Lecture 22 Flashcards
Carolus Linnaeus
The founder of taxonomy
* Binomial nomenclature
* Hierarchical system
of classification
kingdoms
phyla
classes
orders
families
genera
species
What is the Purpose
of a Biological Classification?
Name is a key to shared information on
an organism
* Therefore has predictive power
* Enables interpretation of origins and
evolutionary history
Taxon
single named taxonomic unit at any level
– Plural = taxa
kingdoms
phyla
classes
orders
families
genera
species
Taxonomy
The theory and practice of classification &
naming
Systematics
The study of biodiversity and the evolutionary
relationships among organisms
Terminal nodes
Taxa
Terminal branches
Accumulated
evolutionary change
Internal nodes:
Common ancestors
* Speciation
Internal branches
Accumulated
evolutionary change
Why Conduct Phylogenetic Analysis?
- Understand history of life
- Understand large-scale patterns of evolution
- Understand how many times traits have evolved,
how fast, under what conditions - Practical:
- Where/when did parasites spread?
- Which flu strain was the most successful
last year? - What are the driver mutations as SARS-
COV-2 evolves?
Understanding Phylogenetic Trees
Different relationships among taxa on trees
represent different hypotheses or conclusions
about evolutionary history
Monophyletic group
includes the complete set
of species derived from a common ancestor
- single ancestor gave rise to all
species in that taxon and no species in
any other taxon
Paraphyletic group
contains some, but not all
species derived from a common ancestor
- A taxon whose members are derived
from two or more ancestral forms not
common to all members
Phylogenies as a Forensic Record
Species that share a more recent common ancestor
tend to be more similar
* Descent with modification
A critical step in the reconstruction
of phylogenetic history is
the identification and distinction of
ancestral and derived traits.
Ancestral trait = A trait shared with
a common ancestor
* Derived trait = A trait that differs from
the ancestral trait in a lineage
Homology & Homoplasy
Homology
* Similarity of traits due to shared ancestry
Homoplasy
* Similarity of traits as a result of convergent
evolution
Convergent Evolution
- The independent evolution of structures
that resemble one another and
perform similar functional roles due to the
shared ecology of unrelated organisms
Convergent Evolution in Cichlid Fishes
of the African Great lakes
Independent
evolutionary radiations
in two lakes
* Similarity in form
indicates convergence
in feeding strategies
Why Is Molecular Biology Relevant
to Evolution & Phylogeny?
All life is related through branching descent
* Common genetic code is evidence that all
life is related
* Evolutionary relationships among species
are reflected in their DNA and proteins
– Learning about protein function in one species
can tell us about its function in others
– Mice, rats, flies, worms Humans
Inferring Species Relationships
from DNA Sequences
Genes or parts of a gene can be sequenced
for different species
* Species can be assessed for changes in
the sequence of nucleotides
* Changes can be used to infer relationships
in a branching diagram (phylogeny)
Using Phylogenies to Understand
the Origin and Evolution of Traits
Origin of a novel trait resulting in
adaptive radiation
* Carriers of the trait can exploit new
resources or sets of habitats
* Usually associated with rapid evolutionary
diversification (e.g. adaptive radiations)
Origin of Traits Associated with
Increased Diversification Rate
Diversification = Speciation – Extinction
* Key innovation could increase speciation or
decrease extinction to influence net diversification
Why Do Some Groups
Have More Species Than Others?
Use of replicate “sister group” comparisons
- With one phylogenetic comparison, it is difficult to say
a key trait is involved
* Replicate comparisons of multiple groups adds more
evidence
Herbivory Associates with Higher Diversification Rate
Coevolution between insects and plants
likely drives higher rates of speciation in herbivores
Other Features Associated with
Greater Diversification
- Species with sexual reproduction
- Outcrossing species
- Animal pollination in plants
- Increased dispersal
