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The Effects of Predators, Prey, and Diet on Snake Venom Evolution Abby Pomento Thurs, 3:00 p.m. 14 November 2014

The study of venom evolution has been a high priority for scientists in terms of scientific research. This is due to medical relevance of snake venom, in terms of making anti-venom and cancer research. The more that is known about the composition of venom and the ways it can potentially evolve is very beneficial. There are three main factors that affect venom evolution that have been closely studied: predators of the snake that are resistant to snake venom, prey that are in an evolutionary arms race with snakes, and the specific diets that affect intraspecific evolution of venom. The factor that is new to the research community is the study of predators that affect snake venom evolution. The mammal that has gained the most attention for its invincibility to snake venom is the Opossum (Didelphidae) which is a predator to pit vipers (Crotalinae). Scientists performed experiments on the opossums and found that there were multiple trials that showed replacement to silent subsitutions in the von Willebrand Factor (vWF) gene which encodes for a venom-targeted hemostatic blood protein. These substitutions are thought to weaken the connection between vWF and a toxic snake venom ligand (botrocetin) which changes the net charge and hydrophobicity. These results are significant to the venom evolution because it is the first citation of rapid evolution in a venom-targeted molecule. This shows that an evolutionary arms race may be occurring in terms of defensive purposes. (Jansa et al., 2011) Alternative hypotheses suggest that venom evolution is due to trophic adaption, an adaption pertaining to diet, whereas these scientist believe in this case that selection would occur on traits that help with prey survival in terms of venom evolution instead of predation success. Several other predators of the pit viper (mongooses and hedgehogs) show the same type of relationship between snakes, which helps to support the hypothesis that venom has a very strong defensive role along with a trophic role. Which in turn supports the idea that predation on the snakes can be the arms race that produces snake venom evolution. (Jansa et al., 2011) Before the hypothesis was made about venom evolution being the product of an evolutionary arms race between snake’s predators, a behavioral experiment was conducted to ensure that opossums are in fact an effective predator of the pit viper in nature. In the experiment behaviors of the snake and opossums were recorded before and after the attack. The results of the experiment showed that snakes would react with flight attempt, coiling, cocking, rattling, immobility, and counterattack with strikes and bites. The opossum’s behavior showed no hesitation in attacking the snake either by the head or by the tail. If the opossum was bitten by the snake, it never reacted. Since the data showed great handling and capturing skills by the opossum and the apparent immunity to the venom of the viper, it confirms the biochemical and immunological data presented by others. (Almeida-Santos et al., 2000) In addition to the effect of predators on venom evolution, the effect that resistant prey has on venom evolution has also been studied and attributed to the evolutionary arms race that occurs between predator and prey. The most significant species interaction is between the northern Pacific Rattlesnake (Crotalus viridis oreganus) and the California ground squirrel (Spermophilus beecheyi). Ground squirrels are an important part of the diet of rattlesnakes estimated 69% of the diet of the northern Pacific rattlesnake in one western Sierra Nevada foothills location. (Biardi et al., 2000). The northern Pacific Rattlesnakes are seen near burrow systems during the reproductive season and periods of pup emergence, and are responsible for about 40% of pup and juvenile death in ground squirrel populations. (Biardi et al., 2005) This fact shows that since ground squirrels make up the majority of the diet, the selective pressures on the squirrels can create and evolutionary arms race due to the close predator-prey relationship observed. It is important to understand how the snake venom and squirrel blood interact to understand the predator-prey relationship. Since venom is made up of enzymes, polypeptides, biogenic amines, and inorganic components that immobilize prey and initiate digestion, the prey have to be able to not only protect against the lethal effects of the venom, but also the necrotic aspect that breaks down the tissue. Scientists hypothesized that the ground squirrel serum should inhibit venom proteolytic activity, should show the greatest inhibition in high density areas of rattlesnakes, and should inhibit the northern Pacific rattlesnake venom better than the venom of allopatric snakes (Prairie and Western Diamondback Rattlesnakes). This was done by analyzing proteolytic activity when the serum and venom were mixed. (Biardi et al., 2000) The results showed that California ground squirrels displayed little necrosis after being bitten by the northern Pacific rattlesnake this is because the blood of the ground squirrels were found to hinder venom proteases. The blood from squirrels that were collected from rattlesnake abundant habitats inhibited the venom of the northern Pacific rattlesnake better than venom from allopatric rattlesnakes. This allopatric evidence shows evolutionary specialization. It was also observed that the inhibition rates among the squirrels correlated with history of rattlesnake predation instead of rattlesnake density at the time of the experiment. (Biardi et al., 2000) A similar experiment conducted earlier found the same type of adaptive variation that occurred in the same species. The results also observed intraspecific variation in the ground squirrels ability to inhibit the venom, thought to be the result of differential selection by the northern Pacific Rattlensake. (Poran et al., 1987) Biardi and colleagues took this information and extrapolated on it by looking at the histories of the rattlesnake predation instead of just rattlesnake density like Poran and colleagues. In an additional experiment that keyed in on medical implications found that the specific diet of a snake has been seen to create differences in intraspecific species venom. This is a form of rapid evolution that is affected by diet makeup. This can take on the form of geographical differences and can be important since the bite from one snake could differ from the bite of another and would need different medical treatments. (Daltry et al., 1996) To add to the many examples used above, another study was conducted that showed the venom of the pitviper, Calloselasma rhodostoma, was related to its diet and geographical range. This experiment is unique because it showed how to rule out other conflicting hypotheses. Therefore, there were three hypotheses used to attempt to explain the geographical variation in venom. First being variation in venom could be from geographical distance between groups. The second being the phylogenetic relationships among groups, meaning the populations of recent common ancestry produce similar venoms. The third is that the venom variation is due to geographical variation in diet. The partial Mantel tests and independent contrasts were used to test for other possible causes of the variation, but gene flow and the phylogenetic relationships among populations were rejected as significant influences. Therefore it was found that the venom variation is due to geographical variation in diet. This has significant findings for the medical field. If intraspecific venom variation is different geographically due to diets, then the anti-venom would match the geographic regions. (Daltry et al., 1996) Another study was conducted that addressed the targets of selection, rates of gene turnover, and functional diversity of the evolution of snake venom in divergent diets. Four to seven distinct PLA2 sequences were found in each phylogenetic analysis which suggests rapidly evolving gene family consisting of both paralogous and homologous loci with high rates of gene gain and loss. The evolution of the protein coding sequences was caused by strong positive selection. The results showed that both gene gain and loss and protein sequence evolution due to positive selection are the reason for adaptive divergence in venom proteins in intraspecific snakes as seen in the increase in substitution rates in coding regions and the codon-based analysis of substitution patterns. (Gibbs and Kossiter, 2008) More research was conducted that studied the evolution of snake venom variability in terms of the role diet plays. The stomach was examined and the proportions of arthropod prey consumed vary between the Echis genus. Toxicity seemed to be correlated with the extent and proportion of arthropod feeding. Arthropods are not normal viper prey and therefore should      represent an unusual condition that would impose significant selective pressure, resulting in adaptive evolution of venom composition for increased toxicity to arthropods. The results showed that variation in snake venom is due to adaptive evolution determined by natural selection for different diets. (Barlow et al., 2009) Rapid venom evolution has been an intense area of study for researchers. It is crucial to understand the different factors that can affect venom evolution, so that further studies in the medical field pertaining to anti-venom can progress. The interesting coevolutionary arms race that occurs between predator and prey has been a popular topic for the Red Queen Hypothesis. It is interesting to see that these hypotheses between the different factors could possibly discredit the other, but more research needs to be conducted to determine the specific roles that venom have and the meaning behind the changes that the venom goes through. More research could be conducted as to whether the role for venom is primarily defensive or for obtaining prey.

