Evolution: Patterns of Similarity and Divergence

1. Evolution: Patterns of Similarity and Divergence Vanessa Couldridge Richard Knight http://en.wikipedia.org/wiki/Image:Darwins_first_tree.jpg

2. Classification of Organisms • Species are grouped according to their similarity or evolutionary history • First performed by Linnaeus on the basis of physical characteristics • Molecular techniques more widely used today http://en.wikipedia.org/wiki/Image:Carolus_Linnaeus_%28cleaned_up_version%29.jpg

3. Binomial Nomenclature • Assignment of a unique two part scientific name to each species of organism • Example: Homo sapiens • Scientific name is written in italics and the genus name begins with a Capital Letter • Can be abbreviated, e.g. H. sapiens and H. habilis • Homo sp. means a single species in the genus Homo • Homo spp. means more than one species in the genus Homo Genus Species http://www.msu.edu/~heslipst/contents/ANP440/images/Skhul_5.jpg

4. Homology http://en.wikipedia.org/wiki/Image:Evolution_pl.png • Corresponding structures in different species are the result of a shared common ancestor

5. Homoplasy • Anatomical features in different species resemble each other, but did not arise from a common ancestry • Example: Spider leg and mammal leg http://en.wikipedia.org/wiki/Image:Brachypelma_Smithii.jpg http://en.wikipedia.org/wiki/Image:Legs.jpg

6. Analogy • Non-homologous features share the same function, but not necessarily the same structure • Example: Fish gills and human lungs http://interactive.usask.ca/Ski/media/stills/fisheries/t_fish_gills01.jpg http://www.wpclipart.com/medical/anatomy/lungs_diagram.png

7. Patterns of Evolution • Convergent evolution • Unrelated species become similar • Parallel evolution • Related species continue to evolve similar characteristics • Divergent evolution • Related species become dissimilar

8. Convergent Evolution • Unrelated organisms evolve similar features and come to resemble one another • Example: Marsupials and placental mammals http://en.wikipedia.org/wiki/Image:Golden_Jackal_sa02.jpg http://en.wikipedia.org/wiki/Image:Thylacine.jpg Thylacine (marsupial) Golden jackal (mammal)

9. Parallel Evolution • Two or more species from a similar evolutionary history continue to evolve similar characteristics • Example: Social behaviour in bees, wasps and ants http://en.wikipedia.org/wiki/Image:Bee_swarm_on_fallen_tree03.jpg http://en.wikipedia.org/wiki/Image:Oecophylla.jpg

10. Divergent Evolution • Two or more species that share a common ancestor become progressively dissimilar due to differing environmental pressures • Example: Red fox and kit fox http://en.wikipedia.org/wiki/Image:Vulpes_macrotis_standing.jpg http://en.wikipedia.org/wiki/Image:Vulpes_vulpes_sitting.jpg

11. Cladistics flowering plants spikemosses clubmosses quillworths ferns CLADOGRAM • Method of classifying organisms according to common ancestry, based on their dichotomous branching in an evolutionary tree • Uses shared derived characteristics • Tree of relationships is called a cladogram • Subset of related organisms is called a clade

12. Cladistics: Example CAT DOG SEAL COW LIZARD Retractable claws Carnassial teeth Hair Involuted cheek teeth • Cladogram of five vertebrates: lizard, cow, seal, dog, cat • The presence of hair can be used as the first branching point to separate the lizard from the others • The presence of involuted cheek teeth in the cat, dog and seal, but not the cow, determines the next branching point • The cat and dog can be separated from the seal based on the presence of carnassial teeth • Finally, retractable claws in cats separates them from dogs

13. Systematics • Method of classification that takes into account: • Splitting of branches in the phylogenetic tree • Major evolutionary changes • Systematics differs to cladistics in that it weighs derived characters according to their degree of evolutionary significance, whereas cladistics treats all derived characters equally

14. Systematics COW LUNGFISH TROUT CLADISTIC CLASSIFICATION COW LUNGFISH TROUT EVOLUTIONARY CLASSIFICATION • Consider the relationship between the cow, lungfish and trout as an example • In the cladistic approach, cows and lungfish are more closely related to each other than either is to the trout, because they share a novel feature (internal nares) • In the systematic approach, the lungfish and the trout are more closely related to each other than either is to the cow, because the cow is a mammal and the other two are both fishes

15. Systematic Hierarchy • Organisms classified according to a series of ranks that become progressively less inclusive • Originally proposed by Linnaeus, who identified • Three kingdoms: • Animal, vegetable, mineral • Five ranks: • Class, order, genus, species, variety http://en.wikipedia.org/wiki/Image:Systema_Naturae_cover.jpg

16. Systematic Hierarchy • Eight major ranks: Domain Kingdom Phylum Class Order Family Genus Species • Classification may be further divided, for example, superorder (above order) and suborder (below order) FRUIT FLY DomainEukaryota KingdomAnimalia PhylumArthropoda SubphylumHexapoda ClassInsecta SubclassPterygota OrderDiptera SuborderBrachycera FamilyDrosophilidae SubfamilyDrosophilinae GenusDrosophila Speciesmelanogaster http://en.wikipedia.org/wiki/Image:55542main_maflies_med.jpg