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Unformatted text preview: of characters (see Appendix 1 for explanations). 3‐ You will proceed with the phylogenetic analysis of your data. That is, based on the information included in the coded matrix, you will construct a branching diagram (cladogram). 1. Data Collection One of the thrills of systematics is the discovery of characters that allow one to explain parts of the tree of life. However, since your observations are limited to 90 minutes, you will be assigned 12 characters that you will use in your phylogenetic analysis. Your first task consists of finding the state of characters in each of your nine assigned species. You will determine this information from examining the specimens on display in the lab, reading the provided documents and search the internet. Description of characters The next paragraphs present the list of all characters included in today’s study. Each character is briefly described, and the possible states for each character are indicated (e.g. ‘Present’ and ‘Absent’). Adult nephridial system (kidney type). The ancestral kidney in early vertebrates, as suggested from comparative developmental studies, is the archinephros. It is composed of segmentally arranged tubules that open at one end via a nephrostome to the coelom and at the other, into a common archinephric duct. In fish and amphibians, the functional kidney (mesonephros or opistonephros) is found more posterior, again draining via tubules to a common mesonephric duct. In reptiles, birds and mammals, the adult kidney (metanephros) is once again more posterior and empties via tubules into a common ureter. Character states for this trait are: mesonephros (Ms) or metanephros (Mt). Diagrams showing the different kidney types will be available in the laboratory. 56 Lab3 ‐ Vertebrate phylogeny Amnion. The amnion is an extra‐embryonic membrane that forms the amniotic cavity. Cells of the amnion secrete the amniotic fluid that provides the aquatic environment necessary for the development of the embryo. Possible states for this character are present (P) or absent (A). Elimination of nitrogenous wastes. Vertebrates are classified as ammoniotelic, ureotelic and uricotelic, based on their preferred way of eliminating nitrogen waste: as ammonia and ammonia salts, as urea, or as uric acid. Ammoniotelism is common in aquatic vertebrates. Ammonia is soluble in water, and a large quantity of water is required to eliminate this toxic product from the organism. On land, water conservation has a high priority, and nitrogenous waste is eliminated in a less toxic form requiring less water: urea, or uric acid. Urea is the main product of nitrogen excretion in amphibians and mammals, but plays a role in osmoregulation of various other species, such as sharks. In terrestrial turtles, lizards, snakes, crocodiles, and birds, uric acid is the main nitrogenous excretion product. Compared to urea, uric acid can be transformed into a salt that can be eliminated with very little water. The states for this character are the following: ammonia (amphioxus, hagfish, lamprey, bony fish), urea (Chondrichthyes, amphibians, mamma...
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- Fall '08