Why is it homoplasy?

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ul Bio220 – Diversity of Life HW 2: Phylogenetics First Some Review and Examples… There are several definitions that you will need to be familiar with in order to properly use and understand phylogenetic systematics. – Character: A heritable attribute of an organism. – Plesiomorphy: A primitive or ancestral character. This is a character that was inherited from a distant or ancient ancestor. – Apomorphy: A derived (new) character. An evolutionary novelty that arises new in a taxon, or in the most recent common ancestor of a clade. There are two types of apomorphies: 1. Autapomorphy: An autapomorphy is a derived character that is unique, meaning it is found in only one taxon in the cladogram. It is not useful for reconstructing the evolutionary relationships between taxa. 2. Synapomorphy: A synapomorphy is a shared derived character found in two or more taxa on the cladogram. It is the only kind of character used to arrange organisms into monophyletic groups – Polytomy: A polytomy shows unresolved relationships between taxa on a cladogram. Instead of a two-branched split from a node, three or more branches all emanate from the same node. This generally means that there is not enough data to determine the relationships, and shows systematists where more work needs to be done! (see image below) A B C D – Homology: Features found in two or more organisms are considered homologous if they are the result of common ancestry. One example is the fingers on your right hand, and the fingers on the right forefoot of a lizard. By reconstructing the phylogeny of both lineages, we can see that “fingers on the forelimb’ is a character you and the lizard inherited from the same tetrapod ancestor. Therefore, the presence of these fingers is a homology between the two of you. -Homoplasy (analogy, convergence): This is similarity in form because of similar function, ecology habitat, etc., but not because of similar ancestry. A classic example is the wing of a bird and a bat. Each has wings and each uses them for flying. But the detailed structure of the wing is different, which raises suspicions as to its homology. The evolutionary history of both groups shows that they each independently evolved wings, and that they do not share a winged ancestor. Therefore, the wings of birds and bats are homoplastic, not homologous.
Group Member Names: How does Phylogenetic Systematics work? The relationships of organisms are determined by listine the distribution of characters in a matrix, and then reconstructing all the possible cladograms that can be drawn for the taxa in question (we don’t actually draw them all anymore, computers calculate them for us). First you pick taxa to work with. Then you pick characters that fulfill several criteria. The characters should be 1.) heritable, 2.) independent of one another, and 3.) unambiguous. You also pick an outgroup. The outgroup is a taxon that you feel represents the likely primitive condition for all of your taxa of interest (together called the ingroup). This has the effect of polarizing your characters in the data matrix, or in other words, it lets you know which characters are ancestral and which are derived. In the matrix, taxa go on one axis and characters go on the other: Outgroup Tree Cow Parrot CHARACTERS 1. Cells 2. Feathers 3. Horns 4. Brain 5. Vertebrae 6. Green color 7. Leaves 8. Two pairs of limbs 0 0 0 0 1 1 0 0 1 1 1 0 0 1 1 0 1 1 1 0 1 0 You examine the taxa and score the matrix based upon your observations. From this you can construct the cladogram by working your way up the tree by building more and more derived taxa. In this matrix state “0” means the character is absent; state “1” means it is present in that taxon. Whichever character state is present in the Outgroup is considered ancestral for all other taxa. For example, look at character 1. “Cells”. The outgroup has cells, as do all the other taxa. Therefore, there is no change between the outgroup and ingroup (the organisms with which you are interested). The character is ancestral, and as such is considered a plesiomorphy. Character 2,”Feathers”, is not present in the outgroup, but it is in the parrot. It is therefore derived, but only present in one taxon, making it an autapomorphy. When only three taxa are being studied, there are only three possible sets of relationships between them. For example, take a cow, a tree, and a parrot. The three cladograms showing all the possible evolutionary arrangements between these taxa are given below. The distribution of characters is then mapped onto each cladogram, so that you may see where they evolve. Cladistics operates under the Principle of Parsimony. This means that the most parsimonious (shortest and simplest) hypothesis is most likely the correct one. When deciding which cladogram best estimates relationships based on today’s data. parsimony dictates that the one with the fewest number of character changes, or steps, is probably the correct one.
