systematics taxonomy, phylogeny, and classification
Post on 19-Dec-2015
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TRANSCRIPT
Diversity of Life
• How do we organize it all?– MORPHOLOGY
• What the organisms look like (phenotype).
– EVOLUTIONARY HISTORY• Shared ancestry, relationships.• CLUES:
–Space – Biogeographic distributions of organisms
–Time – Fossil record
Systematics
• Science of organizing the diversity of life.
1. Taxonomy – Identification & Naming
2. Phylogeny – Analyzing evolutionary relationships among groups.
3. Classification – Placing organisms into an organized categorization scheme.
Taxonomy
• Identification & Naming• Taxon: a group of organisms (Taxa)• “Species” – basic group, the only REAL
taxon.– Group of interbreeding populations that are
reproductively isolated from other such groups (and evolving independently of other such groups).
• Lineage – Taxa connected in time by genetic links.
Taxonomy• “Species” are not always easy to detect!
– Variation– Asexual reproduction– Morphology is not enough
• Need anatomy, physiology, ecology, behavior, biochemistry, evolutionary history, etc.
• Identified by experts in their respective fields.
Taxonomy• A “Type Specimen” is
denoted.– A single physical specimen
that all others are later compared to.
– The Latin description is based on this specimen.
– Stored in a special place.• ATCC:• http://www.bioscience.org/urlli
sts/atcc.htm
Taxonomy
• New species each given a “Scientific Name”– Carolus Linnaeus – Binomial Nomenclature– 2-word Latin name.
• Pinus strobus• Dictyostelium discoideum• Bubo virginianus
• “Common Names” also…– Can be misleading
Taxonomy
• Pinus strobus
• 1st word = Genus– A generalized name
• 2nd word = specific epithet– A descriptive name
• Always in italics or underlined.
• Genus is capitalized, epithet is lower case.
• Specific epithet never used alone!
Taxonomy
• “Variants” sometimes used– not different species, but “sub-species”– An additional descriptor is added to the end.
Lampropeltis triangulum var. sinaloae
Lampropeltis triangulum multistriata
Phylogeny• Grouping new species/taxa with closely-
related taxa from an evolutionary perspective.
• Phylogenetic Trees:
Phylogeny
Easier said than done!
3 approaches:1. Evolutionary Systematics
• Grouping based on similarities & differences• Reliance on fossil evidence• Subjective
2. Phenetics• Grouping based on similarities only• Convergence is a problem
Phylogeny
3. Phylogenetic Systematics (Cladistics)• Based on similarities derived from a
common ancestor – “Shared Derived Characters”(if only 1 in the group has the character, it’s no
good)
• Plesiomorphic vs Apomorphic characters• Want “Synapomorphies”• Identifies Monophyletic Groups• Look for homologous structures (not
analagous ones).
Phylogeny
• Tree Polarity – – Need to know which character state is
ancestral (plesiomorphic) and which is derived (apomorphic).
– Fossil Evidence is good, but not always available!
– Outgroup• A closely related organism that is NOT part of the
“ingroup” being studied.• Acts as a means of comparison.
Phylogeny
• Must REALLY know your organism
• Often, genes are used to INFER relationships between whole organisms.
Phylogeny• Phylogenetic Trees
– Represent CURRENTLY LIVING organisms.
– DO NOT represent a This That That That
NOW!
Classification
• Categorizing organisms into a hierarchy of names (hopefully) according to their relatedness.
• Historically – based on convenience.
• Starting at Species (the most exclusive group), organisms are grouped into more and more broad & inclusive Taxa.
• “Species” is the only level that really exists as an true single entity.
Classification
Kingdom
Phylum/Division
Class
Order
Family
Genus
Species
Animalia
Chordata
Mammalia
Primates
Hominidae
HomoHomo
sapiens
Animalia
Chordata
AvesMammalia
StrigiformesPrimates
TytonidaeHominidae
TytoHomo
Classification
Homosapiens
Tytoalba
Classification• Times are changing!• Phylocode (http://www.ohiou.edu/phylocode/)
• Rankless Classification
• Clades are each given a name
Systematics
• Tree of Life: http://tolweb.org/tree/phylogeny.html