1. Copyright © 2007 by Allyn and Bacon Origin of species II. Speciation allopatric sympatric polyploidy habitat differentiation sexual selection I.Biological species concept Reproductive isolation III. Species in hybrid zones Reproductive barriers reinforced, weakened, stabilized

2. Copyright © 2007 by Allyn and Bacon Microevolution: change in allele frequencies in a population over generations

3. Copyright © 2007 by Allyn and Bacon Species: a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring Populations of the same species may exchanges alleles. I. Biological species concept

4. Copyright © 2007 by Allyn and Bacon Reproductive isolation between species 1. Prezygotic barriers no attempt to mate no access of sperm to eggs Bradybaena with shells spiraling in opposite directions Different habitat

5. Copyright © 2007 by Allyn and Bacon Reproductive isolation between species 1. Prezygotic barriers 2. Postzygotic barriers developmental errors survival problem infertile offspring

6. Copyright © 2007 by Allyn and Bacon Biological species concept: based on reproductive isolation Morphological species concept: based on structural features of the species Ecological species concept: based on the ecological niche of the species

7. Copyright © 2007 by Allyn and Bacon Donkey Horse Mule (sterile hybrid)

8. Think Pair Share – Looking at Reproductive Barriers Suppose you are studying two bird species that live in a forest and are not known to interbreed. One species feeds and mates in the treetops and the other on the ground. But in captivity, the birds can interbreed and produce viable, fertile offspring. What type of reproductive barrier most likely keeps these species separate in nature? Explain. Copyright © 2007 by Allyn and Bacon

9. Once separated, different mutations arise, natural selection applies, genetic drift → reproductive isolation Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation II. Speciation 1. Allopatric speciation

10. II. Speciation 1. Allopatric speciation 2. Sympatric speciation a. polyploidy – > 2 sets chromosomes by accident Species A 2n = 6 Normal gamete n = 3 Meiotic error Species B 2n = 4 Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes Unreduced gamete with 7 chromosomes Normal gamete n = 3 Viable fertile hybrid (allopolyploid) 2n = 10 haploid polyploid

11. Copyright © 2007 by Allyn and Bacon II. Speciation 1. Allopatric speciation 2. Sympatric speciation a. polyploidy b. habitat differentiation c. sexual selection

12. EXPERIMENT Normal light Monochromatic orange light P. pundamilia P. nyererei Males of two species

13. Copyright © 2007 by Allyn and Bacon III. Species in hybrid zones 1. Reproductive barriers are reinforced 2. Reproductive barriers are weakened → species fusion 3. Reproductive barriers are stabilized