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Unformatted text preview: s. They only indicate that there are several apomorphic states for this character. In other words, in a character that possesses 3 states (0, 1 and 2) the sequence of events can be 012, 021 or 201. To determine which sequence is correct, you need to have certain knowledge of the phylogeny of the ingroup. You can achieve that by analysing binary characters that show a clear polarization, like we did in this chapter. Once you have placed all binary characters you may continue with multistate characters. To do so, you will follow the same method as for binary characters, except that each derived state has to be placed independently on the cladogram. Generally, one of the 2 derived states defines a monophyletic group and is the most recent state. The other derived state defines a paraphyletic group and is, by comparison, more ancestral. Sometimes, both derived states will define monophyletic groups and the exact sequence of events cannot be determined (this corresponds to the 201 hypothesis). Species A, B, C, D and G possess 6(1). We can see on cladogram 4 from previous step that these species can be grouped within one monophyletic group by creating a branch between [F] and [ABCDG]. Similarly, species E and F possess 6(2) and the transformation point can be placed on the existing branch between SG and E: SG
D A B G 7(1)
6(1) Cladogram 5 3(1)
6(2) Once we have successfully placed both transformations on cladogram 5, we can see that the earliest derived state to appear is 6(2), followed by 6(1). Thus, the sequence of events is 6(0)6(2)6(1). 69 Lab3 ‐ Vertebrate phylogeny Step 6. Character 9 (type of caudal fin) poses another interpretational challenge. We can use the same reasoning as in step 5 and use the information already available on the cladogram. It is then clear that the transformation of 9(0) 9(1) that occurred after species E is earlier than character 9(2), which only exists in species B and G located higher in the cladogram. These two transformations can be placed easily on the cladogram, which becomes: SG E F C DA B G 9(2) 7(1)
2(1) Cladogram 6 6(1)
6(2) Step 7. We have not discussed character 4 until now. The apomorphic state of character 4 (presence of 2 dorsal fins) is found in species C and G. If we apply the principle of parsimony (see Appendix 1), we may conclude that this character is a homoplasy. In fact, too many characters would become homoplasies (reversals at the level of D, A and B) if we decided that C and G form a monophyletic group. Therefore, this means that the evolutionary appearance of a second dorsal fin happened independently twice in the ingroup: the first time in taxon C, and the second time in taxon G. It should be noted that this convergence hypothesis is only arrived at as a result of the phylogenetic analysis. The cladogram is therefore not modified by the addition of this character. 70 Lab3 ‐ Vertebrate phylogeny The homoplasies are identified with asterisks. The final cladogram is the following: SG E F C D B G A 4(1)*
4(1)* 9(2) 7(1)
8(1) 5(1) 2(1) Final cladogram 6(1)
6(2) Note that for your report you will need to include one additional cladogram with the actual species’ names on the phylogenetic tree. Références
Brooks, D.R., D.A. McLennan, J.P. Carney, M.D. Dennison and C.A. Goldman. 1994. Phylogenetic systematics: developing an hypothesis of amniote relationships. Pages 239‐258. Tested studies for laboratory teaching, Volume 15 (C.A. Goldman, ed.). Proceedings of the 15th Workshop/ Conference of the Association for Biology Laboratory Education (ABLE) Darwin, C. 1859. On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. ‐ John Murray, London. 502 pp. Eldredge, N. & J. Cracraft. 1980. Phylogenetic Patterns and the Evolutionary Process. ‐ Columbia University Press, New York.349 pp. Goujet, D. 1984. La cladistique. ‐ Encyclopediae Universalis, 1984: 1189‐1190. Hennig, W. 1950. Grundzüge einer Theorie der phylogenetischen Systematik. ‐ Deutscher Zentralverlag, Berlin. 370 pp. Hennig, W. 1966. Phylogenetic Systematics. ‐ University of Illinois Press, Urbana. 263 pp. Janvier, P. 1984. Cladistics: theory, purpose, and evolutionary implications. ‐ Pages 39‐75 in J. W. Pollard (ed.). Evolutionary Theory: Paths into the Future. John Wiley & Sons Ltd. New York. 271 pp. Janvier, P., P. Tassy & H. Thomas. 1980. Le cladisme. ‐ La Recherche, 11: 1396‐1406. Nelson, G. J. & N. I. Plantnick. 1981. Systematics and Biogeography: Cladistics and Vicariance. ‐ Columbia University Press, New York. 567 pp. Wiley, E. O. 1981. Phylogenetics: the Theory and Practice of Phylogenetic Systematics. ‐ John Wiley & Sons, Inc., New York. 437 pp. 71...
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This note was uploaded on 02/04/2014 for the course BIO 1130 taught by Professor Fenwick during the Fall '08 term at University of Ottawa.
- Fall '08