Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. TAXONOMY AND PHYLOGENY OF ANIMALS Chapter

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Linnaeus and Taxonomy More than 1.5 million species of animals are named – Estimated that these account for Less than 20% of all living animals Less than 1% of extinct animals Taxonomy – Formal system for naming and classifying species Systematics – Broader science of comparative biology 10-3

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Linnaeus and Taxonomy Greek philosopher Aristotle first classified organisms Carolus Linnaeus designed the current scheme of classification – Swedish botanist with extensive experience classifying organisms, especially flowering plants – Used morphology to develop a classification system of animals and plants Published in his work, Systema Naturae – Divided animal kingdom into species and gave each a distinctive name Grouped species into genera, genera into orders, and orders into classes – His classification has been drastically altered, but the basic principle is still followed 10-4

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Linnaeus and Taxonomy Linnaeus’s scheme of arranging organisms into an ascending series of groups of increasing inclusiveness is a hierarchical system of classification Hierarchy of taxonomic ranks now includes 7 major groups – Kingdom, phylum, class, order, family, genus, and species 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, subfamily, suborder, etc. 10-6

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Linnaeus and Taxonomy Linnaeus’s system for naming species is know as binomial nomenclature which consists of two words – First word is the genus and is capitalized – Second is the specific epithet written in lower case Scientific name should be printed in italics or underlined if handwritten – Homo sapiens Genus name – Always a noun – Names of genera must refer only to a single group of organisms 10-7

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Linnaeus and Taxonomy Species epithet – Usually an adjective that must agree in gender with the species – Never used alone A specific epithet may be used in different genera – Sita carolinensis (white-breasted nuthatch) – Poecile carolinensis (Carolina chickadee) Ranks above species are single names written with a capital initial letter – Iguanidae (the lizard family that contains Anolis) 10-9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Species Biologists have repeatedly used certain criteria for identifying species Common Descent Central to nearly all modern concepts of species Smallest distinct groupings of organisms sharing patterns of ancestry and descent Reproductive Community-Member of a species must form a reproductive community that excludes members of other species, Asexually reproducing populations » Entails occupation of a particular ecological habitat in a particular place so that a reproducing population responds as a unit to evolutionary forces

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Species Biological Species Concept – Proposed by Theodosius Dobzhansky and Ernst Mayr – Been refined and reworded several times A species is a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature. – Ability to successfully interbreed is central to the concept – Criteria of “niche” tie in ecological properties 10-11

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Species – Biological species concept Lacks an explicit temporal dimension Gives little guidance regarding the species status of ancestral populations relative to their evolutionary descendants – Proponents of the biological species concept Disagree on the degree of reproductive isolation necessary for considering two populations separate species 10-12

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Species The biological species concept has received strong criticism – A species has limits in space and time Refers to contemporary populations but ignores the species status of ancestral populations Species do not exist in groups of organisms that reproduce only asexually The amount of reproductive divergence necessary for considering two populations separate species may be disagreeable 10-13

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Species Evolutionary Species Concepts – Simpson proposed the evolutionary species concept in the 1940s Concept persists but with modification – An evolutionary species A single lineage of ancestor-descendant populations that maintains its identity from other such lineages and that has its own evolutionary tendencies and historical fate. – Definition accommodates both sexual and asexual forms 10-14

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Species Phylogenetic Species Concept – Phylogenetic species An irreducible (basal) grouping of organisms diagnosably distinct from other such groupings and within which there is a parental pattern of ancestry and descent. – Both asexual and sexual groups are covered 10-15

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Species – Main difference in practice between the evolutionary and phylogenetic species concepts – The latter emphasizes recognizing as separate species the smallest groupings of organisms that have undergone independent evolutionary change – Disagreement should not be considered discouraging – No one concept is comprehensive or final; All need to be understood to understand future concepts 10-16

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Species DNA barcoding –used to diagnose organisms to species using sequence information form a standard gene present in all animals 10-17

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Taxonomic Characters and Reconstruction of Phylogeny Major goal of systematics – Infer an evolutionary tree or phylogeny that relates all extant and extinct species – Accomplished by studying organismal features formally called characters that vary among species – Characters are any feature used to study variation within and among species Identified by observing patterns of similarity of morphological, chromosomal, and molecular features 10-18

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Taxonomic Characters and Reconstruction of Phylogeny Homology – Character similarity resulting from common ancestry Similarity does not always reflect common ancestry Homoplasy – Character similarity that misrepresents common descent 10-19

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Taxonomic Characters and Reconstruction of Phylogeny Using Character Variation to Reconstruct Phylogeny First step is to determine which variant form of each character occurred in the most recent common ancestor of the entire group The character state present in the common ancestor – Ancestral character state All other variant forms of the character arose later within the group – Evolutionarily derived character states 10-20

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Taxonomic Characters and Reconstruction of Phylogeny Polarity of a character – The ancestral/descendant relationships among the alternative states of a character in a particular group of organisms constitute the polarity of the character Outgroup comparison – Method used to examine the polarity of a variable character – Outgroup Group that is phylogenetically close but not within the group being studied Infer that any character state found both within the group being studied and the outgroup is ancestral for the study group 10-21

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Taxonomic Characters and Reconstruction of Phylogeny Organisms or species that share derived character states – Form subsets within the study group called a clade Derived character shared by members of a clade – Synapomorphy of that clade Syapomorphies are used as evidence of homology – Infers that a particular group of organisms forms a clade A clade corresponds to a unit of evolutionary common descent 10-22

