Download Systematics – Chapter 12

Systematics – Chapter 12
What is phylogeny?
Phylogeny defined
 Phylogeny is the history of descent of a group of taxa such as species from
their common ancestors, including the order of branching and sometimes the
absolute times of divergence
 Or the evolutionary history of a group
Other terms defined
 Systematics: Classification of organisms
 Taxonomy: Naming of organisms
Phylogenetic trees
 The True Tree is almost never known, so phylogenies represent estimates of
the true tree
How can we find phylogenetic history?
 Phylogentic trees are based on comparison of traits - individuals with common
traits are placed together
 Using characters
 Phenotypic – external and internal morphology
 Behavior
 Cell structure
 Biochemistry
 DNA
Creating a phylogenetic tree
 Character states or traits are different possible forms of each character
 Example: character - flower color, character state – blue or red
 Example: character – nucleotide, character state - T
Character states or traits
 Character states inherited from a common ancestor are termed homologous
 Character states that differ from the ancestor are termed derived
 Character states that are the same as the ancestor are termed ancestral
 Phylogenetic inference based on synapomorphy = shared, derived character
states
 This phylogenetic tree is called a cladogram
Synaptomorphies indicated by bars on cladogram
The problem of homoplasy
 Homoplasy complicates the building of phylogenetic trees
 Homoplasy is the possession by two or more groups of a similar or identical
character state that has not been derived by both species from their common
ancestor; includes convergence, parallel evolution and evolutionary reversal
Convergent evolution
 Similar character states evolve independently in different lineages due to
similar natural selection pressures
Parallel evolution
 Similar character states evolve independently in related lineages
Solution to homoplasy
 Use slowly evolving characters
 Use multiple lines of evidence
 Morphology
 DNA sequences
Which tree is correct?
 Use principle of parsimony
 The simplest explanation is the best explanation
 Most widely used method, but not perfect
 Best tree is the one that has the fewest evolutionary changes
Tree length and maximum parsimony
Molecular clocks
 DNA sequences may evolve at a constant rate
 This “molecular clock” may allow us to estimate the absolute time of
divergence
 Clock will vary from gene to gene, lineage to lineage and base to base
Evidence for a molecular clock
Difficulties
 Some events (such as adaptive radiation) happen too quickly to develop
distinct synapomorphies
Adaptive radiation is common
 Adaptive radiation is the divergent evolution of a lineage within a relatively
short time
 Mammal and angiosperm diversification during Mesozoic and Cenozoic
 Cichlid fishes in rift lakes of Africa
 Darwin’s Finches on the Galapagos Islands
 Honeycreepers in Hawaii
What causes adaptive radiations?
 Opportunity
 Colonization of isolated habitats

Cuts off gene flow

Many new niches available

Lack of competition
 Mass extinction
 Climate Change
 Evolutionary innovation
Colonization of isolated habitats
Mass extinctions
Evolution of land plants includes major innovations
Three kingdom system
Kingdom Fungi
 Eukaryotic, multicellular absorbers
 More closely related to animals than plants
Kingdom Protista
 Unicellular, colonial, and simple multicellular eukaryotes
Kingdom Plantae
 Includes eukaryotic, multicellular photosynthesizers
 Primarily sexual reproduction with cycles of haploid and diploid generations
Alteration of generations
 The first eukaryotic organisms were probably haploid
 Zygotic meiosis
 Evolution of delayed meiosis (gametic meiosis) results in production of
gametes
 In plants meiosis (sporic meiosis) results in the production of spores
 Spores can divide by mitosis and produced a multicellular haploid organism
Kingdom Fungi – Chapter 14
Fungi
 Hetertropic organisms
 Absorbers due to rigid cell walls made of polysaccharide chitin
 Most fungi are filamentous
 Each filament is called a hyphae and a mass of hyphae from one organism
is called a mycelium
 70,000 species identified
Fungi are important as decomposers
Medical and economic mycology
 Cladosporium herbarum attack meat
 Fungal infections
 Yeast
 Antibiotics
Fungal symbioses
 80% of all vascular plants have mycorrhizal relationships
 Endophytes live inside leaves of healthy plants and produce protective
secondary metabolites
 Lichens include mycobiont and photobiont
Predaceous fungi
Classification of fungi
Cytridiomycota
 Predominantly aquatic group
 Motile cells
 Do not develop mycelium
Zygomycota
 Most live on decaying organic matter
 Some are parasites, endomycorrhizae
 Profuse, rapidly growing hypae
 Form zygospores
Ascomycetes
 Food spoilage fungus
 Powdery mildews
 Yeasts
 Form ascospores
Basidiomycetes
 Most familiar fungi
 Include gill fungi
 Forms basidiospores