Chapter 13. How Populations Evolve. Lectures by Edward J. Zalisko

Transcription

1 Chapter 13 How Populations Evolve PowerPoint Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition Eric J. Simon, Jean L. Dickey, and Jane B. Reece Lectures by Edward J. Zalisko 2013 Pearson Education, Inc.

2 Figure 13.4 Darwin in 1840 Galápagos Islands Fernandina 0 0 Isabela 40 km Pinta Marchena Santiago PACIFIC OCEAN Equator Daphne Islands Pinzón 40 miles Santa Cruz Florenza Genovesa Santa Fe San Cristobal Española North America PACIFIC OCEAN ATLANTIC OCEAN South America Tierra del Fuego Great Britain Europe Africa Cape of Good Hope Cape Horn HMS Beagle Asia Equator Australia Tasmania New Zealand

3 CHARLES DARWIN AND THE ORIGIN OF SPECIES Natural selection is a process in which organisms with certain inherited characteristics are more likely to survive and reproduce than are individuals with other characteristics. As a result of natural selection, a population, a group of individuals of the same species living in the same place at the same time, changes over generations Pearson Education, Inc.

4 Darwin s Theory of Natural Selection Unequal reproductive success (natural selection) Those individuals with traits best suited to the local environment generally leave a larger share of surviving, fertile offspring Pearson Education, Inc.

5 Figure Insecticide application Chromosome with gene conferring resistance to pesticide

6 Figure Insecticide application Chromosome with gene conferring resistance to pesticide

7 Figure Insecticide application Chromosome with gene conferring resistance to pesticide Survivors Reproduction

8 5 EVIDENCE OF EVOLUTION 1. the fossil record, 2. biogeography, 3. comparative anatomy, 4. comparative embryology, and 5. molecular biology Pearson Education, Inc.

9 Figure 13.6

10 Figure Transitional fossils

11 Biogeography Biogeography, the study of the geographic distribution of species, first suggested to Darwin that today s organisms evolved from ancestral forms. Darwin noted that Galápagos animals resembled species of the South American mainland more than they resembled animals on similar but distant islands Pearson Education, Inc.

12 Figure 13.8 distribution of marsupial mammals in Australia. Common ringtail possum Australia Koala Common wombat Red kangaroo

13 Comparative Anatomy Comparative anatomy is the comparison of body structure between different species and attests that evolution is a remodeling process in which ancestral structures become modified as they take on new functions Pearson Education, Inc.

14 Human hand Bat wing

15 Figure 13.9 Homology is the similarity in structures due to common ancestry Cat Whale Human remodeling of the pattern of bones forming the forelimbs of mammals Bat

16

17 Comparative Embryology Early stages of development in different animal species reveal additional homologous relationships. For example, pharyngeal pouches appear on the side of the embryo s throat, which develop into gill structures in fish and form parts of the ear and throat in humans. Comparative embryology of vertebrates supports evolutionary theory Pearson Education, Inc.

18 Figure Pharyngeal pouches Post-anal tail Chicken embryo Human embryo

19 Molecular Biology The hereditary background of an organism is documented in its DNA and the proteins encoded by the DNA. Evolutionary relationships among species can be determined by comparing genes and proteins of different organisms Pearson Education, Inc.

20 Figure Primate Chimpanzee Percent of selected DNA sequences that match a chimpanzee s DNA 92% 96% 100% Human Gorilla Orangutan Gibbon Old World monkey

21 Evolutionary Trees Darwin saw the history of life as analogous to a tree. The first forms of life on Earth form the common trunk. At each fork is the last common ancestor to all the branches extending from that fork. The tips of millions of twigs represent the species living today Pearson Education, Inc.

