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Chapter 24 ~Macroevolution Origin of Species

Chapter 24 ~Macroevolution Origin of Species. What is a species?. A population whose members have the potential to interbreed and produce viable, fertile offspring. Horse. +. Zebra. Zorse = not-fertile. Patterns of Evolution. Divergent Evolution

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Chapter 24 ~Macroevolution Origin of Species

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  1. Chapter 24 ~Macroevolution Origin of Species

  2. What is a species? A population whose members have the potential to interbreed and produce viable, fertile offspring Horse + Zebra Zorse = not-fertile

  3. Patterns of Evolution Divergent Evolution • 2 or more species originate from a common ancestor

  4. Patterns of Evolution Convergent Evolution • 2 unrelated species share similar traits due to adaptation to similar environments • Unrelated species will never evolve into a single species

  5. Patterns of Evolution Parallel Evolution • 2 or more related species make similar evolutionary changes

  6. Patterns of Evolution Co-Evolution • Two interacting species evolve together

  7. Macroevolution For macroevolution to occur, two populations must be reproductively isolated (or separated) from one another • Large-scale evolution: • The descent of different species from a common ancestor over many generations. Over time, the two populations of beetles are eventually considered different species, since they can no longer produce viable, fertile offspring.

  8. Pre-zygotic Isolating Mechanisms Isolating mechanisms that prevent fertilization Ova/egg

  9. Pre-zygotic Isolating Mechanisms 1) Habitat Isolation 2 populations live in different habitats and rarely meet Ex. Terrestrial vs. Aquatic Garter Snakes

  10. 2) Behavioral Isolation 2 populations can not recognize differences in courtship rituals Pre-zygotic Isolating Mechanisms 2 subspecies of tropical finches have been separated enough to have variations in song that they do not recognize

  11. 3) Temporal Isolation 2 populations that breed during different times of day or seasons Pre-zygotic Isolating Mechanisms Day vs. Night Blooming Lily

  12. 4) Mechanical Isolation incompatible sex-organs/genitalia 5) Gametic Isolation Sperm can not survive in the reproductive tract of females or gametes fail to recognize each other Pre-zygotic Isolating Mechanisms

  13. Post-zygotic Isolating Mechanisms Fertilization is successful, but zygote is prevented from developing into a viable adult Ova/Egg

  14. Post-zygotic Isolating Mechanisms 1) Hybrid Inviability – genetic incompatibility causes early miscarriage 2) Hybrid Sterility - Hybrid is viable, but sterile 3) Hybrid Breakdown – Hybrid is viable and fertile, but its offspring is sterile

  15. Modes of Speciation(How new species are formed) • Allopatric Speciation • Adaptive Radiation • Sympatric Speciation

  16. Allopatric Speciation Allo patric When a speciation occurs due to geographic isolation between two populations ~ “other” ~ “homeland” Back to Modes of Speciation

  17. Adaptive Radiation • Type of allopatric speciation • Rapid evolution of many species from a single ancestor due to colonization of an area w/diverse conditions (ex. Darwin’s finches) Back to Modes of Speciation

  18. Sympatric Speciation • When new species are formed w/o a geographic barrier (more common in plants) • This can an occur due to the following reasons: • Polyploidy • Allopolyploidy • Balanced Polymorphism

  19. Sympatric Speciation (due to polyploidy) • Mutant condition occurs when a non-disjunction error in meiosis causes gametes that are diploid. • Mutant zygotes are triploid (3N) or tetraploid (4N) as a result and can propagate a new species

  20. Sympatric Speciation (due to allopolyploidy) • Type of hybridization • When two different species interbreed and combine their chromosomes • Usually sterile, but can breed new species asexually

  21. Sympatric Speciation (due to balanced polymorphism) • When there are different phenotypes in a population, members can self-isolate and “selectively breed” with those of their own. • Over time, two populations of differing phenotypes (ex. colors) can evolve into two different species

  22. Does macroevolution occur gradually or suddenly? Evolution occurs due to -abrupt changes in the environment (ex. Catastrophes) that drives rapid speciation -New species appear quickly, then changes very little over time ** supported by fossil evidence • Evolution occurs due to • gradual accumulation of small changes over time • ** not supported by fossil evidence, since existence of “intermediate” fossils are few or inadequate to support the theory • [;’p • ; Two models of evolutionary thought: 1) Gradualism 2) Punctuated Equilibrium Gradualism Punctuated Equilibrium

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