Cladograms & Dichotomous Keys (Topic 5) How do scientists figure out which organisms are closely related, and which are distantly related? How do scientists identify organisms? Cladograms & Dichotomous Keys (Topic 5)

Which animals seem most alike? Why? Morphology: branch of biology that deals with the form and structure of organisms Which animals seem most alike? Why?

Bats and sea lions (mammals) are more closely related to each other than either one is related to a shark (cartilaginous fish) or an eagle ( bird). Why do you think the sea lion and the shark look so similar even though they are very different species?

Convergent Evolution: non-related species develop similar structures due to similar response to environmental pressures (not due to shared ancestry) ; result in analogous structures

Divergent Evolution : different structures arise due to specific environmental pressure  new species

Observe the following image finches from the Galapagos Islands Observe the following image finches from the Galapagos Islands. Which type of evolution is this?

Observe following image of succulents from two continents that are only distantly related (do NOT share a common ancestor) What type of evolution is this? Carnegiea gigantea Saguaro from North America Euphorbia virosa from Africa

How are cladograms interpreted?

Where would you place a lizard, rat, and goldfish?

What are dichotomous keys? Why do we use them? dicho = Greek root for “two” tome = Greek root for “to cut” Tool used to identify new, and unknown organisms Based on a system of pairs of contrasting statements Can be developed/used to do any type of classification  

How can you create a dichotomous key of your own? Start with a concept map to sort all items/organisms Convert concept map in to dichotomous statements Start with one side of concept map – continue statements until you’ve keyed out all organisms on one side. THEN do the other side. For number of steps in your key, you should end up with 1 less than the number of items your are identifying. (If there are 12 items, there should be 11 steps in your key.)

Example of a Dichotomous Key: 1.  Organism is a plant ...................................................................................... Go to Q2      Organism is not a plant (animal) ................................................................ Go to Q5 2.  Has no 'true' leaves or roots ....................................................................... Bryophyta      Has leaves and roots ................................................................................... Go to Q3 3.  Has no seeds (sporangia) .......................................................................... Filicinophyta      Has seeds ..................................................................................................... Go to Q4  4.  Has no flowers .........................................................................................Coniferophyta      Has flowers .......................................................................................Angiospermophyta 5.  Asymmetrical body plan ............................................................................. Porifera      Symmetrical body plan ............................................................................... Go to Q6 6.  Has radial symmetry ................................................................................... Cnidaria      Has bilateral symmetry ............................................................................... Go to Q7 7.  Has no anus ..........................................................................................Platyhelminthes      Has an anus ................................................................................................. Go to Q8 8.  Has a segmented body .............................................................................. Go to Q9      Has no visible body segmentation ........................................................... Mollusca 9.  Have an exoskeleton ................................................................................. Arthropoda      Have no exoskeleton ................................................................................. Annelida