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Do you think Speciation can only be observed over millions of years? Explain. 1.

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Presentation on theme: "Do you think Speciation can only be observed over millions of years? Explain. 1."— Presentation transcript:

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2 Do you think Speciation can only be observed over millions of years? Explain. 1

3 Do you think species are going extinct, but no new species are forming on Earth? A.Yes B.No Explain your answer. 2

4 What is a Species? A Case Study 3

5 4 The Apple Maggot Fly Rhagoletis pomonella

6 Hawthorn trees are native to North America. 5 The hawthorn fruit is eaten by the larvae of the hawthorn maggot fly, Rhagoletis pomonella. 13 mm average Size fruit

7 Rhagoletis pomonella life cycle 1.The female lays fertilized eggs in the fruit. 2.Maggots (larvae) emerge from the egg, feed on the fruit, and grow. 3.Healthy maggots drop from the tree with the fruit and burrow in the soil. Pupation takes place in the soil. 4. Adult maggot flies emerge from the soil and fly to fruit trees, where they mate on the surface of the fruit. 6

8 But there are parasites! Parasitoid wasps try to lay eggs in the maggot’s body, paralyzing and ultimately killing the maggot. 7

9 Apples Domesticated apples (Malus domesticus) were introduced to North America in the 1600s. They are now the most widely grown fruit in North America. A typical commercial apple has a diameter of 70 mm. 8

10 Rhagoletis Host Shift Rhagoletis pomonella Hawthorn (Crataegus spp) ♀ lays eggs on fruit 1864: First noted apple Infestation (147 years Ago) Apple (Malus domesticus) 9

11 Apple vs. Hawthorn: The Maggot’s Viewpoint The large apple fruit provides 220 times more food than hawthorn fruit. But the nutritional quality of hawthorn fruit is superior: 52% of hawthorn maggots survive vs. 27% of apple maggots. 10

12 Apple vs. Hawthorn: The Risk of Attack Larger fruits of apples are much deeper than hawthorn fruits. Apple maggots can burrow to avoid parasitoid wasps. Apple maggots carry fewer parasitoid wasp eggs than hawthorn maggots do. 11

13 Today: There are Hawthorn & Apple Maggot Flies Hawthorn and apple maggot flies are physically indistinguishable. – However, they are genetically distinct, with different genetic profiles. There is no geographic isolation or physical separation between hawthorn and apple maggot flies. 12

14 Hawthorn & Apple Maggot Flies Maggot flies tend to mate with their own kind. – Hawthorn maggot flies strongly prefer to mate on and lay fertilized eggs in hawthorn fruit. – Apple maggot flies strongly prefer to mate on and lay fertilized eggs in apple fruit. There is only a 4-6% hybridization rate between hawthorn and apple maggot flies. 13

15 Rhagoletis Host Shift Hybrids are viable and fertile. No post-zygotic barriers Hawthorn- raised Apple- raised 14

16 Timing of Host Fruit Ripening Different ripening time of host fruit leads to temporal separation of apple and hawthorn flies. 15

17 Based on the information provided, are hawthorn and apple maggot flies separate species? Explain your reasoning. 16

18 17

19 1. According to the biological species concept, are hawthorn and apple maggot flies separate species? 18

20 Which information is relevant to the biological species definition? A.Hawthorn and apple maggot flies are physically indistinguishable. B.There is a 4-6% hybridization rate between hawthorn and apple maggot flies. C.Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. D.Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively. 19

21 Ecological species concept A species is a set of organisms exploiting a single niche. The key aspects of this definition are the resources exploited and the habitat occupied by the members of a species. 20

22 2. According to the ecological species concept, are hawthorn and apple maggot flies separate species? 21

23 Which information is relevant to the ecological species definition? Explain. A.Hawthorn and apple maggot flies are physically indistinguishable. B.There is a 4-6% hybridization rate between hawthorn and apple maggot flies. C.Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. D.Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively. 22

24 Morphological species concept A species is a set of individuals with morphological features in common. The key aspect of this definition is the morphology of the members of a species. Individuals of a species are morphologically similar to one another, yet morphologically distinct from individuals from another species.

