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March 25th Lecture.docx

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Jon Houseman

Echinodermata (the sea star, the sea urchin and all of the other organisms associated with that particular group) Autapomorphies - Pentaramous symmetry- radial symmetry based on 5 - Stereom spicules - Water vascular system- a mechanism of moving sea water within their body as a hydrostatic skeleton that they are going use for locomotion and feeding strategy- the tube feet - Mutable connective tissue One of the unique thing is that they have radial symmery and it was thought to be weird because it is ususally at the base of the evolutionary tree. And for the longest time this group was associated with the Cniderians would have be the diploblast with radiam symmetry and the Echinoderms would have been the triploblast with radial symmetry. And it all made sense. And this radials symmetry that is based on five. Another thing is that they have internal skeleton- an endoskeleton. The calcerous skin that makes up their body is covered in spicules , blocks of mineralized calcium that are connected to each other and it is not solid but is spongy with lots of pores, that makes up the fundamental unit of their whole skeleton. In addition, they can take those spicules and connect them together with connective tissues, and the tissue that holds the elements together has a unique characteristic; it can change its consistency, it can be near fluid, liquid or can be solid and lock two cuticles together. And this is all under the nervous control, which can determine whether the connections are lose and flexible or rigid. In terms of the group, there isnt’ a lot of them out there, they are not a winner. And if take a look at the diversity, we see a whole range of things such as sea stars, with their pentaramous symmetry , Sear urchin , to sand dollars, or brittle stars which can disconnect an arm if it is picked up and the star can escape and regenerate another one, and Sea cucumber which are very consumble and slow moving, and defend themselves by throwing out their whole digestive system at the predator. The question is why? Why did a group of organisms with bilateral symmetry decide for radial symmetry which is often associated with sessile organisms? Their early larval stages are bilateral but they quickly settle down and pick up the Echinoderm lifestyle. And what we now understand is that at the time the the Echinoderms appear, there were sessile, they were attached to a substrate and had their arms stuck up with a series of tubes at their ends. They were actually gathering any types of food particles that would come down to the bottom of the oceans. And if it kanded in the centre of their umbrella, the tube feet would be able to move it down to the mouth and eat it. So by catching the organic debris, and other dead orgamisns flooding in the water column, they were able to tap into a food resource that the others crawling at the bottom of the ocean did not. And that was probably why there were succesfful. In some of the primitive ones, the arms were not always 5m but they all had the same morphology , designed for catching food. Now only one group is still sessile. Once they do leave the substrate, they flip their body, so that once these tubes that were used for feeding can now pull the organism up the water colum. When you look at the underside of the sea star, you can see all of these tubes, and they are part of the water vascular system. They are filled with sea water. Each of these are small little hydrostatic skeleton that will be used for locomotion. But in addition, the sea water that circulates in there is a transport fluid, where gases such oxygen and food particules can be circulated or we can move nitrogenous waste out of the system. ROLE OF WATER VASCULAR SYSTEM : Respiration, Excretion, circulations , and locomotion. Water Vascular system What we basically have is an outside opening,Madreporite iwhere the sea water goes in. There is no water that is being pumped in or pumped out; it is just a giant puddle of water. There are cilia beating there that move it there, but it is just a reservoir of water. There are thse polian vesicles that swell and fill up with extra water if necessary, but it is not a circulatory system. Just a pool of sea water. Tube feet And when you look at the little tube feet that extend down, you are seeing miniature hydrostatic skeleton with suction cup at the end. When we look at the anatomy of the tube feet, we are seeing a connection to the rest of the water vascular system. But there is also a valve here that shuts, and it becomes an isolated hydrostatic skeleton. There is also a reservoir here on top; the Ampulla. But the secret here is that there are muscles in the tube, and when the muscles contract, it can tilt the foot in either direction. Where the muscle is attached to the base of the foot where there is a suck, that pulls the base up to make the suction attachment to the base, then the foot tilts and you drag the animal along. When the Echinoderms decided dedicate themesleves to the water vascular system , they have prevented variation which means that they can never leave the water. Th water vascular system is going to be important as tube feet for locomotion. The fluid in the system will be moved around by the cilia and will act as circulatory passing around oxygen. The surface is good for diffusion of metabolic waste.Tehy don’t have metanephridia, and do they are locked into the marine environment. Body wall On the body wall you will see spine, and that is where the group gets its name; the spine organism. PEdicellaria You will also see that they are also covered with little structures, PEDICELLARIA- two little osicles of the skeletal structure. These animals are so slow moving that it is in danger of being settled on . So it uses the pedicllaria to ensure that nothing else settles on it. As well, the whole outer surface of the skin is covered in cilia, so that if sediments settle on it, it is moved away. Another strcture that is visible on the skin is a finger- like projection known as DERMAL BRANCHIA, extensions of the coelomic space within the star fish.TRI-PARTATE COELOM – procoel, mesocoel, and metacoel. Within this particular group, the metacoel is the one that made the water-vascular system and the meso is the one that makes the body there are two coelomic spaces and Dermal brancia is extensions from coelomic space, and that is another respiratory surface. So fingers sticking out on aboral for respiration. Tube feet on oral surface for respiration. Digestive sustem With the exception of sea urchin, most are carnivorous, and so you see these big digestive glands – PYLORIC CECI that extend out into each arm and this is where digestion and breakdown of the food occurs. Then we have a two-parted stomach justlike we have in our lophophores; the PYLORIC STOMACH-fixed inside and branches out to all the pyloric cecum and the CARDIAC STOMACH- towards the outside. And when this animal feeds, the brough is brough to the cardiac, then to pyloric, then to ceci. Sea Star When the animal wants to reproduce, you have the gonads expanding indifr each arm, gonads sitting next to cecum, and gonads can easily feed. The interesting thing about this is that the cardiac stomach can be squeezed out, and this