Thursday, April 9, 2009
Arms race
On page 166 Carroll discusses the "evolutionary arms race," between the Oregon rough skinned newt and common garter snake. Explain what is meant by arms race, and explain how it applies to this situation. Also provide other examples of this evolutionary arms race, and can this possibly lead to changes in humans to try to match other species.
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An evolutionary arms race is when two competing species continue to develop adaptations and counter-adaptations in order to be a “step ahead” and have a higher relative fitness than the other. This arms race includes co-evolving genes of both species, as the functional proteins made by the evolving genes allow the species to become more and more lethal against the other species. In the case of the Oregon rough skinned newt and the common garter snake, the evolutionary arms race involves the genes creating tetrodotoxin and resistance to this toxin. Taricha granulose (Oregon rough-skinned newt) produces a toxin called tetrodotoxin (TTX). TTX is able to block sodium channels needed for proper nerve function; therefore, it is able to cause paralysis, abnormal heart beats, and even death. However, Thamnophis sirtalis (common garter snake) is the only predator known to be resistant to TTX. The level of TTX production by newts and TTX resistance by garter snakes varies among individuals. Although, as Carroll states, “selection favors increasingly resistant snakes and increasingly toxic newts” (166). This is because the newts want to produce more and more TTX so they can kill the snakes that eat them, and the garter snakes want to become more and resistant to TTX so they can eat the newts without being affect by the toxin. As Carroll states on page 167, evolutionary arms races such as that between the common garter snake and the Oregon rough-skinned newt creates an intense selection more individuals with a higher ability to survive and reproduce; therefore, the rate of evolutionary change is accelerated.
ReplyDeleteThere are two types of evolutionary arms races: symmetrical and asymmetrical. Symmetrical evolutionary arms races involve added pressure for natural selection of two species in the “same direction”. This means that accelerated evolution would lead to two competing species to change in a similar way, such as how trees in a forest grow taller due to competition for light. In this case, natural selection selects for those trees that are taller than the others because they have more access to light; a higher rate of evolution between to species of trees would therefore result in both species being taller and taller over time. Asymmetrical evolutionary arms races involve added pressure for natural selection of two species in opposing ways. An example of an asymmetrical arms race is the one between the Oregon rough-skinned newt and the common garter snake. Selection on the species of newts results in them producing more and more TTX, and selection on the species of snakes results in them become more and more resistant to TTX. Production and resistance of toxins are opposing selective advantages that allow the two species to have higher chances of surviving and reproducing in different ways.
Evolutionary arms races often times occur between humans and microorganisms. Microorganisms such as bacteria can enter our bodies and cause parasitic effects. If this is so, medical researchers can try to develop antibiotics that can destroy the invading bacteria. As the antibiotics are taken, many of the bacteria die; however, a few of the bacteria may be resistant to this particular antibiotic. This would result in these resistant bacteria proliferating inside the body, and eventually the antibiotic will become useless. Humans would have to keep producing more and more antibiotics in order to kill of the bacteria. This is a good example of an asymmetrical evolutionary arms race: humans are producing more and more antibiotics to kill of a certain type of bacteria, and bacteria are becoming more and more resistant to human-produce antibiotics.
Source:
http://en.wikipedia.org/wiki/Evolutionary_arms_race
As Josh explains, an evolutionary arms race is when two competing species continue to develop adaptations and counter-adaptations in order to survive. Josh also explains well how garter snake and skinned newt develops genes creating terodotoxian and resistance to this toxin. In addition, Josh also gives an example of arms race between humans and bacteria and development of super bugs.
ReplyDeleteIn addition to josh’s terrific answer, I would like to add some more detailed examples of evolutionary arms race. The arms race is wonderful factor that leads to co-evolution. Evolutionary arms race can be found everywhere including plants between bugs and any organisms that hunt and organisms that are being hunted. An example of this evolutionary arms race can be found between cuckoos and foster birds. Recently, scientists who are studying Cuckoos have discovered that birds have become aware of cuckoo chicks in the nest. Scientists say that this marks the newest line of defense in an ongoing evolutionary arms race.
Cuckoos were successful in laying their eggs in other bird’s nest because they lay eggs that mimic the eggs of the superb fairy-wren. However, once the birds started to recognize the cuckoo’s nestlings, cuckoos started to develop the same begging call of the foster birds. This evolutionary arms race is still going on but only one more question remains. Will there be a winner in this evolutionary arms race? Langmore, one of the scientists that studied cuckoos, state that : “ there certainly can be winners, a study has revealed that a small warbler is now so good at discriminating eggs on the basis of size that cuckoos no longer parasitize the species.” However it doesn’t always mean that loser will die out. Cuckoos can always evolve another way.
This evolutionary arms race can certainly develop humans to match other species. We see this every day through out the history. We try to survive against bacteria and predators. Another example of arms race can be found between humans and weeds. Just 40 years ago, Silent Spring, a book written by Rachel Carson documented detrimental effects of pesticides on the environment. During that time, there were no such weeds that were resistant to the herbicides. However, today, weed scientists have identified 273 species that are resistant to herbicides. Apparantely, weeds too, are evolving to survive in this harsh world.
