Introductory Questions #32

1. Introductory Questions #32 • How can allele frequencies change in a population and increase variation? Give three examples. What do we call this when this is happening? • Does natural selection operate directly on the phenotype or genotype of organisms? Briefly explain your choice. • Name the three modes of selection. Explain how each mode is different and draw a graph representing each mode. • Define what genetic polymorphism is and why balanced polymorphism is unique. Give the two mechanisms observed for balanced polymorphism. • If the frequency of the heterozygote is 48% and the frequency of the recessive allele is greater than the frequency of the dominant allele, what is the frequency of the dominant allele? Show all of your reasoning in addition to the answer.

3. Macroevolution & Speciation Chapter 24 & 26 • Define a Species • Isolation • Extinction Events • Geological Timetable • Phylogenetics

4. The origin of new species, or speciation • Is at the focal point of evolutionary theory, because the appearance of new species is the source of biological diversity • Evolutionary theory • Must explain how new species originate in addition to how populations evolve • Macroevolution • Refers to evolutionary change above the species level

5. The biological species concept emphasizes reproductive isolation • Species • Is a Latin word meaning “kind” or “appearance” • Species= as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but are unable to produce viable fertile offspring with members of other populations

6. Macroevolution: the origin of new taxonomic groups • Speciation: the origin of new species • 1-Anagenesis(phyletic evolution): accumulation of heritable changes. Ancestral species becomes extinct. • 2-Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)

7. Overview of the Existence of Species • Estimated number of 13-14 million different species • Only 1.75 million have been scientifically named • The breakdown: -250,000 Plants -42,000 Vertebrates -750,000 Insects How would you define a species?

8. What is a species? • Biological species concept (Ernst Mayr): a population or group of populations whose members have the potential to interbreed & produce viable, fertile offspring(genetic exchange is possible and is genetically isolated from other populations) Other definitions of Species pg 476

9. Limitations of the Biological Species Concept • The biological species concept cannot be applied to • Asexual organisms • Fossils • Organisms about which little is known regarding their reproduction

10. What is a Species? • Considered separate species if they cannot interbreed (or are reproductively isolated)

11. How Does a new Species Emerge? • There has to be some ISOLATION event that separates a population of individuals • Separation has to be maintained with barriers • Applies to sexually reproducing organisms • Asexual reproducers: species concept is difficult to apply -classified by structural & biochemical differences

12. Problem With “Species” Definition: If they never have the opportunity to interbreed, how do you know if they can?

13. What if they breed, but don’t produce viable offspring?(mules)

14. We Can Separate Species Based On % Of Shared Dna How Much of a difference is needed to call 2 organisms separate species?

15. Other Definitions of Species • The morphological species concept • Characterizes a species in terms of its body shape, size, and other structural features • The paleontological species concept • Focuses on morphologically discrete species known only from the fossil record • The ecological species concept • Views a species in terms of its ecological niche • The phylogenetic species concept • Defines a species as a set of organisms with a unique genetic history

16. Prezygotic Barriers • Prezygotic barriers:impede mating between species or hinder the fertilization of the ova • Habitat (snakes; water/terrestrial) • Behavioral (fireflies; mate signaling & courtship) • Temporal (salmon; seasonal mating) • Mechanical (flowers; pollination anatomy) • Gametic (frogs; egg coat receptors)

17. Prezygotic barriers impede mating or hinder fertilization if mating does occur Behavioral isolation Habitat isolation Temporal isolation Mechanical isolation Individualsof differentspecies Matingattempt HABITAT ISOLATION MECHANICAL ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION (g) (b) (d) (e) (f) (a) (c) Figure 24.4 Prezygotic barriers

18. Postzygotic Barriers Postzygotic Barriers: fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult Reduced hybrid viability- mixed genes impair hybrid development frogs; zygotes fail to develop or reach sexual maturity Reduced hybrid fertility–hybrid is sterile mule; horse x donkey; cannot backbreed Hybrid breakdown – 1st generation fertile and viable; 2nd are feble or sterile cotton; 2nd generation hybrids are sterile

19. Gameticisolation Reducehybridfertility Reducehybridviability Hybridbreakdown Viablefertileoffspring Fertilization REDUCED HYBRID VIABILITY GAMETIC ISOLATION HYBRID BREAKDOWN REDUCED HYBRID FERTILITY (k) (j) (m) (l) (i) (h)

20. Other Definitions of Species • The morphological species concept • Characterizes a species in terms of its body shape, size, and other structural features • The paleontological species concept • Focuses on morphologically discrete species known only from the fossil record • The ecological species concept • Views a species in terms of its ecological niche • The phylogenetic species concept • Defines a species as a set of organisms with a unique genetic history