is one of the major feeding methods. When the meal is caught, the star surrounds the meal, and turns its stomach inside out to eat it. When it is feeding on coral reefs, which conists of a lot pulaps on the surface, the sea star places itself on the surface of the coral, turns the stomach inside out, and secrets a lot digestive enzyme to liquid all the polyps , then cilia transfers the food to the digest tracts. They are also major predators of bivalves- the clams. Since they don’t move too fast, they will choose predators that don’t move or move slower than them. Reproductive system Contains eggs and spems Sea Star Arm At the ampula of the tube feet, it is surrounded by a layer of coelomic tissue,making the entire thing 2 cell layers thick great for diffusion of oxygen to the coelmic cavity, and diffusion of nutritients from the coelomic cavity to the tube feet. Sea Urchin- it is such a radically different modification. Has long spines that can be used for walking, using the muscular to move across the substrate. Especially modified because it is a herbivores. Water vascular system- one of the things that need to occur when you are a herbivore is the lengthening of the digestive tract, containing little pouches and spaces to deal with the plant material. One of the massive things in the sea urchin is the digestive tract that spirals from the oral opening, spirals back on to itself and spirals to the anus. This huge SA is to process the plant because when the food source is poor in nutrient, you need to keep in the digestive tract long in order to extract all the possible values. Suspend from the top of the shell are the gonads. And that is all what the sea urchin is; digestive tract and gonads. Eating sea urchin gonads as a food source is a delicacy. But if we take along at the body wall and surface, we get all these spines. Echinoid spines and pedicellaria The thing about the spine is that the tube also has to be longer because if it is going to be used for locomotion, it needs to be longer than the spines. The spines are great for walking, but if you want to stick to the substrate, then the tube feet are required. And so you end up with extremely long tube feet. On the oral surface You will see five sets of little teeth alined with the five rows of where the tube feet are going to be. Aristotle’s lantern What is phenomenal is that how detailed the little bones on it are to be able to feed and scrape plant material off rocks. The whole lantern is suspended by muscles so that it can be pushed out, pulled back in and titled and changes the orientation. There are 5 pyramidal teeth that can be moved back and forth, closes and open to create biting motion. In addition, inside the pyramid, there is the main tooth, which is considered to be the cutting surface. And this small tooth in the middle is the cutting tool, and is subject to wear. As it wears away, it is regenerated from the top. So you end up with an organism that can process large amounts of plant material. Digestive system When we get inside though, the esophagus is going to propel the food to the digestive tract. A Second tube makes it appearance ; the SIPHON as part of the stomach, and as the good enters oral intestine, the water is pulled out of it and put in a different set of plumbing, and this increases the food concentration inside the digestive tract, which means better digestion by the enzymes as the substrate concentration has increased. So we take the water out, pass it through the digestive system, add the enzymes and try to absorb as much of the nutrients as we can. On the opposite side of this sea urchin is the aboral intestine, and the water that we took out in the oral side is put back in because the undigested food is so solid and rigid that it has the ability to tear the system down. And so addition of water makes it more fluid, and it can then be excreted through the anus. There is large anus because it has to get rid of a lot of plant material unlike the sea star. Hemichordates and Invertebrate chordates Animal innovations ( Symplesiomorphies) - Pharyngeal gill slits- slits where water are going to move, initially part of feeding mechanism, after food taken in, water moves out, and also good for gas exchange - Dorsal hollow nerve cord-found in hemichordate For the longest time, hemichordate were placed in chordate because they thought they had seen the other two hallmarks,notochord and undulating swimming motions. Because they only had 2/4 hallmarks of chordates, they got their name HEMICHORDATES. They are bit unusual because of their unique structure- STOMOCHORD PROBOSCIS COMPLEX, which is a structure to support oral opening for feeding, and proboscis- part of body extending out to the front is what the food is held in. WE are also going to find a unique form of excretory structure- GLOMERULUS- you are going to create your ultra filterate of the blood by pressure-put blood pressure on the blood, and pass it through a thing memebrane and that pressure will force the blood out of the wall, and take everything else with it. Proboscis worm-Hemichordate Has the tri-partate coelom; protocoel- Proboscis, mesocoel- the collar, and the metacoel- all the rest that is divided into different functional regions. Branchiogential trunk – where we will see the movement of water through the opening of the gills. We also see the gonads here. Hepatic is where the final digestion of food takes place. Stomochord proboscis complex- filters blood This structure at the front is the secret to how these function because what we ended up with is the di-reticulum of the gut- a piece of the gut folding back on itself- creating rigid structure- making a skeletal element- important because of where it is located- hold mouth open. Feeding- the PROBOSCIS is covered in cilia, and these cilia are constantly brining water current with organic particulates towards the mouth. If the food particles are too large, they will be pushed away and let go, but if they are of a good size, the cilia will guide them towards the PRE-ORAL CILIARY ORGAN, down to the esophagus, and the water will exit gill pores while the concentrated food passes to the gut for digestion. Locomotion Does not have much musculature associated with it. The only place they have some muscle is their PROSBOSCIS, and they will move using that- very little movement. Chordates-Vertebrates Autapomorphies -Neurotube-notochord-mesoderm complex- -Pharyngeal slits and endostyle -Post-anal tail and tadpole-like swimming th March 25 Lecture-Fish Bony fish- Osteichthyes They have developed a number of things to maintain neutral buoyance. We have talked about the swim bladder. One of the things is that they can feed while they are hovering in the water. We have finished talking about the suction feeding that occurs within the group. This is all part of the modification of the jaw, at the front of the fish. What the fish has done is added extra bones, expanded bones, added membranes in between so that they can open their mouth wide to feed. What we need to realize is that, as a fish moving forward in the water, it is sending ultrasonic sound of vibration of the water as it moves forward and it is to warn other fish that it is coming. The other fish can pick up the signals using their lateral line systems. The whole idea here is to be able to explode the mouth faster and faster in