Chapter 26 Phylogeny and the Tree of Life

Objective SWBAT explain and demonstrate that organisms share many conserved core processes and features that evolved and are widely distributed among organisms today.

Agenda Chapter 25 Quiz Chapter 26 notes: sections 26.1, 26.2, and 26.3 Guided practice with phylogeny Homework: a) Phylogeny Worksheet. Due Monday, September 22 b) Read all of Chapter 26 this weekend for Monday.

Phylogeny and the Tree of Life Chapter 26 http://www.youtube.com/watch?v=H6IrUUDboZo

The Origin of Species As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever-branching and beautiful ramifications. ~ Charles Darwin

Evolution as a branching, tree-like process Darwin’s Tree of Life Evolution as a branching, tree-like process

A phylogenetic tree of the bacterial domain. A phylogenetic tree represents a hypothesis of the order in which evolutionary events are assumed to have occurred.

Phylogenetics Phylogenetics is the study of evolutionary relatedness among various groups of organisms, which is discovered through molecular sequencing and morphological data. Tucuxi

What do phylogenetic trees represent? Madison DR (2012) Phylogeny of Bembidion and related ground beetles. Molecular Phylogenetic and Evolution 64:553-576

Going back in time…

Present Past

on connecting branches 2 leaves… on connecting branches How can we hypothesize that this speciation event occurred ~ 1.5 million years ago?

The key is in the DNA Species vary in their gene pools (the alleles for all traits) The gene pool of a population changes over time natural selection genetic drift genetic recombination mutation

Mutation Change in nucleotide sequence of an organism’s DNA

Molecular clock The mutation rates of particular genes are relatively constant, thus the rate of mutations can be used as a molecular clock If mutation rates are constant, then we can use such genes to extrapolate when speciation events took place Example: The gene that codes for hemoglobin experiences 0.56 changes per base pair per billion years

The cytochrome c gene reflects a pattern of differences in DNA sequences due to mutations. The changes accumulate at a constant rate, and can be used as a molecular clock to help date evolutionary divergences.

Order Family Genus Species Panthera pardus (leopard) Felidae Panthera Figure 26.4 Order Family Genus Species Panthera pardus (leopard) Felidae Panthera Taxidea taxus (American badger) Taxidea Carnivora Mustelidae Lutra lutra (European otter) Lutra Figure 26.4 The connection between classification and phylogeny. Canis latrans (coyote) Canidae Canis Canis lupus (gray wolf)

(a) Monophyletic group (clade) (b) Paraphyletic group Figure 26.10 (a) Monophyletic group (clade) (b) Paraphyletic group (c) Polyphyletic group A A A B Group  B B Group  C C C D D D E E Group  E Figure 26.10 Monophyletic, paraphyletic, and polyphyletic groups. F F F G G G

on connecting branches 2 leaves… on connecting branches How can we hypothesize that this speciation event occurred ~ 1.5 million years ago?

Answer: Use the amount of variability between DNA sequences to estimate the time of speciation events

The evolution of HIV

1884 – 1924 1966 2010 HIV jumped from chimps to humans Africa  Haiti  U.S. (Robert R., first HIV/AIDS death in U.S., 1969) 2010 Evidence that a newer strain of HIV jumped to humans from gorillas http://evolution.berkeley.edu/evolibrary/news/081101_hivorigins

We can also use morphological differences to deconstruct evolutionary relationships Derived Ancestral

Hair is a shared derived trait (synapomorphy) of mammals We can also use morphological differences to deconstruct evolutionary relationships Derived Ancestral Hair is a shared derived trait (synapomorphy) of mammals

Parsimony: evolution takes the easier path

Parsimony: evolution takes the easier path

Guided Practice on Parsimony: which one is the most parsimonious tree?

Parsimony: evolution takes the easier path

Guided Practice: What is the difference between these trees?

Guided Practice: What is the difference between these trees? They are all the same. B and C are sister species. In addition, A, B, and C share a common ancestor in all trees.

Guided Practice: What is the difference between these trees?

What is the difference between these trees? They are all the same. Humans, chimps, and common ancestor 1 are monophyletic. Gorillas are an outgroup to humans and chimps. Orangutans are also an outgroup to common ancestor 2 and its descendants.

Using phylogenetics to solve a crime

Summary Phylogeny is the evolutionary history of a species or group of related species The discipline of systematics classifies organisms and determines their evolutionary relationships Systematists use fossil, molecular, and genetic data to infer evolutionary relationships

Binomial Nomenclature In the 18th century, 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

Species: Panthera pardus Genus: Panthera Family: Felidae Order: Figure 26.3 Species: Panthera pardus Genus: Panthera Family: Felidae Order: Carnivora Class: Mammalia Figure 26.3 Linnaean classification. Phylum: Chordata Kingdom: Animalia Domain: Bacteria Domain: Archaea Domain: Eukarya