Classification, Taxonomy and Patterns of Organization Unit 1.4.

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Presentation transcript:

Classification, Taxonomy and Patterns of Organization Unit 1.4

Taxonomy Taxonomy produces a formal system for naming and classifying species to illustrate their evolutionary relationship.

Taxonomy & Systematics Taxonomy Formal system for naming and classifying species. Systematics Broader science of classifying organisms based on similarity, biogeography, etc. Systematic zoologists have three goals: To discover all species of animals. To reconstruct their evolutionary relationships. To classify animals according to their evolutionary relationships.

Taxonomy Introduction of evolutionary theory into animal taxonomy changed taxonomist’s role from one of classification to systematization. Classification denotes the construction of classes. Grouping of organisms that possess a common feature called an essence used to define the class.

Linnaeus and Classification Carolus Linnaeus designed our hierarchical classification scheme. Kingdom Phylum Class Order Family Genus Species

Linnaeus and Classification All animals are placed in Kingdom Animalia. Names of animal groups at each rank in the hierarchy are called taxa (taxon). Each rank can be subdivided into additional levels of taxa. Superclass, suborder, etc.

Linnaeus and Classification Binomial nomenclature is the system Linnaeus used for naming species. Genus and species Names are latinized and italicized, only the genus is capatilized. Sitta carolinensis

Species Defining a species can be difficult. Criteria: Common descent The smallest distinct groupings of organisms sharing a pattern of descent. Morphological & molecular techniques Members of a species must form a reproductive community that excludes other species.

Species The geographic range of a species is its distribution in space. Evolutionary duration of a species is its distribution in time. A worldwide species is cosmopolitan. One with a very localized range is called endemic.

The Biological Species Concept The biological species concept emerged during the evolutionary synthesis. “A species is a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature.” Mayr 1982 Sibling species fit this category, but can only be differentiated with molecular techniques. Lacks a temporal dimension. Degree of reproductive isolation necessary? Species that reproduce asexually?

Investigating the Tree of Life A major goal of systematics is to infer the evolutionary tree or phylogeny – the evolutionary history of a species or group of related species. Phylogenies are inferred by identifying organismal features, characters, that vary among species. Morphological Chromosomal Molecular Behavioral or ecological

Phylogeny Shared characters that result from common ancestry are homologous.

Sorting Homology from Analogy A potential misconception in constructing a phylogeny is similarity due to convergent evolution, called analogy, rather than shared ancestry.

Sorting Homology from Analogy Convergent evolution occurs when similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different evolutionary lineages.

Shared Primitive and Shared Derived Characteristics A shared primitive (ancestral) character: Is a homologous structure that predates the branching of a particular clade from other members of that clade. Is shared beyond the taxon we are trying to define. Example – mammals all have a backbone, but so do other vertebrates.

Shared Primitive and Shared Derived Characteristics A shared derived character is an evolutionary novelty unique to a particular clade. All mammals have hair, and no other animals have hair.

Phylogeny The form of the character that was present in the common ancestor of the entire group is called ancestral. Variant forms of the character arose later and are called derived character states. Determining polarity of a character involves determining which state is ancestral.

Phylogeny Polarity is determined by using outgroup comparison. An outgroup is closely related, but not part of the group being examined (the ingroup). If a character is found in both the study group and the outgroup, it is considered ancestral for the study group. Character groups found in the study groups but not the outgroups are derived.

Phylogeny The nested hierarchy of clades can be represented as a cladogram that is based on shared synapomorphies.

Phylogeny A phylogenetic tree is another way of representing evolutionary relationships. Branches represent real lineages that occurred in the evolutionary past. Includes information about ancestors, duration of evolutionary lineages, amounts of evolutionary change that has occurred.

Sources of Phylogenetic Information Characters used to construct cladograms can be found using: Comparative morphology – examine shapes and sizes of organismal structures, including developmental origins. Comparative biochemistry – examine sequences of amino acids and nucleotides to identify variable characters. Comparative cytology – uses variation in numbers, shapes, and sizes of chromosomes and their parts.

Cladistics A valid clade is monophyletic. Signifying that it consists of the ancestor species and all its descendants.

Cladistics A paraphyletic clade is a grouping that consists of an ancestral species and some, but not all, of the descendants.

Cladistics A polyphyletic grouping includes numerous types of organisms that lack a common ancestor.

Traditional Evolutionary Taxonomy Evolutionary taxonomy utilizes common descent and the amount of adaptive evolutionary change to rank higher taxa. Sometimes this type of classification includes paraphyletic groupings.

Maximum Parsimony and Maximum Likelihood Systematists can never be sure of finding the single best tree in a large data set. Narrow the possibilities by applying the principles of maximum parsimony and maximum likelihood.

Parsimony Among phylogenetic hypotheses the most parsimonious tree is the one that requires the fewest evolutionary events to have occurred in the form of shared derived characters. Occam’s Razor

Molecular Systematics Much of an organism’s evolutionary history is documented in its genome. Comparing nucleic acids or other molecules to infer relatedness is a valuable tool for tracing organisms’ evolutionary history.

Major Divisions of Life Aristotle’s two kingdom system included plants and animals. One-celled organisms became a problem Haeckel (1866) proposed Protista for single- celled organisms. R.H. Whittaker (1969) proposed a five- kingdom system to distinguish prokaryotes and fungi.

Major Divisions of Life Woese, Kandler and Wheelis (1990) proposed three monophyletic domains above kingdom level—Eucarya, Bacteria and Archaea—based on ribosomal RNA sequences.

Major Divisions of Life More revisions are necessary to clarify taxonomic kingdoms based on monophyly. “Protozoa” Neither animals nor a valid monophyletic taxon. “Protista” Not a monophyletic kingdom. Most likely composed of seven or more kingdoms.