order to be able to catch the prey before the prey detects the fish. So that is really what the suction feeding mechanism is all about. But what is also interesting is that inside the mouth, father down in the back, there is a modification of the gill arches, now that the jaw is involved in suction feeding, into a secondary has teeth on it to be able to hold on to the prey, or to be able to grip the prey before it is swallowed down into the digestive system. So they have quiet an elaborate feeding mechanism. Fish integument The bone on the dermal bone turns into scales, and the scales are exactly the same story as when we took a look at the sharks. The idea is that scales create micro-turbulence on the surface of the fish, and that micro-turbulence eliminates laminar flow over the body of the of the surface. And that means that we eliminate friction, which means that we have more effective movement through the water. Fish Scales There are basically three different types of scales.The most primitive are the ganoid scales, and they are found on sturgeons and some of the very ancient fish.They are very dense, interlocking, overlapping set of scales.Very much like a suit of armor, and it creates quiet abit of weight, and they are replaced by two other sets of scales; Circular, overlapping ones called Cycloid, or a series of scales called the Ctenoid scales. Ctenoid scales get their name from the little set of teeth that are associated with the margins of the scale. It doesn’t really matter which of the three types that are there because they are all doing the same thing; they are creating micro-turbulance on the surface of the fish so that as it swims through the water, it is much more effective in terms of that swimming motion. Trunk musculature And associated with that swimming motion is a really complex overlay;mayomeres that run the length of the body, the little muscles blocks that are there.Earlier we saw them as little W- shaped things that overlapped in the early fishes, as we saw in the cephlo-chordat .By the time we get to these fish, we notice a considerable overlapping. And if you have ever had salmon in steak form, you will notice these overlapping w-forms which create up to seven layers that when we get contraction, we don’t get the whole side of the fish contracted, instead we have gradual contraction on each block that ripples down the length of the fish to create it nice, and smooth undulating motion that gives them that forward movement. So both of these are tied together. Movement is enhanced. We got movement of the fins; pectoral and pelvic fins which would allow them to hover, and we have now got the tail movements,for the major propulsive (ability to propel) force for moving . Opercular gills Now the other thing that happens is that these animals are also able to breath when they are sitting still.What we are heading for is a fish that can hover in one place because the swim bladder allows it to maintain a neutral buoyance , it can monover in one place by using the delicate motions of its pectoral fins, but we still have the issue of ventilating the gills. HOW DO WE GET WATER OVER THE GILLS? And one of the things that has happened with the modification of the jaw, is the big bony OPERCULUM; a covering. And that covering is over the surface of where the gills are, and it can swing out and in. and as it would swing out, what it would do is pull water across the gills.Particularily, the mouth opens at the same time,so if we open the mouth and swing the operculum out, we would be able to pull water in , and create a kind of flow from that is based on the changes in the mouth cavity. So we can open the mouth, suck some in, we can close the mouth, we can squeeze the mouth down,we can open the operculum, and we can force the water out.In another words, we have a very effective pumping mechanism associated with the mouth. And that is a spin of the sucking pharynx that was there at the beginning because that too was used to bring water into the mouth. The two are closely related to each other. And what we end up with is a fish that can hover in one place, and sit there and stalk prey , or hide from predators, and do all of those things that none of the other fish had been able to do before up until this point in time. And perhaps one of the best examples of this is one of the very highly modified fish. Video- Sea horse called the sea dragon. What I want you to focus on is how it is hover, and there you can see the pectoral fins, and it is using it to sort of maneuver itself in the tank.also using the pelvic fins further in the back, what this animal is able to do is to maneuver so still that it mimics the sea weeds, in which it hides. And it sits there, hiding in the sea weed, and feeds on small prey such as small fishes that come along using its vicious suction feeding structure to pull them into the mouth and ingest them. While it is maneuvering, it is very passive, fighting the current to stay in one place. So this is a huge advantage, and is one of the reasons why this group diversifies because they have this ability to hover in space that no other fish is going to have. And it is one of one of their reasons for their tremendous success as a group. Opercular gill So all that put together, there is more going on in this respiratory mechanism because we are pumping water in at all times, and we are pumping water over the gill surface, inside the gill, and artery, and veins that extends blood vessels down into these gill filaments. Gill Arch Counter current exchange But there is something important going on here, and that is the fact that these gill filaments are set up with disc-like structures. And in these disc-like structures, the blood is following a uni- directional path. In other words, it is coming in from the blood vessel, across into the next blood vessel. The vein is going to take it towards the heart. The other one is going to be bringing it from the body to the heart. And now we are getting the pumping mechanism. What is important here is that the water is flowing over these little disc-like structures in the opposite direction. And this is an important phenomenon in biology called COUNTER CURRENT EXCHANGE. And what happens is that when you have two fluids in close proximity to each other and they are moving in opposite directions, you enhance between those two fluids. It can be gases. You probably have a counter current exchanger somewhere at home. For instance,a high efficiency furnace. It is highly efficient because it takes the air from the outside and it heats it up to distributed in the house. But if you get the air that is slightly warmer, then you don’t need to burn as much fuel,and so what happens in almost all furnaces now is that the heat that is rising up with the gas,being vented out of the system in other words, the hot air that is being produced from the burning of the system is placed beside another pipe which is the incoming current coming into the chamber where we are gonna have the fuel. In old furnaces. What would be going on is that you would bring outside air into the chamber, and burn it, and you would sent the hot air up. And that was not very efficient. But if you take the hot air,and as it rises through the chimney, and the cold air beside it moves down, and they can exchange with each other, you that heat that you lost in