21. Modes of Reproductive Isolation Pgs. 474-475

22. Speciation can take place with or without geographic separation 2 Modes of speciation (based on how gene flow is interrupted) • Allopatric: populations segregated by a geographical barrier; can result in adaptive radiation (island species) 2. Sympatric:reproductively isolated subpopulation in the midst of its parent population (change in genome); -polyploidy in plants (wheat) -cichlid fishes (pg 480)

23. Figure 24.11 Adaptive Radiation • Adaptive radiation • Is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities

24. Adaptive Radiation

25. N 1.3 million years Dubautia laxa MOLOKA'I KAUA'I MAUI 5.1 million years Argyroxiphium sandwicense O'AHU LANAI 3.7 million years HAWAI'I 0.4 million years Dubautia waialealae Dubautia scabra Dubautia linearis Figure 24.12 • The Hawaiian archipelago • Is one of the world’s great showcases of adaptive radiation

26. Failure of cell divisionin a cell of a growing diploid plant afterchromosome duplicationgives rise to a tetraploidbranch or other tissue. Offspring with tetraploid karyotypes may be viable and fertile—a new biological species. Gametes produced by flowers on this branch will be diploid. 2n 2n = 6 4n 4n = 12 Figure 24.8 • An autopolyploid • Is an individual that has more than two chromosome sets, all derived from a single species

27. Unreduced gamete with 4 chromosomes Unreduced gamete with 7 chromosomes Viable fertile hybrid (allopolyploid) Hybrid with 7 chromosomes Meiotic error; chromosome number not reduced from 2n to n Species A 2n = 4 2n = 10 Normal gamete n = 3 Normal gamete n = 3 Species B 2n = 6 Figure 24.9 • An allopolyploid • Is a species with multiple sets of chromosomes derived from different species

28. Habitat Differentiation and Sexual Selection • Sympatric speciation • Can also result from the appearance of new ecological niches

29. Monochromatic orange light Researchers from the University of Leiden placed males and females of Pundamilia pundamilia and P. nyererei together in two aquarium tanks, one with natural light and one with a monochromatic orange lamp. Under normal light, the two species are noticeably different in coloration; under monochromatic orangelight, the two species appear identical in color. The researchers then observed the mating choices of the fish in each tank. Normal light EXPERIMENT P. pundamilia P. nyererei Under normal light, females of each species mated only with males of their own species. But under orange light, females of each species mated indiscriminately with males of both species. The resulting hybrids were viable and fertile. RESULTS The researchers concluded that mate choice by females based on coloration is the main reproductive barrier that normally keeps the gene pools of these two species separate. Since the species can still interbreed when this prezygotic behavioral barrier is breached in the laboratory, the genetic divergence between the species is likely to be small. This suggests that speciation in nature has occurred relatively recently. CONCLUSION Figure 24.10 • In cichlid fish • Sympatric speciation has resulted from nonrandom mating due to sexual selection

30. Introductory Questions #1 • How would you define a species? What are two key factors you must consider? • Explain the difference between a prezygotic barrier and a postzygotic barrier. • How is allopatric speciation different from sympatric speciation? Why is sympatric speciation more common in plants vs. animals? • Which model (gradualism or punctuated equilibrium) is more reflective of the fossil record? Briefly explain why? • Define these terms and provide an example: allometric growth, paedomorphosis, Hox genes, and allopolyploidy • What is an index fossil? • When was the last mass extinction event? How many have occurred in the last 600 million years?

31. 2 modes for the tempo of speciation • Tempo of speciation: gradual vs. divergence in rapid bursts; Niles Eldredge and Stephen Jay Gould (1972); helped explain the non-gradual appearance of species in the fossil record Punctuated Equilibrium (mutations/sudden environmental changes) Gradualism See pg. 482

32. Evolutionary Novelties • Most novel biological structures • Evolve in many stages from previously existing structures

33. Pigmented cells (photoreceptors) Pigmented cells Epithelium Nerve fibers Nerve fibers (a) Patch of pigmented cells. The limpet Patella has a simple patch of photoreceptors. (b) Eyecup. The slit shell mollusc Pleurotomaria has an eyecup. Cornea Cellular fluid (lens) Fluid-filled cavity Epithelium Optic nerve Pigmented layer (retina) Optic nerve (d) (c) Pinhole camera-type eye. The Nautilus eye functions like a pinhole camera (an early type of camera lacking a lens). Eye with primitive lens. The marine snail Murex has a primitive lens consisting of a mass of crystal-like cells. The cornea is a transparent region of epithelium (outer skin) that protects the eye and helps focus light. Cornea Lens Retina Optic nerve Complex camera-type eye. The squid Loligo has a complex eye whose features (cornea, lens, and retina), though similar to those of vertebrate eyes, evolved independently. (e) Figure 24.14 A–E • Some complex structures, such as the eye • Have had similar functions during all stages of their evolution

