2. History
Taxonomists have sought to construct a system that
would reflect evolutionary relationships.
Use morphology to recognize and construct species
3. 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
4. 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.
5. 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.
6. 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
7.
8. 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.
9. 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
10. 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
14. Characters
Homoplasy
Similar characters in different taxa inferred to have arisen
through convergent evolution, not a common ancestor.
No use in cladistics
17. 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.
18. Monophyletic group
A group consisting of:
A common ancestor
All descendants of that common ancestor
19.
20.
21.
22.
23.
24. Paraphyletic group
A monophyletic grouping that certain descendent tax
have been removed from due to their possession of
additional synapomorphic characters.
25. 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