the chimney and transfer it to the cold air that is coming into the fire chamber. Consequently, you don’t need to burn as much fuel to raise the temperature. And that is exactly what is happening with the counter current exchange in the fish because the fluids that are going across the gill, the water is saturated in oxygen.the blood that is moving the opposite way is low in oxygen because it just finished travelling through the body, and it has been dumping out its oxygen to the tissues. Concurrent exchange And there are two ways that this can happen. Counter current is when they are both going in opposite directions. Concurrent is when they go in the same direction. And if we have concurrent flow, we are gonna have to keep our mind in two places at once here. Here is the blood, 20% saturated in oxygen coming into the gills, here comes water from the outside, it is 100% saturated in oxygen. And so what is going to happen is that, this very early point in the gill, when the two solutions are next to each other, water will be highly saturated, blood will be low, and you get oxygen diffusing between the two.This water slowly loses oxygen,and its saturation level goes down, as the blood saturation level increases. But we will still get some exchange until we reach the mathematical equilibrium between the two (60%), and then it will stop. And we still have oxygen in the water that we can’t extract because the blood has reached equilibrium with the blood that is passing by it. And so we have an uneffiecient system where there is more oxygen in the water that we could have potentionally trapped,and used but we can’t do anything about it because we have the blood with the same concentration that is there. Counter current What happens in the counter current is that because we have the flow in opposite directions, the water that comes in, 100% saturated in oxygen will meet up with some blood that is at 100%, and as it moves , it will meet with blood that is at 90%,and will have exchange. And as the water saturation goes down, the blood that is counter flowing is always low in oxygen. And so what we end up doing is that as the saturation level of the water goes down, even at 30%,it is meeting blood that is lower in oxygen saturation as it is only at 20%,so oxygen will still get exchanged. And so, by having things move in counter directions, we optimally extract in this case the oxygen from the system. So the end result is that we get, much more effiecient transfer of oxygen from the fluids to the blood, and better loading of oxygen to the system. This actually happens somewhere else. Swim bladder ….because when we were looking at the swim bladder, and the rete mirable, what we had there was a counter current exchange where blood vessels were moving into the rete, and out. And of course what is happening is that this is dumping oxygen out. And let’s say that is this is highly saturated in oxygen, e.g 100% saturated in oxygen, the blood moving up is at 100%, but the blood moving down is only at 90%.And so we transfer it. By the time the blood gets to the top again, it is at normal concentration, 20% that we would associate with the blood. And this is how the swim bladder manages to get oxygen and gases concentrations at such tremendously high levels because you pump the oxygen in, even though it diffuses into the blood, as the blood stream moves away, it passes that highly concentrated oxygen to the blood that is coming into the capillaries of the rete mirable. And we end up with high concentrations. The opposite thing is happening on the other side, and this is how this particular system is using counter current exchange. Counter current exchangers are all the way through animals. They are one of the most commons things that all of the zoology courses tend to put it in with the fish gill model but we will see it in a couple of more places. All of this is hooked into a circulatory system that… Circulatory system …a circulatory system that has a two- chambered heart,still a very simple heart, nothing major is happening with this particular heart from what we have seen from the hearts of the other organisms we have looked at so far. It is very much like the shark heart. The only difference is that we have come down now to four aortic arches. We have gone from 6 to 5, now we are down to 4, and one of the things that is going to be happening as we take a look at the circulatory system is that we will see a reduction in the aortic arches. Nothing really new in the circulatory system at this point.But fish are faced with one issue… A tale of two fishes ….and that issue has to do with their ancestory.In the mass extinctions that occurred,in particular the Permian,and earlier ones, the fish were wiped out of the oceans.What we see today as fish , none are survivors of the big extinction. The fish that came into the oceans are all from the fresh water. So one of the things we often forget are during these times that we get destructions to the marine environment, quite often, the fresh water bodes such as the lakes would have still had fish in them. And those fish are the ones that repopulate the oceans when all of the fish went extinct.And when these fish came to the ocean, they brought with them an adaptation that they had developed from living in the fresh water. And the problem for fish when they move into fresh is the isotonic, hypertonic, and hypotonic.Now the fish scale provide a body surface that is water proof, that is not a major issue. Gas exchange is occurring through the gills. And if gas can diffuse through the gills, so can water. And now you got this animal that is swimming around in fresh water, circulatory system that contains salty solution blood. When the blood is passing through to pick up oxygen, it is also going to pick up water as well. So fish are faced with this situation when they are in the fresh water that they are HYPEROSMOTIC to their environment ( they are saltier than their surrounding). Over the time that the fish evolved in the fresh water environment in millions of years, one of the solutions was to slowly lower the salinity of their blood. So the salt level in the blood system of a fish from the fresh water that is about to come back to the oceans is lower than those in the marine environement. Now we got the same issue, a body surface that is covered in scales, and is water proof. So we don’t lose any water there, but when we get into the marine evironement, because you are less salty than the marine environment, you are constantly in a situation that you are going to lose your water, lose your salts, or minerals across the gills instead. In the marine evironement, we are in danger of losing salts, and minerals across those gas exchange surfaces.HYPOOSOMOTIC problem in the marine, and HYPEROSMOTIC problem in the freshwater. And what happens is that we end up with two very unique solutions; a fresh water fish because it does not want of that water anywhere in its system,will not drink any water. It will not drink any of the water in which it lives. Now, it will obviously during consumption of food take in some water, and some water will move into the digestive trac, but it will at all costs try to avoid it. And the kidney is going to produce a large amount of hypo osmotic urine to get all the excess water out of the system. And of course it will be trying