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PHYLOGENY AND SYSTEMATICS

PHYLOGENY AND SYSTEMATICS. A little bit about taxonomy, classification and phylogeny. Systematics - study of the diversity and relationships of organisms both now and in the past. Taxonomy - classification, naming and description of taxa.

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PHYLOGENY AND SYSTEMATICS

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  1. PHYLOGENY AND SYSTEMATICS

  2. A little bit about taxonomy, classification and phylogeny Systematics - study of the diversity and relationships of organisms both now and in the past. Taxonomy - classification, naming and description of taxa. Phylogeny - The evolutionary development and history of a species or higher taxonomic grouping of organisms.

  3. Evolutionary systematics Phenetics Cladistics Methods of establishing phylogenies Evolutionary systematics - use several fixed levels of a hierarchy, such as kingdom, phylum, class, order, and family.

  4. Evolutionary systematics Phenetics Cladistics Methods of establishing phylogenies Phenetics (numerical taxonomy) - based on taking lots of measurements on organisms & then using computer algorithms to assign relationships among them Robert R. Sokal Problems - ignored ancestral vs. derived characteristics C.D. Michener

  5. Evolutionary systematics Phenetics Cladistics Methods of establishing phylogenies Cladistics - classifies species of organisms into hierarchical monophyletic groups (clades) - based on shared derived characteristics (or characters) Willi Hennig Basic idea - members of a group (clade) share a common evolutionary history - share unique features that are not present in distant ancestors Shared derived characteristics - synapomorphies

  6. Important to separate shared derived characters from just shared. Jelly fish Starfish Human Invertebrate ✔✔✗ Vertebrate ✗✗✔ Water living ✔✔✗ Radial symmetry ✔✔✗ ✔

  7. ASSUMPTIONS OF CLADISTICS 11. Any group of organism are related by common descent from a common ancestor (clade) 2. There is a bifurcating pattern of cladogenesis. 3. Change in characteristic occurs in lineages over time.

  8. Clades - Can be nested Clade 1 Clade 2 Clade 3

  9. Evolutionary systematics Phenetics Cladistics Methods of establishing phylogenies Some definitions Plesiomorphy -or ancestral character that is present at the base of the tree. For example, the presence of a dorsal nerve chord(shared by all chordates) can be hypothesized to have existed in some common ancestor. Apomorphy - derived state is a characteristic believed to arisen in a recent common ancestor or a recently evolved feature that appears only in a group of closely related species. The hair of mammals serves to separate them from all other vertebrates

  10. HOW TO CONSTRUCT A CLADOGRAM 1. Choose taxa – must be clades 2. Determine which characters to use - examine each taxon to determine character states (i.e does the taxon have each character) 3. Determine polarity of character state (i.e. is character state original or derived) 4. Group taxa based on synapomorphies (shared derived characters) 5. Build cladogram according to the following rules: i. All taxa go at endpoints of cladogram ii. Nodes must have a list of synapomorphies common to all taxa above the node iii. Synapomorphies should appear only once

  11. A SAMPLE CLADOGRAM Species A Species B Species C Species D Node 3 Node 2 Node 1

  12. CAMINACULES

  13. CAMINACULES

  14. CAMINACULES ‘ ‘ 5. Front appendages with ’toes’ 4. Colour pattern on abdomen 3. 1 pair of front appendages 6. Toes are rounded 7. Front appendage jointed 2. Front appendages 1. body divided into head and thorax

  15. TYPES OF CLADOGRAMS

  16. Methods of establishing phylogenies Paraphyletic groups - contain ancestor and some but not all descendant species Polyphyletic groups - contain taxa from two or more different monophyletic groups Monophyletic groups - contain ancestor and all descendant species Sister group (or outgroup)

  17. WHAT KINDS OF CHARACTERS ARE USED? A. Structural, physiological, behavioural i. Traits expressed in development ii. In juveniles iii. In adults B. Molecular data i. Amino acid substitutions in proteins ii. Genomic genes and gene products iii. Mitochondrial genes

  18. KINDS OF TRAITS 1. Ancestral ✔ 2. Derived ✔ 3. Homologous traits - traits derived from same ancestral trait (e.g. limbs in arthropods) 4. Homoplastic traits - traits resemble but not due to common ancestry (e.g. reduction in size to exploit boundary layer)

  19. Having said all this …….. There is always some dispute about the relationships in a cladogram. These were all derived from the same data set Chelicerata Chelicerata Crustacea Myriapoda Myriapoda Crustacea Hexapoda Hexapoda Chelicerata Chelicerata Crustacea Myriapoda Crustacea Myriapoda Hexapoda Hexapoda

  20. Problems with this phylogeny?

  21. Four Major Evolutionary Trends 1. Evolution of multicellularity and the Metazoa 2. Evolution of triploblastic phyla 3. Evolution of the Arthropoda 4. Evolution of Echinodermata and Urochordata

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