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Annotated Bibliography for the Evolutionary use of Tusks Patrick Hughes, Thursdays 10:20am

Burgess, E. A., J. M. Lanyon, and T. Keeley. "Testosterone and Tusks: Maturation and Seasonal Reproductive Patterns of Live, Free-ranging Male Dugongs (Dugong Dugon) in a Subtropical Population." Reproduction 143.5 (2012): 683-97. Reproduction. Web. 14 Sept. 2014. . Researchers that conducted this study looked at how the presence of tusks was involved in the sexual maturity of dugongs. They studied testosterone levels in relationship with the presence of tusks and body size. It was discovered that tusks were found for the most part in males that were larger in the study and on those who had higher levels of testosterone. This led the researchers to the conclusion that tusks are a signal that a male is a better option to mate with when females are looking for a mate. It signifies that the males with tusks are the biggest and most virile in the group Chelliah, Karapagam, and Raman Sukumar. "The Role of Tusks,musth and Body Size in Male-male Competition among Asian Elephants, Elephas Maximus." Animal Behaviour 86.6 (2013): 1207-214. Science Direct. Web. 14 Sept. 2014. . This article discusses the use of tusks in male to male competition amongst Asian elephants. The study compares how musth, body size, and tusk sizes are used to establish dominance amongst the males of the population. After viewing fights between many different males who had all different combinations of characteristics including tuskless, long tusked, large body size, and so on. After all the data was collected it showed that tusks were only used as deciding factor when the musth and body size were the same. This could be due to the fact that Asian elephants are rapidly evolving to no longer need their tusks because the poaching done by humans have eliminated many of the elephants with the biggest and strongest tusks. Emlen, Douglas J. "The Evolution of Animal Weapons." Annual Review of Ecology, Evolution, and Systematics 39.1 (2008): 387-413. Annual Reviews. Web. 14 Sept. 2014. . This article focuses on the evolutionary process behind tusks. Throughout the paper the author address the many different types of weapons that were developed by a wide variety of animals and how they came to be. With this research it became clear when tusks were developed and why they were useful enough to animal’s ancestors to be passed on through natural selection.

Gerson, Helen B., and John P. Hickie. "Head Scarring on Male Narwhals (Monodon Monoceros): Evidence for Aggressive Tusk Use." Canadian Journal of Zoology 63.9 (1985): 2083-087. NRC Research Press. Web. 14 Sept. 2014. . This article observes the aggressive uses for the  narwhals possess. They observed many injuries such as head scarring and embedded tips of tusks in adult males. When they compared this data with the data found of these same injuries in young males and females they noted that the adult males sustained these injuries at a much higher rate. They use their tusks to fight one another and the winners would be the more dominant of the two individuals.

One sentence and citation: The way that females know how a male has reached sexual maturity is by the eruption of tusks in the male since tusks erupt in males when testosterone levels reach a high enough level.

Link: https://en.wikipedia.org/wiki/Dugong

Suggestions:

maturity
I would like to see a section added to the page or at least a mention as to how tusks relate to the sexual maturity of some animals such as dugongs.

dominance
The article mentions how some species use tusks as a display of dominance, but I would like some elaboration as to how they are used to display dominance? is it just size of tusks or do certain species fight one another?

evolution
This article needs to have a section added as to how tusks arose through evolution and how the tuskss gave species a big enough reproductive advantage to e passed down through the generations.

Hughes.1332 (talk) 17:54, 30 September 2014 (UTC)hughes.1332

Link: https://en.wikipedia.org/wiki/Talk:Tusk

Miller, Edward H. "Walrus Ethology. I. The Social Role of Tusks and Applications of Multidimensional Scaling." Canadian Journal of Zoology 53.5 (1975): 590-613. NRC Research Press. Web. 14 Sept. 2014. . The research that was done for this article examined how tusk length and body size related to the dominance between walruses in certain populations. The walrus that had larger body sizes and longer tusks frequently displayed a more aggressive nature while the males exhibiting smaller sizes would be much more passive. This shows that with a larger tusk sizes comes a more natural predisposition for dominance. This dominance is then aided by using their large tusks to fight of competitive males.

Edits

https://en.wikipedia.org/wiki/Talk:Narwhal#Male_fighting

Narwhals have been known to use their tusks as a defensive weapon as well. Even though the tusk is not the toughest found in the animal kingdom the narwhal uses it as a sword or spear when fighting with threats to their group. Many of the males have been found with large gashes on their heads along with pieces of tusks found lodged in the front of their skull that have been left behind from vicious fights they had endured. This has lead researchers to believe that the narwhals fight amongst one another for a variety of reasons including territory defense and displays of dominance.

Gerson, Helen B., and John P. Hickie. 1985 "Head Scarring on Male Narwhals (Monodon monoceros): Evidence for Aggressive Tusk Use." Canadian Journal of Zoology 63: 2083-087.

https://en.wikipedia.org/wiki/Dugong The adolescent male dugongs have their tusks constantly growing but are un-erupted until their body size reaches that of a mature male. This is because the adolescent males don’t need to have tusks for signaling females because they are unable to reproduce yet. If they had tusks the process of sexual selection would unable to work since the females would be confused about who to mate with. Once the males reach their appropriate size, one at which they can successfully protect their mate and offspring, their tusks erupt and signal to females that they are ready to begin mating.

