1. Speciation & Macroevolution
Packet #61
Chapter #24
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2. Introduction Species Biological Species Concept
The concept of distinct kinds of organisms.
Derived from Latin meaning “kind”
Biological Species Concept
Introduced by Ernst Mayr in 1942
Species consists of one ore more populations whose members interbreed in nature to produce fertile offspring and do not interbreed with members of a different species
Problem
Applies to sexually reproducing organisms
Sometimes, there is successful interbreeding
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3. Introduction II Evolutionary Species Concept
Aka Phylogenetic Species Concept
In order to be declared as a separate species, a population must have undergone “evolution” long enough for statistically significant differences in diagnostic traits to emerge.
Not all species have been studied at this level
If totally embraced, the number of species would probably double
Why?
The increase would occur because many closely related populations that are classified as subspecies or varieties under the biological species concept would fit the requirements of separate species under the evolutionary species concept.
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4. REPRODUCTIVE BARRIERS & SPECIATION
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5. Reproductive Barriers
Restrict of gene flow between species.
Possible “evolutionary” mechanism that explain how the millions of species originated from ancestral species and the rates of evolutionary change
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6. REPRODUCTIVE ISOLATING MECHANISMS
Prezygotic Barriers
REPRODUCTIVE ISOLATING MECHANISMS
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7. Prezygotic Barriers
Reproductive isolating mechanisms that prevent fertilization from taking place
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8. Prezygotic Barriers
Reproductive isolating mechanisms that prevent fertilization from taking place
Temporal Isolation
Two species reproducing at different times of the day, season or year
Habitat Isolation
Two closely related species that live and breed in different habitats in the same geographic area
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9. Prezygotic Barriers II
Behavioral Isolation
Distinctive courtship behaviors prevent mating between species
Mechanical Isolation
Incompatible structural differences in reproductive organs of similar species
Gametic Isolation
Gametes of different species are incompatible
Egg and sperm cannot unite
Due to molecular and chemical differences
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10. Figure 24.4
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11. REPRODUCTIVE ISOLATING MECHANISMS
Postzygotic Barriers
REPRODUCTIVE ISOLATING MECHANISMS
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12. Postzygotic Barriers Definition
Reproductive isolating mechanisms that prevent gene flow after fertilization has taken place
Generally, the embryo of an interspecific hybrid, the result of mating between different animal species, spontaneously aborts.
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13. Postzygotic Barriers II
Hybrid Inviability
Death of interspecific embryos during development.
Eggs of bullfrog fertilized with sperm of leopard frog
Hybrid Sterility
Prevents interspecific hybrids that survive adulthood from reproducing successfully
Problems occurring during meiosis
Common in parents that have different chromosome numbers
Offspring of female horse (2n = 64) with male donkey (2n = 62)
Offspring is sterile with ploidy of 2n = 63
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14. Postzygotic Barriers III
Hybrid Breakdown
Prevents offspring of hybrids that survive to adulthood and successfully reproduce, from reproducing beyond one or a few generations.
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15. Post zygotic Barriers Postzygotic Barriers Hybrid Inviability
Death during development
Hybrid Sterility
Surviving hybrids cannot are sterile
Hybrid Breakdown
Hybrids that are able to reproduce are only able to sustain a few generations
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16. SPECIATION
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17. Speciation
The “evolution” of a new species from an ancestral population
More likely to occur when the population is small.
There are two types
Allopatric speciation
Sympatric speciation
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18. Allopatric Speciation
One population becoming geographically isolated from the rest of the species
Eventually leading to divergent evolution
Death valley pupfish
Kaibab squirrels
Porto Santo rabbits
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19. Sympatric Speciation
New species “evolves” within the same geographic region
Divergence of two or more populations, from a single parent species in the same geographic region, occurs when reproductive isolating mechanisms evolve.
Common in plant species
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20. Sympatric Speciation II
Plants
Results from allopolyploidy
Polyploid individual (organisms in possession of more than two sets of chromosomes) is a hybrid derived from two species
Reproductive isolation occurs when polylpoidy organism arise from diploid (2n) parents
Autopolyploid
Multiple sets of chromosomes from single species
Allopolyploid
Multiple sets of chromosomes from two or more species
Much more common in nature
Extremely rare in animals
As many as 80% of flowering species are polyploids
Provides mechanism for rapid speciation
Kew primroses and hemp nettles
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21. Sympatric Speciation III
For allopolyploids to be established as a new species, selective pressures cause one of three outcomes
New species may not compete successfully with species already established
May assume new role in the environment and co-exist with both parental species
New species may successful compete with either or both parental species
Traits confer greater fitness
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22. Sympatric Speciation III
Animals
How sympatric speciation occurs—remains to be determined
Fruit maggot flies and cichlids
Homework
What are some of the hypotheses proposed by scientists?
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23. RATE OF “EVOLUTIONARY” CHANGE
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24. Theories Punctuated Equilibrium Gradualism
Evolution of species that occur in spurts
Short periods of active speciation are interspread with long periods of stasis.
Gradualism
Populations diverge slowly from one another by the accumulation of adaptive characteristics within a population.
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25. MACROEVOLUTION
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26. Macroevolution I Definition
Large-scale phenotypic changes in populations that warrant their placement (species) in taxonomic groups at the species level and higher. (new taxons)
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27. Macroevolution II
Appearance of evolutionary novelties may be due to changes that occurred during development
Changes in regulatory genes could cause structural changes in the organism.
Allometric Growth
Varied different rates of growth for different parts of the body
Result in a change in the overall shape of an organism
Paedomorphosis
Retention of juvenile characteristics in the adult
Occurs to changes in the timing of development
Adult axolotl salamanders with external gills and tail fins
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28. Macroevolution III Preadaptation
Variations in structures that were pre-existing
Development of homologous structure
Structures that originally fulfilled one role but changed in a way that was adaptive for a different role.
Feathers
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29. Macroevolution IV Adaptive Radiation Extinction
Process of diversification of an ancestral species into many new species.
Species taking advantage of adaptive zone(s), ecological opportunities, that were not used by their predecessors.
Extinction
Death of a species
Adaptive zones once occupied become vacant
Background extinction
Continuous low level extinction of species
Mass extinction
Extinction of numerous and higher taxonomic groups in both terrestrial and marine environments
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30. Macroevolution Preadaptation Adaptive Radiation Macroevolution
Extinction
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31. REVIEW
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