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Recitation: Tuesday 10:20 TA: Matt Holding

Wiki 300 word contribution https://en.wikipedia.org/wiki/Evolutionary_arms_race

The interactions between garter snakes and newts have been studied to understand the coevolution between the two species. In populations where the two live together, higher levels of TTX and resistance to TTX are observed in newts and garter snakes respectively. In populations where the species are separated, the TTX levels and resistance are lower when compared to the sympatric populations (Brodie et al. 2003). While isolated garter snakes have lower resistance, they still demonstrate an ability to resist some levels of TTX exposure. This fact suggests that garter snakes are predisposed to the development of TTX resistance and that it may be an ancestral trait (Brodie et al. 2002). The resistance of garter snakes is measured by observing a snake’s crawling speed after it has ingested TTX. The most resistant snakes continue to crawl at normal speeds even after high levels of TTX have been injected. The snakes on the lower end of the spectrum show decreased movement and signs of paralysis when exposed to TTX (Brodie 2005).

The lower levels of resistance observed in separated populations of newts and garter snakes suggest that there is a fitness cost associated with TTX resistance. The snakes with high levels of TTX resistance have slower average crawl speeds when compared to isolated populations of snakes (Brodie et al. 2003). Slower crawl speeds make the snakes more susceptible to predators. This illustrates that while it is advantageous to be resistant to TTX when newts are present, it becomes more costly in the absence of selective pressures from the newt. The same pattern is seen in isolated populations of newts. In these populations, where garter snakes are absent, newts produce lower levels of TTX in their skin. The choice to not produce TTX demonstrates that there is some cost to the newt when they produce the toxin (Brodie 1991). This relationship creates a geographic pattern of resistance in populations. There are areas known as hotspots in which levels of TTX and resistance are extremely high. This alludes to a close interaction between newts and snakes. There are also areas of coldspots where newts and snakes have minimal interaction leading to lower levels of TTX production and resistance (Brodie et al. 2003).

Final Draft There is a complex interaction between organisms in nature that leads to the evolution of unique traits. Species living in the same environment have the ability to place selective pressures on one another leading to coevolution. The garter snake and newt have been placing selective pressures on one another for years resulting in increasingly exaggerated traits, causing a phenomenon known as an evolutionary arms race. An Evolutionary Arms race occurs when co-occurring species, often predator and prey, continue to develop adaptations and counter adaptations as they compete against one another for survival. The mechanisms behind these interactions must be better understood in order to gain insight into how organism evolve in nature.

The newts are one of many species that uses poison to protect themselves form predators. The development of defense mechanisms in prey species helps to correct for the predator-prey imbalance that is normally seen in nature (Williams, et al. 2010). This means that while there is usually a higher cost for the prey in these interactions, adaptations by prey species, such as toxins, has lead to a more equal fitness cost between predator and prey in which they both face the potential for death (Williams, et al. 2010). The evolutionary arms race between garter snakes and newts has lead to the evolution of one of the most poisonous species there is. The newt has the ability to produce high levels of the neurotoxin tetrodotoxin (TTX). TTX acts on the sodium channels in organisms causing the loss of function in nerve and muscle tissues. The result of the inhibition on sodium channels leads to paralysis of the affected organism and potential death (Soong, et al. 2006). Respiratory failure is the usual cause of death from TTX poisoning (Geffeney, et al. 2002). Newts are not the only organisms that can produce TTX. TTX was first discovered in the puffer fish, which utilizes the toxin to protect itself from predators (Soong, et al. 2006). Through years of adaptation, the newt has developed such high levels of TTX that there is only one organism, the garter snake, that can prey on it without suffering immediate death.

