pathways of evolution. divergent & convergent pathways divergent evolution two or more species...
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Divergent & Convergent PathwaysDivergent & Convergent Pathways
Divergent 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.
Convergent Evolution• 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.
Coevolution – Working TogetherCoevolution – 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.
Phylogeny – What it is…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?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 CladisticsApplying 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 CladisticsApplying Cladistics
Hair Lungs Bony Shell
Grasping Hands
Jaws
Lamprey - - - - -
Turtle - + + - +
Gorilla + + - + +
Lungfish - + - - +
Pike - - - - +
Wolf + + - - +
Human + + - + +
Applying Genetic EvidenceApplying 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-UpThe 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.