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