References Almeida-Santos, S.M., M.M. Antoniazzi, O.A. Sant'Anna, and C. Jared. 2000. Predation by the opossum Didelphis Marsupialis on the rattlesnake Crotalus Durissus. Curr. Herpetology 19:1-9. Barlow, A., C. E. Pook, R. A. Harrison, and W. Wuster. 2009. Coevolution of diet and prey-specific venom activity supports the role of selection in snake venom evolution. Biol. Sci. 276.1666: 2443-449. Biardi, J. E., D.C. Chien, and R.G. Coss. 2005. California ground squirrel (Spermophilus Beecheyi) defenses against rattlesnake venom digestive and hemostatic toxins. Chem. Ecol. 31.11: 2501-518. Biardi, J. E., R.G. Coss, and D.G. Smith. California ground squirrel (Spermophilus Beecheyi) blood sera inhibits Crotalid venom proteolytic activity. Toxicon 38.5: 713-21. Web. Daltry, J.C., W. Wüster, and R.S. Thorpe. 1996. Diet and snake venom evolution. Nature 379.6565:537-40. Gibbs, L.H, and W. Rossiter. 2008. Rapid evolution by positive selection and gene gain and loss: PLA2 venom genes in closely related sistrurus rattlesnakes with divergent diets. Journal of Molecular Evol. 66.2: 151-66. Jansa, S.A., and R.S. Voss. 2011. Adaptive evolution of the venom-targeted VWF protein in opossums that eat pitvipers. Ed. Paulo Lee Ho. PLoS ONE 6.6: E20997. Poran, N.S., R.G. Coss, and E. Benjamini.1987. Resistance of California ground squirrels (Spermophilus Beecheyi) to the venom of the Northern pacific rattlesnake (Crotalus Viridis Oreganus): A study of adaptive variation. Toxicon 25.7: 767-77.