to recover as much of the salts as possible. So what you have got is water being inundated in , coming across the gills, and we are in a situation where we are trying to avoid putting water in , but it is still happening . so what the kidney does is that it filters the blood,creates a urine that is dilute, hypoosmotics , very low in salt because the kidney is going to do whatever it takes to recover the salts. There will be a problem though; when the kidney can’t keep up and we start to lose minerals, because the kidney is not 100% effective in retaining the sodiums, chloride, the magnesium and the calcium and all of those minerals. There is always leeching that moves out.So what happens in this particular group, the cells on surface of the gills are capable of plucking out minerals from the water that moves across them. They are active at sequestering things like sodium,chlorine, and all of the minerals that are essential. And that is how they compensate for their ionic balance. Marine environment fish The fish in the marine evironement is constantly in a situation where it is losing water. As a result, this fish gulps and drinks a lot of water.It wants to flood the system because it needs to bring water in.When it does this, and it wants to conserve the water and not lose it to the outside evironement, the fish in this case is producing very little environment. We are making sure to always bring lots of water in to compensate for the water loss, and we are not producing lots of urine. But now we have all this sea water that is coming in that is loaded with ions; totally different situation than the fresh water fish. Now on the gills of marine fish, the complete opposite happens, the gills of the fish expels ions, and excretes them out. Now what happens is that in these two types of fish, the gill system along with the kidney that produces a lot or little urine combine together to produce an Osmo-regulatory system, which allows these organisms to live in fresh water or in marine. When considering the fishes to migrate between these two different evironments, we are looking at the fish’s ability to switch its ion pumps to either sequester ions from the water or secrete the extra ions into the water across the gills. Reproduction Reproduction within the group; things are very straight forward in most fish. Vast majority of them, eggs are laid in the water, the male spawn release a large number of sperm over the surface of the fish, and after that the fish embryos hatch and we end up with large number of fish fry, which is the very opposite of what we saw in the shark, where they spent a large amount of their time in producing very few young. And there is one exception to this; the sea horse. The sea horse are one of the most famous for parental care. The male attempts to attract the female by displaying himself, and showing her that he is interesting in taking care of the young as the female sea horse would take her eggs, and put them in the male pouches. Then the male would incubate the eggs in his pouch for long periods of time. And that is it for the bony fish! Lobed Fin fishes The lobed fin fishes are important to us, in these animals, the fins aren’t supported by bony rays, and they are actually supported internally by hardened bones. Those hardened bones are the reason we called them lobed fin fishes. These are re-enforced pedal with actual bone inside. Transition to land If we take a look inside these lobed fins, what we see is the tetrapod limb that is going to come. Because there is always a base bone that is attaching to the main body, there is always a paired set of bones, and smaller set of bones that are associated with it. So we end up with the starting of the single bone, double bone, and smaller bone, which is typical of all the tetrapods and invertebrates that are to come. This group is important because most of them crawled and peddled along the bottoms of the water, and they are all freshwater animals. One of the things that happens in the Devonian, which is just before the really wet and moist carboniferous, the land starts to dry out, and the planet starts to get really warm, fresh water environments become compromised. Small lakes are starting to dry up, they are not oxygenated, and there is low levels of oxygen associated with them. And what these fish had as advantage was that they could use these limbs to push their head up out of the water, and breath oxygen in these bags that they had inside their body.So these fish don’t have swim bladder but they have lungs. And those lobed fins that allowed them to push up also allowed them to crawl out on land that was no too dry, moist enough that they could get from one puddle to another to be able to survive and feed. As a result, we end up with a shift in locomotion as these animals move up on land and move into more optimal freshwater evironments. One of the other things that happens is that these fish are also making contact with the insects that are also starting to appear during this time. And the very first insects were not very vigorous flyers, and what these fish were also able to do it, they were also the first group to feed in these insects and crawling arthropods such as the centipede and other things that were starting to colonize the land. And none of the tetrapods had ever been able to feed on them before. And so when they move up on land, they ended up with two distinct advantages; they ended up with a new food source, and they were able to survive in these new bodies of water.There are two main groups of survivors today, and they are called lungfish. Lungfish And they get their name from the fact that they have a lung. They are distributed in the southern hemisphere, and are associated with southern part of Gondwana, and the freshwaters that were part of the super continent before. Then the super continent broke up . They all have the typical circumstance of having pedal like fins. Now the African fish have become very much filamentous since then because the African lungfish does a bit less swimming, and does more burrowing. In fact, both the African lungfish and the Austrialian are both burrowers. And what they do is that, they will burrow into the mud sediments, and so they do not have the typical lobes that we associated with lobes fishes. As they burrow, they go into states of dormancy and sleep, waiting for ideal conditions to come along . the Australian lungfish spends a fair amount of time in the water .when the streams and ponds dry out seasonally, what they do is burrow into the moist, wet mud and they wait it out until the water comes back. The African lungfish is slightly hardier. It can go into complete dormant state and hibernate. It will dig into the mud, and surround itself in a mucilaginous cocoon , and that will protect it from desiccation , and the dirt and the soil around it can completely dry out. And the African lungfish can survive in dormancy for fairly long periods of time, sometime more than a year, waiting for mud to become moisten. So the difference between the two is that one needs to hibernate in moist mud, while the other can survive in dry mud. The one thing that they have that all of the other fish don’t have is that they have a three-chambered heart. These and the amphibians, which are going to descent from them, they are going to end up with two circulatory