Sunday, April 12, 2009
Delicious Newt Death
On pages 165- 167 it talked about a man deserving one of the most honorable awards, the Darwin Awards by swollowing an extremely toxic newt. The man died within 24 hours, but the common garter snake, Thamnophis sirtalis, is able to survive, and yet experience slight side effects of eating the newt. Carroll says this sets the stage for "coevolutionary" arms race. What exactly is coevolution? What allows the snakes to survive the TTX poison? What genetic trait factors into it? Is it a chemical or physical adaptation that allows the snake to survive? Carroll also talks about a trade-off betweeen advantage of an abudnant food source nad feeling lousy for a while. How can you relate this to humans? Why do we do it? (REmember at the beginning of this class... all the way back in august, when we talked about being energy efficient and seeking food versus consuming it?) What are other examples of coevolution other than the garter snake and newt
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Coevolution can be defined as the related evolution that takes place between two living things, whether what is meant by "thing" is microscopic (related mutations taking place such as within a molecule among several amino acids) or macroscopic (the relationship and subsequent evolutions that take place between different species). There are two examples in the world today in which coevolution plays a major part. One is pollination and the relationship between the insect and the plant. The other is relationship that exists between predator and prey.
ReplyDeleteCertain plants have evolved so that only certain insects are able to pollinate them, such as the evolution of the yucca plant, which changed the shape of its flower so that only the yucca moth is able to pollinate it. Why? What is the selective advantage of this? Well, flowers that attract specific insects have an advantage over those that don't in that they are more efficient in their usage of pollen (less pollen is wasted). For the pollinators, it is an advantage to be involved in this type of relationship because there is less competition among the various organisms for the chance at pollinizing the flower (the playing field has been decreased). In fact, yucca plants are pollinated by only 2 different types of moths.
Additionally, coevolution is witnessed as it relates to the predator-prey relationship. Prey, throughout the years, have developed several different types of evasion tactics. One of those include Batesian mimicry. In Batesian mimicry, a palatable (harmless) species changes its appearance so that it resembles an unpalatable (harmful). For example, certain butterflies are able to store various poisons that they consumed as a caterpillar and if a bird tries to eat that butterfly, it will not do so again in the future as it would remember that that specific type of butterfly contains unpalatable chemicals within its body. Harmless butterflies, then, mimic the visual patterns of the harmful butterflies so that they gain protection from birds that have attempted to eat the harmful butterflies. This in itself is a coevolutionary relationship. If palatable butterflies continue mimicking unpalatable butterflies, then the birds may think that all butterflies that look similar to the palatable one they just consumed are palatable, leading to danger for the unpalatable ones. For that reason, "the mimics (evolve) toward the color patterns of the models, and the models (evolve) away from the converging mimics." Outside of the butterfly species, birds also go through adaptations, as they learn to distinguish between palatable and unpalatable butterflies.
Coevolution is a change in the genetic composition of one species (or group) in response to a genetic change in another Coevolution can occur at multiple levels of biology: it can be as microscopic as correlated mutations between amino acids in a protein, or as macroscopic as covarying traits between different species in an environment. Each party in a coevolutionary relationship exerts selective pressures on the other, thereby affecting each others' evolution. Species-level coevolution includes the evolution of a host species and its parasites, and examples of mutualism evolving through time. Evolution in a one-on-one interaction, such as that between predator and prey, host-symbiont or host-parasitic pair, is coevolution.
ReplyDeleteThe garter snake, Thamnophis sirtalis, and the newt are “locked into a life-or-death battle”(166). The only predetor known to be resistant to newt’s TTX are the garter snakes. Over time the garter snakes have become more and more resistant to the TTX. The levels of resistance varies in different snakes and so does the level of TTX production in netws. This variation in predetor and prey is the main reson for coevolution. When TTX production increases the snakes must eveolve to become more resistant to it. And as the snakes become more resistant the newts must increase amount of TTX production.
Another example of coevoltion can be seen with the pollination of Angraecoid orchids by African moths. These species coevolve because the moths are dependent on the flowers for nectar and the flowers are dependent on the moths to spread pollen so they can reproduce. The evolutionary process has led to deep flowers and moths with long probosci.Coevolution can occur between predator and prey species as in the case of the Rough-skinned Newt (Taricha granulosa) and the common garter snake (Thamnophis sirtalis). In this case, the newts produce a potent nerve toxin that concentrates in their skin. Garter snakes have evolved resistance to this toxin through a set of genetic mutations, and prey upon the newts. The relationship between these animals has resulted in an evolutionary arms race that has driven toxin levels in the newt to extreme levels.
http://biomed.brown.edu/Courses/BIO48/27.Coevolution.HTML
http://en.wikipedia.org/wiki/Coevolution
Coevolution happens when two species compete for something and they both evolve in order to stay step ahead and survive and thrive. The relationship between garter snake and poisonous new is an example of coevolution by arms race. The newt toxin, TTX affects a sodium channel that the snakes’ or any other organisms’ nerve and muscle cells need t o function. However, garter snakes developed special nerve and muscles cells that are resistant to TTX. Garter snakes have slightly differently shaped sodum channels which aren’t blocked as effectively by TTX. Therefore, I would say that it is a physical adaptation of garter snakes that allows them to be resistant.
