1. Resistance of Mycobacterium tuberculosis to antibiotics n This bacterium that causes tuberculosis has been one of the scourges of humankind Caused 25% of all deaths in New York City in 1804 Caused 33% of the deaths in Paris in the 19th century n It still kills more people than any other viral or bacterial disease n However, improved nutrition and sanitation caused a decline in TB in industrialized countries n The drugs rifampin and isoniazid are effective against the TB bacteria

2. Incidence of TB infections in 1997 (per 100,000 people) Less than 10 10-24 25-49 50-99 100-250 More than 250 Figure 21.6

3. n In the late 1980’s, the World Health Organization declared TB a global health emergency n A number of strains of M. tuberculosis were largely or completely resistant to rifampin and isoniazid n The case of an HIV-positive man in Baltimore provides insight into the acquisition of resistance by M. tuberculosis

4. n This man was diagnosed with an acute case of TB n A 39-month regimen of antibiotics resulted in clear x-rays of his lungs and no sign of the bacteria in his body - the antibiotics seemed to have cleared the infection n Two months later, the man was readmitted to the hospital with tuberculosis-like symptoms n Despite aggressive antibiotic treatment, the man died 10 days later

5. n The man’s physician and his research team analyzed the DNA from the resistant M. tuberculosis from the man as well as DNA from M. tuberculosis cells taken from the man when he was first admitted n The research team sequenced much of the DNA from the two strains and found only a single difference, a point mutation at a locus that codes for a portion of RNA polymerase (the protein that transcribes DNA to mRNA) n The mutation changed a TCG codon to TTG n The mutant RNA polymerase had leucine instead of serine at the 153rd amino acid in the polypeptide chain

6. n Rifampin acts by binding to the RNA polymerase of M. tuberculosis n The substitution of leucine for a serine apparently kept the rifampin from binding tightly to the RNA polymerase

7. The chain of events n The mutation arose early in the course of the infection n The mutant cells stayed at low frequency during the initial infection n After antibiotic treatment began, the mutant cells had a selective advantage n The mutant cells grew in population size, eventually causing a relapse of TB for the patient n Being resistant to rifampin, antibiotic treatment was ineffective

8. Did evolution by natural selection occur? n Was there variation in the population? Yes, there were resistant and non-resistant strains n Was this variation heritable? Yes, the researchers showed that the phenotypes of the two strains were due to variation in their genotypes n Did natural selection occur? Yes, only a small fraction of the M. tuberculosis cells survived the first round of antibiotics n When selection occurred, did a non-random subset of the population survive better and reproduce more? It is clear that cells with the mutant allele conferring antibiotic resistance increased through time

9. In tundra habitats above timberline, the alpine skypilot is pollinated primarily by bumblebees. In forested habitats below timberline, the alpine skypilot is pollinated primarily by flies. Below-timberline flower: small and skunky-smelling Flower size (mm) Number of individuals 10 12 14 16 18 20 22 10 8 6 4 2 0 Tundra flower: big and sweet-smelling Flower size (mm) Number of individuals 28 24 20 16 12 8 4 0 10 12 14 16 18 20 22 Figure 21.7 a,b

10. Tundra flower: big and sweet-smelling In tundra habitats above timberline, the alpine skypilot is pollinated primarily by bumblebees. Tundra pollinator: bumblebee Flower size (mm) Number of individuals 28 24 20 16 12 8 4 0 10 12 14 16 18 20 22 Figure 21.7a

11. In forested habitats below timberline, the alpine skypilot is pollinated primarily by flies. Below-timberline flower: small and skunky-smelling Below-timberline pollinator: fly Flower size (mm) Number of individuals 10 12 14 16 18 20 22 10 8 6 4 2 0 Figure 21.7b

12. Large flowersSmall flowers Short stemsTall stems –3–2–1012 –4 Size score 110 100 80 60 40 20 0 Bee visits received Figure 21.8

13. 020 40 60 80100110 Bee visits received 1.0 0.8 0.6 0.4 0.2 0 Relative fitness (fecundity) Figure 21.9

14. 810 8 Mother’s flower size (mm) Offspring’s flower size (mm) 12141618 12 14 16 18 Figure 21.10

15. 911131517 911131517 0 4 8 12 16 0 4 8 12 16 Number of individuals Flower size (mm) 4. Measure flower sizes and plot data. Average = 13.1 mm 4. Measure flower sizes and plot data. Average = 14.4 mm 3. Plant seedlings into randomly assigned locations in the field. 3. Plant seedlings into randomly assigned locations in the field. 2. Collect seeds; germinate in greenhouse 2. Collect seeds; germinate in greenhouse POLLINATION EXPERIMENT: CONTROL GROUP POLLINATION EXPERIMENT: EXPERIMENTAL GROUP 1. Hand pollinate a large, random sample of skypilots. 1. Allow bees to pollinate a large sample of skypilots. Figure 21.11