Species and SpeciationSpecies and Speciation

ALBIO9700/2006JK

Species:Species:• A group of organisms, with similar A group of organisms, with similar

morphologicalmorphological, , physiologicalphysiological, , biochemicalbiochemical and and behaviouralbehavioural features, features, which can which can interbreed to produce fertile interbreed to produce fertile offspringoffspring, and are , and are reproductively reproductively isolatedisolated from other species from other species

ALBIO9700/2006JK

ALBIO9700/2006JK

ClassificationClassification• TaxonomyTaxonomy – the study of the classification – the study of the classification

of organismsof organisms

• Homologous featuresHomologous features – shared features – shared features between different organismsbetween different organisms

• BinomialBinomial – two-word Latin name for every – two-word Latin name for every speciesspecies

• Phylogeny Phylogeny – the evolutionary history of – the evolutionary history of living organismsliving organisms

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Classification (cont)Classification (cont)

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New species usually develop due New species usually develop due to:to:

• geographical isolation geographical isolation

((allopatric speciationallopatric speciation) )

• reproductive isolation reproductive isolation ((sympatric speciationsympatric speciation) )

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Allopatric speciationAllopatric speciation

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Start with an Start with an interbreeding interbreeding populationpopulation of one species. of one species. 

                     

The population becomes The population becomes divided divided by a physical barrierby a physical barrier such as such as water, mountains, desert, or just a water, mountains, desert, or just a large distance. This can happen large distance. This can happen when some of the population when some of the population migrates or is dispersed, or when migrates or is dispersed, or when the geography changes the geography changes catastrophically (e.g. earthquakes, catastrophically (e.g. earthquakes, volcanoes, floods) or gradually volcanoes, floods) or gradually (erosion, continental drift). (erosion, continental drift).

                     

If the two environments (abiotic or If the two environments (abiotic or biotic) are different (and they almost biotic) are different (and they almost certainly will be), then the two certainly will be), then the two populations will experience different populations will experience different selection pressures and will evolve selection pressures and will evolve separately. Even if the environments separately. Even if the environments are similar, the populations may are similar, the populations may change by random genetic drift, change by random genetic drift, especially if the population is small.especially if the population is small.

                     

Even if the barrier is removed and the Even if the barrier is removed and the two populations meet again, they are two populations meet again, they are now so different that they can no now so different that they can no longer interbreed. They are therefore longer interbreed. They are therefore reproductively isolated and are two reproductively isolated and are two distinct species. They may both be distinct species. They may both be different from the original speciesdifferent from the original species, , if it still exists elsewhere.if it still exists elsewhere.

                     

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Sympatric speciationSympatric speciation• Genetic isolationGenetic isolation

• Formation of a new species can take place in the Formation of a new species can take place in the same geographical areasame geographical area, e.g. mutations may result , e.g. mutations may result in in reproductive incompatibilityreproductive incompatibility

• A new gene producing, say, a hormone, may lead an A new gene producing, say, a hormone, may lead an animal to be rejected from the mainstream group, but animal to be rejected from the mainstream group, but breeding may be possible within its own groups of breeding may be possible within its own groups of variantsvariants

• When this mechanism results in the production of a When this mechanism results in the production of a new species it is known as new species it is known as sympatric speciationsympatric speciation

• Polyploidy, autopolyploid, allopolyploids?Polyploidy, autopolyploid, allopolyploids?

ALBIO9700/2006JK