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