1.  Until recently, over 500 species of cichlid fishes lived in East Africa’s Lake Victoria –Where did these species come from? –Why are they disappearing? Copyright © 2009 Pearson Education, Inc. Introduction: The Rise and Fall of Cichlids

2. Copyright © 2009 Pearson Education, Inc.  A species can be defined as a group of organisms whose members can breed and produce fertile offspring, but who do not produce fertile offspring with members of other groups Introduction: The Rise and Fall of Cichlids

3. Copyright © 2009 Pearson Education, Inc.  Two closely related species of cichlid, Pundamilia nyererei and Pundamilia pundamilia, feed at different depths  The males of the two species differ in color Introduction: The Rise and Fall of Cichlids Pundamilia nyererei Pundamilia pundamilia

4.  Lake Victoria’s cichlids diversified 100,000 years ago –Different species of cichlid have specialized mouthparts that allow them to specialize on different food sources –The bright colors of the males vary with species, as females chose males with specific colors  Groups isolated by diet or female mate choice may have lost the ability to interbreed Copyright © 2009 Pearson Education, Inc. Introduction: The Rise and Fall of Cichlids

5. Copyright © 2009 Pearson Education, Inc.  Over the last 30 years, 200 species of cichlids have disappeared from Lake Victoria –Some were eaten by the Nile perch, an introduced predator  In the polluted waters of Lake Victoria, it is more difficult for females to choose brightly colored males of the right species –As a result, the gene pools of separate species are mixing, as two species fuse back into one Introduction: The Rise and Fall of Cichlids

6. Copyright © 2009 Pearson Education, Inc. 14.1 The origin of species is the source of biological diversity  Speciation is the emergence of new species  Every time speciation occurs, the diversity of life increases  The many millions of species on Earth have all arisen from an ancestral life form that lived around 3.6 billion years ago

7. Copyright © 2009 Pearson Education, Inc. 14.2 There are several ways to define a species  Taxonomy is the branch of biology that names and classifies species and groups them into broader categories  Carolus Linnaeus developed the binomial system of naming organisms using physical characteristics to distinguish over 11,000 species  Similarities between some species and variation within species can make defining species difficult

8. Copyright © 2009 Pearson Education, Inc.  The morphological species concept classifies organisms based on observable phenotypic traits  It can be applied to asexual organisms, fossils, and in cases when we don’t know about possible interbreeding  There is some subjectivity in deciding which traits to use 14.2 There are several ways to define a species

11. Copyright © 2009 Pearson Education, Inc.  The ecological species concept defines a species by its ecological role or niche –Consider the cichlids, which are similar in appearance but feed at different depths in the lake 14.2 There are several ways to define a species

12. Copyright © 2009 Pearson Education, Inc.  The phylogenetic species concept defines a species as a set of organisms representing a specific evolutionary lineage –Morphological or DNA similarities or differences can be used to define a species –Defining the amount of difference required to distinguish separate species is a problem 14.2 There are several ways to define a species

13. Copyright © 2009 Pearson Education, Inc.  The biological species concept defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce fertile offspring  Reproductive isolation prevents gene flow and maintains separate species 14.2 There are several ways to define a species

14. Copyright © 2009 Pearson Education, Inc.  Can the biological species concept always distinguish species from each other?  Not if they reproduce asexually  Not if they are extinct  But since reproductive isolation is an essential factor in the evolution of species most scientists find the biological species concept most useful 14.2 There are several ways to define a species

15. Copyright © 2009 Pearson Education, Inc. MECHANISMS OF SPECIATION How does reproductive isolation occur

16. Copyright © 2009 Pearson Education, Inc. 14.4 In allopatric speciation, geographic isolation leads to speciation  In allopatric speciation, populations of the same species are geographically separated, separating their gene pools  Changes in the allele frequencies of each population may be caused by natural selection, genetic drift, and mutation, unaffected by gene flow from other populations

17. Copyright © 2009 Pearson Education, Inc.  Gene flow between populations is initially prevented by a geographic barrier –The Grand Canyon and Colorado River separate two species of antelope squirrels 14.4 In allopatric speciation, geographic isolation leads to speciation

18. Copyright © 2009 Pearson Education, Inc. 14.5 In sympatric speciation, speciation takes place without geographic isolation  In sympatric speciation, new species may arise within the same geographic area as a parent species  Gene flow between populations may be reduced by factors such as polyploidy, habitat differentiation, or sexual selection

19. Copyright © 2009 Pearson Education, Inc.  Many plant species have evolved by polyploidy, the multiplication of the chromosome number due to errors in cell division  A tetraploid (4n) plant can arise from a diploid parent 14.5 In sympatric speciation, speciation takes place without geographic isolation

20. Parent species 2n = 6 Tetraploid cells 4n = 12 1

21. Parent species 2n = 6 Tetraploid cells 4n = 12 1 Diploid gametes 2n = 6 2

22. Parent species 2n = 6 Tetraploid cells 4n = 12 1 Diploid gametes 2n = 6 2 Viable, fertile tetraploid species 4n = 12 Self- fertilization 3

23. Species A 2n = 4 Gamete n = 2 Species B 2n = 6 Gamete n = 3

24. Species A 2n = 4 Gamete n = 2 1 2 Species B 2n = 6 Gamete n = 3 Sterile hybrid n = 5 Chromosomes not homologous (cannot pair)

25. Species A 2n = 4 Gamete n = 2 1 2 Species B 2n = 6 Gamete n = 3 Sterile hybrid n = 5 Chromosomes not homologous (cannot pair) Viable, fertile hybrid species 2n = 10 3

