1. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Chapter 24: The Origin of Species

2. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Speciation, the origin of new species, is at the focal point of evolutionary theory Speciation, the origin of new species, is at the focal point of evolutionary theory Microevolution consists of adaptations that evolve within a population, confined to one gene pool Microevolution consists of adaptations that evolve within a population, confined to one gene pool Macroevolution refers to evolutionary change above the species level Macroevolution refers to evolutionary change above the species level

3. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Biological Species Concept The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations LIMITATIONS- cannot be applied to fossils or asexual organisms (including all prokaryotes) LIMITATIONS- cannot be applied to fossils or asexual organisms (including all prokaryotes)

4. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 24-2 (a) Similarity between different species (b) Diversity within a species

5. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Reproductive Isolation Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring Hybrids are the offspring of crosses between different species (horse+donkey=mule) Hybrids are the offspring of crosses between different species (horse+donkey=mule)

6. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Prezygotic barriers block fertilization from occurring by: Prezygotic barriers block fertilization from occurring by: –Impeding different species from attempting to mate –Preventing the successful completion of mating –Hindering fertilization if mating is successful 1. Mechanical isolation: Morphological differences can prevent successful mating 2. Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species

7. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 3. Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers 4. Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes 5. Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers Video: Albatross Courtship Ritual Video: Albatross Courtship Ritual Video: Crocodile Courtship Ritual Video: Crocodile Courtship Ritual Bird of paradise Courtship Ritual Bird of paradise Courtship Ritual

8. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 24-4a Habitat IsolationTemporal Isolation Prezygotic barriers Behavioral Isolation Mating attempt Mechanical Isolation (f) (e) (c) (a) (b) (d) Individuals of different species Water-dwelling Thamnophis Terrestrial Thamnophis c. Eastern spotted skunk (Spilogale putorius) d. Western spotted skunk (Spilogale gracilis) Courtship ritual of blue- footed boobies Bradybaena with shells spiraling in opposite directions

9. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 24-4i Prezygotic barriers Gametic Isolation Fertilization Reduced Hybrid Viability Postzygotic barriers Reduced Hybrid FertilityHybrid Breakdown Viable, fertile offspring (g) (h) (i) (j) (l) (k) Sea urchins Ensatina hybrid Donkey Horse Mule (sterile hybrid) Hybrid cultivated rice plants with stunted offspring (center)

10. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult: Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult: –Reduced hybrid viability –Reduced hybrid fertility –Hybrid breakdown

11. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 1. Reduced hybrid viability: Genes of the different parent species may interact and impair the hybrid ’ s development 2. Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile 3. Hybrid breakdown: Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile

12. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Other Definitions of Species Other species concepts emphasize the unity within a species rather than the separateness of different species Other species concepts emphasize the unity within a species rather than the separateness of different species 1. The morphological species concept defines a species by structural features 2. The ecological species concept views a species in terms of its ecological niche 3. The phylogenetic species concept: defines a species as the smallest group of individuals on a phylogenetic tree

13. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Speciation can take place with or without geographic separation Speciation can occur in two ways: Speciation can occur in two ways: –Allopatric speciation- (“other country”) gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations –Sympatric speciation- (“same country”) speciation takes place in geographically overlapping populations

14. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation

15. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Process of Allopatric Speciation The definition of barrier depends on the ability of a population to disperse The definition of barrier depends on the ability of a population to disperse Regions with many geographic barriers typically have more species than do regions with fewer barriers Regions with many geographic barriers typically have more species than do regions with fewer barriers

16. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 24-6 A. harrisi A. leucurus

17. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Factors of Sympatric Speciation 1. Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division 1. Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division –An autopolyploid is an individual with more than two chromosome sets, derived from one species –An allopolyploid is a species with multiple sets of chromosomes derived from different species

18. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 24-11-4 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

19. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 2. Habitat Differentiation Sympatric speciation can also result from the appearance of new ecological niches Sympatric speciation can also result from the appearance of new ecological niches For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees 3. Sexual Selection Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria

20. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Allopatric VS Sympatric Speciation Allopatric speciation Allopatric speciation –geographic isolation 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 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

21. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Adaptive Radiation The evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges The evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges Typically occurs when a few organisms make their way to new, often distant areas or when environmental changes cause numerous extinctions, opening up ecological niches for the survivors Typically occurs when a few organisms make their way to new, often distant areas or when environmental changes cause numerous extinctions, opening up ecological niches for the survivors

22. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Hybrid zones A hybrid zone is a region in which members of different species mate and produce hybrids A hybrid zone is a region in which members of different species mate and produce hybrids Can occur in a single band where adjacent species meet Can occur in a single band where adjacent species meet

23. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 24-13 EUROPE Fire-bellied toad range Hybrid zone Yellow-bellied toad range Yellow-bellied toad, Bombina variegata Fire-bellied toad, Bombina bombina Allele frequency (log scale) Distance from hybrid zone center (km) 4030 20 10 0 0.01 0.1 0.5 0.9 0.99

24. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Hybrid Zones over Time When closely related species meet in a hybrid zone, there are three possible outcomes: When closely related species meet in a hybrid zone, there are three possible outcomes: –Strengthening of reproductive barriers –Weakening of reproductive barriers –Continued formation of hybrid individuals

25. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Patterns in the Fossil Record Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change

26. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Studying the Genetics of Speciation The explosion of genomics is enabling researchers to identify specific genes involved in some cases of speciation The explosion of genomics is enabling researchers to identify specific genes involved in some cases of speciation Depending on the species in question, speciation might require the change of only a single allele or many alleles Depending on the species in question, speciation might require the change of only a single allele or many alleles