2. THE ORIGIN OF SPECIES Chapter 24

3. Origin of Species Macroevolution – the origin of new taxonomic groups Speciation – the origin of new species

4. Figure 24.1 Two patterns of speciation

5. SPECIES Species - population(s) whose members interbreed in nature and produce fertile offspring Figure 24.2a The biological species concept is based on interfertility rather than physical similarity

6. Figure 24.2b The biological species concept is based on interfertility rather than physical similarity

7. 1.Prezygotic – impede mating between species by hindering the fertilization of ova 2.Postzygotic – impede mating between species by preventing the zygote from developing into a viable, fertile adult Barriers that prevent different species from interbreeding:

8. Figure 24.5 A summary of reproductive barriers between closely related species

9. PREZYGOTIC BARRIERS a.Habitat Isolation – living in different habitats within same area Example: snakes in water vs. land b.Behavioral Isolation – special signals to attract mates (probably most important barrier) Example: fireflies using different blinking signals

10. Figure 24.3 Blue-footed boobies: Males high step as part of a courtship ritual. This creates a behavioral barrier between species

11. c.Temporal Isolation – breeding during different seasons or years Example: skunks mating in summer vs. late winter d.Mechanical Isolation – cannot mate due to anatomical differences Example: Snails e.Gametic Isolation – gametes unable to fuse together to make zygote Example: sperm not surviving vaginal environment

12. POSTZYGOTIC BARRIERS a.Reduced Hybrid Viability – zygotes/embryos aborted (miscarriage) Example: frogs (Ranus) b.Reduced Hybrid Fertility – offspring end up being mostly sterile Example: horses mating with donkeys to make sterile mules c.Hybrid Breakdown – offspring are fertile, but next generation is sterile Example: cotton

14. FAULTS WITH THE BIOLOGICAL SPECIES CONCEPT Extinct organisms Asexual organisms Too rigid: dogs and coyotes Gene flow through subspecies

15. OTHER SPECIES CONCEPTS Morphological – physical features Recognition – mating adaptations Cohesion –phenotype (genes and adaptations) Ecological – live and do (niches) Evolutionary – sequence of ancestral and descendant populations

16. SPECIATION 1.Allopatric – a geographic barrier isolates populations blocking gene flow 2.Sympatric – intrinsic factors alter gene flow

17. Figure 24.6 Two modes of speciation

18. ALLOPATRIC SPECIATION  Geographical barriers – mountains forming, canyons forming, climate changing land  Example: pupfishes (Cyprinodon) in springs of Death Valley CA and OR (drying caused separated “pools” in which speciation occurred)

19. Figure 24.7 Allopatric speciation of squirrels in the Grand Canyon. On left is Antelope squirrel (A. harris) and on right White-tailed antelope squirrel (A. leucurus)

20. Figure 24.8 Has speciation occurred during geographic isolation?

21. Conditions Favoring Allopatric Speciation Peripheral isolate already different from original population (ex. Phenotypic extremes) Genetic drift at work because smaller population size Different natural selection in new environment

22. ADAPTIVE RADIATION Evolution of many diversely adapted species from a common ancestor –Example: Hawaiian islands and the finches of Galapagos Islands

23. Figure 24.11 A model for adaptive radiation on island chains

24. Figure 24.10 Long-distance dispersal

25. SYMPATRIC SPECIATION Polyploidy – extra set of chromosomes (common in plants) Autoploidy –more than 2 chromosome sets from same original Allopolyploid – two different species contribute to the polyploidy hybrid

26. Figure 24.13 Sympatric speciation by autopolyploidy in plants

27. Figure 24.16 Mate choice in two species of Lake Victoria cichlids: females chose mates that have same color as themselves. Under monochromatic light, females chose both colors equally because they look the same. (Nonrandom mating causes sympatric speciation)

28. POPULATION GENETICS LEADING TO SPECIATION Adaptive divergence – when 2 populations adapt to different environments, they accumulate differences in their gene pools –Reproductive barriers may evolve coincidentally causing the populations to differentiate into 2 species

29. OUTCOMES OF DIVERGENCE Two populations get back together and interbreed = no new species Two populations get back together and do not interbreed = 2 new species Hybrid Zone = where 2 populations get back together and interbreed to make hybrids only around the region where they overlap

30. PUNCTUATED EQUILIBRIUM Species diverge in spurts of relatively rapid change, instead of slowly and gradually –Species undergo most of their changes as they first bud from parent species

31. Figure 24.17 Two models for the tempo of speciation

32. Punctuated Gradualism

33. SUMMARY Evolution is a response to interactions between organisms and their current environment. Evolution does not imply some intrinsic drive toward a preordained state.

34. Figure 24.24 The branched evolution of horses