1. The Evolutionary History of Biodiversity
Phylogeny
and the Tree of Life

2. Phylogenies show evolutionary relationships
Phylogeny
 the evolutionary history of a species or group of related species
the cornerstone of a branch of biology called systematic taxonomy
classifies organisms and their evolutionary relationships using
fossils
morphology
Genes
molecular evidence

3. Phylogenies show evolutionary relationships
Taxonomy the ordered division of organisms into categories based on similarities and differences.
Binomial nomenclature two part naming system consisting of the genus /species. Developed by Carolus Linnaeus

4. Carl von Linné (Carolus Linnaeus) 1707 – 1778
Swedish biologist considered the father of modern taxonomy.
The binomial nomenclature Linnaeus used was developed in the late 16th and early 17th century by the Swiss botanists (brothers) Gaspard and Johann Bauhin, for some of the 6000 plants they described in their works, but it was Linnaeus who used it consistently and systematically.

5. Hierarchical Classification

6. Hierarchical Classification
Organisms are classified into a hierarchies that group closely related organisms and progressively include more and more organisms. Each categorization at any level is called a taxon.
                      

7. Phylogenetic trees
The aim is to figure out the evolutionary relationships among species.
Branching diagrams called phylogenetic trees hypothesize evolutionary relationships thought to exist among groups of organisms.
It does not show the ACTUAL evolutionary history of organisms.
Why a hypothesis?

8. Phylogenetic trees
In a phylogenetic tree the tips of the branches specify particular species and the branching points represent common ancestors.

9. Phylogenetic trees
Phylogenetic trees are constructed by studying features of organisms formally called characters.
Characters may be morphological or molecular.

10. Morphology
Comparing physical structural characteristics

11. Homologous Structures
Similarities due to shared ancestry

12. Analogous Structures Convergent Evolution
These animals have evolved similar adaptations for obtaining food because they occupy similar niches.

13. Analogous Structures Convergent Evolution
Similar solutions to similar problems

14. Molecular Systematics

15. Using DNA
The more alike the DNA sequences of two organisms, the more closely related they are evolutionarily.
Early phylogenetic tree of amniotes based on cytochrome c gene by Fitch and Margoliash (1967).
Note numbers on branches.
These represent estimated numbers of mutational changes in gene.

17. Cladograms
Cladograms are diagrams that display patterns of shared characteristics.
If shared characteristics are due to common ancestry (are homologous) the cladogram forms the basis of a phylogenetic tree.
Within a tree a clade is defined as a group that includes an ancestral species and all of its descendants.
Cladistics is the science of how species may be grouped into clades.

18. Ancestral vs. Derived Characters
Character present in the common ancestor of both groups
Derived
Character that evolved in one group but not the other
What derived character is shared by all the animals on the cladogram on the next slide?

20. Cladograms and Phylogenetic Trees
A cladogram and a phylogenetic tree are similar, but not identical.
Traditional evolutionary taxonomy is subjective and therefore more prone to bias. A phylogenetic tree’s branches put more emphasis on certain characters rather than others.
Cladistics treats each character equally. It is more objective by ignoring how some characters have a higher impact on evolution. It is thought that evolutionary success is dependent on high-impact events.

21. Rate of Evolution
An organism’s evolutionary history is documented in its genome
The rate of evolution of DNA sequences varies from one part of the genome to another
Comparing the different sequences helps us to investigate relationships between groups of organisms that diverged long ago
DNA that codes for ribosomal RNA and mitochondrial DNA are both used
rRNA changes relatively slowly –used with taxa that diverged hundreds of millions of years ago
Mitochondrial DNA evolves rapidly – used to explore more recent events

22. The Molecular Clock Hypothesis
Used to measure the absolute time of evolutionary change.
Amount of genetic difference between sequences is a function of time since separation.
Assumes that the rate of molecular change is constant (enough) to predict times of divergence

23. Taxonomy in Flux
When the authors of your text book were in high school they were taught two kingdoms: plants and animals.
When your teacher was in high school she was taught five kingdoms: Monera, Protista, Plantae, Fungi and Animalia

24. Taxonomy in Flux Now biologists have adopted a three-domain system
Discovery that there are two distinct lineages of prokaryotes
Characteristic
Bacteria
Archaea
Eukarya
Nuclear envelope No
Yes
Membrane-enclosed organelles
Introns
Histone proteins associated with DNA
Circular chromosome