Biology, 9th ed,Sylvia Mader Chapter 20 Chapter 20 Classification of Living Things Classification of Living Things

Outline Taxonomy Binomial System Species Identification Classification Categories Phylogenetic Trees Systematics Taxonomy (naming of organisms) Classification (placing species in the proper categories) Systematics Today Cladistic Systematics Phenetic Systematics Classification Systems The Five Kingdom System The Three Domain Ssytem

Began with the ancient Greeks and Romans Taxonomy Branch of biology concerned with identifying, naming, and classifying organisms Began with the ancient Greeks and Romans Aristotle classified organisms into groups such as horses, birds, and oaks John Ray (1627–1705) Believed that each organism should have a set name Otherwise, “men…cannot see and record accurately.”

Classifying Organisms

Taxonomy: Binomial System Mid-eighteenth century, Linnaeus developed the binomial system of nomenclature First word is genus name Second word is specific epithet Refers to one species (of potentially many) within its genus A species is referred to by the full binomial name (Genus species) Genus name can be used alone to refer to a group of related species

Taxonomy: Distinguishing Species Distinguishing species on the basis of structure can be difficult Members of the same species can vary in structure Attempts to demonstrate reproductive isolation is problematic because: Some species hybridize, and Reproductive isolation is difficult to observe

Hybridization between species Zebroids are horse-zebra hybrids.

Classification Categories Modern taxonomists use the following classification: Species Genus – one or more species Family – one or more genera Order – one or more families Class – one or more orders Phylum – one or more classes Kingdom – one or more phyla Domain – one or more kingdoms

Eukarya- membrane-bounded nucleus Animalia- motile, multicellular, internal cavity for digestion of nutrients Chordata- organisms that at one time have a dorsal hollow nerve cord, a notochord, pharyngeal pouches, and a postanal tail Mammalia- warm-blooded vertebrates with mammary glands; body with hair; Primates- well-developed brain opposable thumb Hominidae- upright stance and bipedal locomotion Homo- Full brain development, hand anatomy for making tools Species- sapiens modern humans; speech centers

Classification Categories The higher the category, the more inclusive Organisms in the same domain have general characteristics in common In most cases, classification categories can be subdivided into additional categories Superorder Order Suborder Infraorder

Systematics - the diversity of organisms at all levels Phylogenetic Trees Systematics - the diversity of organisms at all levels One goal of systematics is to determine phylogeny (evolutionary history) of a group Phylogeny often represented as a phylogenetic tree A diagram indicating lines of descent Each branching point: Is a divergence from a common ancestor Represents an organism that gives rise to two new groups

Phylogenetic Trees Classification lists the unique characters of each taxon and is intended to reflect phylogeny Primitive characters: Present in all members of a group, and Present in the common ancestor Derived characters: Present in some members of a group, but Absent in the common ancestor

Tracing Phylogeny Fossil Record Homology Fossil record is incomplete It is often difficult to determine the phylogeny of a fossil Homology Refers to features that stem from a common ancestor Homologous structures are related to each other through common descent Analogy-wings of an insect and the wings of a bat are analogous Similarity due to convergence-similar characters in distantly related lines of descent.

Ancestral Angiosperm

Tracing Phylogeny Convergent Evolution Parallel Evolution The acquisition of a feature in distantly related lines of descent The feature is not present in a common ancestor Parallel Evolution The acquisition of a feature in two or more related lineages

Convergent Evolution-both like dry, hot environments & succulent with spiny leaves but not closely related.

Molecular Data Protein Comparisons RNA and DNA Comparisons Immunological techniques Degree of cross reaction used to judge relationship Amino acid sequencing Similar sequence in same protein indicates close relationship RNA and DNA Comparisons Systematics assumes: Two species with similar base-pair sequences are assumed to be closely related Two species with differing base-pair sequences are assumed to be only distantly related Molecular Clocks Use non adaptive nucleotide sequences Assumed constant rate of mutation over time

Ancestry of Giant Pandas

Cladistic Systematics Traces evolutionary history of the group under study Uses shared derived characters to: Classify organisms, and Arrange taxa into a cladogram A cladogram is a special type of phylogenetic tree A clade is an evolutionary branch that includes: A common ancestor, together with All its descendent species

Constructing a Cladogram

Cladists are always guided by the principle of parsimony The arrangement requiring the fewest assumptions is preferred This would: Leave the fewest number of shared derived characters unexplained Minimize the number of assumed evolutionary changes The reliability of a cladogram is dependent on the knowledge and skill of the investigator

Cladistic Versus Traditional View of Reptilian Phylogeny

Phenetic Systematics Assumes it will never be possible to construct a truly phylogenetic classification system Species are classified according to the total number of shared similarities Disregards assumed phylogenetic considerations Ignores issues of convergent or parallel evolution

Traditional Systematics Mainly uses anatomical data Classify organisms using assumed phylogeny with emphasis on phenotype Stress both common ancestry and degree of structural difference among divergent groups Construct phylogenetic trees by applying evolutionary principles to categories Not strict in making sure all taxa are monophyletic

Classification Systems Until the middle of the twentieth century, biologists recognized only two kingdoms Plantae (plants) Animalia (animals) Protista (protists) were added as third kingdom in the 1880s Whittaker expanded to five kingdoms in 1969 by adding Fungi and Monera

Three-Domain System-compare table 20.3 The Bacteria and Archaea are so different they have been assigned to separate domains Similar in that both are asexually reproducing unicellular prokaryotes Distinguishable by: Difference in rRNA base sequences Plasma membrane chemistry Cell wall chemistry

Unicellular and multicellular organisms Three-Domain System Domain Eukarya Unicellular and multicellular organisms Cells with a membrane-bounded nucleus Sexual reproduction common Contains four kingdoms Kingdom Protista Kingdom Fungi Kingdom Plantae Kingdom Animalia

The Three-Domain System of Classification

The Three Domains of Life

Review Taxonomy Binomial System Species Identification Classification Categories Phylogenetic Trees Systematics Taxonomy (naming of organisms) Classification (placing species in the proper categories) Systematics Today Cladistic Systematics Phenetic Systematics Classification Systems The Five Kingdom System The Three Domain System

Biology, 9th ed,Sylvia Mader Chapter 20 Ending Slide Chapter 20 Classification of Living Things Classification of Living Things