Download - Evolutionary biology
Evolutionary Biology: Phylogeny and Cladistics
History
Taxonomists have sought to construct a system that would reflect evolutionary relationships. Use morphology to recognize and construct
species
History Grande (2004)
Proposes that we view morphology and morphological variations 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 how most individuals have been compared. Biological Species
Sexually interbreeding or potentially interbreeding group of individuals normally separated from other species by the 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 common ancestry for the same genotype.
Parallelism 2 species with the same phenotype descended from a
common ancestor w/ different phenotype and genotype Convergence
2 species with the same phenotype whose common ancestor is very far in the distant past.
What is Cladistics? Method of hypothesizing evolutionary
relationships among organisms.
Based upon the analysis of traits shared by organisms.
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 a common ancestor
There is a bifurcating or branching pattern of lineage and splitting.
The Principle of Parsimony The principle of parsimony reasons that given
several solutions to a problem, the simplest one should 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 the available data
Understanding Cladogram The root of Cladogram represents the
ancestral lineage and the tips the descendants.
Branching points in the cladograms are called nodes and represents speciation events.
Part of each lineage’s history is unique to it alone.
Each lineage has ancestors that are unique and ancestors that are shared with other lineages.
A B C D E F
TIME
speciation
Cladogram or Phylogenetic Tree
TAXA
Understanding Cladograms Clade: a group comprising an ancestral
lineage and all its descendant lineages.
Characters Inheritable feature of an organism.
Physical characteristics (morphology) Genetic sequences Behavioral traits
Characters Homologous characters
A character possessed by two or more organisms due to their sharing of a common ancestor.
Characters Homoplasy
Similar characters in different taxa inferred to have arisen through convergent evolution, not a common ancestor.
No use in cladistics
euphorb spines
cactus spines
Plesiomorphy Considered to be ancestral or less derived
Apomorphy Features considered to be derived from an
ancestral clade 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 tax have been removed from due to their possession of additional synapomorphic characters.
Constructing a Cladogram Outgroup Method
Works by identifying tow groups of taxa Ingroup: group being studies Outgroup: for the establishment of plesomorphic and
apomorphic character states in the ingroup The outgroup should comprise taxa closely related
to the ingroup so homologous characters can be established
Character states and Character Matrix
notochord vertebrae jaws skull lung enamel 4 true limbs
Outgroup 0 0 0 0 0 0 0
Tunicate 1 0 0 0 0 0 0
lamprey 1 1 0 1 0 0 0
Cladoselache 1 1 1 1 0 0 0
trout 1 1 1 1 1 0 0
lungfish 1 1 1 1 1 1 0
present 1
absent 0