Gladistics refers to the method of hypothesizing the evolutionary relationships between species. As for a cladogram, it is the name of the branching diagram. This one illustrates these relationships. For instance, the cladogram on the right shows that deer are more related to turtles compared to worms. In the thing called the Clagodrams Gizmo, creating cladograms can be done by using morphological (physical characteristics) and molecular data.
There are some questions about Cladograms Gizmo. The answer key of these questions can be found below:
Prior Knowledge Questions
- Look at the images below. Which two organisms do you think are most closely related?
Deer and turtle
- Why do you think so?
They both share the characteristic of four legs and a tail unlike the worm.
To begin, make sure Plants is selected for the Organism group and Morphological is selected for the Data type. Click on one of the characteristics to the left of the table on the TABLE tab. Information about the characteristic will be shown on the ORGANISM tab. Using the information on the ORGANISM tab, describe each of the characteristics below.
- Xylem and phloem: tissues in plants that transport water and solutes up the plant (xylem) and food down the plant (phloem)
- Flowers: a part of plant containing reproductive organs surrounded by brightly colored petals
- Multicellularity: composed of more than one cell
Activity A: Morphological cladogram
Question: How do you build a simple cladogram based on physical characteristics?
- Fill in: Using what you learned in the warm-up, fill in the table. Clicking one of the boxes of the table will add a check mark to indicate the presence of a characteristic. Then, select Check table and adjust any of the boxes you may have filled in incorrectly.
Which organism has the fewest shared characteristics? Algae
- Organize: Now you are ready to organize the table.
A. How many characteristics (check marks) does each organism have? Drag the arrows below the table to order the organism columns from fewest characteristics on the left to most on the right. Algae: 0 Arabidopsis: 3 Cycad: 2 Moss: 1B.
B. How many organisms have each characteristic? Drag the arrows to the right of the table to order the characteristics from fewest organisms on the top to most on the bottom. Multicellularity: 3 Xylem and phloem: 2 Flowers: 1
- Build: Select the CLADOGRAM tab at the top left. The goal of a cladogram is to show the relationships among a group of organisms. Organisms that are most closely related should share the most recent common ancestor (highest branch on the tree). Organisms that are most distantly related should share the oldest common ancestor (lowest branch on the tree).
Click the segments on the cladogram template to build your own cladogram that shows how you think the different plants are related.
Sketch your cladogram in the space to the right.
Answer the following questions based on your cladogram
A. Which two organisms are most closely related? Cycad and Arabidopsis
B. Which organisms are most distantly related? Algae and Arabidopsis
- Analyze: On a completed cladogram, the orange dot that connects two branches represents a common ancestor. In the cladogram to the right, organisms B and C descended from a common ancestor (D) that was more recent than the common ancestor (E) of organisms A, B, and C.
Describe how the organisms in your cladogram are related through common ancestors.
Arabidopsis and Algae share the most distant common ancestor. After that Arabidopsis and Moss share a common ancestor. Arabidopsis and Cycad share the most recent common ancestor.
- Label: The purple lines represent a characteristic change, or adaptation. On the cladogram above, organisms B and C share characteristic 3. Organism B either gained or lost characteristic 1 after diverging from organism C.
In the Gizmo, select a purple line to open a text box and fill in the characteristics.
Based on your cladogram, from oldest to newest, in what order did the three characteristics (flowers, multicellularity, and xylem/ phloem) evolve?
Multicellularity, xylem/phloem, flowers
- Score: The parsimony principle states that the most likely solution is usually the simplest. In general, biologists try to create cladograms that require the fewest evolutionary changes. For example, it is more likely that xylem and phloem evolved once rather than multiple times. The “parsimony score” calculate show many changes occur in a given cladogram.
A. How many changes (purple lines) occurred in your cladogram? 3
B. Select Show parsimony score. What is the score of yourcladogram? 3
C. Select Show best possible parsimony score. Have you created a cladogram with the least number of possible characteristic changes? 3
- Revise: If you have not created a cladogram with the lowest possible parsimony score, adjust the cladogram until you do. Make sure that the organisms are ordered from fewest shared characteristics on the left to most shared characteristics on the right.
Select Show accepted cladogram. Does your cladogram match the scientifically accepted cladogram?
Click the camera to take a Screenshot of your cladogram. Right click the inmate, select Copy, and then paste the image into the space below.
Activity B: Cladogram practice
Question: How do you create parsimonious cladograms with more complex branching?
- Build: As you did in activity A, use the information provided to fill in the table of characteristics for insects. Check that your table is correct. On the CLADOGRAM tab, use your table to create an insect cladogram. Make adjustments until you achieve the lowest possible parsimony score, and then compare your cladogram to the accepted cladogram. When you are done, take a snapshot of the cladogram and save it in your document.
What is the lowest possible parsimony score? 4
Which two insects are most closely related? Bee and beetle
- Build: Create cladograms for the Primates and Animals groups (skip the Artiodactyla for now). These cladograms are a little more complex, and you may have to include multiple branches at the same level, such as in the example shown at the right. When you have built cladograms with the lowest possible parsimony score, compare them to the accepted cladogram.
Take Screenshots of the finished cladograms and paste them in the space below.
- Observe: Sometimes a trait can evolve separately in different groups. For example, both bats and birds have wings, but their common ancestor did not have wings.
In the Animals cladogram, which trait evolved two different times?
- Think and discuss: What could cause similar traits to evolve independently in different species?
The different species could be in a similar habitat. Although they are different species they may need to develop those similar traits to adapt to their common habitat and surroundings.
Species that live in the same environment or face similar threats may need to develop traits that help them adapt to their situations. For example, hedgehogs and porcupines independently evolved prickly spines to protect themselves from predators. This process is called convergent evolution, where similar characteristics evolved in species of different lineages.