22 Figure Lungfishes 1 Tetrapod limbs 2 Amnion 3 Amphibians Mammals Lizards and snakes Tetrapods Amniotes 4 Crocodiles Homologous trait shared by all groups to the right 5 Feathers 6 Ostriches Hawks and other birds Birds

23 Figure Common ancestor of lineages to the right Lungfishes 1 Tetrapod limbs 2 Amnion 3 Amphibians Mammals Lizards and snakes Tetrapods Amniotes 4 Crocodiles Homologous trait shared by all groups to the right 5 Feathers 6 Ostriches Hawks and other birds Birds

24 Figure 13.UN09 Observations Overproduction of offspring Individual variation Conclusion Natural selection: unequal reproductive success

25 Figure Variation exists among individuals in a population. Much of this variation is heritable.

26 Figure 13.19

27 Darwin s Theory of Natural Selection Individual variation Variation exists among individuals in a population. Much of this variation is heritable Pearson Education, Inc.

28 Genetic Variation in Populations Individual variation abounds in all species. Not all variation in a population is heritable. Only the genetic component of variation is relevant to natural selection Pearson Education, Inc.

29 Figure Frequency of individuals Pressure of natural selection Original population Evolved population Phenotypes (fur color) Black allele Original population White allele (a) Directional selection (b) Disruptive selection (c) Stabilizing selection

30 THE MODERN SYNTHESIS: DARWINISM MEETS GENETICS The modern synthesis is the fusion of genetics with evolutionary biology Pearson Education, Inc.

31 Populations as the Units of Evolution A population is a group of individuals of the same species, living in the same place at the same time and the smallest biological unit that can evolve Pearson Education, Inc.

32 Figure (a) Two dense populations of trees separated by a lake (b) A nighttime satellite view of North America

33 Populations as the Units of Evolution The total collection of alleles in a population at any one time is the gene pool. When the relative frequency of alleles changes over a number of generations, evolution is occurring on its smallest scale Pearson Education, Inc.

34 Analyzing Gene Pools A gene pool consists of all the alleles in a population at any one time and is a reservoir from which the next generation draws its alleles. Alleles in a gene pool occur in certain frequencies Pearson Education, Inc.

35 Analyzing Gene Pools Alleles can be symbolized by p for the relative frequency of the dominant allele in the population, q for the frequency of the recessive allele in the population, and p + q = 1. Note that if we know the frequency of either allele in the gene pool, we can subtract it from 1 to calculate the frequency of the other allele Pearson Education, Inc.

36 Analyzing Gene Pools Genotype frequencies can be calculated from allele frequencies (if the gene pool is stable = not evolving). The Hardy-Weinberg formula p 2 + 2pq + q 2 = 1 can be used to calculate the frequencies of genotypes in a gene pool from the frequencies of alleles Pearson Education, Inc.

37 Figure 13.UN10 Frequency of one allele Frequency of alternate allele Frequency of homozygotes for one allele Frequency of heterozygotes Frequency of homozygotes for alternate allele

38 Figure 13.20

39 Figure Allele frequencies p 0.8 (R) q 0.2 (r) R p 0.8 Eggs r q 0.2 R p 0.8 RR p Rr pq 0.16 Sperm r q 0.2 rr rr pq 0.16 q Genotype frequencies p pq 0.32 q (RR) (Rr) (rr)

40 Population Genetics and Health Science The Hardy-Weinberg formula can be used to calculate the percentage of a human population that carries the allele for a particular inherited disease Pearson Education, Inc.

41 Microevolution as Change in a Gene Pool How can we tell if a population is evolving? A non-evolving population is in genetic equilibrium, also known as Hardy-Weinberg equilibrium, meaning the population s gene pool is constant over time. From a genetic perspective, evolution can be defined as a generation-to-generation change in a population s frequencies of alleles, sometimes called microevolution Pearson Education, Inc.

42 Evolutionary Fitness Relative fitness is the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals Pearson Education, Inc.

43 MECHANISMS OF EVOLUTION The main causes of evolutionary change are genetic drift, gene flow, and natural selection. Natural selection is the most important, because it is the only process that promotes adaptation Pearson Education, Inc.

