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Evolutionary biology

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Evolutionary biology

  1. 1. Evolutionary Biology: Phylogeny andCladistics
  2. 2. History Taxonomists have sought to construct a system thatwould reflect evolutionary relationships. Use morphology to recognize and construct species
  3. 3. History Grande (2004) Proposes that we view morphology and morphologicalvariations in three ways Taxonomic Ontogenic Individual Ability to interbreed Biological species concept  Evolutionary species concept
  4. 4. Species Concept Morphological Species Generally used morphological criteria because this is howmost individuals have been compared. Biological Species Sexually interbreeding or potentially interbreeding groupof individuals normally separated from other species bythe absence of genetic exchange. Evolutionary Species species as an evolutionary entity.
  5. 5. Phylogeny Species evolve from existing species. Classification of species Homology 2 species bearing the same phenotype caused by commonancestry for the same genotype. Parallelism 2 species with the same phenotype descended from a commonancestor w/ different phenotype and genotype Convergence 2 species with the same phenotype whose common ancestor isvery far in the distant past.
  6. 6. What is Cladistics? Method of hypothesizing evolutionary relationshipsamong organisms. Based upon the analysis of traits shared byorganisms. Cladogram: represents evolutionary relationships. Willi Hennig 1950 German zoologist
  7. 7. Assumptions of Cladistics The Characteristics of organisms change over time. All organisms are related by a descent from acommon ancestor There is a bifurcating or branching pattern of lineageand splitting.
  8. 8. The Principle of Parsimony The principle of parsimony reasons that givenseveral solutions to a problem, the simplest oneshould be accepted. The principle of parsimony does not: Provide absolute truth Necessarily reveal the true phylogeny The principle of parsimony does: Reduce conjecture Indicates those cladistic groupings best supported by theavailable data
  9. 9. Understanding Cladogram The root of Cladogram represents the ancestrallineage and the tips the descendants. Branching points in the cladograms are called nodesand represents speciation events. Part of each lineage’s history is unique to it alone. Each lineage has ancestors that are unique andancestors that are shared with other lineages.A B C D E FTIMEspeciationCladogram or Phylogenetic TreeTAXA
  10. 10. Understanding Cladograms Clade: a group comprising an ancestral lineage andall its descendant lineages.
  11. 11. Characters Inheritable feature of an organism. Physical characteristics (morphology) Genetic sequences Behavioral traits
  12. 12. Characters Homologous characters A character possessed bytwo or more organisms dueto their sharing of acommon ancestor.
  13. 13. Characters Homoplasy Similar characters in different taxa inferred to have arisenthrough convergent evolution, not a common ancestor. No use in cladistics
  14. 14. euphorbspinescactusspines
  15. 15.  Plesiomorphy Considered to be ancestral or less derived Apomorphy Features considered to be derived from an ancestralclade Synapomorphy An apomorphic feature that defines a clade.
  16. 16. Monophyletic group A group consisting of: A common ancestor All descendants of that common ancestor
  17. 17. Paraphyletic group A monophyletic grouping that certain descendent taxhave been removed from due to their possession ofadditional synapomorphic characters.
  18. 18. Constructing a Cladogram Outgroup Method Works by identifying tow groups of taxa Ingroup: group being studies Outgroup: for the establishment of plesomorphic andapomorphic character states in the ingroup The outgroup should comprise taxa closely related to theingroup so homologous characters can be established
  19. 19. Character states and Character Matrixnotochord vertebrae jaws skull lung enamel 4 true limbsOutgroup 0 0 0 0 0 0 0Tunicate 1 0 0 0 0 0 0lamprey 1 1 0 1 0 0 0Cladoselache 1 1 1 1 0 0 0trout 1 1 1 1 1 0 0lungfish 1 1 1 1 1 1 0present 1absent 0

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