Evolutionary biology
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Evolutionary biology

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    Evolutionary biology Evolutionary biology Presentation Transcript

    • Evolutionary Biology: Phylogeny andCladistics
    • History Taxonomists have sought to construct a system thatwould reflect evolutionary relationships. Use morphology to recognize and construct species
    • 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
    • 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.
    • 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.
    • 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
    • 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.
    • 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
    • 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
    • Understanding Cladograms Clade: a group comprising an ancestral lineage andall its descendant lineages.
    • Characters Inheritable feature of an organism. Physical characteristics (morphology) Genetic sequences Behavioral traits
    • Characters Homologous characters A character possessed bytwo or more organisms dueto their sharing of acommon ancestor.
    • Characters Homoplasy Similar characters in different taxa inferred to have arisenthrough convergent evolution, not a common ancestor. No use in cladistics
    • euphorbspinescactusspines
    •  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.
    • Monophyletic group A group consisting of: A common ancestor All descendants of that common ancestor
    • Paraphyletic group A monophyletic grouping that certain descendent taxhave been removed from due to their possession ofadditional synapomorphic characters.
    • 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
    • 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