5.6: Creating a Monster Phylogeny (Worksheet)

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Background

A phylogeny is a diagram depicting evolutionary relationships among organisms (taxa). Phylogenies are sometimes referred to as evolutionary trees or cladograms. These “family trees” are developed based on analysis of physical characters, or, increasingly, genetic information, that provide clues about the evolutionary relationships between these organisms. An example phylogeny of the order Primates is provided below.

Tree of life SVG by Ivica Letunic: Iletunic, retraced by Mariana Ruiz Villarreal: LadyofHats, has been designated to the public domain (CC0), and was modified (made grayscale, rotated, labels added) and used as Figure 4.1 in Explorations: An Open Invitation to Biological Anthropology under a CC BY-NC 4.0 License.

Each of the tips of the phylogeny represents a type of organism (taxon, singular for taxa). These are usually different species, but could be individuals. A node, where a phylogeny branches into two (or more) descendant branches, represents a common ancestor. Typically those in the field of cladistics (who create and study evolutionary trees and clades, as defined below) assume that when a lineage splits, it splits into exactly two groups. However, sometimes the data is insufficient to identify in which order the splits occurred.

Phylogenetic trees can be oriented in various directions, with the common ancestor at the bottom, side, or even spiraling out from the center.

Figure. Phylogenetic tree examples, original to Explorations Biological Anthropology Lab Book by Beth Shook, are under a CC BY-NC 4.0 License.

Phylogenetic trees depict clades. A clade is defined as a common ancestor and all of its descendants (living and extinct). Phylogenies will include many clades—often with clades nested inside of other clades. In fact, the entire tree can be conceptualized as one clade—since they all share one common ancestor. Thus, when describing part of a phylogeny, it is important to clearly identify which clade is being discussed—members of a clade will often share a scientific name.

Clades (Figure 9.2), original to Explorations: An Open Invitation to Biological Anthropology by Katie Nelson, is under a CC BY-NC 4.0 License.

Cladistics assumes that characteristics (physical and/or genetic) will change over time. It is when these traits change that we are able to differentiate between lineages or groups. The original form of the trait (held by ancestors and relatives outside a designated clade) is considered “primitive” or plesiomorphic. Be careful not to assume primitive traits are more simple or inferior, though, as evolution does not imply improvement or increased complexity! Changed traits are referred to as “derived” or apomorphic. All members of a clade can be distinguished from all other taxa in the tree because they inherited a shared derived trait or traits that were novel to the common ancestor of that clade.

Steps

For this activity, you will use the 10 imaginary characters provided for you, to create a classification key and a corresponding phylogeny. You will need a couple sheets of blank paper, a pencil with an eraser (to draw your phylogeny and erase/move lines, if needed), and colored pens, to complete the activity.

To Build the Classification Key

1. Lay out the 10 characters in front of you. Identify a character trait(s) that divides the 10 characters into two groups, for example: two legs versus four legs or green versus blue. The 10 characters do not need to be divided exactly in half; dividing them into one small and one large group based on the trait you select is equally fine. The precise trait(s) you select is not critical for this activity; what matters is that your categorization is strong. Take careful notes along the way to document the new groups you made and the traits you used to divide them.

   

   Example: Green versus Blue. Monster phylogenies, by Beth Shook, are licensed as CC BY-NC 4.0 International.

2. Repeat the process with each of the small groups, selecting a new trait each time. For example, you could now divide the green group by those with horns and those without. The number of individuals in each group does not matter—a group of five could be divided into one and four, or two and three. Again, take careful notes along the way to document the new groups you made and the trait(s) you used to divide them.

   

   Example: Horns versus No Horns. Monster phylogenies, by Beth Shook, are licensed as CC BY-NC 4.0 International.

3. Continue dividing up all subgroups with two or more imaginary characters until each individual can be classified as unique by the traits it possesses. Again, take careful notes along the way!
4. Now write out a simple key—it does not need to be perfect but it must be legible and clearly represent each of the divisions of your characters. At the bottom of the key, where all individuals have been separated, it may be helpful to give each character a name to help you distinguish it on both the key and the phylogeny. Here is an example of a key. Be sure to include the derived traits that you use to divide your characters next to the brackets.

   

   Phylogenetic trees, by Beth Shook, are licensed as CC BY-NC 4.0 International.

To Build the Phylogeny

5. Using a pencil and a new blank sheet of paper organized on a landscape layout (so the long edge is horizontal), list all 10 characters across the top of the page in the same order that they were at the bottom of your key (left to right). You may draw them or use an identifying name (e.g., green three-eyed monster).
6. Starting just below the characters, draw lines down to connect the characters who are most closely related (share the most traits and were the last to be separated in the key.)

7. Continue connecting individuals/groups (at their node) to complete the phylogeny.

8. Label the phylogeny with all the traits from your key approximately where they evolved (just below the last common ancestor node).

9. Using three different colored markers, draw a circle around three distinct clades (one color for each clade).

10. To the side, or on the back of your finished phylogeny, answer the following questions based on your tree.

a. Define clade.
b. What are represented by the tips of the phylogeny?
c. What are represented by the nodes of the phylogeny?
d. For each of the three clades, name a shared derived trait and a primitive trait. Please record the color and corresponding trait; for example: For the red clade, a primitive trait is three teeth and a shared derived trait is fur.
e. Are there any traits from your phylogeny that were identified as a primitive trait for one clade and a derived trait for another clade? Why does this occur?

11. When you are finished, label your phylogeny with your name and submit it to your instructor.