Phylogeny 9/8/2014. Evolutionary Relationships. Data Supporting Phylogeny. Chapter 26

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1 Phylogeny Chapter 26 Taxonomy Taxonomy: ordered division of organisms into categories based on a set of characteristics used to assess similarities and differences Carolus Linnaeus developed binomial nomenclature, a two-part naming system that consists of the genus to which the species belongs as well as the organisms species within the genus Tyrannosaurus rex, Escherichia coli, Homo sapien The hierarchical classification of organisms consists of the following levels, from largest to most specific. Each level is called a taxon. Domain kingdom phylum class order family genus species Taxonomic Classification of Three Mammals Taxon Human Lion Dog Domain Eukarya Eukarya Eukarya Animalia Animalia Animalia Phylum Chordata Chordata Chordata Class Mammalia Mammalia Mammalia Order Primates Carnivora Carnivora Family Hominidae Felidae Canidae Genus Homo Panthera Canus Species sapiens leo familiaris Phylogeny Evolutionary history of a species or a group of related species It is created by using evidence from systematics, a discipline that focuses on classifying organisms and their evolutionary relationships Based on common ancestries involving fossils, morphology, genes, and molecular evidence Systematics hypothesizes phylogenies using molecular data Applies the principle of parsimony simplest explanation; fewest evolutionary events that explain the data Choose the tree that explains the data invoking the fewest number of evolutionary events Involves taxonomy and binomial nomenclature Evolutionary Relationships Phylogenetic trees are used to depict hypotheses about evolutionary relationships Branches reflect hierarchical classifications of groups nested within more inclusive groups Phylogenies are inferred from morphological and molecular data Similarities are based on common ancestry, but beware of analogous structures and convergent evolution! Homologous structures Convergent evolution Analogous structures Molecular systematics Data Supporting Phylogeny Homologous structures: similarities due to shared ancestry Whale s flipper and tiger s paw Convergent evolution: takes place when two organisms develop similarities as they adapted to similar environmental challenges, but not as a result of common ancestry Streamlined bodies of tuna and a dolphin Likenesses that are a result of converge evolution are considered analogous they do not indicate relatedness, but similar solutions to similar problem Butterfly and bat wings both are adapted for flight Molecular systematics: uses DNA and other molecular data to determine phylogeny; the more alike the DNA sequences of two organisms, the more closely related they are evolutionarily 1

2 Phylogenetic Trees Groupings Show how each species is related to other closely related species Shows common ancestors Use fossils and other evidence to reconstruct an organisms history Monophyletic group (clade): an ancestral species and ALL descendants Trace a single common ancestor and every species that descended from it Paraphyletic group: ancestral species and some descendants, but not all Polyphyletic group: includes species that may not share the same common ancestor Outgroup: group that diverged before the lineage evolved Constructing Phylogenetic Trees Cladogram: depicts patterns of shared characteristics among taxa serves as the basis of a phylogenetic tree A clade, within a tree, is a group of species that includes an ancestral species and all descendants Shared derived characters are used to construct cladograms they are evolutionary novelties unique to a particular clade. Hair is a shared derived character of mammals Organizing the World of Organisms The Tree of Life Organize creatures by structure and function Organize them into groups of closely related creatures Constantly being revised, but currently there is a 3-domain system in place 3 Domains: Eukarya (eukaryotic), Archaea (prokaryotic), and Bacteria (prokaryotic) Prokaryotes Characteristic Bacteria Archaea Eukarya Nuclear envelope Bacteria Archaebacteria Eukaryotes Protist Membrane-enclosed organelles Introns Histone proteins associated with DNA Circular chromosome Fungi Plant Animal 2

3 Note: Every phylogenetic tree is a hypothesis! Scientists narrow down the possibilities by using the principle of maximum parsimony This states that one should follow the simplest explanation that coincides with the facts AKA don t make things too complicated! Vertebral column (backbone) Derived Traits for Building a Phylogenetic Tree Lancelet (outgroup) Lamprey Bass Frog Turtle Leopard Hinged jaws Four walking legs Amnion Hair Genomic Changes Includes comparison the similarities and differences in DNA and protein differences DNA sequence evolution varies from one part of the genome to another Comparing different sequences helps investigate relationships between groups of organisms that diverged a long time ago DNA coding for rrna changes relatively slowly and is useful for divergence that occurred hundreds of millions of years ago DNA coding for mtdna evolves rapidly and can be used to explore recent evolutionary events Molecular Analysis Advantages Most accurate Large numbers of traits/proteins to analyze Allows us to differentiate between closely related species that appear very similar Disadvantages Individuals of the same species differ in DNA Molecular Clocks Methods used to measure the absolute time of evolutionary change based on the observation that some genes and other regions of the genome appear to evolve at constant rates Trace variations in genomes to date evolutionary changes by plotting base differences and branch points Rate of change is calculated and then extrapolate back DNA Base Pair Differences 1 x x x x x 3

4 1 x x x x x Practice (# of base pair differences in a gene) Phylogenetic Tree Cat Dog Wolf Skunk Otter Cat x Dog 28 x Wolf 26 2 x 9 8 Skunk x 2 Otter x Time Homology/Anatomy Analysis Find an adaptation that is present in one lineage, but not in another The phylogenetic tree branches when these new features evolved Cladistic Tables Different Species Character A? Yes Yes Yes Yes Yes Character B? No Yes Yes Yes Yes Character C? No No Yes Yes Yes Character D? No No No Yes Yes Character E? No No No No Yes 4

5 Time 9/8/2014 Character A? Yes Yes Yes Yes Yes Character B? No Yes Yes Yes Yes Character C? No No Yes Yes Yes Character D? No No No Yes Yes Character E? No No No No Yes Practice DNA Organelles Cell Walls Amnion Hair Reptiles Y Y N Y N Plants Y Y Y N N Mammals Y Y N Y Y Bacteria Y N N N N Amphibians Y Y N N N Ancestral reptile Ancestral fish Ancestral animal Advantages Homologous structures show relationships Allows us to determine when changes occurred (using fossils) Best way to analyze extinct species Anatomy Analysis Disadvantages Analogous structures do not and can be confused Not all species leave fossils The fossils we have collected are incomplete 5

6 Homology vs. Analogy Embryology Analysis Homology means two features are similar due to ancestry Wings in bats, arms in humans, fins in whales Called homologous structures Caused by divergent evolution Analogy is when two organisms have similar features but are not closely related Wings in bats and birds Caused by convergent evolution Evolved the same solution Advantages Allows us to see similarities even when adults of the species look very different i.e. reptiles and birds look more closely related Disadvantages Often similarities are lost later in development i.e. We have gills early on in development We did not evolve from chimpanzees! 6