Monday, March 30, 2009
The Evolutionary Arms Race
At the beginning of Chapter 7, Carroll discusses the Oregon rough-skinned newt, an animal which has developed the ability to produce the TTX poison. Carroll also mentions that this happens in the puffer fish as well. Why do animals such as these develop poison instead of adapting other techniques? Where else have we seen the development of poison inside a species outside of that mentioned? Where has the predator of these animals developed resistance to the poison, and what was the next step those animals took? What are some other techniques used for survial that we've learned about?
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Animals such as the rough-skinned newts and puffer fish develop poison as a means to give predators a reason to not eat them. If they are poisonous, other species know not to eat them. Poison is probably used opposed to other techniques because it is the most effective in completing its task in causing predators to not eat them. The reason it is so effective is that it creates a direct correlation between eating the newt and death. If the newts had an unpleasant smell, this might keep predators away, but it wouldn’t create the powerful symbol of fear that fatal poison gives. It is much more effective to have your species synonymous with death rather than an unpleasant smell. Based on this principle of creating a identity correlated with death, any species that creates a defense mechanism that causes death after eating them would be just as effective as poison.
ReplyDeleteOther than the newt and puffer fish that have been shown, many other species use poison as a way to make their species synonymous with dead in the eyes of predators. Examples are plants that cannot run away from herbivores so they must use poison to punish predators. Strychnos toxifera produces the poison strychnine, opium poppies produce morphine, tobacco plants produce nicotine, and mescaline is produced from the peyote cactus. All of these methods by plants are to resist predators, and they evolve because those organisms who successfully resist prey because of their poison will survive to reproduce and pass on these toxin genes.
After looking at these defense mechanisms, it is reasonable to wonder why the predator won’t evolve equally as fast to keep up with the defense mechanisms proposed by the prey. The predators do continue to evolve, and this spurs coevolution, where two species evolve with each other. In Carroll’s example, certain garter snakes can survive after consuming a newt, and this increases their availability of food, giving them an increased chance of survival and passing on their genes for resisting the toxin.
As an effect of coevolution, many other different traits have evolved in species for defense other than toxins, for example mimicry, both Batesian and Mullerian. In Batesian mimicry, a species mimics the appearance of an unpalatable or harmful species, whereas in Mullerian mimicry two or more species resemble each other to make their numbers look larger. With coevolution, many people wonder if this “arms race” will ever end. Usually, a species will dominate a competing species if it is able to compete much faster with that other species. In the case of the snake and the newt, they are evolving at the same rate because their mutation rates and reproduction frequency are very similar. An example of a case where one species evolves faster than the other is the case of phages versus bacteria. As we have learned, phages reproduce quicker and they make more errors in their reproduction, so they evolve quicker than bacteria. Because of this, phages will always be able to evolve to find a way to evade defense mechanisms set up by bacteria. Superimposing this scenario between humans and bacteria, we see that because bacteria reproduce much quicker than humans, they evolve much quicker than our immune systems, and as a result there are more “superbugs” seen today that our immune systems cannot keep up with. In conclusion, coevolution stimulates evolution between two species and if those two species are evolving at the same rates, then the defense and predatory methods will continue to heighten.
I think that one of the keys to understanding to evolution of poison in organisms as a method of protection over other methods of defense is that there really is no reason. The organisms could develop any number of ways it is just that poison was what happened to develop in that particular species. Carroll emphasizes throughout the book that evolution is all chance and it is fine-tuned by natural selection. In the newt case, the poison originally developed as a mutation that created a selective advantage as it increased the newts’ chances of survival and therefore spread throughout the population through natural selection, gradually becoming more and more prevalent as those individuals with the poison were surviving at greater rates than those without it.
ReplyDeleteAnother organism that has developed poison as a means of protection is the poison dart frog. They are relatively well-known mostly because of their bright coloration which serves as an indication that they are dangerous. Their poison is actually synthesized from their diets which consist mostly of ants and mice. Their poison is highly toxic with the ability to kill roughly 10 humans. Because of this, they are able to live alongside many otherwise threatening predators. Their only know predator is the Amazon ground snake which has developed a resistance to the toxin, however they are not immune. These snakes, while not killed by the poison, become very distressed and are not functional for hours after ingesting the frog.
Aside from poison, organisms have developed a wide range of other defenses against predators. One such method seen commonly in lizards is the shedding of flesh. They sacrifice their tails in order to get away from predators. Some other physical defenses seen in animals are shells and spines which protect and deter predators and increase the preys’ chances of survival.
Animals such as the rough-skinned newts and puffer fish develop poison as a means to give predators a reason to not eat them. This works in the process in a process of coevolution. They develop something that will let others know that if they eat they, you will die. Then other animals must find a way to overcome the poison to survive. This lends to the adaptions of different ways to protect themselves. If they are poisonous, other species know not to eat them. Poison is probably used opposed to other techniques because it is the most effective in completing its task in causing predators to not eat them. The reason it is so effective is that it creates a direct correlation between eating the newt and death. If the newts had an unpleasant smell, this might keep predators away, but it wouldn’t create the powerful symbol of fear that fatal poison gives. It is like a skunk, it gives a horrible stench off, to warm other animals, but it has no natural defenses that can protect it or give a scare tactic. It is much more effective to have your species synonymous with death rather than an unpleasant smell. Based on this principle of creating an identity correlated with death, any species that creates a defense mechanism that causes death after eating them would be just as effective as poison.
