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Chapter 16 ~ The Origin of Species. Macroevolution: the origin of new taxonomic groups. Speciation: the origin of new species

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Macroevolution: the origin of new taxonomic groups

  • Speciation: the origin of new species

  • 1- Anagenesis (phyletic evolution): A pattern of evolution that results in linear descent with no branching or splitting of the population - accumulation of heritable changes

  • 2- Cladogenesis (branching evolution): The evolutionary change and diversification resulting from the branching off of new taxa from common ancestral lineagesbudding of new species from a parent species that continues to exist (basis of biological diversity)


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What is a species?

  • Biological species concept:a population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring (genetic exchange is possible and that are reproductively isolated from other such populations)


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Reproductive Isolation (isolation of gene pools), I

  • Prezygotic barriers (Premating Isolation):impede mating between species or hinder the fertilization of the ova

  • Geographical (separation of populations by a physical barrier )

  • Behavioral (lack if interbreeding between pollutions of animals that differ in courtship and mating rituals)

  • Temporal (inability of populations to interbreed because of different breeding seasons)

  • Mechanical (inability of male and female organisms to exchange gametes because of incompatibility)

  • Ecological (lack of interbreeding between populations that occupy distinct habitats within the same general area)


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Reproductive Isolation, II

  • Postzygotic barriers( Post mating Isolation): fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult

  • Gametic Incompatibility – the inability of sperm from one population to fertilize eggs of another

  • Hybrid infertility - reduced hybrid fertility (mule; horse x donkey; cannot backbreed)

  • Hybrid inviability- the failure of a hybrid offspring of two different populations to survive (cotton; 2nd generation hybrids are sterile)


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Modes of speciation (based on how gene flow is interrupted)

  • Allopatric:populations segregated by a geographical barrier; can result in adaptive radiation when a species gives rise to many new species in relatively a short period of time (island species- when populations of a single species invade a variety of new habitats and evolve in response to the differing environmental pressures)

  • Little or no gene flow occurs and if pressures of natural selection differ in the separation locations, then populations may accumulate genetic differences


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Sympatric:reproductively isolated subpopulation in the midst of its parent population (change in genome); polyploidy in plants (the acquisition of multiple copies of each chromosome)

Modes of speciation (based on how gene flow is interrupted


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What causes Extinction?

Everglade Kite feeds exclusively on apple snail, found in swamps , such behavioral specialization renders the kite extremely vulnerable to any environmental changes

  • Extinction ~ natural phenomenon, however, rate is of concern…..

  • 50% loss of species when 90% of habitat is lost

  • Major Threats:

  • Habitat destruction ~ single greatest threat; cause of 73% of species designation as extinct, endangered, vulnerable, rare; 93% of coral reefs


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Competition by exotic (non-native) species ~ cause of 68% of species designation as extinct, endangered, vulnerable, rare; travel

Overexploitation ~ commercial harvest or sport fishing; illegal trade

Devils hole pup fish found only in one spring fed water hole in the Nevada Desert. As rainfall decreases pupfish population become isolated in shrinking streams and small springs

What causes Extinction?


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