26. Copyright © 2009 Pearson Education, Inc. 14.6 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation  80% of all living plant species are the descendants of ancestors that formed by polyploid speciation  Hybridization between two species accounts for most of these species –What advantage might there be to hybridization?  Polyploid food plants include oats, potatoes, bananas, peanuts, barley, plums, apples, sugarcane, coffee, and bread wheat  Cotton is also polyploid

27. Triticum monococcum (14 chromosomes) Hybridization AABB AB Sterile hybrid (14 chromosomes) 1 2  Cell division error and self-fertilization Wild Triticum (14 chromo- somes) AA BB DD  Sterile hybrid (21 chromosomes) ABD Hybridization 3 4 Cell division error and self-fertilization T. tauschii (wild) (14 chromosomes) T. turgidum Emmer wheat (28 chromosomes) AA BB DD T. aestivum Bread wheat (42 chromosomes)

28. Copyright © 2009 Pearson Education, Inc.  Sympatric speciation in animals more commonly occurs through habitat differentiation and sexual selection –Remember the cichlids in Lake Victoria! 14.5 In sympatric speciation, speciation takes place without geographic isolation

29. a.b.

30. Copyright © 2009 Pearson Education, Inc. 14.7 Reproductive barriers may evolve as populations diverge  So in order for speciation to occur reproductive barriers have to arise.  How do reproductive barriers arise?

31. Copyright © 2009 Pearson Education, Inc. 14.3 Reproductive barriers keep species separate  Reproductive barriers serve to isolate a species gene pool and prevent interbreeding  Reproductive barriers are categorized as prezygotic or postzygotic, depending on whether they function before or after zygotes form

37. Copyright © 2009 Pearson Education, Inc.  Postzygotic Barriers –Postzygotic barriers operate after hybrid zygotes are formed –In reduced hybrid viability, most hybrid offspring do not survive –In reduced hybrid fertility, hybrid offspring are vigorous but sterile –In hybrid breakdown, the first-generation hybrids are viable and fertile, but the offspring of the hybrids are feeble or sterile –The process of speciation depends on whether reproductive barriers prevent gene flow between populations 14.3 Reproductive barriers keep species separate

39. Prezygotic barriers Temporal isolation Habitat isolation Behavioral isolation Mechanical isolation Gametic isolation Zygote Gametes Postzygotic barriers Viable, fertile offspring Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown

40. Initial sample of fruit flies Maltose medium Starch medium Mating frequencies in experimental groups Starch Mating frequencies in starch control groups Maltose Mating experiments Results Female Starch Maltose 22 9 8 20 Male Population Pop#1 Pop#2 18 15 12 15 Male #1 #2

41. Copyright © 2009 Pearson Education, Inc. 14.8 Hybrid zones provide opportunities to study reproductive isolation  What happens when isolated populations renew contact?  In hybrid zones, members of different species meet and mate to produce hybrid offspring

42. Ancestral species 2 1 Gene flow Population (five individuals are shown) Barrier to gene flow New species Hybrid zone Hybrid Gene flow 3 4

43. Copyright © 2009 Pearson Education, Inc.  What may happen in a hybrid zone?  Reinforcement: If hybrids are less fit than parent species, natural selection strengthens reproductive barriers  Fusion: Weak reproductive barriers between the two species, with considerable gene flow, reverses speciation and two species become one again 14.8 Hybrid zones provide opportunities to study reproductive isolation

44. Copyright © 2009 Pearson Education, Inc.  Stability: Many hybrid zones are stable, continuing to produce hybrids; this allows some gene flow between populations, but each species maintains its own integrity –Which of these three outcomes—reinforcement, fusion, or stability—is happening to the Pundamilia species of cichlids in Lake Victoria? 14.8 Hybrid zones provide opportunities to study reproductive isolation

45. ReinforcementStability Fusion

46. Copyright © 2009 Pearson Education, Inc. 14.10 Adaptive radiation may occur when new opportunities arise  In adaptive radiation, many diverse species evolve from a common ancestor  Adaptive radiations occur –When a few organisms colonize new unexploited areas –After a mass extinction  Adaptive radiations are linked to new opportunities: lack of competitors, varying habitats and food sources, evolution of new structures

47. Copyright © 2009 Pearson Education, Inc. 14.11 Speciation may occur rapidly or slowly  What is the total length of time between speciation events (between formation of a species and subsequent divergence of that species)? –In a survey of 84 groups of plants and animals, the time ranged from 4,000 to 40 million years –Overall, the time between speciation events averaged 6.5 million years and rarely took less than 50,000 years Animation: Macroevolution

48. Time Punctuated Equilibrium-speciation is abrupt, speciation seems to have occurred relatively rapidly based on Fossil evidence

49. Time Gradualism- species diverged gradually over long periods of time

50. Copyright © 2009 Pearson Education, Inc. You should now be able to 1.Explain how the diverse assemblage of cichlid species evolved in Lake Victoria; explain why many of these species no longer exist 2.Compare the definitions, advantages, and disadvantages of the different species concepts 3.Describe five types of prezygotic barriers and three types of postzygotic barriers that prevent populations belonging to closely related species from interbreeding

51. Copyright © 2009 Pearson Education, Inc. 4.Explain how geographical processes can fragment populations and lead to speciation 5.Explain how sympatric speciation can occur, noting examples in plants and animals 6.Explain why polyploidy is important to modern agriculture; explain how modern wheat evolved 7.Explain how reproductive barriers might evolve in isolated populations of organisms You should now be able to

52. Copyright © 2009 Pearson Education, Inc. 8.Explain how hybrid zones are useful in the study of reproductive isolation 9.Explain the conditions that can lead to adaptive radiation 10. What is difference between gradualism model of speciation and the punctuated model of speciation You should now be able to