44 Genetic Drift Genetic drift is a change in the gene pool of a small population due to chance Pearson Education, Inc.

45 Figure RR RR Rr rr RR Rr RR Rr RR Rr Generation 1 p 0.7 q 0.3

46 Figure Only 5 of 10 plants leave offspring RR RR rr RR Rr Rr rr RR RR rr Rr Rr RR Rr rr RR RR Rr Generation 1 p 0.7 q 0.3 Rr Generation 2 p 0.5 q 0.5 Rr

47 Figure Only 5 of 10 plants leave offspring Only 2 of 10 plants leave offspring RR RR rr RR RR Rr Rr RR RR rr RR RR rr RR RR Rr Rr RR RR RR Rr rr RR RR RR Rr Generation 1 p 0.7 q 0.3 Rr Generation 2 p 0.5 q 0.5 Rr RR RR Generation 3 p 1.0 q 0.0

48 The Bottleneck Effect The bottleneck effect is an example of genetic drift and results from a drastic reduction in population size. Passing through a bottleneck, a severe reduction in population size, decreases the overall genetic variability in a population because at least some alleles are lost from the gene pool, and results in a loss of individual variation and hence adaptability Pearson Education, Inc.

49 Figure Original population

50 Figure Original population Bottleneck event

51 Figure Original population Bottleneck event Surviving population

52 Figure 13.25

53 The Bottleneck Effect Cheetahs appear to have experienced at least two genetic bottlenecks: 1. during the last ice age, about 10,000 years ago, and 2. during the 1800s, when farmers hunted the animals to near extinction. With so little variability, cheetahs today have a reduced capacity to adapt to environmental challenges Pearson Education, Inc.

54 The Founder Effect The founder effect is likely when a few individuals colonize an isolated habitat. This represents genetic drift in a new colony. The founder effect explains the relatively high frequency of certain inherited disorders in some small human populations Pearson Education, Inc.

55 Figure Africa South America Tristan da Cunha

56 Gene Flow Gene flow is another source of evolutionary change, is separate from genetic drift, is genetic exchange with another population, may result in the gain or loss of alleles, and tends to reduce genetic differences between populations Pearson Education, Inc.

57 Figure 13.27

58 Three General Outcomes of Natural Selection If we graph the coat color of a population of mice, we get a bell-shaped curve. If natural selection favors certain fur-color phenotypes, the populations of mice will change over the generations and three general outcomes are possible Pearson Education, Inc.

59 Three General Outcomes of Natural Selection 1. Directional selection shifts the overall makeup of a population by selecting in favor of one extreme phenotype. 2. Disruptive selection can lead to a balance between two or more contrasting phenotypic forms in a population. 3. Stabilizing selection favors intermediate phenotypes, occurs in relatively stable environments, and is the most common Pearson Education, Inc.

60 Figure Frequency of individuals Original population Original population Evolved population Phenotypes (fur color) (a) Directional selection (b) Disruptive selection (c) Stabilizing selection

61 Figure 13.UN11 Original population Evolved population Pressure of natural selection Directional selection Disruptive selection Stabilizing selection

62 Sexual Selection Sexual selection is a form of natural selection in which individuals with certain traits are more likely than other individuals to obtain mates. Sexual dimorphism is a distinction in appearance between males and females not directly associated with reproduction or survival Pearson Education, Inc.

63 Figure (a) Sexual dimorphism in a finch species (b) Competing for mates

64 Evolution Connection: An Evolutionary Response to Malaria We can see the results of past natural selection in present-day humans. Malaria first emerged as a serious threat to people in Africa just 10,000 years ago, long after humans had established populations around the globe, therefore only producing evolutionary responses in malarial regions Pearson Education, Inc.

65 Evolution Connection: An Evolutionary Response to Malaria Sickle hemoglobin is a mutation that denies the malarial parasite essential access to human hemoglobin and distorts the shape of red blood cells. Individuals with one copy of this sickle allele (heterozygotes) are relatively resistant to malaria. Individuals with two copies (homozygotes) are usually fatally ill Pearson Education, Inc.

66 Evolution Connection: An Evolutionary Response to Malaria In the African tropics, malaria is most common and the frequency of the sickle-cell allele is highest Pearson Education, Inc.

67 Colorized SEM Figure Asia Africa Frequencies of the sickle-cell allele 0 2.5% % % Areas with high incidence of malaria % % 12.5%