Burgess, E. A., J. M. Lanyon, and T. Keeley. 2012. "Testosterone and Tusks: Maturation and Seasonal Reproductive Patterns of Live, Free-ranging Male Dugongs (Dugong dugon) in a Subtropical Population." Reproduction 143: 683-97.

https://en.wikipedia.org/wiki/Talk:Walrus#Dominance

Walrus use their tusks to both establish and maintain their dominance within their social groups. Males will use their tusks while fighting with one another to become the dominant male. Once their dominance is established they use their tusks in a new way to stay the dominant male. If a challenger approaches the dominant male they will prop themselves up and point the ends of their tusks at the challenger to try to intimidate them. If the challenger is intimidated then the altercation will end, but if the challenger does not then a fight will ensue between the two and the winner will be the dominant male form that point on in the group.

Miller, Edward H. 1975. "Walrus Ethology. I. The Social Role of Tusks and Applications of Multidimensional Scaling." Canadian Journal of Zoology 53: 590-613.

Final paper

Tusks, the Evolutionary Wonder Tool PH5365 Thurs, 10:20 AM

Introduction Fangs, claws, horns, and many other adaptations have evolved throughout the history of planet earth, all having their specific purpose that makes them indispensable to the organisms that use them. Whether they are the suppliers of food or a final line of defense, it can clearly be seen that they are an evolutionary advantage to many diverse types of organisms. However, there is one that stands out for its uniqueness, and that is the evolutionary feature of tusks. Tusks can be used for all of the reasons above and more due to the diversity in forms of tusks themselves and the wide range of animals that they belong to. Very few other features are seen today that both aquatic and terrestrial animals use with such frequency. The fact that these organisms use their tusks for similar tasks regardless of their environment, size, or social makeups is what makes tusks the most impressive tool evolution has ever developed. Evolutionary History of Tusks The evolutionary history of the tusk can be traced back to the Carboniferous period when many of the planet’s first vertebrates had just begun to evolve. During this time, roughly 300 million years ago, many amphibious and reptilian vertebrates were just beginning to evolve and expand into the harsh world that existed. To survive and thrive during these hard times, organisms needed to develop safety mechanisms that were built into their bodies to not only fight off predators, but also to control their territory. One of the first species to develop tusks was the Southeast Asian voiceless frog. This frog had an enlarged head with spines to go along with its tusks. These adaptations were then used to defend their mates and burrows from many of the newly evolved species at the time (Emlen 2008). Although these frogs were among the first species to develop tusks, they were certainly not the last. Many other species from different phylogenetic branches began coevolving tusks due to the fitness advantage they gave an organism. Mammals were one of those coevolving groups that followed the frogs’ lead, and have turned into the group of organisms that we most recognize today with tusks. The first pair of tusks to be recorded in mammals was found to be from roughly 10 million years ago (Emlen 2008). A wide variety of mammal species began to develop tusks, many of which resemble some of the most unique mammal species in existence today. Through the use of fossil records, researchers have been able to find many of these tusked species that share many traits with extant species in today’s environments, which has allowed us to find other evolutionary advantages that tusks could have given mammals in the past. A prime example of this has been the comparison of the extinct American Mastodon, (Mammut americanum) and the extant African Elephant, (Loxodonta Africana). The sheer morphological similarities between these two have led scientist to believe that the African Elephant is a closely related descendant to the Mastodon. With more details about this evolutionary connection becoming available, researchers are given a much more precise picture of the uses and advantages tusks gave mammals as they have evolved throughout time. By studying the activities of the African elephant today, the uses for tusks have multiplied from just a protection mechanism to a much broader array of functions, including food gathering, displays of dominance in intrasexual competition, and for many different manners of social interaction (Smith eat al. 2013). With these traits being linked back to an ancient species such as the mastodon, it has become obvious why tusks have persisted for over 300 million years. This clear evolutionary pathway that tusks took to become the tool they are now gives us a clear backdrop for why so many different types of organisms have this adaptation. Now it is necessary to take a look at why tusks will continue to persist in future organisms by exploring how tusks assist species and give them an evolutionary advantage over other organisms in today’s world. Defense Defense is the most ancient purpose for tusks, but even to this day it holds a key role in the life of an organism. An organism that uses their tusks best for this function better than many others is the narwhal, (Monodon monoceros). The narwhal has a long sharp tusk protruding from its head that has a variety of uses, especially as a weapon of defense. Large male narwhals, which are seen as dominant, show many body scars from using their tusks to defend their social group and have even been found with pieces of tusks broken off in and around their heads, (Gerson et al. 1985). Even though these fights have never been observed due to the ice packs that these narwhals live under, the wounds give strong evidence as to the defensive role the tusks are used for. The female species particularly look for males with strong defensive and tusk capabilities when selecting a suitable mate. This means that in addition to being evolved for defense purposes, the tusk is heavily involved in sexual selection. Sexual Selection The idea of sexual selection is brought to mind when one is thinking about the size of an animal or its ability appear more desirable to the females of the group through bright colors or elaborate displays. These are not the only methods by which sexual selection can occur and this concept is shown very clearly by dugongs, (Dugong dugon). This species has large upper incisor tusks that were originally thought to be used in assisting the dugong in feeding by grasping and cutting the plants. This may have been true in past species, but it is not how the tusks are used in the modern day dugong, (Domning et al. 2007). Instead of being used for feeding assistance, these tusks have been linked to the process of sexual selection. This has been discovered due to what the presence of tusks mean to the females that are looking to find a mate. It has been found that males with erupted tusks are larger and have higher levels of testosterone than the males who lack erupted tusks, (Burgess et al. 2012). This presence of tusks signals females which dugongs are the more viable mates. With a positive correlation to both body size and testosterone levels, this means that the males with larger tusks have better genetic compositions to both support a higher level of evolutionary fitness and to be better protectors of their spouses and children. In this way, females are more likely to select the larger-tusked males during mating. With this process of sexual selection, how do the individuals who in fact contain tusks rank against one another? Dominance A display of dominance is the process that members of a species use to separate from all of the other members of the species containing tusks. This process is seen the most in males of a species and is primarily displayed in one of two ways, through physical altercations or through social displays, both of which are aided by the presence of tusks. Physical altercations are mainly used in establishing an individual’s dominance. One species where this is seen most drastically is in the African Giant Forest Hog, (Hylochoerus). These boars use their tusks in extreme physical altercations when trying to establish their dominance in the group. Two boars will charge each other and butt-heads against one another. Once they are locked in their head-butt, they use their lower tusks to slash at each other in an attempt to cut their opponents, (Geist 1966). The winners of these battles are the ones that are the least wounded because they prove to their herd that they know how to fight and would make an excellent protector of the group from any outsiders or predators. Once dominance is established, the use for tusks is switched from dominance battles to maintaining the dominance by sending signals and intimidation displays. This is seen in the social interactions in groups of walruses, (Odobenus rosmarus). The dominant walrus will take its tusks and point them at a challenger to intimidate the challenger and to assert its dominance, (Miller 1975). By showing its tusks in a threatening manner, the dominant walrus can eliminate the need for fighting and a physical altercation while still maintaining that it is the biggest and strongest male that there is. As supported by these two examples, dominance is the most common use for tusks in modern animals today. With all of the research pointing to tusks as being positively correlated to dominance, this shows why tusks will persist as a key tool in many future evolutionary processes. Conclusion Throughout this paper, we have examined why tusks have persisted for over 300 million years. Their uses of defense, sexual selection, and dominance make them key features that are of great importance to the survival of species, and thus it can be argued that tusks provide more evolutionary advantages than any other tool that has arisen throughout the evolutionary history of the world. The only factor that stands in the way of tusks continued existence would be humans. An example of this detriment to tusks is exhibited in a species such as Asian elephants, (Elephas maximus). There has been such a large amount of poaching on these elephants for their ivory tusks that they have begun to develop ways around needing tusks, such as using body size and musth to determine dominance instead of fighting with tusks, (Chelliah et al. 2013). Cases like these Asian elephants do exist, but if left alone without human interference, the tusk will continue on as the wonder tool of the evolutionary process.