The garter snake is the only known organism that has the ability to feed on newts (Geffeney, et al. 2002). After years of feeding on newts, garter snakes have developed a resistance to TTX, resulting in minimal side affects from consuming high levels of the toxin. While the exact mechanisms behind resistance in the snakes are unknown, it is suggested that the way that TTX binds to the sodium channels in garter snakes is different when compared to other organisms (Brodie, et al. 2002). The interactions between garter snakes and newts have been studied to understand the coevolution between the two species. In populations where the two live together, higher levels of TTX and resistance to TTX are observed in newts and garter snakes respectively. In populations where the species are separated, the TTX levels and resistance are lower when compared to the sympatric populations (Brodie et al. 2003). While isolated garter snakes have lower resistance, they still demonstrate an ability to resist some levels of TTX exposure. This fact suggests that garter snakes are predisposed to the development of TTX resistance and that it may be an ancestral trait (Brodie et al. 2002). The resistance of garter snakes is measured by observing a snake’s crawling speed after it has ingested TTX. The most resistant snakes continue to crawl at normal speeds even after high levels of TTX have been injected. The snakes on the lower end of the spectrum show decreased movement and signs of paralysis when exposed to TTX (Brodie 2005).

The lower levels of resistance observed in separated populations of newts and garter snakes suggest that there is a fitness cost associated with TTX resistance. The snakes with high levels of TTX resistance have slower average crawl speeds when compared to isolated populations of snakes (Brodie et al. 2003). Slower crawl speeds make the snakes more susceptible to predators. This illustrates that while it is advantageous to be resistant to TTX when newts are present, it becomes more costly in the absence of selective pressures from the newt. The same pattern is seen in isolated populations of newts. In these populations, where garter snakes are absent, newts produce lower levels of TTX in their skin. The choice to not produce TTX demonstrates that there is some cost to the newt when they produce the toxin (Brodie 1991). This relationship creates a geographic pattern of resistance in populations. There are areas known as hotspots in which levels of TTX and resistance are extremely high. This alludes to a close interaction between newts and snakes. There are also areas of coldspots where newts and snakes have minimal interaction leading to lower levels of TTX production and resistance (Brodie et al. 2003).

Garter snakes have not only developed physiological defenses against newts, they have also developed behavioral changes. Garter snakes that have lower levels of resistance tend to avoid newts that have high levels of TTX in their skin (Williams et al. 2010). This behavior in the snakes leads to a better understanding of how the evolutionary arms race between the two species began. If a snake consumes a newt with high levels of TTX in the skin, then the newt cannot pass on its genes, and the escalation of the arms race does not occur. It has been shown, however, that even after the snake has ingested a newt, the snake can choose to regurgitate the newt if the TTX levels are too high (Brodie et al. 2002). When this occurs, the newt remains unharmed and can then pass on its genes to the next generation. The rejection by the snakes of the newts with high levels of TTX places selective pressure on the newts to become increasingly more toxic. This in turn places selective pressure on the snakes, so that only those that have high levels of resistance survive the encounter with the newts, and then pass on their genes to the next generation (Williams et al. 2010). A new theory suggests that garter snakes may have a more complex relationship with newts than previously thought. It has been shown that garter snakes have TTX stored in their liver weeks after they have consumed a newt. The storage of TTX in the liver results in the snake becoming poisonous to any predator who chooses to consume it. This indicates that the snakes may be using the newts to obtain TTX, so that they can use it as a defense mechanism themselves (Williams et al. 2004). The liver is an often sought after target of predators due to its high levels of nutrients. It has been observed that some birds will single out the liver of the garter snake for this exact reason. The storage of TTX in the liver of snakes may be due to the fact that any predator that chooses to eat the snake will become ill or even die after doing so, leading to an avoidance of the snake in the future (Williams et al. 2004). When minimal amounts of TTX are ingested in rats, the liver quickly removes the toxin from the body. The opposite trend is observed in garter snakes. The elimination of TTX from the snake’s liver is very slow and lasts for weeks. It is believed that garter snakes do not need to completely eliminate TTX from their system before they can function normally. This means that snakes remain poisonous to potential predators for weeks, while being able to function normally (Williams et al. 2004). The behaviors observed illustrate just another feature of the complex interactions between the newt and garter snake.

The coevolution between the Garter snake and newt is extremely complex and is just one example of how organisms can place selective pressures on one another. Similar mechanisms can be seen when observing the evolution of antibiotic resistance in Staphylococcus aureus or the development of pesticide resistance in mosquitoes (Brodie et al. 2004). The interactions between garter snakes and newts can help us better understand the coevolution of the species around us.