CONTRIBUTION TO SNAKE VENOM PAGE.........EVOLUTION SECTION https://en.wikipedia.org/wiki/Snake_venom#Evolution

"The study of venom evolution has been a high priority for scientists in terms of scientific research. This is due to medical relevance of snake venom, in terms of making anti-venom and cancer research. The more that is known about the composition of venom and the ways it can potentially evolve is very beneficial." was added to the beginning of a paragraph.

"There are three main factors that affect venom evolution that have been closely studied: predators of the snake that are resistant to snake venom, prey that are in an evolutionary arms race with snakes, and the specific diets that affect intraspecific evolution of venom." added to the middle of a paragraph "Scientists performed experiments on the opossums and found that there were multiple trials that showed replacement to silent subsitutions in the von Willebrand Factor (vWF) gene which encodes for a venom-targeted hemostatic blood protein. These substitutions are thought to weaken the connection between vWF and a toxic snake venom ligand (botrocetin) which changes the net charge and hydrophobicity. These results are significant to the venom evolution because it is the first citation of rapid evolution in a venom-targeted molecule. This shows that an evolutionary arms race may be occurring in terms of defensive purposes.Alternative hypotheses suggest that venom evolution is due to trophic adaption, an adaption pertaining to diet, whereas these scientist believe in this case that selection would occur on traits that help with prey survival in terms of venom evolution instead of predation success. Several other predators of the pit viper (mongooses and hedgehogs) show the same type of relationship between snakes, which helps to support the hypothesis that venom has a very strong defensive role along with a trophic role. Which in turn supports the idea that predation on the snakes can be the arms race that produces snake venom evolution." added as a new paragraph with a sentence that I had written earlier.

Abby Pomento EEOB 3310 Thursday at 3pm 15 September 2014

Effects of Predators, Prey, and Diet on Venom Variation: An Annotated Bibliography

Barlow, A., C. E. Pook, R. A. Harrison, and W. Wuster. "Coevolution of Diet and Prey-specific Venom Activity Supports the Role of Selection in Snake Venom Evolution." Proceedings of the Royal Society B: Biological Sciences 276.1666 (2009): 2443-449. Web.

Researchers studied venom variability in pit vipers that had shifts in their diet. The researchers did this by examining the gut content of the vipers. The differences in venom variability was observed to be relevant to the amount of arthropods consumed. This paper gives a great example of venom evolution effected by diet.

Biardi, James E., David C. Chien, and Richard G. Coss. "California Ground Squirrel (Spermophilus Beecheyi) Defenses against Rattlesnake Venom Digestive and Hemostatic Toxins." Journal of Chemical Ecology 31.11 (2005): 2501-518. Web.