circuits, one that goes to the lung, and one that goes to the rest of the body. This makes them superior. The other consequence is that because the amphibians that we see are going to ascend from them, the amphibians are fresh water, and the lungfish are freshwater and none of them have made back to the marine environments. There is one fish that comes up always; the Coelacanth Coelacanth ( marine fish) The Coelocanth was first found during the was thought to be a missing organism because there was skeletons and fossils. The zoologists were very excited about it because it had loby fins that were very muscular, they were able to use them in alternating gates, in other words, the fins did not have to be pedaling at the same time. You could making these walking motions with them. As a result, for a long time , it was considered to be the ancestors of the animals on land. Then in about 1998, it was discovered that it was nothing weird , because a zoologist, perhaps in Malaysia was walking in the market, and looking over the fish specimen. Then he sees a big ugly one and identifies it as a coelacanth and wonders where it came from. The fisherman told him where. And so the whole zoological world got really excited about it all because here was supposedly the missing link between the fish and all the land tetrapods. Of course they did the genomic work. The Coelacanth is a really weird organism because it is almost blind; it uses mostly electrical sensing of its prey which is done mostly using the top of the head. It fishes for prey with its nose down, and its tail up at the bottom of the ocean. And it spends most of its time living in a cave. Uses its fins as if it is walking in the water, and its three-lobed fin is found on no other fish. The transition on to land will start and then will stop because the carboniferous will come along and it will be a very moist environment, and there is no driving force to solve the issue of moving on land and that is why we are going to get our amphibians. Amphibian Lecture .This is an interesting group, because as mentioned, they start to make transition to the land but they don’t solve it. But before we go off on land, there are a couple of things we need to do. 1. Waterproof our respiratory surfaces because we don’t want them to dry out. So we are going to have to figure out how to waterproof those surfaces. 2. Support ourselves against gravity, because we are not in the buoyant water anymore. We are not in a situation where we have air as our supporting system instead of water, and we need to deal with that. 3. Mating- we need to be able to develop eggs and sperms in such a way that they are not going to dry up. What we are going to see is that the amphibians are the first ones to descent from our lobed fin fishes. Although they have moved on land, they seem have only solved half of the problems because as mentioned, the world got really damp and moist, they became specialists at living moist environments on land. It is going to be the reptiles and mamals, which are going to figure out how to live on land in dry environments. So they basically become specialists in that moist environment. The other thing as we take a long at the amphibians is that they will within three main categories. 1. Snake-like ones that are very rare 2. Salamander, which are structurally very similar to the lobed-fin ones hence that they still have a tail. 3. Jumpers!  The frogs and the toads. What we see today is a very small remnants of the amphibians that have since disappeared because what happens is that they diversify on land and we don’t even know how that diversification occurs because our record is very short on the intermediary. Perhaps due to the fact that they were in moist environment and there is little fossil remnants. So today we end up with three very bizzare group of organisms; the snake-like burrowing amphibians, thOsteichthyes mmmmmmmmmmm me salamander nude amphibians, and of course the jumping frogs. And so it is really hard to make generalizations about the group, but there are things about being a tetrapod. The one important thing to realize is that around the world, this is one class of animals, the class amphibia that is declining at a fast rate. The decline was first noticed about 6 or 7 years ago, but it was never really understood why. Because they have to breath through their skins, they were getting UV damage, due to decreasing ozone layer, and higher UV penetration. It was thought that they were dying from pesticides and chemicals that were leeching into the fresh water systems from agriculture and industries.and because they breath across their skin, it is also a main method of mineral exchange, similar to fish gills. They were taking these toxins in , and were not able to deal with them. From the many reasons, only the last few years, the reason for the decline has been understood becase there a certain type of fungus, called the accreted fungus that infect amphibians. This fungus gets underneath the skin, and the hyphae of the fungus branch out and start to destroy the epidermal layer, which means that the frog ends up getting starved. And it turns out that there was a phenomenally bad decision made during the 60s/70s. There was a pregnancy test shifted from using rabbits to frogs. They took lepoeard frogs and these were the mediums to check whether a woman is pregnant or not, and they cultured them in huge numbers for this test. And they were also used as research frogs for amphibian biological research as well. So they were being grown everywhere around the world. And it turns out that these frogs were resistant to the accreted fungus that they were infected with. And as these frogs got out and escaped from all of these medical facilities, they inoculated this fungus in the natural environment. It hit its peak about 10 years ago. Initially there was no sign of this fungus of this fungus in the amazon forest, but after this incident, they were able to plot as the fungus moved around and into the amazon forest.Herpitalogist noticed that one year there were lots of frogs singing in the rainforest, and in the next year, or two years later, they are all gone, and they are never seen again. So this is wipping out species and genera entirely world wide. Most of the amphibians will most likely disappear by the end of our life time, as currently 30% of them are under special care in hopes of being re-introduced to the wild again. So this little group was successful and had three survivors, and these three survivors are in trouble now. The first amphibians did not appear like any that you would think of. Ichthyostega That is how dramatically different the group is.but what they do havem and what is important is that they have those 4 legs, those 2 pairs of appendages that give the tetrapod their name; the legged animal. These four appendages, the anterior and posterior, the pectoral and pelvic, are used to lift the animal off the ground and move. But when that happens, the appendages are attached to the vertebral skeletal, the axial skeletal. Vertebrae And when that happens, we lift up and take the weight of the gravity against the skeleton, if we had the vertebrate like we had in the fish, there are perfect little discs beside each other. And of course, if you push on that under any type of gravitation, the discs are gonna slip passed