References

Brodie, Edmund D., III, Brodie,Edmund D., Jr.,. 1991. Evolutionary response of predators to dangerous prey: Reduction of toxicity of newts and resistance of garter snakes in island populations. Evolution 45(1). Brodie, Edmund D., Brodie, Edmund D., Motychak,Jeffrey E.,. 2002. Recovery of garter snakes ( thamnophis sirtalis ) from the effects of tetrodotoxin. Hpet Journal of Herpetology 36(1):95-8. Brodie, Edmund, Feldman, Chris, Hanifin, Charles, Motychak, Jeffrey, Mulcahy, Daniel, Williams, Becky,Brodie, Edmund,. 2005. Parallel arms races between garter snakes and newts involving tetrodotoxin as the phenotypic interface of coevolution. J Chem Ecol 31(2):343-56. Brodie ED, Ridenhour B, Brodie E. 2003. The evolutionary response of predators to dangerous prey: Hotspots and coldspots in the geographic mosaic of coevolution between garter snakes and newts. Evolution 56(10):2067-82. Geffeney S, Brodie ED Jr, Ruben PC,Brodie ED 3rd,. 2002. Mechanisms of adaptation in a predator-prey arms race: TTX-resistant sodium channels. Science (New York, N.Y.) 297(5585):1336-9. Soong TW VB,. 2006. Adaptive evolution of tetrodotoxin resistance in animals. Trends in Genetics : TIG 22(11):621-6. Williams, Becky L., Hanifin, Charles T., Brodie, Edmund D., Brodie III,Edmund D.,. 2010. Tetrodotoxin affects survival probability of rough-skinned newts (taricha granulosa) faced with TTX-resistant garter snake predators (thamnophis sirtalis). Chemoecology 20(4):285-90. Williams BL, Brodie ED Jr,Brodie ED 3rd,. 2004. A resistant predator and its toxic prey: Persistence of newt toxin leads to poisonous (not venomous) snakes. J Chem Ecol 30(10):1901-19.

Edited page

https://en.wikipedia.org/wiki/Common_Garter_Snake

Garter snake article

One thing that could be added is a discussion on the relationship between the garter snake and newts. The article does not mention anything about the co-evolution between the two organisms. More information could be added on how the newt and garter snake evolved together.

Another thing that could be added to the article is a discussion on the evolution of resistance in the garter snake. Garter snakes have developed such a high resistance to TTX, which is the toxin that newts produce, that they are now the only predator that can feed on the newt.

Finally a discussion on the relationship between location of the garter snake and its level of resistance could be brought up. A study has shown that the location of garter snakes can be correlated to levels of resistance.

1.	Brodie ED, Ridenhour B, Brodie E. 2002. The evolutionary response of predators to dangerous prey: Hotspots and coldspots in the geographic mosaic of coevolution between garter snakes and newts. Evolution 56(10):2067-82

Sentence addition

Garter snakes have the ability to absorb the toxin from the newts into their body making them poisonous, and deterring potential predators.

1.	Williams BL, Brodie ED Jr,Brodie ED 3rd,. 2004. A resistant predator and its toxic prey: Persistence of newt toxin leads to poisonous (not venomous) snakes. J Chem Ecol 30(10):1901-19.

Topic and Annotated Bibliography

Topic- The coevolution of Newts and Garter snakes.

1.	Geffeney S, Brodie ED Jr, Ruben PC,Brodie ED 3rd,. 2002. Mechanisms of adaptation in a predator-prey arms race: TTX-resistant sodium channels. Science (New York, N.Y.) 297(5585):1336-9.

This source talks about the development of resistance of the garter snake to the toxin tetrodotoxin (TTX). It looks at how resistant gartner snakes are to different levels of TTX and how heritable resistance is in populations of snakes. The research found that resistance to TTX in garter snakes is very heritable and is passed down to the next generation. The article went into detail on how The TTX toxin works on skeletal muscles.