Researchers studied the venom resistance which was occurring in the California Ground Squirrel and observed the effect that it had on venom toxins. It was found that the squirrels living in areas with dense rattlesnake populations, showed a higher resistance to the venom than did the squirrels living in areas where rattlesnakes are rare. This paper gives an example of how rapid evolution in rattlesnake venom can be effected by the rattlesnake’s prey, in this case the California Ground Squirrel.

Daltry, Jennifer C., Wolfgang Wüster, and Roger S. Thorpe. "Diet and Snake Venom Evolution." Nature 379.6565 (1996): 537-40. Web.

Researchers observe the effect of diet on venom composition. Researchers used the Mantel test and independent contrast to come to this conclusion. This paper will help show an example of how rapid evolution in venom can be effected by the pit viper’s diet.

Jansa, Sharon A., and Robert S. Voss. "Adaptive Evolution of the Venom-Targeted VWF Protein in Opossums That Eat Pitvipers." Ed. Paulo Lee Ho. PLoS ONE 6.6 (2011): E20997. Web.

Researchers observed a number of replacements to silent substitutions in the gene encoding von Willebrand Factor in Opossums. Opossums are known to be predators to pit vipers and also are resistant to snake venom. There is an apparent arms race between the venom composition and the venom-targeted molecules in the Opossums. This paper will help show an example of how rapid evolution in venom can be effected by the pit viper’s predator, in this case the Opossum.

Poran, Naomie S., Richard G. Coss, and Eli Benjamini. "Resistance of California Ground Squirrels (Spermophilus Beecheyi) to the Venom of the Northern Pacific Rattlesnake (Crotalus Viridis Oreganus): A Study of Adaptive Variation." Toxicon 25.7 (1987): 767-77. Web.

Researchers observed a resistance in venom for the California Ground Squirrels to the Venom of the Northern Pacific Rattlesnakes. The researchers also used Squirrels from Central Alaska as a non-adapted variable for the research. This will give me another example of how venom evolution can be effected by the rattlesnake’s prey.

Suggestions and Sentence
https://en.wikipedia.org/wiki/Snake_venom#Evolution

Suggestions: 1.Rapid Venom Evolution can also be explained by the arms race between rapid-venom targeted molecules in resistant predators and the snake venom that targets the molecules. This statement could be added to the evolution portion of this page.

Jansa, Sharon A., and Robert S. Voss. "Adaptive Evolution of the Venom-Targeted VWF Protein in Opossums That Eat Pitvipers." Ed. Paulo Lee Ho. PLoS ONE 6.6 (2011): E20997. Web.

2.The article mentions rapid evolution in venom due to the arms race between the snake’s prey, however a good example is not given. One of the main studies on this topic is the California Ground Squirrel (Spermophilus beecheyi) and the northern Pacific Rattlesnake (Crotalus oreganus). The ground squirrels have significantly more resistance to the norther Pacific Rattlesnake venom compared to resistance for any other rattlesnake in the area.

Biardi, James E., David C. Chien, and Richard G. Coss. "California Ground Squirrel (Spermophilus Beecheyi) Defenses against Rattlesnake Venom Digestive and Hemostatic Toxins." Journal of Chemical Ecology 31.11 (2005): 2501-518. Web.

3.The article mentions that venom can vary depending on diets, however that stamen can be extrapolated by saying that venom can vary geographically due to natural selection for feeding on local prey. The example of calloselasma rhodostoma in the paper cited below would be a great addition to the evolution section

Daltry, Jennifer C., Wolfgang Wüster, and Roger S. Thorpe. "Diet and Snake Venom Evolution." Nature 379.6565 (1996): 537-40. Web.

Sentence and Citation: Rapid Venom Evolution can also be explained by the arms race between venom targeted molecules in resistant predators, such as the Opossum, and the snake venom that targets the molecules.

Jansa, Sharon A., and Robert S. Voss. "Adaptive Evolution of the Venom-Targeted VWF Protein in Opossums That Eat Pitvipers." Ed. Paulo Lee Ho