CHAPTER 17 – CLASSIFICATION OF ORGANiSMS 17-1: Biodiversity 17-2: Systematics 17-3: Modern Classification

17-1: Biodiversity Biologists have named and classified almost 2 million species Over time, scientists have created various systems of classification to organize their knowledge of the tremendous # of species each system places species into categories based on particular characteristics

Classifying organisms Biodiversity The variety of organisms considered at all levels from populations to ecosystems Terry Erwin (1980s) Catalogued insect species in tropical rain forest Found over 1000 species in only 19 trees

Classifying organisms Every year, biologists discover 1000s of new species and seek to classify them in a meaningful way Ex. – the pangolin Grouped with lizards + crocodiles due to scales? Grouped with animals that use sticky tongues to eat ants?

Taxonomy Taxonomy The science of describing, naming, + classifying organisms Taxon Any particular group within a taxonomic system

Taxonomy Aristotle Classified organisms in 2 taxa: Plants Grouped them based on stem differences Animals Grouped them based on where they lived: Land, water, or air

Taxonomy Aristotle’s system was inadequate Common names were not useful either Ex. Robin or Fir tree Vary from place to place More than one common name Don’t accurately define a species (i.e. Jellyfish)

The linnaean system Carolus Linnaeus System that grouped organisms into hierarchical categories according to their form + structure (morphology) System had 7 levels

Levels of classification Kingdom Phylum Class Order Family Genus Species

Binomial nomenclature Linnaeus gave an organism a species name, or scientific name, with two parts: Genus Species identifier Examples: Homo sapiens Thamnophis melanogaster Drosophila melanogaster Binomial nomenclature

Your classification Kingdom Animalia Phylum Chordata Subphylum Vertebrata Class Mammalia Order Primates Family Hominidae Genus Homo Species sapiens

Binomial nomenclature Subspecies Species that live in different geographic areas Example: Terrapene carolina triungui

Classification video

17-2: Systematics Modern biologists consider not only the VISIBLE SIMILARITIES but also similarities in: Embryos Chromosomes Proteins DNA Systematics Goal is to classify organisms in terms of their natural relationships organize in context of evolution

phylogenetics Systematic taxonomists agree that an organism’s classification should reflect PHYLOGENY (evolutionary history) Phylogenetics The analysis of the evolutionary or ancestral relationships among taxa.

phylogenetics Use comparisons to classify: Living species vs. fossils Embryonic development + gene expression Chromosomes or macromolecules (DNA/RNA)

phylogenetics Represent hypotheses by a phylogenetic tree (diagram) Branching pattern indicates how closely related a subset of taxa are thought to be May be revised with new discoveries or evidence

Evidence of shared ancestry Biologists use fossils as important clues for the timing of evolutionary changes + divergence The fossil record my lack evidence… May also compare… Homologous features (jaws of pangolin + dogs) Analogous features (scales of snakes + pangolin) Embryology (amnion) The greater the # of features shared by organisms, the more closely related the organisms are

Cladistics 1966 – Willi Hennig Cladistics A system of phylogenetic analysis that uses shared + derived characters as the only criteria for grouping taxa Shared – feature that all members of a group have in common Ex. Hair in mammals or feathers in birds Derived – feature that evolved only within the group

Cladistics Cladistics assume that organisms share one or more derived characters Probably inherited them from an common ancestor Group known as a “clade” Includes its ancestors + all descendants No other categories (i.e. order, class, etc..) Creates a cladogram to show their hypothesis

Example - A cladogram

Constructing a cladogram Out-group Organism that is only distantly related to the other organisms Acts as a starting point for comparisons

Molecular cladistics Biologist can count the shared, derived amino acids at each position in a protein to make a cladogram

Molecular cladistics “Molecular Clock” A tool for estimating the sequence of past evolutionary events Suggests that the greater the differences between a pair of sequences, the longer ago those two sequences diverged from a common ancestor

chromosomes If two species have the same banding pattern in regions of similar chromosomes, the regions are likely to have been inherited from a single chromosome in the last common ancestor of the two species

Putting it all together To classify an organism and represent its systematics in an evolutionary context, biologists use many types of information to build and revise phylogenetic models: Physical features Embryos Genes in nucleus Mitochondrial DNA Ribosomal RNA

17-3: modern classification Taxonomists have revised two Linnaean-inspired categories Domains Kingdoms

The tree of life Based on cell types, scientists can divide all life into two groups: Eukaryotes Prokaryotes Carl Woese - 1977 Proposed major revision of 6 kingdom system Compared rRNA sequences of different organisms and grouped them according to their similarities

Three domains of life Insights from rRNA analyses: Data is consistent with hypotheses that all living organisms inherited their rRNA genes from ancient organisms or form of life All living things can be grouped into 1 of the 3 domains: BACTERIA, ARCHAEA, or EUKARYA Species in domain ARCHAEA are greatly different than bacteria

Domain bacteria Small, single-celled prokaryotes Have cell walls Contain peptidoglycan Reproduce by binary fission One circular chromosome

Domain archaea Have distinctive cell membranes Made of hydrocarbons, not fatty acids Some are autotrophic (chemosynthesis) May inhabit harsh environments

Domain eukarya Consists of eukaryotic organisms Includes plants, animals, fungi, + some single-celled organisms

Six kingdoms The 6 kingdoms are more of a traditional taxonomic system Eubacteria Archaebacteria Protista Fungi Plantae Animalia