This article does a good job explaining the basics behind the coevolution between Garter snakes and Newts. It shows how resistance varies among populations, and explains the coevolution between the Newt and Garter snake.

This article is useful because it helps to illustrate the mechanisms behind the coevolution between the Newt and Garter snake. This material could be used as background information in order to understand the topic of arms race.

2.	Williams, Becky L., Hanifin, Charles T., Brodie, Edmund D., Brodie III,Edmund D.,. 2010. Tetrodotoxin affects survival probability of rough-skinned newts (taricha granulosa) faced with TTX-resistant garter snake predators (thamnophis sirtalis). Chemoecology 20(4):285-90.

This article looks at the chemical defenses of prey species, specifically the Newt. The article looked at the interaction between the Newt and Garter snake and how the Newts toxin helps to correct the predator-prey imbalance. The article found that newts that had higher concentration of the toxin TTX, would be more likely to be rejected by Garter snakes. The article concluded that both concentration of TTX and resistance to it, creates a strong coevolution between snakes and Newts.

This article does a good job looking into the interaction between newts and garter snakes. It showed how different concentrations of TTX affect the survival rate of newts and can lead to more resistance in garter snakes. The article also thoroughly explained their research methods and how they controlled for certain variables, such as size of the newts.

This article can be used to show how varying levels of TTX affect the survival rates of newts. It can also be used to illustrate predator-prey interaction among species. It can also be used to show the escalation of the arms race between the newt and garter snake.

3.	Brodie ED, Ridenhour B, Brodie E. 2002. The evolutionary response of predators to dangerous prey: Hotspots and coldspots in the geographic mosaic of coevolution between garter snakes and newts. Evolution 56(10):2067-82.

This article wanted to know if there was a link between garter snake resistance and geographical location. The study looked at different populations of garter snakes across North America to determine if there was a link between geographical location and snake resistance. The study found that there existed some populations, which had a higher level of resistance when compared to the others.

The study did a good job looking into different factors that influence coevolution. It did a good job illustrating the results of the study, and showed that there were populations of garter snakes that had a higher level of resistance, and how their location affected their resistance.

This study can be used to show how geographical location affects the strength of selection. It can be used to show how the resources available in a species environment can affect its degree of resistance. This article is useful in showing different factors that contribute to coevolution.

4.	Brodie, Edmund, Feldman, Chris, Hanifin, Charles, Motychak, Jeffrey, Mulcahy, Daniel, Williams, Becky,Brodie, Edmund,. 2005. Parallel arms races between garter snakes and newts involving tetrodotoxin as the phenotypic interface of coevolution. J Chem Ecol 31(2):343-56.

This article looked at the basics of evolutionary arms races, and how phenotypic variance contributes to coevolution. The article looked at the example of the newt and garter snake and how phenotypic variation lead to coevolution between the species.

This article does a good job explaining the basics of coevolution and the factors that must be present in order for it to occur. It does a good job using specific examples to show how phenotypic variation contributes to the coevolution of species.

This article will be useful in understanding the driving forces of coevolution. It will also be useful in understanding the relationship between the garter snake and newts.

5.	Brodie, Edmund D., Brodie, Edmund D., Motychak,Jeffrey E.,. 2002. Recovery of garter snakes ( thamnophis sirtalis ) from the effects of tetrodotoxin. Hpet Journal of Herpetology 36(1):95-8.

This article looked into the affects of tetrodotoxin on garter snakes. The study found that high levels of tetrodotoxin lead to slow locomotor function in garter snakes. The study found that Tetrodotoxin resistance is not affected by repeated exposure to the substance. It also looked into how long it takes the garter snake to recover from the toxins.

This study did a good job explaining the affects of TTX on Garter snakes. It also did a good job illustrating the relationship between time of injection and recovery of the garter snake.

This study can be used to better understand how the tetrotoxin, produced by newts, affect the physiology of garter snakes. It can also be used to show how long it takes the snakes to recover form a dose of tetrodotoxin, and how a snakes resistance to the toxin affects its recovery time.