1. Big Idea 1
Ch Phylogeny

2. Overview: Investigating the Tree of Life
Phylogeny is the evolutionary history of a species or group of related species
To get information about ancient organisms and their relationship to current species, biologists draw on the fossil record

3. Systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time.
used to understand the evolutionary history of life on Earth
Systematists use morphological, biochemical, and molecular comparisons to infer evolutionary relationships (they also examine fossils)

4. The Fossil Record Sedimentary rocks are the richest source of fossils
Soft
Haven’t been heated or melted like igneous and metamorphic
Sedimentary rocks are deposited into layers called strata

5. LE 25-3
Rivers carry sediment to the ocean. Sedimentary rock layers containing fossils form on the ocean floor.
Over time, new strata are deposited, containing fossils from each time period.
As sea levels change and the seafloor is pushed upward, sedimentary rocks are exposed. Erosion reveals strata and fossils.
Younger stratum
with more recent
fossils
Older stratum with
older fossils

6. The fossil record is based on the sequence in which fossils have accumulated in such strata
Fossils reveal ancestral characteristics that may have been lost over time

7. LE 25-4 Leaf fossil, about 40 million years ago
Petrified trees in Arizona, about 190
million years old
Insects preserved whole in amber
Dinosaur bones being
excavated from sandstone
Casts of ammonites, about
375 million years old
Boy standing in a 150-million-year-old
dinosaur track in Colorado
Tusks of a 23,000-year-old mammoth, frozen whole
in Siberian ice

8. Morphological and Molecular Homologies
In addition to fossils, phylogenetic history can be inferred from morphological and molecular similarities in living organisms
Organisms with very similar morphologies or similar DNA sequences are likely to be more closely related than organisms with vastly different structures or sequences

9. Sorting Homology from Analogy
In constructing a phylogeny, systematists need to distinguish whether a similarity is the result of homology or analogy
Homology is similarity due to shared ancestry
Analogy is similarity due to convergent evolution (the evolution of similar traits in unrelated lineages)
Ex – opossums have opposable thumbs like primates, even though they aren’t related

10. Convergent evolution occurs when similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different evolutionary lineages

11. Evaluating Molecular Homologies
Systematists use computer programs and mathematical tools when analyzing comparable DNA segments from different organisms

12. LE 25-6 1 2
Deletion 1 2
Insertion 1 2 1 2

13. Phylogenetic systematics connects classification with evolutionary history
Taxonomy is the ordered division of organisms into categories based on characteristics used to assess similarities and differences (putting things into groups based on similarities)
In 1748, Carolus Linnaeus published a system of taxonomy based on resemblances.
Two key features of his system remain useful today: two-part names for species and hierarchical classification

14. Binomial Nomenclature Cont.
Rules:
All living things are given a two-part name.
The first part of the name identifies the genus
The second part of the name identifies the species
*Both parts together name the species (not the specific epithet alone)
The genus is ALWAYS capitalized and the species is ALWAYS lowercase
Both words are ALWAYS either italicized or underlined
Latin or Greek

15. Hierarchical Classification
Linnaeus introduced a system for grouping species in increasingly broad categories
*the more levels shared, the more organisms will have in common and the more closely related they will be

16. LE 25-8 Panthera pardus Species Panthera Genus Felidae Family
Carnivora
Order
Mammalia
Class
Chordata
Phylum
Animalia
Kingdom
Eukarya
Domain

17. Linking Classification and Phylogeny
Systematists depict evolutionary relationships in branching phylogenetic trees
Each branch point represents the divergence of two species
“Deeper” branch points represent progressively greater amounts of divergence

18. LE 25-9 Panthera pardus (leopard) Mephitis mephitis (striped skunk)
Lutra lutra
(European
otter)
Canis
familiaris
(domestic dog)
Canis
lupus
(wolf)
Species
Genus
Panthera
Mephitis
Lutra
Canis
Family
Felidae
Mustelidae
Canidae
Order
Carnivora

19. Phylogenetic systematics informs the construction of phylogenetic trees based on shared characteristics
A cladogram depicts patterns of shared characteristics among taxa
Takes characteristics of certain organisms and putting together a hyposthesis of how you think they may be related
A clade is a group of species that includes an ancestral species and all its descendants
Clades can be nested in larger clades, but not all groupings or organisms qualify as clades
Cladistics studies resemblances among clades
Primative to derived characteristics

20. Types of clades:
monophyletic, signifying that it consists of the ancestor species and all its descendants
A paraphyletic grouping consists of an ancestral species and some, but not all, of the descendants
A polyphyletic grouping consists of various species that lack a common ancestor

21. Shared Primitive and Shared Derived Characteristics
In cladistic analysis, clades are defined by their evolutionary novelties
A shared primitive character is a character that is shared beyond the taxon we are trying to define
A shared derived character is an evolutionary novelty unique to a particular clade
derived is when a trait shows up that was NOT present in a common ancestor. ancestral/primitive characters WERE present in a common ancestor.
E.G. Among primates, the relatively shortened and straight spine of a gorilla is a derived trait (it was not present in the common ancestor of all primates). However, the shortened spine of a gorilla is ancestral to apes (it is present in all apes and in the common ancestor of apes).

22. Outgroups
An outgroup is a species or group of species that is closely related to the ingroup, the various species being studied
“one of these things is not like the other”
Systematists compare each ingroup species with the outgroup to differentiate between shared derived and shared primitive characteristics
Outgroup comparison assumes that homologies shared by the outgroup and ingroup must be primitive characters that predate the divergence of both groups from a common ancestor
It enables us to focus on characters derived at various branch points in the evolution of a clade

23. LE 25-11 TAXA (outgroup) Salamander Lancelet Lamprey Leopard Turtle
Tuna
Turtle
Hair
Amniotic (shelled) egg
CHARACTERS
Four walking legs
Hinged jaws
Vertebral column
(backbone)
Character table
Leopard
Turtle
Hair
Salamander
Amniotic egg
Tuna
Four walking legs
Lamprey
Hinged jaws
Lancelet (outgroup)
Vertebral column
Cladogram

24. Phylograms
A phylogram is a phylogenetic tree that indicates the amount of evolution in addition to the branching order.
the length of a branch in a cladogram reflects the number of genetic changes that have taken place in a particular DNA or RNA sequence in that lineage

25. Phylogenetic Trees as Hypotheses
The best hypotheses for phylogenetic trees fit the most data: morphological, molecular, and fossil
Sometimes the best hypothesis is not the most parsimonious (simplest, fewest changes)

26. LE 25-16 Lizard Bird Mammal Four-chambered heart Mammal-bird clade
Lizard-bird clade

27. The Universal Tree of Life
The tree of life is divided into three great clades called domains: Bacteria, Archaea, and Eukarya
The early history of these domains is not yet clear