parrot parrot parrot TTTO Go through and tally up the number of changes on each cladogram. If you do this correctly you should see that cladogram C is the shortest. Therefore, it probably represents the most likely evolutionary relationships between the tree, cow, and parrot. Questions, Part I: 1. A) In the above figure, Q1 designates an): a. apomorphy b. branch c.node d. terminal taxon B) What does Q1 represent biologically? 2. In the above figure, Q2 designates a(n): a, apomorphy b. branch c. node d. terminal taxon
roup Member Names 3. Label the type of group circled on each cladogram below: A) Group type: B) Group type: 4. A) Which phylogenies provide the same information about relationships? Some trees may match more than one other tree. Some trees may not match any other trees. A B C D E F A B C D E F B ADF EC E F D C B A A B C D E F A B F EDC B) In the space to the right, redraw Tree number 6 as a square-style tree. 5. In the space on the next page, draw a cladogram showing the relationships and character distribution described by the following statements (taxon names are in bold font): blee and blap are sister taxa; an autapomorphy for blap is the presence of zam; ploo is diagnosed by pim; looz is the sister taxon to ploo: nurn is the name of the monophyletic clade including the most recent common ancestor of ploo and looz; an autapomorphy for looz is the behavior hirm; nurn is diagnosed by muss and plz: the monophyletic clade including the most recent common ancestor of blee and blap and all of that ancestor’s descendants is named ploo.
up Member Names Questions. Part II: Base your answers on the cladogram shown below. Gymnophiona -Caudata Rhyncocephalia Mammalia Serpentes Anura Testudines Iguania Crocodylia Aves + limb loss scales into feathers Squamata Archosauria limb loss Batrachia + carotid labyrinth + quadrate hinge parental care + shel Amphibia fur Lepidosauria + overlapping scales lactation + pedicellate teeth + levator bulbi muscle Reptilia + color vision + scaly skin Amniota amniote egg Tetrapoda Limbs with digits
ap Member Names: 6. How many monophyletic groups are represented on this tree? 7. List all of the autapomorphies shown on the tree. 8. Produce a paraphyletic group by circling part of the tree. 9. What is the name of the monophyletic group including the most recent common ancestor of Aves and Squamata? 10. Amniote egg is what type of character (auto, synapo, plesio) for Amniota? Why? 11. What is the sister taxon to Amphibia? 12. What is the sister taxon to Gymnophiona? 13. Is there a polytomy on this tree? Where is it? Why is it a polytomy? 14. Is Rhyncocephalia more closely related to Crocodylia or Mammalia? Why? 15. List all of the terminal taxa expected to have these features if you surveyed them today: Limbs with digits: Pedicellate teeth: Amniote ege Scaly skin: 16. a) Tor E: More recent time is portrayed as you move from right to left on this cladogram, so we can conclude that Aves and Croes are the most evolved taxa. b) Why is this Tor F?
up Member Names: Questions, Part III: For questions 17-22, you are chief astrozoologist on a Mars mission. After prospecting for several days, you assemble a collection of life forms. It is now your job to determine their evolutionary relationships. 17. Fill in the matrix using the list of characters and treating Oliver as your Outgroup. Use state “O” to represent absence and “1” to indicate presence. Remember to treat characters separately (for example, pinchers: present/absent is a different character from tentacles: present/absent). Harpo Zeppo Groucho Chico Oliver 1. Eyes 2. mouth 3. tentacles 4. horn 5. pincers 6. legs 7. teeth Oliver Groucho Zeppo Chico Harpo 18. Which characters will be useful for making groups? Which will not? WHY? 19. Construct a cladogram based upon your matrix. Map all of your character transformations onto the tree. (hint: you may need to try a few trees before discovering the shortest one). 20. How many evolutionary steps are there on your tree?
ip Member Names_ 21. While further studying these interesting creatures you notice two of them performing an odd behavior. Both Chico and Harpo are observed spinning in circles. Add “spinning” as an 8″character and fill in the matrix. 22. Below, draw the two shortest possible trees (i.e. hypotheses of relationships) that could result from the addition of this character. (hint: start with your original tree, because most of your matrix is unchanged! Then think about whether a second arrangement of relationships could shorten the number of times characters evolve). 23. Which of the two trees is more parsimonious? Can this be determined from the data available today? 24. List one example of homology in your second tree. Why is it homology? 25. List one example of homoplasy in your second tree. Why is it homoplasy?
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