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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 - - - - - Turtle - + + - + Gorilla + + - + + Lungfish - + - - + Pike - - - - + Wolf + + - - + Human + + - + + 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