Evolutionary history of a group of organisms Phylogeny Evolutionary history of a group of organisms

Phylogenetic tree: ancestor-descendant relationships among populations/species

=Outgroup Root Branch Node Tip

Each phylogenetic tree is a hypothesis Approaches Phenetic – overall similarities between populations (genetic distance – summarizes average percentage of bases in a DNA sequence that differ) More divergent populations are on more distant branches Cladistic: based on shared derived characters (synapomorphies)

Synapomorphy: a trait that exists in a certain group of organisms but exists in no others (due to common ancestry) Monophyletic group: an ancestral species and ALL of its descendants (based on synapomorphy) AKA: lineage, clade ONE Snip test: if you cut a branch and all the branches and tips fall off, then it is monophyletic

5 of the 6 trees listed describe the same relationship 5 of the 6 trees listed describe the same relationship. Which tree is different?

Homology (same source): derived from a common ancestor Homoplasy (same form): similar but not due to common ancestry.

Homologous (1) or Homoplasy (2) a. the dorsal fins of a dolphin (mammal) and a salmon (fish) b. the flippers of a dolphin and arm of a human c. a rhesus monkey’s tail and a human’s coccyx d. the bracts (red leaves) of a poinsettia and green leaves of a rose e. the bracts (red leaves) of a poinsettia and red petals of a rose f. the scales on a reptile and the feathers on a bird

Why don’t we place homologous characteristics on a tree twice? Basics of Phylogeny: Cladograms Why don’t we place homologous characteristics on a tree twice? This implies the characteristic evolved more than once Recall this involves a random mutation (rare event) that happens to occur in an organism that is in an environment where this mutation creates a favorable adaptation. This kind of thing takes millions of years (ex. limbs evolving on fish). Very low probability it would happen more than once: But if this does happen, it is called convergent evolution Place analogous characteristics on trees, but don’t CREATE trees using them. (Fig 27.2 )

Using the basics of phylogeny to construct the Tree of Life Organism Classification: Before the Tree of Life Linneaus Organisms that didn’t move, made their own food: Plants. Organisms that moved, ate others for food: Animals. Problems with this system?

Organism Classification: Before the Tree of Life II. Then…fundamental division at the cellular level between prokaryotes and eukaryotes discovered Eukaryote: “true-kernel” Prokaryote: “before-kernel” ~_no nucleus__ ~__smaller_____________ ~__Nucleus (membrane bound)___ ~__larger______________

Organism Classification: Before the Tree of Life III. 1960s = 5 kingdoms prokaryotes Set of shared characteristics defined kingdom members. eukaryotes Most Characteristics: _______morphological________

Major Changes in Organism Classification: The Tree of Life Carl Woese et al: __RNA_____to study relationships Compared gene sequence for ____16S and 18 S RNA___________ in all cells make up part of ribosomes location of protein synthesis Eukaryote Prokaryote ribosomes

Why compare sequence for rRNA gene? Ribosomes found in ALL organisms and serve the same function Ribsosomal RNA (rRNA) therefore in ALL organisms The DNA that encodes for rRNA in ALL organisms This gene happens to be HIGHLY conserved (similar) among species but not identical The amount of change in the DNA sequence of this gene over time is consistent and understood

So what happens when organisms are classified this way? Major division among organisms NOT between prokaryotes and eukaryotes but between Bacteria, Archaea, Eukarya I. Bacteria II. Archaea III. Eukarya Prokaryotes ~no memb-bound organelles (no nucleus,mitochondria, etc.) ~circular chromosomes ~single-celled Eukaryotes ~memb-bound organelles ~linear chromosomes

So what happens when organisms are classified this way? BUT, Molecular Data conflicts with morphological data… I. Bacteria II. Archaea III. Eukarya Prokaryotes ~no nucleus, mitochondria, etc. ~circular chromosomes ~single-celled Molecularly Similar ~rRNA sequence ~RNA polymerase ~How DNA is packaged in the cell

FYI: You should be able to Draw both types of trees Place characteristics on trees in correct location Be able to recall specific characteristics that create one tree versus the other (ex. circular vs linear chromosomes and complex versus simple RNA polymerase) so if a tree was drawn for you, you could come up with the correct characteristics to place on a specific tree Understand how work of Woese et al changed how we classify organisms

Which of the following is more closely related to green algae? Red algae because they share the MRCA Land plants because they share the MRCA Red algae because it is also an algae Land plants because they also have chlorophyll (green)

Which of the following is more closely related to land plants? Chordates b/c they share the MRCA at the root of the tree Mollusks b/c they share the MRCA at the root of the tree Land plants are equally related to Chordates and Mollusks b/c they share the MRCA at the root of the tree Neither b/c they don’t share a MRCA

Jellyfish are more closely related to chordates than to fungi? True because the MRCA of jellyfish and chordates is above the MRCA of jellyfish and fungi True because the MRCA of jellyfish and chordates is below the MRCA of jellyfish and fungi False because the MRCA of jellyfish and chordates is above the MRCA of jellyfish and fungi False because jellyfish are equally as related to chordates and fungi based on their equal MRCA

Identify the tree that shows a different set of relationships between the 9 taxa than the other two trees. The difference is in tree 1 The difference is in tree 2 The difference is in tree 3

If species a–i are a group of flowering plants, assume taxa a–d have red flowers, taxa f–i have blue flowers, and taxa e has white flowers. Draw the locations of flower color changes on trees 1–3. How are the three trees similar? How are they different?

How do we know about the “history” in the phylogenies? Fossil record is the only DIRECT evidence Fossil record is biased though Habitat bias Taxonomic bias Tissue bias Temporal bias Abundance bias

How do we get the “branches” on our phylogenetic trees? Evolution. Sometimes there is fast and huge divergence from a single ancestor =Adaptive radiation Why? Ecological opportunity Morphological innovation

Why don’t we see ALL the species that ever evolved? Extinction Background rates Normal environmental change Emerging disease competition Mass extinction (above background average) Sudden, extraordinary environmental change