Evolutionary arms race is a solid proof that evolution is real and that its happening everywhere. The process of evolution is very complex and there are many factors that affect the process of evolution. Every organism is trying to stay alive and pass on their gene. In this constantly changing environment, evolution is the key for us to survive and thrive.
http://news.nationalgeographic.com/news/2003/03/0311_030312_cuckoo_2.html
http://food.change.org/blog/view/evolutionary_arms_race
The evolutionary arms race that is described in the book can be compared to the one that took place in the Cold War, between the US and the USSR. In fact, it’s nearly identical- except it’s not two countries rushing to beat one another to nukes, then to space, then to the moon, then to giant satellites that shoot missiles out of the sky- instead, in an evolutionary arms race, it’s two species, a predator and a prey, or two organisms competing for the same niche, as we’ve seen previously in our book, with figure 53.2, where two organisms are competing for the same spot. And as can be seen, Chthalmus can't weed out the Balamus from its spot, but the Balamus hasn't evolved to survive where the Chthalmus can.
ReplyDeleteAs Josh states above, and as Carroll writes in his book, “selection increasingly favors resistant snakes and more toxic newts”, partially because of their ability to survive, but also because as the survivors, their genes are treasure as useful, and slowly, non-resistant snakes will be weeded out- not at once, but over time, even if by luck they stop avoiding these toxic newts, their inability to swallow all prey will be their downfall. The newt gene, however, is to ward off their predators from their kin- more toxic newts aren’t more likely to survive, but are more likely to leave the permanent impact or kill, as where less toxic newts might leave a temporary impact.
We can see this arms race, where prey attack their predators, all around us in nature. Monarch butterflies and Admiral butterflies are both poisonous and mimic each other in terms of looks- allowing them to leave impacts in the mouths of birds unlucky enough to try and eat them. Some animals will go on the offensive- attacking ejecting toxins or overwhelming smells, even squirting blood out of their eyes in an attempt to get rid of attackers.
And we also know of species who fail to keep up in this race for survival- most frequently with indigenous species in the areas that introduced species have come in contact to. Rabbits have less predators and mate quickly, thus speeding up and pushing out some of their fellow prey in order to survive. The young of cane toads are toxic, allowing most to survive, and cane toads also digest dead matter, furthering their chance for survival- and for rooting other indigenous species out. Trees introduced to foreign lands start to take up huge amounts of light on lands with sparse forests, killing off some of the plants that lived down below.
http://en.wikipedia.org/wiki/antipredator_adaption
http://en.wikipedia.org/wiki/invasive_species
An “evolutionary arms race” is a competition between two organisms in which co-evolving genes develop adaptations and counter-adaptations against each other. In the case of the rough skinned newt and the common garter snake, the rough skinned newt is under selective pressure to develop more potent forms of the toxin tetrodotoxin (TTX) and the common garter snake is under pressure to develop higher levels of resistance to TTX. For the snakes, the side effects of consuming the toxic newts (inability to hold their heads steady, flaccidity, and inability to right themselves) are not outweighed by the benefits of an abundant food source.
ReplyDeleteAnother example of the evolutionary arms race is between the cuckoo and the wren. The cuckoo lays its eggs in other birds’ nests. The hatchling, even though it is obviously different from the hosts’ nestlings, pushes out its “foster siblings” and monopolizes its foster parents’ time, who cannot recognize the impostor in their nests and sometimes die trying to satisfy the cuckoo chick’s voracious appetite. Recently, researchers in Australia have noticed that the superb fairy-wren has learned to identify Horsfield’s bronze-cuckoo chicks and abandon them in the nest. The cuckoo has developed eggs that mime those of the fairy-wren, one of it’s favorite hosts, so the ability of the fairy-wren to recognize cuckoo chicks is an evolutionary advantage. The cuckoo has responded by imitating the call of the fairy-wren’s chicks. This has happened in the Australian birds because the benefits are greater than they are for birds in other regions. The breeding season is much longer, so the fairy-wren is able to abandon the cuckoo chick and build re-nest. While it would be better to reject the egg instead of the chick, the cuckoo has become so good at mimicking the fairy-wren’s egg that it is likely that they would abandon their own eggs instead. In Europe, the reed warblers do not have as long a breeding season, and so there is less of a chance to re-nest, meaning there is less of a benefit to reject the cuckoo chick.
Humans, too, are involved in an evolutionary arms race, though not in quite the same way as the previous two examples. Bacteria are quickly evolving resistance to antibiotics, challenging scientists to come up with new ways to knock out diseases. The difference between the human/bacteria arms race and the rough skinned newt/common garter snake arms race is that in the human/bacteria arms race, the only organisms who are evolving are the bacteria. Us humans take the easy way out, using chemicals and other “artificial” means to battle the tiny microbes. Staphylococcus aureus is one such microbe, having evolved resistance to penicillin, methicillin, tetracycline, and erythromycin, then vancomycin, and most recently, linezolid. We humans better come up with another solution fast, because S. aureus is one of the fastest evolving microbes out there.
http://news.nationalgeographic.com/news/2003/03/0311_030312_cuckoo.html
http://en.wikipedia.org/wiki/Evolutionary_arms_race
oh, I also used
ReplyDeletehttp://en.wikipedia.org/wiki/Antibiotic_resistance