each other. And so when the tetrapod stand, not only do we have 4 appendages used for walking, we also get major modification of the spinal column with overlapping bones; zygapophysis,Diapophysis, and Parapophysis.These take the fish vertebrae which are columsn of discs, and adds overlapping bones structures to re-enforce the whole vertebrae column, and they give it its rigidity down its length, so that when we lift up, we can move the whole body. There are also different sets of vertebrae associated. Skeletal support And of course with this are changes in the vertebrae, and where they are located. There are a set of vertebraie that located between the first set of appendages and the head; the cervical vertebrae, and they are highly specialized in movement of the head. They cannot have all of these locked together and have the head immobile. So they always have a very different morphology. On the opposite end, there is a vertebrae that is associated with the tail; Sacral vertebrae, and in between associated with the trunk, depending on whether we have any ribs or not, there could be a set of vertebrae ther as well. So we get specializations in the vertebrae. And of course the most special one are the ones that attach the sets of limbs to the body. Axial skeleton The pelvic girdle, basically if we take a look at our salamander, the centre is our axial skeleton, from the sides are extensions that go down and connect to the limbs. There is a bony plate underneath to help support the internal organs and we got the limbs sticking out to the side. It is the same on the anterior side as well because the morphology of an amphibian is such that when it rests, it is lying on the grounding, the stomach is touching the ground, and when it move, because its legs stick out to the sides, what it is going to do is that it is going to do a push up, off the ground and start to move.and this is not extremely effective method of locomotion because you have to push yourself to move yourself off the ground. Walking and respiration But that movement comes from the ancestors because what the amphibians are going to do is that they are going to push themselves off the ground, and then your undulating motions to move. So what happens is that the whole body undulates, and what the amphibian on the land is going to do is tha tis is going to use the limbs to create the undulation that goes down the body as it moves and advances each limb. And so we end up with this very unique form of movement that starts with a push up. Now the problem is going to come, and the amphibians don’t solve this, is that if you have a pair of lungs, and you are on land, and you have appendages that one moves forward and the other remains back, you are going to compress the organs against the wall on one side. And if there is a lung in there, you are going to compress the lung. In other words, this lung will not be available for respiration because you end up squeezing air out of it at this point. So this lateral movement ends up in such a way that it compresses the lung. Movement becomes affected by locomotion, or walking and respiration become linked but NOT IN A GOOD WAY because this animal can’t move and inflate both lungs at the same is restricted by the movements of its limbs. And we will see solutions to this as move PAST THIS GROUP. The amphibians are still stuck with them. Tetrapod stance What they do give us is the bones structure for every tetrapod that is going to come. It is always going to be one large bone, a set of paired bones, a set of small articulating bones, with a set of flanges extending beyond. And of course this comes from our lobed fin fish; one base one, one paired bone, single bones and articulating pieces that were associated with the lobed fins. They have articulation that is associated with the shoulder, the hip, the elbow, the knee, the wrist, and the ankle. They are all the same in every single group from here on. And this makes its appearance for the first time in the amphibians. So all of that in place, the Amphibian, this particular group, as mentioned is highly endangered, but they give us some very interesting modifications. March 28 Lectures The thing that we have to remember is that the amphibians were the solution to the drying out of the terrestrial environment during the Devonian. The fresh water organism were in danger of drying out during the Devonian because the water quality decline. The lakes and rivers were drying out and were low in oxygen concentration.the lung fish had the advantage of being able to poke their nose out of the water to breath, and because of the extra re-enforcing, they were able to leave the merky water in hopes o finding better habitat.But what happens is that when we see this transition occurring, the world goes really moist and damp again at the beginning of the carboniferous , and so terrestrial adaptations begin to appear in the amphibians but they don’t complete themselves. And so what we get in the vertebrate linage is a group of organisms that are half- adapted to the life on land, but still having to return to the water. It is important to keep that in mind that is not until we get to the mammals, and the reptiles or the di-apsets and synapsed that we are going to see this complete itself. There are four main characteristics that we identify amphibians by. We should not be surprised that very often in vertebrates; we identify them using the shape and forms of their teeth; the acquisition of the jaw, and the teeth on it. Once we get to mammals, where we see all different types of teeth, it is one of the key diagnostic characters for identification of organisms within the tetrapod. That is why sometimes in the articles you might see something that they found a jaw with a few bones on it, and they are able to identify the organism because most of the characteristics are based on jaw dentation and d the teeth. In this group, we are going to take a look at what is known as the Pedicellate teeth. The other thing is that, they are going to move on land, and they are still going use their skin as the primary respiratory system. But what they are also going to do is start breathing using their lungs. And this is going to add a third thing; the mechanism of how they fill their lung which is going to be very different from the other two. So filling the lung and the skin as primary respiratory system are both linked.and then finally the bones in the head are going to do something unusual and create a secondary acoustic pathway . So sound is not only going to be detect by vibration in the ear,but also different parts of the body. So let’s take a look at this. Pedicellate teeth It is a very unusual form of teeth, and it goes all around the jaw. It is not modified into different types, but what is weird is that they have a constriction in the diameter of the teeth, midway down. So if I were to exaggerate this, we would have a tooth, then we would have a constriction, then we would have the rest of the tooth embedded in the jaw. And that is not seen anywhere else in the vertebrates.Usualy the tooth is a conical, or smooth structure leading to the root. Secondary Acoustic pathway One of the more prominent characteristics associated with the skull is the secondary acoustic pathway, and what has happened is that the very first amphibians that were on land, they rest