Organizing Biodiversity

with Evolutionary

Trees

Classification & Taxonomy

• Aristotle - first classification system

• John Ray - developed classification system and a new concept of species

• Carolus Linnaeus - system of hierarchical classification and binomial nomenclature

What is Systematics?

• Systematics is the branch of Biology that seeks to classify biodiversity using everything known about an organism in order to understand its evolutionary relationship to other organisms.

Early Classification vs. Modern Analysis

Organisms are grouped according to similar physical characteristics

Organisms are grouped according to evolutionary relationships

Pre- Darwinian Post-Darwinian

Dichotomous Keys vs. Phylogentic Trees

• How is the purpose of each of these diagrams different?

• How is the structure different?

Tree of Life

• All organisms are related, but some are more closely related than others.

• To represent the idea that all living things, despite their diversity, share a common ancestor, Darwin used the metaphor of a “tree of life”.

Tree Thinking

Charles Darwin, On the Origins of Species (1859)

“The affinities of all the beings of the same class have sometimes been represented by a great tree…The green and budding twigs may represent existing species; and those produced during each former year may represent the long succession of extinct species… As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life.”

Darwin’s Tree

This “tree” illustration was the only one included in Darwin’s Origin of Species.

Image taken from http://www.mala.bc.ca/~johnstoi/darwin/origin_abridged.htm

The Tree of Life Project• The Tree of Life

Web Project (ToL) is a collaborative effort of biologists from around the world. The project seeks to create a “super tree” which organizes the diversity of organisms on Earth through their evolutionary history.

Creating Evolutionary Trees

• Comparative studies and fossils may be used to create initial phylogentic hypotheses

• Molecular techniques may be used to test or refine initial hypotheses

• Computer programs are readily available to analyze vast amounts of phylogenetic data

Based on the following character table, draw a tree

Cladograms and Phylogenetic Trees

How to read a cladogram

• Lines represent history through time.

• Nodes represent ancestors that are extinct, but common to organisms

Clade-istics

• Clade--group of organisms that share their most recent common ancestor

Evolutionary trees are hypotheses!

• Different sources of evidence may lead to the development of competing trees

• The principle of parsimony (choosing the least complex hypothesis) guides systematists in their reconstruction of trees

What is Cladistics?• A method of analyzing evolutionary relationships

between groups to construct a cladogram or “family tree”

• The branching tips of a cladogram must represent a clade, an ancestral species and ALL its descendents.

Clades

Using cladistics, the traditional reptile grouping does not include ALL descendents

No more Reptiles??

http://www.enchantedlearning.com/subjects/reptiles/printouts.shtml

Methods

• Primitive - characteristics that all members of a group share

• Derived - modified characteristics that only some members share

Cladistic analysis involves comparing similarities (homologies) between organisms in order to determine primitive vs. derived characteristics.

Data Sources

Fossils Morphology

Geography

Molecular Evidence

Geology

Physiology Behavior

Ecology

Reading

• Read “Tree Thinking Challenge”– Which tree is more

accurate?– What is the basis for

trees?– What do nodes

represent?

Practice

• Try the “odds” today and the “evens” for homework.

• You will get an answer key on Wednesday!

• They get harder as you go on!

Today’s Activity

Birdwing Butterflies: We will use a combination of geographic, physical, and genetic evidence to determine the evolutionary history of birdwing butterflies.

More Activities Later in the Year

• HIV Evolution: We will use a computer program to compare HIV virus and determine the evolutionary origin.

Tools• Available Software for Phylogenetic

Analysis

• Molecular Data Bases on the WebGenbank http://www.ncbi.nim.nih.gov/Entrez

Protein Information Resource (PIR)http://pir.georgetown.edu

PAUP http:/onyx.si.edu/PAUPHennig86 http://www.vims.edu/`mes/hennig/software.htmlMacClade http://phylogeny.arizona.edu/macclade/macclade.htm

Resources• “A Science Primer: Classification and Phylogenetics” http://www.ncbi.nih.gov/About/primer/phylo.html• Baum, D.A.,et al. “ The Tree Thinking Challenge” Science 310:979-980. • Campbell, N.A. and Reece, J. B. Biology 6th edition. San Francisco: Benjamin Cummings, 2002.• Clos, L.M. “What is Cladistics?” [6/8/06] http://www.fossilnews.com/1996/cladistics.htm• Filson, R. “Island Biogeography and Evolution: Solving a Phylogenetic Puzzle with Molecular Genetics”

http://www.accessexcellence.org/AE/AEPC/WWC/1995/simulation_island.html • Kramer, B. and Flammer, L. “Making Cladograms: Phylogeny, Evolution, and Comparative Anatomy”

Evolution & Nature of Science Institutes (ENSI/SENSI), University of Indiana. [6/8/06] http://www.indiana.edu/~ensiweb/lessons/mclad.html

• “Names & classifying living things” http://www.backyardnature.net/names.htm• Singer, F., et al “The Comparative Method, Hypothesis Testing & Phylogentic Analysis” The American

Biology Teacher 63(7): 518-523.• Skelton, P. W., A. Smith, et al. (2002). Cladistics a practical primer on CD-ROM. Cambridge, The Open

University; Cambridge University Press.• “The Tree of Life Web Project’ http://www.tolweb.org/tree/ • “Tree-thinking Group” http://www.tree-thinking.org• “Understanding Evolution: An Evolution Web Site for Teachers” http://evolution.berkeley.edu/• “What did Trex taste like? An introduction to how life is related”

http://www.ucmp.berkeley.edu/education/explorations/tours/Trex/guide/index.html