25 3. According to the morphological species concept, are hawthorn and apple maggot flies separate species? 24

26 Which information is relevant to the morphological species definition? A.Hawthorn and apple maggot flies are physically indistinguishable. B.There is a 4-6% hybridization rate between hawthorn and apple maggot flies. C.Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. D.Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively. 25

27 Phylogenetic species concept A species may be defined by its unique genetic history as a tip of a phylogenetic tree. Species are defined by their unique derived features and shared ancestry. 26

28 4. According to the phylogenetic species concept, are hawthorn and apple maggot flies separate species? 27

29 Which information is relevant to the phylogenetic species definition? A.Hawthorn and apple maggot flies are physically indistinguishable. B.There is a 4-6% hybridization rate between hawthorn and apple maggot flies. C.Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. D.Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively. 28

30 Reproductive isolation 5. How do two similar species maintain genetic isolation if they come (or remain) in contact with each other? 29

31 Reproductive isolation Reproductive isolating mechanisms prevent two individuals from distinct species from interbreeding or produce viable and fertile hybrid offspring. 30

32 31

33 Sympatric speciation In sympatric speciation, there is no geographic barrier to gene flow. 32

34 6. Explain what type of Speciation is occuring or has occurred with Rhagoletis based on the evidence given. 33

35 7. What reproductive barriers limit interbreeding between hawthorn and apple maggot flies? Explain. 34

36 Timing of Host Fruit Ripening Different ripening time of host fruit leads to temporal separation of apple and hawthorn flies. 35

37 8. Are apple and hawthorn maggot flies a separate species? 36

38 Genetic divergence Genetic divergence is the accumulation of genetic differences between two populations. 37

39 Evolutionary Significant Units 38

40 Factors causing genetic divergence between isolated populations Founder effect Mutation Genetic drift Differential selection 39

41 Reproductive isolation Reproductive isolating mechanisms prevent two individuals from distinct species from interbreeding or produce viable and fertile hybrid offspring. 40

42 41

43 Reproductive isolation: Prezygotic barriers Habitat isolation Behavioral isolation Temporal isolation Mechanical isolation Gametic isolation 42

44 Obstacle to mating or to fertilization if mating occurs PRE-reproduction barriers behavioral isolation geographic isolation ecological isolation temporal isolation mechanical isolation gametic isolation

45 Ecological isolation Species occur in same region, but occupy different habitats so rarely encounter each other – reproductively isolated 2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial

46 Temporal isolation Species that breed during different times of day, different seasons, or different years cannot mix gametes – reproductive isolation – sympatric speciation “same country” Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

47 Behavioral isolation Unique behavioral patterns & rituals isolate species – identifies members of species – attract mates of same species courtship rituals, mating calls reproductive isolation Blue footed boobies mate only after a courtship display unique to their species

48 Mechanical isolation Morphological differences can prevent successful mating – reproductive isolation Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen. Plants sympatric speciation?

49 Mechanical isolation For many insects, male & female sex organs of closely related species do not fit together, preventing sperm transfer – lack of “fit” between sexual organs: hard to imagine for us… but a big issue for insects with different shaped genitals! Damsel fly penises Animals

50 Gametic isolation Sperm of one species may not be able to fertilize eggs of another species – mechanisms biochemical barrier so sperm cannot penetrate egg – receptor recognition: lock & key between egg & sperm chemical incompatibility – sperm cannot survive in female reproductive tract Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

51 Reproductive isolation: Postzygotic barriers Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown 50

52 When a male donkey mates with a female horse, the hybrid offspring is an infertile mule. Explain what type of reproductive barrier this is. X

53 Mules are vigorous, but sterile Reduced hybrid fertility Even if hybrids are vigorous they may be sterile – chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes Donkeys have 62 chromosomes (31 pairs) Horses have 64 chromosomes (32 pairs) Mules have 63 chromosomes!

54 Reduced hybrid viability Genes of different parent species may interact & impair the hybrid’s development Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.

55 Hybrid breakdown Hybrids may be fertile & viable in first generation, but when they mate offspring are feeble or sterile In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species. In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species. sympatric speciation?

