if they receive a signal, they turn their head, they point at it, and the signal passes down those lines and enables them to continue perceiving it along the length. So it's not just organized on the bill, their brains are also very organized. So what we have here is the platypus cortex. The cortex is the most advanced part of the brain. It's where all of the signal processing occurs. And in all animals, you can measure how important an organ is by how much of the brain is devoted to it. So you can see here's like these little platypus bodies, their little feet, there's almost nothing devoted to that. And they just have this disproportionately massive part of the brain that's devoted to sensory processing from the bill. So this kind of interdigitated pattern is sort of repeated here. And what we have is these kind of complicated stripe-like patterns of neurons that are processing information from the receptors in the bill. Interestingly, these neurons in the brain receive input from both types of receptors. So every single receptor in the brain receives input from a mechanoreceptor and an electroreceptor. So what is it doing there? Well, let's kind of break it down a little bit. So we have two systems. Whoa, I love this slide. So we have two systems, both of which receive different input from the same stimulus, the animal that these guys are after. One of them is electrical, one of them is mechanical. And we have a distributed, clearly organized pattern that communicate together to the same neurons in the brain. So let's talk really briefly about some generalities of sensory systems. So all sensory systems are tuned to a specific stimulus, but beyond that, each individual receptor is specifically tuned as well. So for example, like in your retina, an individual cone has a preferential wavelength of photon that it absorbs. So let's say a single one prefers to absorb 440 nanometers. A second one may prefer to absorb 600 nanometers. Same thing, let's say in your olfactory sense, in your sense of smell. An individual olfactory receptor will be particularly sensitive to an individual chemical, another one will be receptive to another. And the way that this works in the brain is the whole sense that you perceive and that you feel and that you interpret is because your brain takes in all of these millions of pieces of individual points of data and combines them and produces an idea that we have of the reality that we perceive. So what are our specifics for our platypus neurons? Let's watch our little guy go around again and we'll see if we can figure it out. Okay, so there he is. So he's in the tank kind of whirling around. They've dropped in a bunch of scrumptious mealworms for him. You can see he's doing his little head motion back and forth where he's kind of chasing him down. You can also see that as he gets a little closer to him, he kind of narrows in on him, munches him up. There he goes, nom nom nom nom. And obviously the system works because blind deaf and unable to smell, he has successfully nommed some delicious worm. So let's look at the electroreceptive side of this in a little greater detail. So I said that each of these neurons have different levels of sensitivity and that's true for the specifics of the electroreceptors. So each electroreceptor kind of has a field of a perceptive field that's different from others. There are more and less sensitive receptors. That's what the forward and down is. So in this graph, this is kind of illustrating the receptive field for electrical signals that the platypus is able to interpret. And you can see in that forward and down direction, that's the longer range of these lines. Those lines correspond to the minimum voltage that they can perceive, which in nature is basically how far away they are from the animal that's producing a consistent voltage. So these are our receptive fields. Let's have a look at how that kind of turns out in practice. So these are graphs of the platypus's motion when it's looking for prey. So down here on the bottom, this is kind of a typical scanning motion for these animals. You can see that the primary receptive fields, the more sensitive areas are laid out here with the triangles. So these guys are kind of going down, they're looking around, they're kind of swinging their heads back and forth, just sort of looking in a general area on a riverbank or on the bottom of a lake. And when they receive a signal, they zoom in, they do that head motion we talked about, they narrow in on it and they do a narrow scope of the area that they're looking at. So a good way to kind of imagine what these guys are doing is if you've ever seen people with like metal detectors at the beach, kind of swing them back and forth, it'll start beeping, and then all of a sudden they go in a smaller area. So that's what these guys are doing here. So this gives us an idea of how they pinpoint the direction of a signal. It gives us some idea of how they can kind of guess at the distance, but it's not enough information for them to be able to do that without any other senses. And it doesn't address our friends, the mechanoreceptors. So let's remind ourselves of the brain here. We've got our intertwined regions that are incorporating both pieces of data. We've got our neurons in here that can interpret both and deal with both. So we'll kind of look at this in the end. So mechanoreceptor, electroreceptor, neurons come together. So here's where our sensitivity comes in. So each and every single one of these different neurons in the brain is specifically sensitive to latencies between the way that the signals are received. So electrical signals travel faster in water than mechanical signals. And each of these guys has a preferential latency. So when the brain is kind of interpreting this, it knows that it's gonna get different amounts of information at different times. So it knows what region of the bill the signal is being received. And it knows that there are both electrical receptors and mechanical receptors in that region. And it knows the difference in time between the signals at that point. So this kind of complicating process, complicated processing goes on in here and that combined data enables it to kind of take all of that bits of information, the difference in time that they receive it and put it together to give an idea of how, of where the prey is located in three-dimensional space. So kind of a sort of similarity in that and a good way to think about it is the way that the primate visual cortex interprets two different images. So on the retina, you get slightly different images because you're seeing two different things with your two different eyes. And they have a kind of similar form of processing where they take those two images, interpret them together and produce a three-dimensional image that has meaning for direction and for distance. And the platypus does something very similar to that. It does it with two completely different types of data and it gives them a three-dimensional pinpoint in space. So, to close, to close, I will answer the question of what the plural form of platypus is, which so many people question. So we'll do audience participation on this one. So who here thinks it's platypus, like fish, fish, platypus, platypus? Okay, we've got a couple for platypus, platypus. How about platypi? Platypi, how about platypuses? Okay, we got some of that too. Okay, so you get two options here. You get acceptable, which means I will not be pedantic at a bar until you're wrong if you say platypuses. But because it comes from the Greek, technically the correct plural form of platypus is platypides. And speaking of being pedantic, if you want to at bars, this works for octopus too. So octopus octopides. And the slide that you guys are most likely to actually remember from this, and a bonus verb word here, is the correct form for a baby platypus is a puggle. So that was a little brief, but thank you very much.