CHAPTER 14 The Origin of Species

1. CHAPTER 14The Origin of Species Modules 14.3 – 14.9

2. MECHANISMS OF SPECIATION 14.3 Geographic isolation can lead to speciation • When a population is cut off from its parent stock, species evolution may occur • An isolated population may become genetically unique as its gene pool is changed by natural selection, genetic drift, or mutation • This is called allopatric speciation Figure 14.3

3. 14.4 Islands are living laboratories of speciation • On the Galápagos Islands, repeated isolation and adaptation have resulted in adaptive radiation of 14 species of Darwin’s finches Figure 14.4A

4. 1 Species Afrom mainland 2 B • Adaptive radiation on an island chain A B 3 B B 4 C C C C D C D 5 Figure 14.4B

5. 14.5 New species can also arise within the same geographic area as the parent species • In sympatric speciation, a new species may arise without geographic isolation • A failure in meiosis can produce diploid gametes • Self-fertilization can then produce a tetraploid zygote Parent species Zygote Meioticerror Self-fertilization Offspring maybe viable andself-fertile 2n = 6Diploid 4n = 12Tetraploid Figure 14.5A Unreduced diploid gametes

6. Sympatric speciation by polyploidy was first discovered by Dutch botanist Hugo de Vries in the early 1900s Figure 14.5B

7. 14.6 Connection: Polyploid plants clothe and feed us • Many plants are polyploid • They are the products of hybridization • The modern bread wheat is an example Figure 14.6A

8. AA BB WildTriticum(14 chromo-somes) Triticummonococcum(14 chromosomes) • The evolution of wheat AB Sterile hybrid(14 chromosomes) Meiotic error andself-fertilization AABB DD T. turgidumEMMER WHEAT(28 chromosomes) T. tauschii(wild)(14 chromosomes) ABD Sterile hybrid Meiotic error andself-fertilization AA BB DD T. aestivumBREAD WHEAT(42 chromosomes) Figure 14.6B

9. 14.7 Reproductive barriers may evolve as populations diverge • This has been documented by • laboratory studies (fruit flies) Initial sampleof fruit flies Maltose medium Starch medium Results ofmating experiments Femalepopulations Female Starch Maltose Same Different Same Starch 22 9 18 15 Malepopulations Male 8 20 12 15 Maltose Different Mating frequenciesin experimental group Mating frequenciesin control group Figure 14.7A

10. examples in natural populations (pupfish in Death Valley) Figure 14.7B

11. 14.8 The tempo of speciation can appear steady or jumpy • According to the gradualist model of the origin of species • new species evolve by the gradual accumulation of changes brought about by natural selection • However, few gradual transitions are found in the fossil record Figure 14.8A

12. The punctuated equilibrium model suggests that speciation occurs in spurts • Rapid change occurs when an isolated population diverges from the ancestral stock • Virtually no change occurs for the rest of the species’ existence Figure 14.8B

13. 14.9 Talking About Science: Peter and Rosemary Grant study the evolution of Darwin’s finches • The occasional hybridization of finch species adds to the genetic variation of parent populations • This may have been important in the adaptive radiation of finch species Figure 14.9