Transcript Pathways of Evolution

Pathways of Evolution
Divergent & Convergent Pathways
Divergent Evolution
Convergent Evolution
• Two or more species
evolve increasingly
different traits.
• Disruptive selection
may be the precursor.
• Adaptive radiation –
More than two species
resulting from one original
species – a la Darwin’s
finches.
• Two or more species
become increasingly
similar.
• Homoplasies – similar
traits in different species
of uncommon descent.
• The marsupials of
Australia and placental
mammals demonstrate
this. Page 603 – Figure 2
• The shark and the
dolphin converge as well.
Divergent Evolution
Convergent Evolution
Coevolution – Working Together
• Coevolution occurs when one species evolves
in response to the evolution of another species.
• The fig and the fig wasp – the flower depends on
the fig wasp for pollination while the wasp
requires the flower to reproduce.
• Leaf-cutter ants and fungus – the ants bring leaf
pieces to feed the fungus which is eaten by the
ants. Only home for fungus and sole food source
of ants.
Coevolution – Working Together
FIN
Phylogenetic
Relationships
Phylogeny – What it is…
• Phylogeny is the theoretical evolutionary
history of a species – your ancestry.
• Monophyletic group or clade Organisms that belong to the same group
(descendants from a common ancestor).
• These evolutionary relationships can be
illustrated using a phylogenetic tree or
cladogram. These are constructed using
a system of classification based on shared
derived traits called cladistics.
What does “cladistics” do?
• Cladistics uses synapomorphies to construct
cladograms or phylogenetic trees.
• Synapomorphies are shared traits that evolved
only once and have been inherited by two or
more related species.
• The greater number of shared derived traits two
species have, the more closely related they are
in terms of evolutionary history.
Applying Cladistics
• When using cladistics to separate a number of
organisms into separate clades, you must
establish an “outgroup” based on the organisms
being studied.
• The “outgroup” is the first group to have
diverged from the other groups of a clade.
• See the next slide in this presentation…
• Lets go over the construction of this cladogram
together – it uses a variety of members of the
Kingdom Animalia.
Applying Cladistics
Hair
Lungs
Bony
Shell
Grasping
Hands
Jaws
Lamprey
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Turtle
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Gorilla
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Lungfish
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Pike
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Wolf
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Human
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Another Fine Cladogram Example
Applying Genetic Evidence
• Genetic sequences or protein (amino acid)
sequences can also be used to indicate the
evolutionary relationship between two species.
• Why?
• Follow this thought…
– Evolution based on characteristic changes.
– Characteristics based on DNA sequences
– DNA  RNA  Pn
• Therefore, the less differences there are in
amino acid and DNA sequences, the more
closely related two species will be.
The Phylogenetic Wrap-Up
• DNA mutates over time – the sequence of nucleotides
changes and the protein’s amino acid sequence may
change (not always due to codon overlaps).
• The further back in time you have diverged, the more
mutations have occurred – this means you will have
more differences in your codes & sequences.
• Few differences means you have just recently split and
there has not been a lot of time for your codes &
sequences to become all that different from one another
yet.
• The greater the number of differences = the further back
in time your divergence occurred.
FIN