34. Evolution of the Genes That Control Development • Genes that program development • Control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult

35. Changes in Rate and Timing • Heterochrony • Is an evolutionary change in the rate or timing of developmental events • Can have a significant impact on body shape

36. (a) Differential growth rates in a human. The arms and legs lengthen more during growth than the head and trunk, as can be seen in this conceptualization of an individual at different ages all rescaled to the same height. Newborn 2 5 15 Adult Age (years) Figure 24.15 A • Allometric growth • Is the proportioning that helps give a body its specific form

37. (b) Comparison of chimpanzee and human skull growth. The fetal skulls of humans and chimpanzees are similar in shape. Allometric growth transforms the rounded skull and vertical face of a newborn chimpanzee into the elongated skull and sloping face characteristic of adult apes. The same allometric pattern of growth occurs in humans, but with a less accelerated elongation of the jaw relative to the rest of the skull. Chimpanzee fetus Chimpanzee adult Human adult Figure 24.15 B Human fetus • Different allometric patterns • Contribute to the contrasting shapes of human and chimpanzee skulls

38. Ground-dwelling salamander. A longer time peroid for foot growth results in longer digits and less webbing. (a) Tree-dwelling salamander. Foot growth ends sooner. This evolutionary timing change accounts for the shorter digits and more extensive webbing, which help the salamander climb vertically on tree branches. (b) Figure 24.16 A, B • Heterochrony • Has also played a part in the evolution of salamander feet

39. Figure 24.17 • In paedomorphosis • The rate of reproductive development accelerates compared to somatic development • The sexually mature species may retain body features that were juvenile structures in an ancestral species

40. Changes in Spatial Pattern • Substantial evolutionary change • Can also result from alterations in genes that control the placement and organization of body parts

41. Homeotic genes • Determine such basic features as where a pair of wings and a pair of legs will develop on a bird or how a flower’s parts are arranged

42. Chicken leg bud Region of Hox gene expression Zebrafish fin bud Figure 24.18 • The products of one class of homeotic genes called Hox genes • Provide positional information in the development of fins in fish and limbs in tetrapods

43. Most invertebrates have one cluster of homeotic genes (the Hox complex), shown here as coloredbands on a chromosome. Hox genes direct development of major body parts. A mutation (duplication) of the single Hox complex occurred about 520 million years ago and may have provided genetic material associated with the origin of the first vertebrates. First Hox duplication 5 1 3 4 2 In an early vertebrate, the duplicate set of genes took on entirely new roles, such as directing the development of a backbone. Hypothetical vertebrate ancestor (invertebrate) with a single Hox cluster A second duplication of the Hox complex, yielding the four clusters found in most present-day vertebrates, occurred later, about 425 million years ago. This duplication, probably the result of a polyploidy event, allowed the development of even greater structuralcomplexity, such as jaws and limbs. Second Hox duplication Hypothetical early vertebrates (jawless) with two Hox clusters The vertebrate Hox complex contains duplicates of many ofthe same genes as the single invertebrate cluster, in virtuallythe same linear order on chromosomes, and they direct the sequential development of the same body regions. Thus, scientists infer that the four clusters of the vertebrate Hoxcomplex are homologous to the single cluster in invertebrates. Vertebrates (with jaws) with four Hox clusters Figure 24.19 • The evolution of vertebrates from invertebrate animals • Was associated with alterations in Hox genes

44. Small genetic changes in a population • Change in frequency of a single allele due to selection Microevolution

45. Macroevolution • Large-scale changes in organisms • Involves new genera

46. The End

47. Extinction • The elimination of a species from the earth • Background Extinction Rate - relatively constant rate of extinction in the fossil record • Mass Extinction - major loss of species: climate change, humans, catastrophies

48. ? Cretaceousextinctions 90 million years ago 80 70 65 60 Figure 15.5

50. Mass Extinctions - These mass extinctions may have been a result of an asteroid impact or volcanic activity • Every mass extinction reduced the diversity of life • But each was followed by a rebound in diversity Ex. Mammals filled the void left by the dinosaurs