Bibliography Burgess, E. A., J. M. Lanyon, and T. Keeley. 2012. "Testosterone and Tusks: Maturation and Seasonal Reproductive Patterns of Live, Free-ranging Male Dugongs (Dugong dugon) in a Subtropical Population." Reproduction 143: 683-97. Chelliah, Karapagam, and Raman Sukumar. 2013 "The Role of Tusks,musth and Body Size in Male-male Competition among Asian Elephants, Elephas Maximus." Animal Behaviour 86: 1207-214. Domning, Daryl P., and Brian L. Beatty. 2007. "Use of Tusks in Feeding by Dugongid sirenians: Observations and Tests of Hypotheses." The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology 290: 523-38. Emlen, Douglas J. 2008 "The Evolution of Animal Weapons." Annual Review of Ecology, Evolution, and Systematics 39: 387-413.

Geist, Valerius. 1966. "The Evolution of Horn-Like Organs." Behaviour 27: 175-214. Gerson, Helen B., and John P. Hickie. 1985 "Head Scarring on Male Narwhals (Monodon monoceros): Evidence for Aggressive Tusk Use." Canadian Journal of Zoology 63: 2083-087. Miller, Edward H. 1975. "Walrus Ethology. I. The Social Role of Tusks and Applications of Multidimensional Scaling." Canadian Journal of Zoology 53: 590-613. Smith, Kathlyn M., and Daniel C. Fisher. 2013. "Sexual Dimorphism and Inter-Generic Variation in Proboscidean Tusks: Multivariate Assessment of American Mastodons (Mammut americanum) and Extant African Elephants." Journal of Mammalian Evolution 20: 337-55.