This preview shows page 1. Sign up to view the full content.
Unformatted text preview: hile the sister group possesses slits on the sides of the branchial cavity. Therefore, the no resolution cladogram can be modified to reflect the distribution of character 1 states and well as the transformation point of character 1(0) to 1(1). To do so, a new branch is created between the SG that carries the state (0), and taxa [A‐G] that possess the derived state (1). The transformation of character 1 is represented with a tick mark on the new branch, 66 Lab3 ‐ Vertebrate phylogeny which is labelled with the character number followed by the new (derived) state of this character between brackets: 1(1). This creates a new monophyletic group: [A‐G]. GF A B C D E F G Cladogram 2a 1(1) About parsimony: Creating a common ancestor to species A‐G is the solution we chose, because it involved less evolutionary events than alternate solutions (such as 7 independent transformation events happening to A). This is the parsimony principle. It doesn’t tell you that your hypothesis is necessarily true, but that it is the most likely (in term of odds) to represent the correct sequence of events that actually took place. Step 3. The next character to be added is character 3. It is found in its ancestral state in species SG and E, and is derived in the other taxa. Once again, we’ll try and regroup species possessing the derived state of this character (A, B, C, D, F and G) using the principle of parsimony. This will require the use a fundamental property of cladograms: the fact that the order of branches that are directly connected to a node (representing a common ancestor) can be rearranged: GF
D F G Cladogram 2b: Rearranged cladogram 2a 1(1)
67 Lab3 ‐ Vertebrate phylogeny We can see on cladogram 2b that the branch that carries species E has been moved to the left of the ingroup. Remember, the information presented on cladogram 2b is strictly identical to cladogram 2a. The 3(0) 3(1) transformation, can be added easily, thus creating the monophyletic group [ABCDFG] (cladogram 3). SG
F G Cladogram 3 3(1) 1(1) Step 4. The same reasoning can be made for characters 2 (reproduction), 5 (parental behaviour), 7 (position of the eyes), and 8 (teeth)*. Adding the transformation points for these characters creates 2 additional monophyletic groups [CD] and [ABG], both defined by 2 synapomorphies. This concordance in the distribution of derived characters reinforces the hypothesis presented on your cladogram. SG
DA 7(1) 8(1)
Cladogram 4 3(1) 1(1) *Note: several characters have been added during step 4 to keep this chapter shorter (intermediate step are available on the lab website). However, when writing your report, only ONE character will be added at each step. 68 Lab3 ‐ Vertebrate phylogeny Step 5. Characters with several derived states. How do we analyze a character that presents more than two states? First, we need to encode the states: the plesiomorphic state is coded 0 as usual and apomorphic states are coded 1, 2, 3… The numbers used for apomorphic states do not reflect the sequence of character modification...
View Full Document
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