were their stomach on the ground, they have to do a push to dmove, one of the things that happened is that in the lower jaw line, they were starting to pick up other words, they were picking up ultrasonic low vibrations from the soil and substrate that they were resting on becaue their jaw was sitting on the ground. This was good because as a prey, you could sense the stomping of the predator and then design a strategy from the predator. In this particular group, they have taken advantage of that. Over time the bone that is normally located in between the branches of the jaw, the hyomandubalr bone that is normally associated with the tongue, now has a new role; because it is making a connection between the skull, it used to between the jaw, the bone, and the skull, and the bone has changed its position, and attached itself to the pectoral gurgle, attached to the forelimbs. The bone is now continuous from the pectoral gurdle, the foot on the ground, from their up to the skull, and from the skull to the inside of the ear. And it becomes known as the STAPES or the COLUMBELLA. Typically what happens in the ear is that the tempenum vibrates the sensory system within the ear, and that is how we pick up sound. But this connection between the stapes, to the legs, and down to the ground means that we are also picking up low frequency vibtrations that are coming through the soil. And so we have a secondary acoustic pathway. We don’t have the oringial one, where the tempnaum vibrates on an air space, which then creates the sounds that an organism dectects, we have got virabtions that move through the limbs to the sensory apparatus. This sensory apparatus now picking up sounds from two different locations; the tempanum, the outer ear, the prominent one that you can see on the bull frog , but as well the ground and the substate. So the animal becomes specialists at picking up frequencies from medium to high that are associated with sound, and also, the low vibration frequencies that are associated with creation of ultra sounds on the ground. And this is one of the few vertebrates that has this dual audiotory pathway. That is why it ends being important to them. In fact, many of the amphibians are very sensitive to sound and of course of the big things that they do that using sound for communication. In the spring, different groups, such as bull frogs make mating sounds. And they have become essentially auditory specializts in high frequency and low frequency. And that is why we give this trait as an autampomorphy. Buccal force mechanism of respiration Our lung fish were using their lungs to a certain extend and the amphibians were too. But what happens within this group is that, the lung fish were more or less inflating their lungs by expanding their body cavity; the body wall. But what the amphibians are going to do is a very unique method of filling their lungs; BUCCAL FORCE- the amphibian sucks in some air through its nostrils into its mouth cavity, and so opens the mouth cavity, and then closes nostrils, clamps down on the muscles of its mouth, and pushes the air into its lungs. In other words, we are using positive pressure to fill up the lungs. And so the amphibian fills up its mouth, clamps down on it and pushes the air into its lungs. It does that a couple of times. And when it is time to exhale, it clamps down on the musculature of the body wall, and when this musculature contracts, the air is pumped out. Video of Amphibian breathing You can see this in the little video of the amphibian breathing. If you watch closely, you can see that as the bull frog inhales by lowering volume at the base of the mouth, pulls in air through the nostrils, pushes it down, and sends it to the lungs. But at the back, you can see that there isn’t a perfect correspondence between the number of gulps of air and when we exhale. So during respiration, we will pump up the lungs, using that BUCCAL FORCE, that positive pressure, and when the lungs are filled, the body wall contracts, and we exhale. This is only possible because amphibians don’t have very complex ribs and they are still relying on the musculature of the body wall to hold them in place. So we end up with this very different breathing mechanism. It is different because in the two upcoming groups; the dyapsed and the synapsed or the reptiles and mammals, they are going to have a mechanism where they are going to have the rib cage to pull air in, or we are going to have a diaphragm in mammals to pull the air in. In amphibians, we are pushing it in with positive pressure, but all of the rest of the groups are going to suck it in with negative pressure. That is what distinguishes them from the group. Amphibian skin Their main respiratory system is of course their skin. For amphibians, this skin is important because it has to be kept moist at all time in order for gas exchange to occur. We are going to see keratinization of the skin when we get to di-apsed and synapseds; mammals and reptiles. There is a bit of keratinization here, a little added to toughen up the skin. We can’t put too much in there because if we put too much, we won’t be able to get the gas exchange across it. Overall the skin kept moist by a series of mucus gland that are all over skin, and those mucus glands are constantly creating a liquid so that the skin doesn’t dry out and we get the respiration. Now if we are looking at toads, which are adult amphibians that spend most of their time on land,and use their lungs for air, we see a highly keratinized skin because the skin is not used for respiration as much. But what they have lost is any of the fish scales that the ancestors had. The scales provided an advantage when facing a predator, as it would minimize getting crushed by the predator by distributing the force of the jaw all over the body. Of course this type of protection was valid when the predator is your size, not a grizzly bear , and you being a fish. But the reality is that, these animals are still able to protect themselves. In addition to the muscus glands found in surface, there are also POISON GLANDS, sometimes called the granular glands because the content looks granular. These are poisons that the amphibian can produce and secret to the outside. Sometimes touching frogs can irritations, which is basically the skin reaction to the toxins .the idea being is that if a predator picks up an Amazonian frog, it is quickly spet out, and not consumed. And what we usually see is that, organisms with really distinct poison to ward off prey, and they end up with really bright colours. Cane toad as a way to control insects, and was not a native frog. They multiplied in huge numbers in Australia. And little Australian girls made pets from frogs. They contain a poison gland that coats the surface of the skin with hallucinogen. So you had all of these girls being involved with narcotics. In addition, there is a major poison in Ontario a few weeks after the show. Some people in the bush ran out of beers, and had heard that you can get a high from licking frogs, so they sat around and starting catching frogs and licking them. They all became ill and had to be taken to the hospitals. As a result, frogs do have defense mechanisms, and part of the reason why they are so tasty is that as mentioned they have body wall without r
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