Cladistics (Evolutionary Relationships) Understanding Branching Diagrams

Cladistics (Evolutionary Relationships) Understanding Branching Diagrams

What is a Cladistics Diagram? It is a way to organize organisms to show evolutionary relationships and common ancestries. It is how the branches on the Tree of Life are formed.

The Tree of Life is Cladistics! Organisms are arranged on the Tree of Life by their similarities and their differences

How does a cladistics diagram work? The lowest (left) part of the diagram is the common ancestor to all organisms above So the hagfish (left) is a common ancestor to the perch, salamander, lizard, pigeon, mouse, and chimp

How does a cladistics diagram work? If you went all the way back to the beginning (all the way to the left), you would end up at the cyanobacteria the first living organism and a common ancestor to us all!

How does a cladistics diagram work? The organisms at the very top (right side) will be the most closely related, and will share the most common features The mouse & the chimp are most closely related

How does it work? Along the main (bottom) line, it shows where organisms have branched off, meaning that they DO NOT have the characteristics that the other organisms above/to the right have. The characteristic is labeled along the line. All organisms below (to the left of) that spot DO NOT have that characteristic. All organisms above that spot (to the right) DO have that characteristic.

Reading a Cladistics Diagram The hagfish is below (to the left of) the jaw mark. So the hagfish does not have jaws but the others do have jaws (they are above and to the right of the jaw mark)

Reading a Cladistics Diagram The perch is above (to the right) of the jaws mark, so it has jaws. But it is below (to the left of) the lungs mark. The perch does not have lungs, or any of the other later characteristics (claws/nails, fur, etc.)

Reading a Cladistics Diagram The wolf has hair, and it is carnivorous. But it does not have retractable claws, and it does not purr. What do the leopard and the cat have in common? What do they NOT have in common?

Cladistics Practice Activity Now, you will create a cladistics diagram showing the evolutionary relationships among 8 organisms. Work in pairs. Ready? Go to the next slide to get started.

Materials You will need: Eight organism cards (cut them apart) Seven plastic baggies Blank printer paper (or construction paper) Markers Ruler Glue

Step 1 Examine the 8 organisms. Pay careful attention to the descriptions on the cards. Select the two most similar organisms, and place them into one baggie. Seal the baggie.

Step 2 Next, select the one organism that you think is most similar to the first two organisms that you put in the baggie. Put that organism into a second baggie. Now, place the first baggie (with the two organisms) inside the second baggie and seal it up. It will look like this:

Step 3 Continue the process. Each time, choose ONE organism you think is most similar to the organisms already in the baggies. Put each organism into a new baggie, and then put the bag of baggies into the newest baggie. You will end up with one baggie that is holding the other 6 baggies.

Step 4 Now, on your blank white paper, lay out the organism pictures in order (like the colored rectangles in the picture) at the top of the page. The left (green) one is the one in the last baggie. Go in order, baggie by baggie, until you end up with the two in the last baggie on the right hand side. Check in with Mr. Luce before moving on to the next step!

Step 5 Once you ve checked with Mr. Luce, then glue the organism cards onto your paper. Now, use a ruler and marker to neatly draw the lines to create the cladogram (just like in the picture below).

Step 6 Now, you need to determine the characteristics that the organisms have in common (or not in common). The first line shows what ALL the organisms have in common. (They are all multi-cellular.) You will draw the line and label the characteristic. I have done the first one for you, on the next slide.

Multi-cellular

Step 7 Now, you need to determine what the last 7 have in common. Draw the line above (to the right) of the left organism, and below (to the left) of the other 7. Label the line with the characteristics (all 7 are consumers / they eat food). I have done this one for you on the next slide.

Multi-cellular Consumers

Step 8 Continue the process. As you move up the line, consider what one characteristic ALL the organisms above have in common. Draw the line and list the characteristic. See the next slide to see where to add your characteristic lines.

Multi-cellular Consumers

Are you done? Check in with Mr. Luce Next, use binder paper to answer the questions on the next slide. Please write the questions and answer in complete sentences!

Questions 1. What can a cladistics diagram tell you about evolution? 2. If two organisms are very similar, what does that tell you about their ancestry? 3. Do you think it s possible for a cladistics diagram to change (for example, organisms getting moved around to other locations)? If not, why not? If yes, what might cause an organism to move to a new spot on the cladistics diagram?

Great job. J You re Done! Turn in your completed work to Mr. Luce