1 / 29

Chapter 24

Chapter 24. The Origin of Species. Speciation = origin of new species Microevolution = adaptations that evolve within a population (confined to one gene pool) Macroevolution = evolutionary change making new species or new groups of organisms.

kimberley-curry
Download Presentation

Chapter 24

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 24 The Origin of Species

  2. Speciation = origin of new species • Microevolution = adaptations that evolve within a population (confined to one gene pool) • Macroevolution= evolutionary change making new species or new groups of organisms

  3. In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth

  4. I. Reproductive Isolation • Species=a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring • Reproductive isolation= existence of biological factors (barriers) that impede two different species from producing viable, fertile offspring. • Hybridsare the offspring of crosses between different species (horse + donkey = mule)

  5. Fig. 24-2 • (a) Similarity between different species • (b) Diversity within a species

  6. A. Reproductive Barriers • Prezygotic barriers block fertilization from occurring • Postzygotic barriers prevent hybrid from forming viable fertile adult

  7. Reproductive Barriers Between Species • PrezygoticBarriers • PostzygoticBarriers • Habitat • Isolation • Temporal • Isolation • Behavioral • Isolation • Hybrid • Breakdown • Mechanical • Isolation • Gametic • Isolation • Reduced • Hybrid Viability • Reduced Hybrid • Fertility • Individuals • of • different • species • Viable, • fertile • offspring • Mating • attempt • Fertilization • (c) • (e) • (f) • (a) • (g) • (h) • (l) • (i) • (d) • (j) • (b) • (k)

  8. PreZygotic Reproductive Barriers • Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats

  9. Habitat Isolation • Water-dwelling Thamnophis

  10. Habitat Isolation • Terrestrial Thamnophis

  11. PreZygotic Reproductive Barriers • Temporal Isolation: Species that breed at different times (day, seasons, years) • Behavioral isolation: Courtship rituals and other behaviors • Mechanical isolation: Morphological differences can prevent successful mating. • Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species.

  12. Behavioral Isolation Occurs Without Appropriate Mating Rituals • Courtship ritual of blue-footed boobies

  13. Mechanical Isolation: • Bradybaena with shells spiraling in opposite directions

  14. PostZygotic Reproductive Barriers • Reduced hybrid viability -- weak offspring • Reduced hybrid fertility -- sterile offspring • Hybrid breakdown.

  15. PostZygotic Reproductive Barrier • Mule: sterile hybrid offspring between horse and donkey

  16. Concept 24.2: Speciation can take place with or without geographic separation • Speciation can occur in two ways: • Allopatric speciation: geographic barrier separates populations. • Sympatric speciation: no geographic barrier

  17. Speciation • (a) Allopatric speciation • (b) Sympatric speciation

  18. II. Allopatric Speciation • Gene flow is interrupted • Gene pool is reduced when a population is divided into geographically isolated subpopulations • Separate populations may evolve independently through mutation, natural selection, and genetic drift. • Reproductive isolation between populations generally increases as the distance between them increases. • Barriers to reproduction are intrinsic; separation itself is not a biological barrier.

  19. Allopatric Speciation • A. harrisi • A. leucurus

  20. Continental Drift Caused Allopatric Speciation • Mantellinae • (Madagascar only): • 100 species • Rhacophorinae • (India/Southeast • Asia): 310 species • Other Indian/ • Southeast Asian • frogs • 100 • 60 • 20 • 80 • 40 • 0 • 1 • 2 • 3 • Millions of years ago (mya) • 1 • 3 • 2 • India • Madagascar • 56 mya • 88 mya • 65 mya

  21. III. Sympatric Speciation • Speciation takes place in geographically overlapping populations. • Polyploidyis the presence of extra sets of chromosomes due to accidents during cell division. • Polyploidy is common in plants. Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids.

  22. Sympatric Speciation via Polyploidy is Common in Plants • 2n • 2n = 6 • 4n = 12 • 4n • Failure of cell • division after • chromosome • duplication gives • rise to tetraploid • tissue. • Gametes • produced • are diploid.. • Offspring with • tetraploid • karyotypes may • be viable and • fertile.

  23. Sympatric Speciation - Polyploidy --> Allopolyploid • Species B • 2n = 4 • Unreduced • gamete • with 4 • chromosomes • Unreduced • gamete • with 7 • chromosomes • Hybrid • with 7 • chromosomes • Meiotic • error • Viable fertile • hybrid • (allopolyploid) • 2n = 10 • Normal • gamete • n = 3 • Normal • gamete • n = 3 • Species A • 2n = 6

  24. A. Habitat Differentiation and Sexual Selection • Sympatric speciation can also result from the appearance of new ecological niches. • New roles open for organisms to fill (new trees introduced into an area) • Sexual selection can drive sympatric speciation. • Ex. Selection for mates of different colors has contributed to the speciation in cichlid fish in Lake Victoria.

  25. OVERVIEW: Allopatric and Sympatric Speciation • Allopatric speciation, geographic separation restricts gene flow between populations. • Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations. • Even if contact is restored between populations, interbreeding is prevented. • Sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species. • Can result from polyploidy, natural selection, or sexual selection.

  26. IV. Time Needed for Speciation • Punctuated equilibrium= periods of apparent stasis (no change) punctuated by brief periods of rapid change. • Gradualism =slow continuous change over time in a species’ existence

  27. Patterns in Speciation PunctuatedEquilibrium pattern • Change / Time • Gradualism pattern

  28. Speciation - Andersen 12 min

  29. You should now be able to: • Define and discuss the limitations of the four species concepts. • Describe and provide examples of prezygotic and postzygotic reproductive barriers. • Distinguish between and provide examples of allopatric and sympatric speciation. • Explain how polyploidy can cause reproductive isolation. • Define the term hybrid zone and describe three outcomes for hybrid zones over time.

More Related