Chapter 25/26
Taxonomy and Biodiversity
Evolutionary biology
The major goal of evolutionary biology is to reconstruct the
history of life on earth
►Process: a- natural selection
b- mechanisms that change the genetic composition
of populations (evolution of new species)
►History
Phylogeny, the evolutionary history of a group of organisms
Systematics, an analytical approach to understanding the
diversity and relationships of living and extinct organisms
Phylogenetic Systematics
Connecting
Classification with Evolutionary History
Carolus Linnaeus (1748) published Systema naturae
- classification of all plants and animals known at the time, Binomial
naming of living organisms (Genus name and Species name)
Taxonomy is an ordered division of organisms into categories based
on similarities and differences
Linneaus’s classification based on resemblances between organisms
(not based on evolutionary relationships)
Taxonomy employs a hierarchical system of classification;Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Linnaeus in his Systema naturae
What is SPECIES
Species is a largest group of organisms that have common similar
phenotype but they have to be capable to sexually reproduces (i.e.
to combine their genetic material) and produce fertile progeny.
A- Each species has a two-part name, binomial
Genus, is the closest group to which a species belongs
Species (specific epithet, meaning nickname or description
refers to a one species within each genus )
B- Species are organized hierarchically into
broader and broader groups of organisms
Note; The first letter of the genus is capitalized and both names are
italicized and Latinized
Example, Humans (WE; men and women) are named:
Homo sapiens, The “wise man.”
Hierarchical Classification
Means; grouping species into increasingly broad taxonomic categories
Species that appear to be closely related are grouped into the same
genus
Genera are grouped into progressively broader categories:
Family, Order, Class, Phylum, Kingdom, and Domain (or
Superkingdom)
Taxon: Taxonomic unit at any level
Example: Panthera is a taxon at the genus level,
Mammalia is a taxon at the class level
(Mammalia includes all of the many orders of mammals)
Note: Higher classification levels (Genus and above) are not defined
by some measurable characteristic. ( remember; Biological Species
are separated by the reproductive isolation)
The larger categories are not comparable between lineages (ancestries).
• An order of snails does not necessarily exhibit the same degree of
morphological or genetic diversity as an order of mammals
New information
and understanding of the tree of life
The Molecular Data and the evolutionary relationships of life’s diverse
forms
The first taxonomic schemes a- plant kingdom
b- animal kingdom
Whittaker R. H.(1969), Five-kingdom system:
Monera
Protista
Plantae
Fungi
Animalia
Basically: Two fundamentally different types of cells:
Prokaryotic (the kingdom Monera)
Eukaryotic (the other four kingdoms)
kingdoms; Plantae, Fungi and Animalia (multicellular eukaryotes)
distinguished by nutrition
• Plants are autotrophic, making organic food by photosynthesis
• Most fungi are decomposers with extracellular digestion and
absorptive nutrition.
• Most animals ingest food and digest it within specialized cavities
Protista includes all eukaryotes that did not fit the definition of plants,
fungi, or animals.
Most protists are unicellular. But some are multicellular organisms
(Seaweeds, because of their relationships to specific unicellular
protists)
Note: The five-kingdom system prevailed in biology for more than 20 years
But it was challenged by:A- Molecular Data led to: a- Cladistic analysis to taxonomy,
b- Cladograms
B- Systematists sorting out Protista based on their phylogeny
into five or more new kingdoms or assigned into the Plantae,
Fungi, or Animalia
Cladistic:- Cladistic meaning the study of resemblances among a
clade.
Clade:- Clade is a group of species that includes an ancestral species
and all its descendents.
Cladogram:- Cladogram is a diagram which represents patterns of
shared characteristics
The Molecular data led to:Three-domain system as “Superkingdoms.”
Bacteria,
Archaea,
Eukarya
Bacteria differ from Archaea in many key structural, biochemical, and
physiological characteristics.
Many microbiologists divided Bacteria and Archea into multiple
kingdoms based on cladistic analysis of molecular data
Taxonomy; always is a work in progress
Much more research is needed for:* How the three domains of life are
related?
* How many kingdoms should be included
in each domain?
Note: New data, including the discovery of new
groups, will lead to further taxonomic
remodeling.
Keep in mind:* Phylogenetic trees
* Taxonomic groupings
Both are hypotheses that fit the best available
data