Available at http://planet.uwc.ac.za/nisl/Eco_people/Presentations/

Evolution: Patterns of Similarity and Divergence

Vanessa Couldridge

Richard Knight

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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

Classification of OrganismsClassification of Organisms

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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

Binomial NomenclatureBinomial Nomenclature

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GenusGenus SpeciesSpecies

Corresponding structures in different species are the result of a shared common ancestor

HomologyHomology

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Anatomical features in different species resemble each other, but did not arise from a common ancestry

Example: Spider leg and mammal leg

HomoplasyHomoplasy

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Non-homologous features share the same function, but not necessarily the same structure

Example: Fish gills and human lungs

AnalogyAnalogy

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Convergent evolution

Unrelated species become similar

Parallel evolution

Related species continue to evolve similar characteristics

Divergent evolution

Related species become dissimilar

Patterns of EvolutionPatterns of Evolution

Unrelated organisms evolve similar features and come to resemble one another

Example: Marsupials and placental mammals

Convergent EvolutionConvergent Evolution

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Thylacine (marsupial)Thylacine (marsupial) Golden jackal (mammal)Golden jackal (mammal)

Two or more species from a similar evolutionary history continue to evolve similar characteristics

Example: Social behaviour in bees, wasps and ants

Parallel EvolutionParallel Evolution

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Two or more species that share a common ancestor become progressively dissimilar due to differing environmental pressures

Example: Red fox and kit fox

Divergent EvolutionDivergent Evolution

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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

CladisticsCladistics

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CLADOGRAMCLADOGRAM

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

Cladistics: ExampleCladistics: Example

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

Retra

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CATCAT DOGDOG LIZARDLIZARDCOWCOWSEALSEAL

Finally, retractable claws in cats separates them from dogs

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

SystematicsSystematics

LUNGFISHLUNGFISHCOWCOW TROUTTROUT

CLADISTICCLADISTICCLASSIFICATIONCLASSIFICATION

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

SystematicsSystematics

LUNGFISHLUNGFISHCOWCOW TROUTTROUT

EVOLUTIONARYEVOLUTIONARYCLASSIFICATIONCLASSIFICATION

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

Systematic HierarchySystematic Hierarchy

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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)

Systematic HierarchySystematic Hierarchy

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FRUIT FLYFRUIT FLY

DomainDomain EukaryotaEukaryotaKingdomKingdom AnimaliaAnimaliaPhylumPhylum ArthropodaArthropodaSubphylumSubphylum HexapodaHexapodaClassClass InsectaInsectaSubclassSubclass PterygotaPterygotaOrderOrder DipteraDipteraSuborderSuborder BrachyceraBrachyceraFamilyFamily DrosophilidaeDrosophilidaeSubfamilySubfamily DrosophilinaeDrosophilinaeGenusGenus DrosophilaDrosophilaSpeciesSpecies melanogastermelanogaster