Evolution Writing Assignment 1 PDF

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We were to choose a peer-reviewed scientific argument and summarize the predictions, methods, hypothesis, and impact of the findings. ...

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Madeline Wade BIOL 2013 Siler October 4, 2018 Part 1

Figure 1: “The Great Race”: a phylogeny that represents the emergence of new characteristics throughout different lineages and displays an example of convergent evolution. We conducted an experiment that represents the evolution of different traits in a population, as well as the retention of ancestral traits to map a phylogeny representing the process of evolution in a population. During the experiment, we noticed the appearance of two traits that phenotypically were identical. The two squares arose in separate lineages, meaning their analogy is a result of convergent evolution. Convergent evolution occurs when similar characteristics arise in separate lines of ancestry and the appearance of the characteristic is not due to a common ancestral trait. The trait could not be ancestral because it is not shared by entire clades, but is present only in two organisms and must have been derived separately. We

observe this pattern often in nature, and without phylogenies we might be misinformed about the nature of the relationship between two organisms. Without looking closer at evolutionary history, we might think these organisms are more closely related than they are.

Part 2 One example of where researchers have observed convergent evolutionary patterns in evolutionary history is with the trait of poison defense mechanisms found in arthropods (a dietary source of proteins that are transformed to toxic secretions for frogs) in both Madagascar and the Neotropics (Clark et al., 2005). These organisms are in different families and are not closely related microbiologically. The appearance of certain alkaloids in both lineages suggests separate derivation of the trait in response to an environmental condition, physical defense against predation. This study was conducted to understand the relationship between “poison frogs” and other animals that display the characteristic of poisonous alkaloid secretion. The researchers wanted to code and organize the alkaloids found in poison frog and investigate their source, which was discovered to be digestive in nature from several species of arthropods that contained the same alkaloids (Clark et al., 2005). These alkaloids were coded and categorized. The researchers found an example of convergent evolution when coding the alkaloids found in frogs and arthropods in two different regions: Madagascar and the Neotropics. Out of 16 coded alkaloids found in species in Madagascar, 13 were also present in species observed from the Neotropics (Clark et al., 2005). These lines evolved separately and none of the species that shared these alkaloids are closely related by genetic or morphological studies (Saux et al., 2004; Ward & Downie, 2005). This suggests that evolution of alkaloid secretion independently occurred at multiple time periods (Daly et al., 1996; Santos et al., 2003). The reason this trait evolved in separate lineages is because of its natural competitive advantage these organisms have over those

without it. Perhaps the trait arose as a defense against predators, and frogs eventually evolved the ability to sequester the alkaloids and produce toxins. The evolution of such specific chemical secretions in such unrelated species suggests the mutation was advantageous for organisms and became more frequent in both populations through the process of natural selection. The evolution of this characteristic is remarkable because it requires both the presence of arthropod prey containing these alkaloids and the ability to secrete these alkaloids after ingesting them. The evolution of both species to adopt this characteristic shows how the context of the environment. Both lineages evolved the ability to produce the same proteins and had the same source of prey to provide the necessary alkaloids for toxin secretion. This apomorphic trait demonstrates how similar characteristics can evolve in completely unrelated groups.

Literature Cited Clark, V. C., Raxworthy, C. J., Rakotomalala, V., Sierwald, P. & Fisher, B. L. (2005) Proceedings of Natl. Acad. Sci. 102, 11617–11622. Daly, J. W., Andriamaharavo, N. R., Andriantsiferana, M.&Myers, C. W. (1996) Am. Mus. Novit. 3177, 1–34. Santos, J. C., Coloma, L. A. & Cannatella, D. C. (2003) Proc. Natl. Acad. Sci. USA 100, 12792–12797. Saux, C., Fisher, B. L. & Spicer, G. S. (2004) Mol. Phylogenet. Evol. 33, 457–468 Ward, P. S. & Downie, D. A. (2005) Syst. Entomol. 30, 310–335....