ECOL 182L LAB2

Crawling Around the Tree of Life: 

Crawling Around the Tree of Life ECOL 182L Lab 2 Instructor Joanna Gress Sections 23 & 43

Phylogeny: 

Phylogeny Phylogeny= history of exactly how a group of organisms are descended from their common ancestor Phylogenetic tree= representation of that history

Theory of Common Descent: 

Theory of Common Descent Any two organisms can be traced back to a common ancestor We all belong to a big family tree, some more closely related than others

Hypothetical TreeRelating Organisms: 

Hypothetical Tree Relating Organisms

Phylogenetic RelationshipsAmong Organisms: 

Phylogenetic Relationships Among Organisms Entrez: www.ncbi.nlm.nih.gov/Taxonomy Ribosomal database project: http://rdp.cme.msu.edu/ Tree of Life: http://www.tolweb.org/tree/

Phylogeny Applications: 

Phylogeny Applications Tree of life: Analyzing changes that have occurred in evolution of different organisms • Phylogenetic relationships among genes can help predict which ones might have similar functions (e.g., ortholog detection) Follow changes occuring in rapidly changing species (e.g., HIV virus)

What data is used tobuild trees?: 

What data is used to build trees? Traditionally: morphological features (e.g., number of legs, beak shape, etc.) Today: Mostly molecular data (e.g., DNA and protein sequences)

Why do we construct and study Phylogenies?: 

Why do we construct and study Phylogenies? This is the essence of comparative biology Without it misleading statements could be made

Slide9: 

Species Come and Go Best estimates from the fossil record indicate that greater than 99% of species that have exited are now extinct. A typical “lifetime” for a species is about 1 million years. http://www.biology.usu.edu/courses/biol1010-podgorski/Summer%2006/PowerPoints/Macroevolution.ppt

Slide10: 

Mass Extinctions Are a Fact of Life http://www.biology.usu.edu/courses/biol1010-podgorski/Summer%2006/PowerPoints/Macroevolution.ppt

Slide11: 

The Cretaceous/Tertiary Mass Extinction

Slide12: 

Are We Now Causing a Mass Extinction?

Slide13: 

Classifying Life’s Rich Diversity Why bother? An intrinsic reason is that modern classification systems tell who’s related to whom and how we all came to be. http://www.biology.usu.edu/courses/biol1010-podgorski/Summer%2006/PowerPoints/Macroevolution.ppt

Slide14: 

Classifying Life’s Rich Diversity Why bother? A practical reason is that if we want to preserve an environment compatible with human life, we’d better know what’s out there.

Slide15: 

The Linnaean Hierarchical Classification System http://www.biology.usu.edu/courses/biol1010-podgorski/Summer%2006/PowerPoints/Macroevolution.ppt

Slide16: 

How Do We Classify Organisms? Ideally, classification is based on establishing the evolutionary relationships between organisms. Cladistics is the method of classification based on establishing phylogenies (i.e. getting at evolutionary relationships. The evolutionary relationship between organisms is their phylogeny. Cladistics proceeds by comparing shared ancestral and shared derived characters between sets of organisms.

Slide17: 

Cladistics The greater the number of derived characters shared by a pair of organisms, the closer their degree of relationship. The closer the degree of relationship, the closer the most recent common ancestor. http://www.biology.usu.edu/courses/biol1010-podgorski/Summer%2006/PowerPoints/Macroevolution.ppt

Slide18: 

It’s Critical (and often difficult) To Distinguish Homology from Analogy Homologous structures, like the bat wing and gorilla arm, are similar because they are derived by modification of a shared ancestral structure. Homology is the key to establishing phylogenies. http://www.biology.usu.edu/courses/biol1010-podgorski/Summer%2006/PowerPoints/Macroevolution.ppt

Slide19: 

Distinguishing Homology from Analogy Analogy is similarity due to convergent evolution. Analogy mistaken for homology confuses phylogenies. http://www.biology.usu.edu/courses/biol1010-podgorski/Summer%2006/PowerPoints/Macroevolution.ppt

Slide20: 

Another Set of Analogies Created by Convergent Evolution

Slide21: 

Results of Cladistic Analyses Sometimes Run Counter to Classical Classification Schemes Which pair is more closely related? A lizard/crocodile or bird/crocodile? Cladistic analysis indicates that the bird/crocodile pair is more closely related.

Slide22: 

Monophyletic Paraphyletic Polyphyletic Similarity does not always reflect shared ancestry -share a recent common ancestor -group contains the ancestor and all descendants -share a recent common ancestor, but NOT all descendants -doesn’t share a recent common ancestor or contain ancestor and all descendants

Slide23: 

Monophyletic grouping

Slide24: 

Polyphyletic grouping

Slide25: 

Paraphyletic grouping

OUTGROUPS: 

OUTGROUPS

Slide27: 

Cladistic analysis of traits Plesiomorphic – ancestral state of trait Apomorphic – derived state of trait (i.e., a new trait) Symplesiomorphy – shared ancestral trait Synapomorphy – shared derived trait. Most useful

Slide28: 

Cladistic analysis Tree B more Parsimonious than Tree A

Today: 

Today PhylogenyFun quiz! Evolvotron-on computer-get to create a phylogeny and then solve one generated by your peers using bugs-I’ll demonstrate! Constructing a Cladogram in class -can use pine trees, shells, or vertebrate jaws

Homework: 

Homework Read next Week’s lab-there is a lot to do next week-so be prepared or we will be here late I will be giving a quiz on next’s week lab-so read it!-Next week’s lab is on nematode the organism I study so make me proud!