Chapter 4 The tree of life: how biologists use phylogeny to reconstruct the deep past
2 ReadingsRead Chapter 4 of Zimmer and Emlen text
3 Phylogeny All living organisms are descended from a common ancestor.
If we can construct the evolutionary relationships between groups we can gain insight into history of evolutionary change.
4 Figure 4.2 Phylogenies at different scales
(A) The tree of life represents the historical relationships among all living things. Dashed lines represent hypothetical relationships. The entire animal kingdom is contained in the tiny yellow branch at far right (in the metazoans). Adapted from Delsuc et al. (2005). (B) A phylogeny of vertebrates. Adapted from the Center for North American Herpetology (2010). (C) A phylogeny of Micobacterium tuberculosis isolates from human patients around the globe. Adapted from Comas et al. (2010).Figure 4.2 Phylogenies at different scalesEvolution, 1st EditionCopyright © W.W. Norton & Company
5 A phylogeny is similar to a family tree
6 PhylogenyPhylogeny is the study of the branching relationships between populations over evolutionary time.A phylogenetic tree is built up by analyzing the distribution of traits across populations.
7 Traits (characters)A trait (or character) is any observable characteristic of an organism (e.g. anatomical features, behaviors, gene sequences)
8 TraitsTraits are used to infer patterns of ancestry and descent among populations.These patterns are then depicted in phylogenetic trees.
9 Mapping traits onto trees allows us to study the
We use traits both to reconstruct phylogenetic trees and to generate hypotheses about the timing of events in evolutionary history. (A) One set of traits—here genetic sequence data—is used to infer a phylogenetic tree for the species of interest. (B) A second set of traits, here flower color and morphology, are mapped onto the tree, helping us to reconstruct evolutionary events. The origin of the dark flower coloration is indicated by the filled horizontal bar. The origin of the novel flower shape is indicated by the open horizontal bar.Mapping traits onto trees allows us to study thesequence and timing (history) of evolutionary events.Evolution, 1st EditionCopyright © W.W. Norton & CompanyFigure 4.4 Traits and trees
10 Phylogenetic trees are hypotheses
Remember phylogenetic trees are hypotheses about the evolutionary relationships between groups.New evidence can be used to test a tree.
11 How to read a phylogenetic tree
Each branch tip represents a taxon (a group of related organisms).Interior nodes (where branches meet) represent common ancestors of the taxa at the ends of the branches.
12 Figure 4.6 Interior nodes represent common ancestors
Finding the common ancestor for a group involves tracing backward in time. Follow the dashed lines to see the common ancestors of different groups in this phylogeny.Evolution, 1st EditionCopyright © W.W. Norton & CompanyFigure 4.6 Interior nodes represent common ancestors
13 Ladder format Tree format
The two phylogenies of the vertebrates shown each illustrate exactly the same information. The phylogeny on the left (A) is sometimes referred to as a tree representation, whereas that on the right (B) is termed a ladder representation. In each, time flows from left to right, so that the branch tips at the right represent current groups, whereas the interior nodes (nodes on the inner section of the tree) represent ancestral populations. For example, the red dot indicates the common ancestor of birds and crocodilians, whereas the blue dot indicates the common ancestor to all tetrapods. The orange line segment is the root of the tree. Adapted from the Center for North American Herpetology (2010).Tree formatLadder formatEvolution, 1st EditionCopyright © W.W. Norton & CompanyFigure 4.5 Two equivalent ways of drawing a phylogeny
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