Phylogenetic Systematics Excercise

Part I: Reading cladograms:

1. In the following cladogram, which node occurred earliest in time?

cladogram 1

Node 1
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2. In the cladogram for question 1:

  • Which node represents the most recent common ancestor of terminal taxa B and C?

    Node 2
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  • Which node represents the most recent common ancestor of terminal taxa A and B?

    Node 1
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  • Which terminal taxon is B more closely related to, A or C?

    C
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  • How did you know?

    B shares a more recent common ancesotr with C (represented by node 2) than it does with A. (Their most recent common ancestor is represented by node 1.)
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    3. Of the cladograms shown below, which one shows a different evolutionary history from the others?

    cladograms

    Cladogram 3. In it, B and C are shown as sharing the most recent common ancestor, whereas in the others, C shares its most recent common ancestor with D.
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    Part II: Types of groups.

    4. Three taxonomic groups are circled on the cladogram below. Indicate what type of group they represent.

    groups

    Group 1:

    Polyphyletic
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    Group 2:

    Monophyletic
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    Group 3:

    Paraphyletic
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    5. A simple cladogram of vertebrate relationships is shown. A circle has been drawn around all the parts of the cladogram that traditionally would be known as "fish."

    fish cladogram

  • What kind of group is "fish?"

    Paraphyletic
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  • What is the smallest monophyletic group on the cladogram that includes everything that we might refer to as a fish?

    Vertebrata
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    Part III: Synapomorphies

    6. The simplified cladogram of vertebrata is now shown with synapomorphies indicated.

    vertebrate cladogram

  • Of what monophyletic group is "choanae" a synapomorphy?

    Choanata
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  • What synapomorphy is indicated for Tetrapoda?

    Fingers and toes
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  • Name any character on the cladogram that is a plesiomorphy for Tetrapoda.

    Choanae, bony ribs and shoulder girdle, jaws, or vertebrae would be correct.
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  • Of what monophyletic group is the character that you just named a synapomorphy?

  • Choanae - Choanata
  • bony ribs and shoulder girdle - Osteichthyes
  • jaws - Gnathostomata
  • vertebrae - Vertebrata
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    Part IV. A systematist is exploring a planet in another solar system and discovers the following four interesting species. After being told that species "A" is very primitive, our systematist decides to use it as the outgroup for a phylogenetic systematic analysis.

    aliens

    The following character matrix is scored:

    Character
    1. Eyes present
    2. Spines present
    3. Eyes on stalks
    4. "Feet" present
    5. Antennae present
    		 A
    0
    0
    0
    0
    0
    		 B
    0
    1
    1
    0
    0
    		 C
    0
    0
    1
    1
    0
    		 D
    0
    0
    1
    1
    1

    7. A cladogram is generated. Mark on the tree the appearance of all characters.

    cladogram 2
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    8. Answer the following:

  • Which character is present in all four terminal taxa? Does it reveal anything to us about these creatures' relationships?

    Eyes. They reveal nothing.
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  • Which derived characters are present in only one terminal taxon? Do they reveal anything to us about these creatures' relationships?

    Antennae and spines. They reveal nothing.
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  • Which two derived characters are shared by more than one, but not all terminal taxa?

    Eye stalks are shared by B, C, and D. They indicate that these taxa share a more recent common ancestry with one another than any of them do with A. C and D share feet. These suggest that C and D share a more recent common ancestry with one another than either does with A or B.
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  • What are these called?

    Synapomorphies
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  • Which groups do they diagnose (identify) in this cladogram?

    Eye stalks diagnose a group containing the most recent common ancestor of B, C, and D and all of its descendants. Feet diagnose a group containing the most recent common ancestor of C and D and all of its descendants.
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  • How many character state changes do you see on this cladogram? (Remember, if a character is shared by all four taxa it might have been inherited from a distant ancestor, so you can't really count it as a "change.")

    4
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    9. Suppose that our systematist had decided that this was the proper cladogram:

    cladogram 3

    Map the character state changes from the matrix onto this cladogram.


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  • How many character state changes here?

    5
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  • Which tree do we prefer, the one above, or the one in question 8?

    We prefer the one in question 8.
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  • On what basis did you choose?

    We prefer it because it requires fewer character state changes. In other words, it is more parsimonious.
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    Part V. Now you are the systematist, performing a phylogenetic systematic analysis on a group of imaginary beetles. Assume that you have prior knowledge that taxon A is more distantly related to the others than any of the others are to one another. This means that A would be a good choice for an outgroup.

    10. Score the following matrix:

    Give all characters a state of "0" for ancestral (same as outgroup) and "1" for derived (different from outgroup).

    Character
    1. Large jaws present
    2. Small antennae present
    3. Spots present
    4. Stripes present
    		 A
    0
    0
    0
    0
    0
    		 B
    0
    1
    0
    0
    0
    		 C
    0
    1
    1
    1
    0
    		 D
    0
    1
    1
    1
    1

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    Bearing in mind that the character states seen in the outgroup, A, are, by definition, ancestral, answer the following questions:

  • Which of these characters function as synapomorphies in this matrix?

    Characters 1, 2, and 3.
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  • What groups do they diagnose?

  • Character 1 - A group containing the most recent common ancestor of B, C, and D and all of its descendants.
  • Character 2 - A group containing the most recent common ancestor of C and D and all of its descendants.
  • Character 3 - A group containing the most recent common ancestor of C and D and all of its descendants.
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  • Which character tells us nothing about the relationships of these animals?

    Character 4.
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  • Now do it: Draw a cladogram showing the relationships of these beetles. Make sure it is the simplest possible tree, invoking the fewest possible character state changes.


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