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
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