Pathways of Evolution. Divergent & Convergent Pathways Divergent Evolution Two or more species evolve increasingly different traits. Disruptive selection.

Pathways of EvolutionPathways of Evolution

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.

Divergent EvolutionDivergent Evolution

Convergent EvolutionConvergent Evolution

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.

Coevolution – Working TogetherCoevolution – Working Together

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Phylogenetic Phylogenetic RelationshipsRelationships

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 + + - + +

Another Fine Cladogram ExampleAnother Fine Cladogram Example

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.

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