Zoology 101 – McIntyre – Tree Thinking - 27 Apr 20123.5 billion year ago – Common ancestor of all lifeTree Thinking Wrestles With:Definitions: phylogeny & consistent partsProcesses: inferring correct relationshipsApplication: Phylocode, homology, forensics, diversification Assumptions: molecular clockTaxonomic vs. Phylogenic ViewsPhylogenetic Categories ExamplesSpecies Panthera pardusGenus Panthera Family FelidaeOrder CarnivoreClass MammaliaPhylum ChordataKingdom Animalia Domain EurkaryaWhat does a phylogeny represent? Start with a network of individuals based on genetic inheritance Phylogeny = (or phylogenetic tree) diagram representing a hypothesis of evolutionary history as a series of branching events linking ancestors to descendantsTree terminology:Clade – group that includes “all and only” the descendants ofa particular ancestor Modern phylogenetic trees are based on different criteriaShared derived characteristics (morphological data)Shared likelihood (genetic data)Data are usually genetic or morphology. Trees reveal evolutionary history (i.e. evolution of legs)Applications of tree thinking:PhyloCode – a system that only names groups that include a common ancestor and all of its descendants. While PhyloCode would change the way taxa are defined and recognized, the taxonomic names of most species would remain same.Every node has a name you can apply that name to entire clade (descendants). NodeRootTipSister taxaHomology – phenotypic or genotypic similarity due to shared ancestry (Example: flight, feathers, four limbs)Archeopteryx is an ancestor of birds. Tyrannosaurus has feathers as well. NOT Homology: Marsupial “mole” Australia (it is very distantlyrelated to the True Mole in N. America; they have different typesof claws for digging)ForensicsWhale DNA from markets used to prove illegal whaling. Meat labeled Southern Hemisphere Minke whales inmarkets. But the meat was actually from North AtlanticMinke and Fin Whales (endangered species). Diversification rates – the pace at which neospeciesarise within a lineage65 My BP- Crustaceous Boundary (Huge extinction!)Rodents (Rodentia) have highest diversification ratedepends on how wide diversification is. Molecular clock – assumption that nucleotidemutations occur at a constant rate # of mutations increase as divergence time increasesGenotype-based Tree vs. Fossil-based Tree Big-Picture Conclusions:1) Phylogenetic trees represent our best estimate of evolutionary history2) Understanding these relationships informs all aspects of biology3) Molecular clocks merge history of life and microevolutionary presses PRE-LECTURE QUIZ1. What is horizontal gene transfer? [Doolittle interview] The transfer of genetic material between organism usually prokaryotes2. Which of the following is the correct evolutionary relationship?Rabbits and mushrooms are more closely related to each other than either is to tulips3. "Taxon" refers to what level of the Linnaean nomenclatural hierarchy?a. Speciesb. Genusc. Phylumd. The full binomiale. Any of these, depending on context4. What is the Phylocode system? An attempt to replace the Linnaean nomenclatural hierarchy with a system of names based purely on evolutionary relationships 5. Which of the following is an incorrect way to interpret a phylogeny? It depicts patterns of phenotypic similarity 6. Which of the following does not represent a homology? The digging claw of Australian and North American “moles” 7. Phylogenies can constructed based on: Shared derived traits 8. Why are molecular clocks so important? a. They allow estimation of how long ago two lineages divergedb. They allow estimation of how long ago a gene was duplicated within an organismc. They allow us to identify taxa whose DNA is evolving more slowly than in othertaxad. They allow us to estimate the dates of events that are not captured in the fossilrecord e. All of these answers are correct 9. The molecular clock is rooted in neutral theory, which dictates that: Many mutations have no fitness consequences, and therefore are uninfluenced by natural selection10. Under a three-domain perspective on the tree of life, which of following is true? Archaea and Eurkarya are sister domains relative to the common ancestor of all
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