Chapter 24

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Author:
kamrunsreno
ID:
171212
Filename:
Chapter 24
Updated:
2012-09-16 14:03:36
Tags:
Biology
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Exam 1
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  1. Speciation
    Occurs between micro- & macroevolution

    • • Microevolution
    • – Changes in allele frequency in a population
    • – Short time frame (generations)
    • – Ex. Mutation, selection, drift, gene flow

    • • Macroevolution
    • – Broad patterns over long time spans
    • – Origins of entire new groups of organisms
    • – Ex. Origin of mammals, flowering plants etc.

    The Formation of new species
  2. Biological Species Concept
    Species = populations that can interbreed and produce viable and fertile offspring

    • – New species form with reproductive isolation
    • • Different species may appear similar
    • • One species may have great diversity 
  3. Reproductive Isolation
    • Prevents two individuals from producing viable, fertile offspring
    • – Maintains existing species boundaries
    • – Can lead to the formation of new species

    • • Reasons for isolation:
    • – Prezygotic barriers
    • • Before formation of the zygote
    • – Postzygotic barriers
    • • After formation of the zygote
  4. Prezygotic Barriers: habitat
    • Two species rarely encounter each other
    • – Occupy different habitats

    • – Ex. Two species of snakes
    • • One species aquatic, one species terrestrial
    • • Unlikely to be in the same place
  5. Prezygotic Barriers: Temporal Isolation
    • Species that breed at different times
    • • Timeofday,differentseasons,ordifferentyears

    • – Ex. Spotted skunks
    • • One species mates in winter, one mates in summer
    • • Unlikely to be sexually active during same period
  6. Prezygotic Barriers: Behavioral Isolation
    Behavioral isolation

    – Courtship rituals and other behaviors unique to a species are effective barriers

    – Ex. Blue-footed boobies courtship display
  7. Prezygotic Barriers: Mechanical Isolation
    Mating attempted, but morphological differences prevent completion

    – Ex. Snail genital openings don’t align
  8. Prezygotic Barriers: Gametic Isolation
    Sperm of one species cannot fertilize egg of another species

    • • Sperm cannot survive in reproductive tract
    • • Sperm cannot penetrate the egg

    – Ex. Sea urchin egg/sperm proteins won’t fuse
  9. Postzygotic Barriers: Reduced Hybrid Viability
    Incompatible genes from parents interact and impair development and survival

    – Ex. Salamander hybrids that do not fully develop or are frail
  10. Postzygotic Barriers: Reduced Hybrid Fertility
    Reduced Hybrid Fertility

    – Vigorous hybrids produced, but are sterile

    • • Often due to chromosomal differences
    • – Chromosome #, chromosome structure

    –Ex. Donkey+HorseMule(sterile) 
  11. Postzygotic Barriers: Hybrid Breakdown
    Some first generation hybrids are viable and virile, but next generation are weak or sterile

    • • Often accumulate recessive disorder alleles
    • – Ex. Many plant strains 
  12. Mechanisms of allopatric speciation
    • Geographic barriers prevent gene flow
    • – Rivers, oceans, mountains, canyons etc. etc.
    • Ex. 24.6 Antelope squirrels & G. Canyon
    • Ex. 24.8 Shrimp species separated by isthmus
    • Ex. 24.9 Salamander reproductive isolation increases with distance 
  13. Sympatric Speciation
    • Occurs in populations with range overlap
    • Can arise from:

    • – Polyploidy
    • • Subpopulation with an extra set of chromosomes
    • – Habitat differentiation
    • • Subpopulation can exploit a new microhabitat
    • – Sexual selection (24.12)
    • • Ex. Subpopulation with different morphology
    • • New subpopulations no longer interbreed 
  14. Sympatric Speciation: Polyploidy
    • More common in plants
    • – Autopolyploidy

    • • Errors in cell division create new subpopulation within a single original species
    • – Allopolyploidy
    • • Hybridization between two species creates new subpopulation with different chromosome # 
  15. Rates of Speciation
    • Can occur at different rates
    • – Evidence of this in the fossil record
    • • Punctuated equilibrium
    • – Describes long periods of species stability followed by sudden change (rapid speciation)
    • • Gradual change over time also possible 

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