56 55

57 The antennae of male moths can only detect sex pheromones released by a female in his species. Explain this reproductive barrier. 56

58 Question Would you expect natural selection to favor pre-zygotic or post-zygotic isolating mechanisms between sympatric species? 57

59 58

60 Graphic of salamanders - ring species idea, or other. Suppose two long separated populations had an opportunity for renewed contact with each other. explain the possible outcomes? 59

61 In terms of post and prezygotic reproductive barriers, Habitat isolation and temporal isolation are: 60

62 61

63 Notes and outs Follow will go on an information sheet that students will have at each table. 62

64 Rhagoletis pomonella life cycle The female lays fertilized eggs in the fruit. Maggots (larvae) emerge from the egg, feed on the fruit, and grow through several molts. Healthy maggots drop from the tree with the fruit and burrow in the soil. Pupation takes place in the soil. Adult maggot flies emerge from the soil and fly to fruit trees, where they mate on the surface of the fruit. 63

65 Rhagoletis Host Shift Hybrids are viable and fertile. No post-zygotic barriers Hawthorn- raised Apple- raised 64

66 Rhagoletis Speciation Small fruit (13 mm)Large fruit (70 mm) High nutritional qualityLow nutritional quality Shallow burrowsDeep burrows More parasitoid waspsFewer wasps Fruit available laterFruit available early Hawthorn Apple 65

67 Timing of Host Fruit Ripening Different ripening time of host fruit leads to temporal separation of apple and hawthorn flies. 66

68 Which information is relevant to the biological species definition? Explain why you chose your answer. A.Hawthorn and apple maggot flies are physically indistinguishable. B.There is a 4-6% hybridization rate between hawthorn and apple maggot flies. C.Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles. D.Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively. 67

69 Three outcomes… With renewed or continued contact between two populations, there are three possible outcomes: 1.Individuals can hybridize readily. 2. Individuals do not hybridize at all. 3. Individuals hybridize but offspring have reduced fitness. No speciation Full speciation Speciation in progress. Selection for evolution of strong reproductive barriers. 68

70 CQ#1: Speciation can only be observed over millions of years: A.True B.False 69

71 CQ#2: Species are going extinct, but no new species are forming on Earth: A.True B.False 70

72 71

73 Q#1: What would the best salmon look like? Boys: Imagine you are a male salmon. Pick the characteristics you want. Write them down. Girls: Imagine you are a female salmon. Pick the characteristics you want. Write them down. 72

74 Q#2 How did you determine what were the best characteristics? 73

75 Which are the lucky few who make it to reproduce? 74

76 The most dominant males (usually largest and most aggressive) successfully defend their redds and inseminate the eggs. Smaller males that also have the kype lose out in head-to-head competition with larger males. Q#3: Are we seeing natural selection in action here? 75

77 Q#4: Why do these non-dominant males persist in the population over time? Why don’t female mimics get weeded out through natural selection if they are not fit? 76

78 Q#5: Even though female mimics are not dominant, are they fit? 77

79 Q#6: Given the fitness data, what selection pattern would you expect for the salmon? 78 Frequency Body Size of Salmon

80 Q#7: Do individuals have to be the “strongest” to be fit? A.Yes B.No 79

81 What selection pattern would you expect for the moths? 80 Frequency Moth Pigmentation

82 Hawthorns Hawthorns are native North American shrubs. Hawthorn fruits range between 5 mm and 20 mm in diameter, with an average of 12.6 mm. 81

83 Rhagoletis Host Shift When apples were introduced to North America, the larva of Rhagoletis pomonella started feeding on them. 82

84 Rhagoletis Speciation Small fruit (13 mm)Large fruit (70 mm) High nutritional qualityLow nutritional quality Shallow burrowsDeep burrows More parasitoid waspsFewer wasps Fruit available laterFruit available early Hawthorn Apple 83

85 Modes of speciation Allopatric speciation is initiated by a geographic barrier between individuals from two natural populations. Sympatric speciation takes place in a single geographic area. 84


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