ReplyDeleteHowever, there is something very interesting about garter snakes. Even though garter snakes have advantage of having abundant food source that nobody wants to eat, they have traded off their physical fit. What I mean is that being resistant to TTX had made the snakes sluggish. This made snakes to be slow and they were not as efficient crawler as other snakes. This shows that while we are evolving, we may lose some traits in order to survive and thrive. We are just fine tuning to the constantly changing environment. However, I believe that there is not much to compare this kind of process of co-evolution because humans are omnivorous. We eat whatever we want whenever we feel like. We can eat bugs when we run out of foods so there is no worry even if all animals develop toxics.
To give another example of this co evolution by arms race, I will use an example that I have previously used before: cuckoos and other birds. Recently, scientists have found out that birds started to notice cuckoos’ chicks and their eggs. Since cuckoos always lay their eggs in other birds’ nest in order to get by, it is critical for cuckoos to develop new tricks to deceive other birds. Soon, cuckoos started to mimic other birds’ begging call. This co evolution between cuckoos and birds is keep going and soon cuckoos will have to develop new tricks to survive and thrive.
http://www.indiana.edu/~ocmhptst/082302/text/newt.html
http://scienceblogs.com/pharyngula/2008/06/evolving_proteins_in_snakes.php
Here are my sources...I forgot...
ReplyDeletehttp://www.stanford.edu/group/stanfordbirds/text/essays/Coevolution.html
http://biology.clc.uc.edu/courses/bio303/coevolution.htm
http://en.wikipedia.org/wiki/Yucca
http://en.wikipedia.org/wiki/Yucca_moth
http://en.wikipedia.org/wiki/Coevolution
Coevolution can be defined as a change in the genetics of one species in response to a change in genetics in another species. This idea can be traced back to Darwin’s work, “The Origin of the Species,” but the term is usually attributed to Ehrlich and Raven. In 1964, the two scientists did a study regarding butterflies and plants. They noticed that the noxious compounds that the plants produced determined which plants were eaten by each butterfly species. This suggests that different poisons produced by the plants helped to contribute to the diversity of butterfly species. Over time, many have argued that this was not an example of coevolution. They say that it was just an example of one species having an evolutionary effect on another species. In order for something to truly be an example of coevolution, there needs to be evidence of reciprocal interaction between the two species.
ReplyDeleteThis is what we call the “evolutionary arms race.” The example of the newts and snakes in the book are a prime example of this. The newt evolved a toxin called TTX. The snake evolved the ability to resist the toxin so that it could still eat the newt. As a result, the newt evolved more TTX. The snake evolved more resistance, and so on and so forth. There is a clear reciprocal relationship here. Each organism evolves as a result of evolution in the other.
TTX works by blocking the sodium channels in the muscle tissue. The result is that the muscle is unable to contract. The poisoned organism dies because the sodium channels in its heart are blocked. As a result, the heart muscle is unable to contract, and the blood cannot be pumped to the body.
How do garter snakes become resistant to this? They have evolved sodium channels that are resistant to TTX. Sodium channels are protein molecules that are embedded in the cell membrane. Sodium ion channels are proteins that express quaternary structure (i.e. they are composed of two protein subunits). At some point, by random mutation, a form of the protein must have occurred that the TTX was unable to block. Snakes with this mutation were able to eat the newts and survive and those that did not died when they tried to eat the newts. Over the course of time, only snakes that carried the resistant form of the sodium ion channel gene were left.
http://biomed.brown.edu/Courses/BIO48/27.Coevolution.HTML
http://en.wikipedia.org/wiki/Tetrodotoxin
http://www.sciencemag.org/cgi/content/abstract/297/5585/1336
Carroll 166-167
whoa 5 comments soo soon nice...
ReplyDeleteCoevolution can be defined as two species causing a reciprocal evolutionary adaptation in the other. A change in one species acts as a selective force on the first species. This linkage of adaptations requires reciprocal genetic change in the two interacting species populations.
ReplyDeleteTTX is a poison that blocks the pores of sodium ion channels which are critical to nerve function. However selective advantage has favored snakes with a resistance to TTX, because TTX carrying newts is as you said an abundant food source. The genetic mutation that allows for this resistance a change in the molecular structure of a sodium channel expressed in snake skeletal and cardiac muscle sodium channels.
The pore structure altered substitution of 2 amino acids in channel, one from the pore helix and another from the b strand which causes the protein to bend and the hydrophobic residues stabilize it. This relates back to the structures of protein with two secondary structures of a protein, in this case an alpha helix and a beta pleated sheet, undergo a hydrophobic interaction, which gives the protein a more specific shape as well as stabilizes the now tertiary structure.
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