Systematics and Phylogenetic Revolution Chapter 23 Systematics and Phylogenetic Revolution I. Systematics II. Cladistics Cladogram III. Classification Phylogenetic Relationships

All living organism share common characteristics I. Systematics All living organism share common characteristics Composed of cells  Metabolize Respond Reproduce Evolve and adapt to environment

However there is tremendous diversity of life forms Bacteria ----- Whales ----- Sequoia trees ----- Etc.

Biologists group organisms based on shared characteristics.   Systematics: study of evolutionary relationships. Phylogeny: hypothesis about patterns of relationship among species similarities and differences among species

Darwin postulated all species descended from single common ancestor depicting the history of life as branching tree - cladogram

Darwin called process “descent with modification” Divergence Groups after have new derived characters   Evolution changes that occur over time that makes life forms more suited for the environment Common Ancestor Gives rise to new groups

Key to interpreting Phylogeny is tricky. Things to investigate: How recently do species share common ancestor? Does the similarity accurately predict evolutionary relationship? Did oscillating selection occur for a trait? Meaning did a trait evolve in one direction and back the other way? Did convergent evolution take place? Did evolution reversal occur? Where the species re-evolves characteristics of the ancestral species.

II. Cladistics Derived character: similarity inherited from most recent common ancestor of an entire group Ancestral character: similarity or trait that arose prior to common ancestor of group. Cladistics: only shared derived characters are informative about evolutionary relationship. The variation must be identified as ancestral or derived. Character can be any aspect of phenotype: Morphology Behavior Physiology DNA sequence E.g. Hair coat is a shared derived feature of mammals Lungs in mammals are an ancestral feature – present in amphibians and reptiles.

Lamprey Shark Salamander

Lizard Tiger Gorilla

X X X X X X X X X X X X X X X X X X X X X Construction of a Cladogram Clade: species share common ancestor, indicated by shared derived traits.   Traits: Organism Jaws Lungs Amniotic Membrane Hair No tail Bipedal Lamprey   Shark Salamander Lizard Tiger Gorilla Human X X X X X X X X X X X X X X X X X X X X X

Now the data from this chart is used to create a diagram called a cladogram. Gorilla Human Tiger Lizard Bipedal Salamander No Tail Shark Hair Lamprey Amniotic Membrane Cladograms can be constructed using all kinds of data: Physical Structures DNA Sequence Behavior Physiology Lungs Jaws

Classification: how species are placed into taxonomic hierarchy: III. Classification Classification: how species are placed into taxonomic hierarchy: Domain – Kingdom – Phylum – Class – Order – Family – Genus – Species

Grouping of organisms based on phylogenetic relationships Monophyletic group Most recent common ancestor of group and all descendants (clade)

Paraphayletic group Most recent common ancestor or group but NOT all descendants

Polyphyletic group Does not include most recent common ancestor of all member of the group NOTE: Taxonomic hierarchies are based on shared traits therefore they should show evolutionary relationships