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Taxonomic Characters and Reconstruction of Phylogeny Includes all descendants of a particular ancestral linage Pattern of derived states of characters within study group – Forms a nested hierarchy of clades within clades By identifying the nested hierarchy of clades or branches – Patterns of common descent can be formed 10-23

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Taxonomic Characters and Reconstruction of Phylogeny Cladogram – Nested hierarchy of clades To construct a phylogenetic tree – Additional information concerning ancestors, duration of lineages, and amount of evolutionary change must be included 10-24

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Taxonomic Characters and Reconstruction of Phylogeny Sources of Phylogenetic Information – Comparative Morphology Examines varying shapes and sizes of organismal structures, including their developmental origins Skull bones, limb bones, and integument (scales, hair and feathers ) Living specimens and fossils are used 10-26

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sources of Phylogenetic Information – Comparative Biochemistry Analyzes sequences of amino acids in proteins and nucleotides sequences in nucleic acids Recent studies show comparative biochemistry can be applied to fossils – Comparative Cytology Examines variation in number, shape and size of chromosomes Used almost exclusively on living organisms 10-27

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Theories of Taxonomy Two currently popular theories of taxonomy – Traditional Evolutionary Taxonomy – Phylogenetic Systematics (cladistics) A relationship between a taxonomic group and a phylogenetic tree or cladogram is important for both theories Relationship can take on one of three forms – Monophyly A monophyletic taxon includes the most recent common ancestor and all descendants of that ancestor 10-29

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Theories of Taxonomy – Paraphyly A taxon is paraphyletic if it includes the most recent common ancestor of all members of a group and some but not all descendants of that ancestor – Polyphyly A taxon is polyphyletic if it does not include the most recent common ancestor of all members of a group The group has at least two separate evolutionary origins 10-30

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Theories of Taxonomy Traditional Evolutionary Taxonomy The two main principles – Common descent – Amount of adaptive evolutionary change A particular branch on an evolutionary tree – Considered a higher taxon if it represents a distinct adaptive zone Distinct “way of life” – A taxon that represents an adaptive zone is a grade – Evolutionary taxa may be either monophyletic or paraphyletic Phenetic taxonomy – taxonomy should represent a more easily measured feature, overall similarity of organisms evaluated without regard to phylogeny 10-32

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Theories of Taxonomy Phylogenetic Systematics or Cladistics – Challenge to evolutionary taxonomy – Willi Hennig (1950) Emphasizes common descent and cladograms – Cladists avoid paraphyletic groups by defining a long list of sister groups to each more inclusive taxon

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Major Division of Life Aristotle’s two kingdom system – Included plants and animals – Unicellular forms were arbitrarily assigned to one of these kingdoms Haeckel (1866) – Proposed Protista for single-celled organisms R.H. Whittaker (1969) – Proposed a five-kingdom system to distinguish prokaryotes and eukaryotes Woese and coworkers – Proposed three monophyletic domains above kingdom level—Eucarya, Bacteria and Archaea—based on ribosomal RNA sequences

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Major Division of Life More revisions are necessary to clarify taxonomic kingdoms based on monophyly “Protozoa” – Do not form a monophyletic group “Protista” – Not a monophyletic kingdom, it is paraphyletic because this group does not contain all the descendants of its most recent common ancestor 10-38

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Major Subdivisions of the Animal Kingdom Traditional groupings based on embryological and anatomical characters Branch A (Mesozoa): phylum Mesozoa, the mesozoa Branch B (Parazoa): phylum Porifera, the sponges and phylum Placozoa Branch C (Eumetazoa): all other phyla 10-39

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Major Subdivisions of the Animal Kingdom – Grade I (Radiata): phyla Cnidaria, Ctenophora – Grade II (Bilateria): all other phyla Division A (Protostomia): characteristics in Figure 4.10 – Acoelomates: phyla Platyhelminthes, Gnathostomulida, Nemertea – Pseudocoelomates: phyla Rotifera, Gastrotricha, Kinorhyncha, Nematoda, Nematomorpha, Acanthocephala, Entoprocta, Priapulida, Loricifera – Coelomates: phyla Mollusca, Annelida, Arthropoda, Echiura, Sipuncula, Tardigrada, Onychophora 10-40

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Major Subdivisions of the Animal Kingdom Division B (Deuterostomia): characteristics in Figure 4.10 phyla Phoronida, Ectoprocta,Chaetognatha, Brachiopoda, Echinodermata, Hemichordata, Chordata 10-41

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Major Subdivisions of the Animal Kingdom Recent molecular phylogenetic studies have challenged traditional classification of Bilateria – Bilateria Protostomia: – Phyla Acoelomorpha, Chaetognatha – Lophotrochozoa: phyla platyhelminthes, Mesozoa, Nemertea, Rotifera, Gastrotricha, Acanthocephala, Mollusca, Annelida, Echiura, Sipuncula, Phoronida, Ectoprocta, Entoprocta, Gnathostomulida, Micrognathazoa, Brachiopoda – Ecdysozoa: phyla Kinorhyncha, Nematoda, Nematomorpha, Priapulida, Arthropoda, Tardigrada, Onychophora, Loricifera -Deuterostomia: – phyla Chordata, Hemichordata, Echinodermata 10-42

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