Evolutionary Relationships: Cladistics and Phylogeny
Phylogeny
Content Standard Content Standard
The learners demonstrate an understanding of Basic Taxonomic Concepts and Principles, Description, Nomenclature, Identification and Classification Performance Standard
Performance Standard The learners shall be able to:
• make simple cladograms Learning Competency Learning Competency
The learners should be able to describe species diversity and cladistics, including types of evidence and procedures that can be used to establish evolutionary relationships STEM_BIO11/12IIIh-j-16STEM_BIO11/12IIIh-j-16
Specific Learning Outcomes Specific Learning Outcomes
At the end of the lesson, the learners will be able to:
• demonstrate how shared derived characters can be used to reveal degrees of relationship; and
• build cladograms to infer evolutionary relatedness
180 MINS 180 MINS
LESSON OUTLINE Introduction
IntroductionCommunicating Learning Objectives 30 Motivation
Motivation Café Conversation 20
Instruction
Instruction Works in Pairs 50
Practice
Practice Constructing Cladograms 40 Enrichment
Enrichment
Test your Skill 30
Evaluation
Evaluation After Class: Peer Evaluation 10 Materials
Materials
Writing materials, sheets of paper, photos of animals ( may be provided as worksheet)
Resources Resources
(1) Reece JB, Urry LA, Cain ML, Wasserman SA, Minorsky PV, Jackson RB.
Campbell Biology.10th edition. San Francisco, California, USA: Pearson Education Inc.; 2014. 551-558 pp.
(2) Taxonomic Classification and Phylogenetics Trees.trees.http://
www.mhhe.com/biosci/pae/zoology/cladogram/index.mhtml. 17 August 2015
(3) Cladogram and Phylogenetic Trees:Evoution Classifications.http://
study.com/academy/lesson/cladograms-and-phylogenic-trees-evolution-classifications.html. 17 August 2015.
(4) Constructing a Phylogenetic tree. http://evolution.berkeley.edu/
evolibrary/article/0_0_0/phylogenetics_11. 17 August 2015.
INTRODUCTION (30 MINS) Communicating Learning Objectives Communicating Learning Objectives
1. Introduce the following learning objectives using any of the suggested protocols (Verbatim, Own words, Read-aloud)
I. I can demonstrate how shared derived characters can be used to reveal degrees of relationship.
II. I can build cladograms to infer evolutionary relatedness.
Review Review
1. Say, “Look around you, and see the enormous diversity the natural world has to offer. However, amidst such diversity is also an amount of similarity which you can observe. This gives us the idea that somehow, organisms are indeed related. Life is somehow interconnected to each other.”
Systematics is the study of the diversity of organisms in the evolutionary context. It intends to use phylogeny in classifying organisms. Phylogeny is the study of the evolutionary history and relationships among organisms. Evidences from a wide variety of sources including paleontology, embryology, morphology, anatomy and molecular biology can be used to establish phylogeny.
Over the last few centuries systematists have developed different approaches to show relationships among organisms. The most commonly used is cladistics.
2. Discuss briefly:
Cladistics
Cladistics studies relationships between taxa using shared derived characters. The basic assumption behind cladistics is that members of a group share a common recent ancestor and are thus more "closely related" to one another than they are to other groups of organisms. Related groups of organisms are recognized because they share a set of derived characters.These derived characters were inherited from a recent ancestor .
3. Ask your learner to define the following terms in their own words:
I. analogous character II. character III. character state IV. clade V. cladogram VI. homologous character VII. phylogeny
Teacher Tip:
Teacher Tip:
Here are some definition of terms:
Phylogeny
Phylogeny- the evolutionary relationships among organisms
Cladogram
Cladogram- a phylogenetic tree that shows relationship of taxa based on shared derived characters
Character
Character- any trait of an organism that can be described or measured
Character state
Character state- describes the character.
A particular character can have several character states.
Example: Corolla is a character. Character states can be: shape of the corolla, color of corolla, number of petals comprising the corolla.
Homologo
Homologous us characterscharacters- characters having similar structures because these were derived from a common ancestor
Analogou
Analogous characterss characters-characters that have separate evolutionary srcins, but are superficially similar because they perform the same function. Analogous characters are the result of convergent evolution.
Example: Bird and bat wings are analogous since both are used for flying.
Clade
Clade- a group of taxa consisting of an ancestor and all of its descendant taxa
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4. Stress that similarities among existing organisms (including morphological, developmental, and molecular similarities) reflect common ancestry and provide evidence for evolution.
I.
I. Outline:Outline:
A. shared derived characters can be used to reveal degrees of relationship B. constructing and interpreting a phylogenetic tree
MOTIVATION (20 MINS) Café Conversation
1. Ask learners: “Do you remember the last time you had a family reunion? A summer vacation or a family barbecue and the latest family picture taken together? Can you describe your family members? What makes you similar to them and what makes you unique?”
2. Ask learners to list characters or features that served as evidences (e.g. morphological, genetic, etc.) that indeed they belong to the same family. Ask learners to note as many as they can think of.
Sample responses:
Sample responses:
• Color of the eyes (e.g. brown, black)
• Texture and color of the hair (e.g. curly black hair)
• Color of the skin (e.g. fair complexion)
• Blood type (e.g. A, AB, O, B)
• Height
• Shape of the nose
3. Explain, “Basically, a family picture represents a family tree.Family trees show how people are related to each other. Similarly, scientists use phylogenetic trees like cladograms to study the relationships among organisms. Sometimes, family trees are used to show relationships between individuals. Those who are closely related are located closer together than those who are only distantly related. For instance, in a family tree, we can see that the siblings are close together, indicating a close genetic relationship. But the siblings are far from their great aunt, indicating a more distant genetic relationship. Family trees can also be used to see ancestral connections. That is, we can see that all the people in the last generation have the same great-great-grandparents in common.
