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Ch. 26 – Phylogeny and the Tree of Life

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1 Ch. 26 – Phylogeny and the Tree of Life
We can decide in which container to place a species by comparing its traits with those of potential close relatives We will survey the diversity and describe hypotheses regarding how it evolved Phylogeny Systematics Discipline focused on classifying organisms and determining their evolutionary relationships (phylogeny)

2 Phylogeny and Systematics
Taxonomy Science of classification Sort and identify closely related species Specific group is a taxon Binomial nomenclature 2 part Latin name Genus, species

3 Phylogeny and Systematics
Hierarchical classification Linnaeus’ 7 level scheme: Kingdom Phylum (Division for plants and fungi) Class Order Family Genus Species Domains are now above kingdoms 3 exist Taxon Toxonomic unit at any level of the hierarchy

4 Linking Classification and Phylogeny
Phylogenetic Tree Diagram that displays evolutionary relationships The sequence of branching symbolizes historical chronology. The last ancestor common to both the cat and dog families lived longer ago than the last common ancestor shared by leopards and domestic cats. PhyloCode Resulted due to difficulties with the Linnean system Only names groups that include a common ancestor of all its descendents Ranks would no longer exist

5 Linking Classification and Phylogeny
Reading a phylogenetic tree Branch points Divergence Sister taxa Groups of organisms that share an immediate common ancestor Rooted Represents most common ancestor of all taxa in the tree Basal Taxon Lineage that diverges early in the history of a group Polytomy Branch point from which more than two descendent groups emerge

6 Phylogenetic Trees Intended to show patterns of descent
Sequence of branching in a tree does not necessarily indicate the actual (absolute) ages of the particular species Don’t assume that a taxon evolved from the taxon next to it

7 Analyzing the taxonomic distribution of homologies enables us to identify the sequence in which derived characters evolved during vertebrate phylogeny. Construct a cladogram based on the following traits (characters) in the character table Fig

8 Fig

9 Morphological & Molecular Homologies
Homology shared ancestry; causes likeness Can vary in appearance but still not in the genes Analogy convergent evolution acquisition of similar characteristics due to sharing similar ecological roles External appearance very similar but internal anatomy, physiology, and reproductive systems are dissimilar Homoplasies Analagous structures that arise independently

10 Molecular Homologies Comparisons of DNA Molecular Systematics
Uses data from DNA and other molecules to determine evolutionary relationships

11 Cladistics Common ancestry is the primary criterion used to classify organisms Clades Groups that include an ancestral species and all of its descendents Monophyletic group Paraphyletic group Polyphyletic group

12 Cladistics Monophyletic group
Allows a taxon to be equivalent to a clade Group of taxa that consists of an ancestor and all of its descendents Paraphyletic group Ancestral species and SOME of its descendents Polyphyletic group Taxa with 2 or more different ancestors

13 Shared Ancestral & Derived Characters
Shared Ancestral Character Originated in an ancestor of the taxon Backbone of mammals Shared Derived Character Evolutionary novelty unique to a clade Hair in mammals

14 Inferring Phylogenies using Derived Characters
Outgroup A species or group of species from an evolutionary lineage that is known to have diverged before the lineage that includes the species we are studying (ingroup) Evidence used for cladistics Fossil record Homology (morphology, embryology, reproduction) DNA sequences Biogeography Direct observation

15 Gene Duplications & Gene Families
Two distinct types of homologous genes Orthologous genes Found in different species and their divergences traces back to the speciation events that produced the species Paralogous genes Multiple copies of genes have diverged from one another in a species

16 Molecular Clocks Molecular Clock
A yardstick for measuring the absolute time of evolutionary change based on the observation that some genes and other regions of genomes appear to evolve at constant rates Neutral Theory Most evolutionary change has no effect on fitness



19 From Two Kingdoms to Three Domains
Plants and Animals Five Kingdoms Monera, Protista, Plantae, Fungi, Animalia Prokaryotic v. Eukaryotic Unicellular v. Multicellular Autotrophic v. Heterotrophic How does each kingdom classify?

20 From Two Kingdoms to Three Domains
Archaea Bacteria Eukarya Six-Kingdom system Eubacteria and Archaebacteria Extreme halophiles Thermoacidophiles Methanogens



23 Alternatives to the 6 Kingdom System
Eight-Kingdom system - proposed Protists split into 3 kingdoms Fungal like, plant like, animal like Still debate over splitting Archae and Eubacteria even further

24 Phylogeny Summarized (potential FR…hint, hint)
Evolutionary history of organisms Base on principle of parsimony (simplest explanation is the best) Mechanisms of speciation Geographic (allopatric speciation) Sympatric speciation Reproductive isolation by prezygotic barriers Reproductive isolation by postzygotic barriers Investigating phylogeny (evidence, strengths, weaknesses) Fossils Anatomy/Morphology Embryology Molecular biology Behavioral traits

25 Phylogeny Summarized (potential FR…hint, hint)
Mechanisms of speciation Geographic (allopatric speciation) Population of one species becomes physically separated by some geographic barrier such as a river, mountain range, etc. Long term isolation will lead to reproductive isolation Sympatric speciation Occurs when new species arise as a result of reproductive isolation within the population range ex – result of polyploidy or switching mating behaviors Reproductive isolation by prezygotic barriers Habitat, temporal, behavioral, mechanical or gamete incompatibility Reproductive isolation by postzygotic barriers Reduced hybrid variability or fertility leads to speciation

26 Phylogeny Summarized (potential FR…hint, hint)
Investigating phylogeny (evidence) Fossils (strength) Determine time, extinct species (weakness) not all species leave fossils; incomplete chronicle Anatomy/Morphology (strength) homologous structures (weakness) analogous structures, little diversity in taxa, morphology may reflect environment or diet Embryology (strength) similarities in patterns of development not present in adults (weakness) similarities lost in later development (chordates)

27 Phylogeny Summarized (potential FR…hint, hint)
Investigating phylogeny (evidence) Molecular Biology (strength) Lots of traits to study closely related species; most accurate (weakness) virtually no data for extinct species; variation within species blurs variation between species Behavioral traits (strength) genetic based (frog calls) (weakness) culturally transmitted or learned (bird calls)

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