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Unformatted text preview: e mainly composed of cartilage or bony tissue. The states for this character are cartilaginous (C) or bony (B). Stomach. The site where food is stored and digested, the stomach is characterized by its complex muscular wall that breaks down food, its acidic environment (HCl) and proteolytic enzymes. Character states are presence (P) or absence (A) of a stomach. Teeth on jaws. They may be either present (P) or absent (A). Temporal fenestrae. The temporal fenestrae are openings on the side of the skull. The evolution of these fenestrae is associated with the evolution of the jaw muscles in vertebrates. The holes (fenestrae) on the side of the skull provide more room for muscle action, increasing the power of the bite. Possible states for this character are: Absent (0), one pair (1) or two pairs (2) of temporal fenestrae. 2. Coding of Characters You must transform the character states into numerical values. For the analysis, we will use the lamprey as the outgroup for all other species in order to establish the plesiomorphic and apomorphic states. By definition, the state observed in 58 Lab3 ‐ Vertebrate phylogeny the outgroup is defined as plesiomorphic and is coded as zero. Any different state observed for the same character is then apomorphic and coded by “1” (or “2” if there are more than 1 apomorphic state, see appendix 1). 3. Phylogenetic Tree Construction You must successively add each character, one at a time, using the method explained in appendix 2. It requires defining a hierarchy of monophyletic groups based on shared derived characters (synapomorphies). The basic assumption is that the entire group studied (the ingroup) makes up a monophyletic group and that lamprey is the sister group (the outgroup) of all other vertebrates. Steps to Be Completed Step 1. Conduct the phylogenetic analysis, graphically showing (by way of a cladogram) each step of your reasoning. (See Appendix 2). Step 2: Analysis. Once you have a cladogram that shows the phylogenetic relationships between the principal groups of vertebrates, you can use it to verify hypotheses concerning the evolution of other characters such as morphological and physiological characteristics. In order to avoid redundancy while interpreting the evolution of these characters, they should not have been used for defining the cladogram. For instance, in certain vertebrates, the heat produced by metabolism is too low to maintain a sufficient metabolic activity. These vertebrates are called ectotherms. Vertebrates with a sufficient metabolic heat production are called endotherms. Conclusion to write: based on the distribution of endothermy on your cladogram, what can you conclude about the evolution of endothermy within vertebrates? How to proceed: Consider endothermy as a character. Identify species that are endothermic and locate them on your cladogram. Then use your knowledge of the cladistic analysis to formulate a hypothesis regarding the evolution of endothermy within vertebrates: what type of character is it? Does it define a monophyletic group? What i...
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- Fall '08