Teacher Tip:
Suggestion: Include a website or video that learners can view to understand how to construct a cladogram. Explain the rationale of the activity.
This same idea of relationships can be used in science. Biologists use phylogenetic treesphylogenetic trees to illustrate evolutionary relationships among organisms.
4. Stress that for the succeeding activities, focus will be on constructing and interpreting a simple phylogenetic tree.
INSTRUCTION (50 MINS) Discussion:
Discussion:
A. shared derived characters can be used to reveal degrees of relationship B. constructing and interpreting a phylogenetic tree
Work in Pairs and Build that Tree Work in Pairs and Build that Tree
1. Ask learners to choose a partner and work in pairs..
2. For this activity, present to learners a diverse group of vertebrates and ask them to make a phylogenetic tree showing their evolutionary relationships. This tree should be primarily based on physical characteristics
physical characteristics, such as:
I. Presence or absence of a backbone II. Ability to breathe in air or water III. Cold or warm blooded IV. Carnivore, herbivore, or omnivore V. Presence or absence of hair/fur VI. Any other external structures such as horns
Teacher Tip:
Teacher Tip:
Constructing a phylogenetic tree is one way to visualize evolutionary relatedness. In this activity, guide learners on how to construct their own tree from a set of animals provided, using only observable physical features.
This activity gives learners an opportunity to classify organisms on their own, and they can visualize the types of evidence used to show evolutionary relationships.
Due to the open-ended nature of this activity, learners will come up with many different combinations and layouts.
However, the end result should be an evolutionary tree that shows the basic relationship among animals. Arthropods such as the spider and moth should be far
apart from an aquatic mammal such as the walrus.
This is also a good opportunity to gauge how well learners understand the basis of different classifications, such as reptile, amphibian, and mammal.
Phylogenetic systematics emphasize descent and common ancestry in order to determine the evolutionary history of groups of organisms as a determining factor in classification
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Note:
Note: The following outline drawings of animals are provided for the activity. These can be printed and cut out for learners to work with.
3. Ask learners to work in pairs and individually cut out each animal, including the name.
4. Ask them to lay all the animals on their desks and separate them into two groups using the presence or absence of a backbonepresence or absence of a backboneas the first character.
5. On a separate sheet of paper, start constructing the phylogenetic tree like the one shown below.
6. Ask learners to continue separating the animals into smaller groups using the characters in number two.
7. When an animal reaches the tip of the branch, glue it. Repeat for all other animals in the collection.
8. Ask volunteers to present their phylogenetic tree in class.
PRACTICE (40 MINS) 1. Learners will still work in pairs.
2. Ask each pair to construct a cladogram based on the data provided.
Constructing a Cladogram
1. Ask learners to use the data below to arrange the groups of organisms based on their shared derived traits. This time you will be using distantly related organisms or a taxon termed an outgroup.
2. For each group, the traits or characters are already listed. For each character, determine which state is ancestral or primitive and which is derived. This is usually done by comparing with the outgroup. Traits found in the outgroup are likely to be ancestral or primitive. Similarly, traits not found in the outgroup are considered as derived. In cladistics, it is the derived trait shared among taxa that should be placed in the cladogram.
3. Group taxa according to their shared derived character(s).
4. Once you have evaluated all the characters, you may start constructing your cladogram. Where do you place the outgroup?... (Correct, an outgroup is always placed at the base of the cladogram.) 5. Choose a learner to present the cladogram. After this, show them the correct cladogram below.
Homalozoa Homalozoa (Outgroup)
(Outgroup) EEcchhiinnooiid d AAsstteerrooiid d CCrriinnooiid d HHoollootthhuurrooiid d OpOptthhiiuurriioodd
Water vascular system YES YES YES YES YES YES
Number ambulacral of grooves 3 5 5 5 5 5
Madreporita Aboral Aboral Aboral None Internal Oral
Suckers Non on podia On podia On podia Absent On podia On podia
Closed ambulacral grooves No Yes Yes No Yes Yes
Aboral surface reduced No Yes No No Yes Yes
Ambulacral grooves extended from oral to aboral
No Yes No No Yes No
Endoskeleton Highly flexible Not flexible Flexible Highly flexible Highly flexible Highly flexible
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ENRICHMENT (30 MINUTES)
1. Now you're getting the hang of this! Once again, use the data below to arrange organisms based on their shared derived characters. This time work again with your partner and test your skill in building a cladogram. a cladogram.
Of course, this was just an example of the tree-building process. Phylogenetic trees are generally based on many more characters and often involve more lineages. For example, biologists reconstructing relationships between 499 lineages of seed plants began with more than 1,400 molecular characters.
EVALUATION (10 MINUTES)
1. Go online. Choose a group of organisms you are interested to work with (e.g. invertebrates);
2. Download pictures of different species.
3. Print the pictures. In tabular form, list all the characters. Evaluate the characters (whether primitive or derived).
4. Remember that in building your cladogram, use only shared derived characters.
5. Construct your own cladogram.
6. Share this with your seat mate and discuss your cladogram.
7. The outputs may be submitted as soon as it is discussed.
8. Learners can compare their work and provide each other with feedback (peer assessment). Remind learners to make specific suggestions and recommendations and what could be improved. Ask for difficulties they encountered and strategies used to make the task easy.