ReplyDeletePoisonous organisms exist in many wide varieties; from plants to marine and land animals. They all created their own successful protection system. Plants must become poisonous because they are locked into ground and are immovable. They must create effective defense mechanisms to be protected. An example of a plant that did this better than any other is the lily of the valley. All parts, including the berries, of the Lily of the Valley are highly poisonous. Roughly 38 different cardiac glycosides have been found in the plant. The plant also contains saponins. Although deadly, the plant has been used as a folk remedy in moderate amounts. If the plant is touched or handled, hands should be washed before doing anything else. Many mammals as well have created effective defense mechanisms. Rattlesnakes are a prime example of this; they have very strong venom and warn people when they are shaking their tails. Most species of rattlesnakes have hemotoxic venom, destroying tissue, degenerating organs and causing disrupted blood clotting. Some degree of permanent scarring is very likely in the event of a venomous bite, even with prompt, effective treatment, and a severe envenomation, combined with delayed or ineffective treatment, can lead to the loss of a limb or death. Thus, a rattlesnake bite is always a potentially fatal injury. Some rattlesnakes, especially the tropical species, have neurotoxic venom. A bite from these snakes can interfere with or shut down parts of the nervous system. These adaptations to poison help them survive and put scares in many possible predators that are looking for a meal.
Many other defense mechanisms were created because of the need to protect, and were not able to create a posion that would damage other species. One of the most profound types of protection is mimicry. Many animals will look like another dangerous animal (Batesian mimicry) and try to scare potential predators away because it is a warning sign. Many animals that do have similar defense tactics use Müllerian mimicry because they are given the same appearance and their presence of numbers try to scare many other organisms. More commonly used by many species are camouflage and visual adaptations. Like chameleons they are able to change color to match with their background. Others live in environments that are similar to their color and are able to blend it with the other things. Like mentioned before with the skunk, a species might try to detract others by emitting a bad smell knowing it will scare them. Many organisms like an armadillo and others created a hard plated back that will deflect any type of attack made toward the animal. It’s like wearing a metal plate for protection. Another type if defense is through shedding certain body parts that can grow back so they can evade predators.
http://library.thinkquest.org/C007974/2_3rat.htm
Monday, March 30, 2009
ReplyDeleteThe Evolutionary Arms Race
At the beginning of Chapter 7, Carroll discusses the Oregon rough-skinned newt, an animal which has developed the ability to produce the TTX poison. Carroll also mentions that this happens in the puffer fish as well. Why do animals such as these develop poison instead of adapting other techniques? Where else have we seen the development of poison inside a species outside of that mentioned? Where has the predator of these animals developed resistance to the poison, and what was the next step those animals took? What are some other techniques used for survival that we've learned about?
Answer:
Organisms that develop poison use it as a means for survival from predators. Usually, poisonous animals have some kind of marking such as a bright color on them that warns of their poison, or predators will learn not to eat them after time just from experience of living with them. Either way, predators will know not to eat these poisonous species. Poison is effective because it leads straight to death. This defense mechanism is one of the best in the world because we all know that what organisms want the most is to survive and reproduce. Well, although they might think they are getting nutrition from the newt, the eventual cause of death outweighs the thought of food and this is effective in defending the newts from becoming eaten. The poison in the newts originally developed as a mutation and this gene spread through the species through natural selection.
We have also seen poison in many plants such as the oleander. This plant is extremely poisonous and affects the heart, produces severe digestive upset and has caused death. The toxicity of Oleander is considered extremely high and it has been reported that in some cases only a small amount had lethal or near lethal effects. Oleander is also known to hold its toxicity even after drying. It is thought that a handful or 10-20 leaves consumed by an adult can cause an adverse reaction, and a single leaf could be lethal to an infant or child. Ingestion can cause both gastrointestinal and cardiac effects. Reactions to poisonings from this plant can also affect the central nervous system. These symptoms can include drowsiness, tremors or shaking of the muscles, seizures, collapse, and even coma that can lead to death. Oleander sap can cause skin irritations, severe eye inflammation and irritation, and allergy reactions characterized by dermatitis.
Some predators develop resistance to poison such as the garter snakes that Carroll writes about. Different populations of snakes exhibit different degrees of resistance. They can survive after consuming a newt, and this increases their availability of food, giving them an increased chance of survival and passing on their genes for resisting the toxin. This goes along with the theme of Coevolution. Since newts were the primary prey of garter snakes, the snakes evolved in order to adapt to the increasingly toxic newts so that they could still obtain the food necessary for survival. Carroll calls this the “arms race”. Not all snakes evolve resistance to TTX poisoning but the ones that did have an enormous selective advantage and we’ll be sure to see the newts or some other organism evolving a new type of poison soon. Some other techniques for survival include a hard exoskeleton or shell such as the lobster or clam. This protects internal organs and protects the organism from being eaten. Also, camouflage is a great defense mechanism that organisms such as chameleons use to blend in to their environment so that they are not spotted as easily. Both of these protect the animals from being eaten and therefore enhance survival and reproduction.
http://plantanswers.tamu.edu/publications/poison/poison.html