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Chapter 24: The Origin of Species

Chapter 24: The Origin of Species. What is a species? A population whose members can interbreed in nature and produce viable, fertile offspring aka….reproductive isolation What kinds of barriers keep different species isolated so they cannot mate? Figure 24.4

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Chapter 24: The Origin of Species

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  1. Chapter 24: The Origin of Species • What is a species? • A population whose members can interbreed in nature and • produce viable, fertile offspring • aka….reproductive isolation • What kinds of barriers keep different species isolated so they cannot mate? • Figure 24.4 • Pre–zygotic barriers – before mating &/or zygote is formed • Post–zygotic barriers – after zygote is formed

  2. Prezygotic barriers impede mating or hinder fertilization if mating does occur Behavioral isolation Habitat isolation Temporal isolation Mechanical isolation Individualsof differentspecies Matingattempt HABITAT ISOLATION MECHANICAL ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION (g) (b) (d) (e) (f) (a) (c) Figure 24.4 Reproductive Barriers

  3. Gameticisolation Reducehybridfertility Reducehybridviability Hybridbreakdown Viablefertileoffspring Fertilization REDUCED HYBRID VIABILITY GAMETIC ISOLATION HYBRID BREAKDOWN REDUCED HYBRID FERTILITY (k) (j) (m) (l) (i) (h)

  4. Chapter 24: The Origin of Species • What is a species? • What kinds of barriers keep different species isolated so they cannot mate? • How are new species created? • Allopatric speciation • when a geographic barrier isolates a population blocks gene flow • ex. mountain range emerging, new river dividing a field, island • Sympatric speciation • intrinsic factors such as chromosomal changes (plants) or • non-random mating alter gene flow

  5. (a) (b) Sympatric speciation. A smallpopulation becomes a new specieswithout geographic separation. Allopatric speciation. A population forms a new species while geographically isolated from its parent population. Figure 24.5 Two main modes of speciation

  6. Chapter 24: The Origin of Species • What is a species? • What kinds of barriers keep different species isolated so they cannot mate? • How are new species created? • Allopatric speciation – • when a geographic barrier isolates a population blocks gene flow • ex. mountain range emerging, new river dividing a field, island • Adaptive radiation • evolution of many diversely adapted species from a • common ancestor • Seen on islands • Sympatric speciation • intrinsic factors such as chromosomal changes (plants) or • non-random mating alter gene flow

  7. N 1.3 million years Dubautia laxa MOLOKA'I KAUA'I MAUI 5.1 million years Argyroxiphium sandwicense O'AHU LANAI 3.7 million years HAWAI'I 0.4 million years Dubautia waialealae Dubautia scabra Dubautia linearis Figure 24.12 Adaptive radiation

  8. Chapter 24: The Origin of Species • What is a species? • What kinds of barriers keep different species isolated so they cannot mate? • How are new species created? • Allopatric speciation – • when a geographic barrier isolates a population blocks gene flow • ex. mountain range emerging, new river dividing a field, island • Adaptive radiation • evolution of many diversely adapted species from a • common ancestor • Seen on islands • Sympatric speciation • intrinsic factors such as chromosomal changes (plants) or • non-random mating alter gene flow • ex. oats, cotton, tobacco, potatoes, wheat • Autopolyploidy • An individual has more than 2 chromosome sets derived from • a single species from an error in meiosis

  9. Failure of cell divisionin a cell of a growing diploid plant afterchromosome duplicationgives rise to a tetraploidbranch or other tissue. Offspring with tetraploid karyotypes may be viable and fertile—a new biological species. Gametes produced by flowers on this branch will be diploid. 2n 2n = 6 4n 4n = 12 Figure 24.8 Sympatric speciation by autopolyploidy in plants

  10. Chapter 24: The Origin of Species • What is a species? • What kinds of barriers keep different species isolated so they cannot mate? • How are new species created? • Allopatric speciation – • when a geographic barrier isolates a population blocks gene flow • ex. mountain range emerging, new river dividing a field, island • Adaptive radiation • evolution of many diversely adapted species from a • common ancestor • Seen on islands • Sympatric speciation • intrinsic factors such as chromosomal changes (plants) or • non-random mating alter gene flow • Autopolyploidy • An individual has more than 2 chromosome sets derived from • a single species from an error in meiosis • Allopolyploidy • 2 different species produce the polyploid hybrid

  11. Unreduced gamete with 4 chromosomes Unreduced gamete with 7 chromosomes Viable fertile hybrid (allopolyploid) Hybrid with 7 chromosomes Meiotic error; chromosome number not reduced from 2n to n Species A 2n = 4 2n = 10 Normal gamete n = 3 Normal gamete n = 3 Species B 2n = 6 Figure 24.9 One mechanism for allopolyploid speciation in plants

  12. Chapter 24: The Origin of Species • What is a species? • What kinds of barriers keep different species isolated so they cannot mate? • How are new species created? • What is the difference between gradualism & punctuated equlibrium?

  13. Time (b) (a) Gradualism model. Species descended from a common ancestor gradually diverge more and more in their morphology as they acquire unique adaptations. Punctuated equilibrium model. A new species changes most as it buds from a parent species and then changes little for the rest of its existence. Figure 24.13 Two models for the tempo of speciation

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