1

Evolution in Everyday Life

• The evolution of pesticide resistance in insects.

• The evolution of herbicide resistance in weeds.

• The evolution of antibiotic resistance in bacteria.

• The evolution of drug resistance in viruses.

2

Charles Lyell was

A)A contemporary of Darwin.B)A dynamical geologist.C)An important influence on Darwin’s

thinking about how to study biology.D)The captain of the Beagle on Darwin’s

voyage.E)All of the above except (D).

3

The concept that a weak force over a long period of time can have an effect comparable to that of a stronger force in a much shorter period of time is called:

A)Gradualism. B) Adaptation. C) Uniformitarianism. D)Superposition.E) Transmutation.

4

Referring to the Figure above, rank the species pairs (1,2), (2,3), (3,4) from least similar to most similar according to Darwin:

A) (1,2) least < (2,3) < (3,4) most. B) (2,3) least < (3,4) < (1,2) most. C) (1,2) least < (3,4) < (2,3) most. D) (3,4) least < (1,2) < (2,3) most. E) (3,4) least < (2,3) < (1,2) most.

5

Referring to the Figure above, rank the species pairs (1,2), (2,3), (3,4) from least similar to most similar according to Darwin:

A) (1,2) < (2,3) < (3,4). B) (2,3) < (3,4) < (1,2). C) (1,2) < (3,4) < (2,3). D) (3,4) < (1,2) < (2,3). E) (3,4) < (2,3) < (1,2).

(1,2)(2,3)

(3,4)

Dots are Most Recent Common Ancestors

6

Evolution of Penicillin Resistance by Bacteria

• Penicillin discovered in 1896, rediscovered by Fleming in 1928.

• Mass-production of penicillin began in 1943.• Staphylococcus aureus, is usually a harmless

passenger in the human body, but it can cause pneumonia, toxic shock syndrome, the most common cause of food poisoning.

• The first penicillin-resistant strains of “Staph” were isolated in 1947!

• 1967, penicillin-resistant Streptococcus pneumoniae and gonorrhea

7

The First Antibiotic: Penicillin• How Penicillin Kills Bacteria: penicillin attaches

to the cell walls of bacteria and destroys a key molecular component of the cell wall. With its cell wall disrupted, the bacterium dies.

• Resistant bacteria are not killed by penicillin, they have genes which:

(1) alter cell walls to prevent binding by penicillin or

(2) produce enzymes that attack the antibiotic: degrade the penicillin.

8

Staphylococcus aureus is commonly carried on the skin of scalp, arm pit, groin or in the nose of healthy people,

and sometimes in canned mushrooms on pizza. It is the mostcommon cause of food poisoning.

Common name: the “flesh-eating bacterium.”

Staph grows and reproduces from 50 0F to 120 0F, with the most rapid growth occurring near human body temperature (about 98 0F).

MRSA commonly occurs in the hospital setting but, more recently community-associated MRSA (CA-MRSA)

has been found in correctional facilities and athletic teams.

9

Geometric Population Growth

Time in Years

Number of CasesOf CA-MRSA

CA-MRSA cases ranged from 0 to 9 per year from 1990 through 1999 and then increased exponentially from 36 in 2000 to 459 in 2003

1999 20039

459

36

N2003 = b4 N1999 439= b4 (9) implies that b = 2.64!Finite Resource: Humans! 6,000,0000,000

10

Hospital Acquired or Nocosomial infections

• 1983, resistant Enterococcus faecium, hospital-acquired intestinal infection.

• in 1992, 13,300 hospital patients died of antibiotic-resistant bacterial infections

• cost of treating hospital infections is $1-3 billion/yr • Patients with noscomial bacteremia spend $3,600

more in direct hospital costs, and remain in hospital 14 days longer than uninfected patients.

• 500,000 patients in American hospitals contract a staphylococcal infection each year. 80+% of these are penicillin resistant.

11

Methicillinis the antibiotic

that replaced Penicillin in

1975.

99

> 50%

03> 80%

12

Vancomycin the drug of last defense

In 1992: 13,300 hospital patients died of antibiotic-resistant bacterial infections.

For more than a decade, scientists have been dreading but expecting -- an S. aureus strain to emerge that is resistant to vancomycin.

13

Percentage of hospital StaphylococcusThat are multi-drug resistant

"It's a serious threat now, and it's getting worse fast. “

0%

50%

100%

Fiji Belgium USA Japan

14

The “Cost of Resistance”

• There is a life history trade-off for bacteria between Anti-biotic Resistance and Reproductive Capacity in the absence of antibiotics.

• The bacteria live in 2 Environments:(1) The normal environment with a low

level of natural antibiotics produced by competing molds;

(2) The hospital, doctor’s office, or animal feed lot environment containing enormous amounts of man-made antibiotics.

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What is a Life-History Trade-Off?• It is based on the concept that an organism cannot do

everything well.• Football players vs Basketball Players: trade-off

between explosive strength (Football) and aerobic endurance (basketball) involving different kinds of muscle and physiology.

• “Party”students vs “Serious” students: trade-off between fun and study as a result of finite amount of time.

• Growth vs Reproduction: trade-off between acquiring resources for growth and expending resources for reproduction.

16

Evolution in Two Environments• Two kinds of bacteria:

(1) ABS, Anti-Biotic Sensitive (2) ABR, Anti-Biotic Resistant • These bacteria live in 2 Environments:

(1) The normal environment low level of antibiotics produced by competing molds;(2) The hospital, doctor’s office, animal feed lot: environments with vast amounts of man-made antibiotics.

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The Cost of Resistance: a Life History Trade-Off for the bacterium

• In the normal environment, E1

ABS, Anti-Biotic Sensitive bacteria grow faster than ABR, Anti-Biotic Resistant bacteria because:

reproductive capacity: bABS > bABR

• In the environments with antibiotics, E2:

ABR, Anti-Biotic Resistant bacteria grow faster than ABS, Anti-Biotic Sensitive bacteria because:

reproductive capacity: bABR > bABS

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Trade-off in Population Growth

Time in Generations

Antibiotic Environment:

Time in Generations

Normal Environment, No Antibiotics:

bABS > bABR bABR > bABS

NtNt

19

Anti-biotics No Anti-biotics

Environments

High

Low AB-Resistant

AB-Sensitive

b,

Rep

rodu

ctiv

e C

apac

ity

ABR strains Out grow

ABS strains

ABS strains Out grow

ABR strains

Trade-off = X

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bABR > bABS bABS > bABR

Rare Environment in 1950:

Anti-biotics presentABR strains favored

Common Environment in 1950:

No anti-bioticsABS strains favored

Use of Antibiotics Uncommon Before 1950Anti-Biotic Resistance: favored only in the common environment,

selected against everywhere else. Hence, there is a High frequency of anti-biotic resistant bacteria in 2006.

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bABS > bABR

bABR > bABS

Rare Environment in 2006:

Anti-biotics AbsentABS strains favored

Common Environment in 2006:

Lots of anti-bioticsABR strains favored

Antibiotics Common After 1950Anti-Biotic Sensitive: favored only in the rare environment,

selected against everywhere else. Hence, there is a low frequency of anti-biotic sensitive bacteria.

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Change in Use of Antibiotics = Change in the Frequency of the 2 Environments

• Anti-biotic Environments were Rare Before 1950 but became Common After 1970

• 1985: 6 million antibiotic prescriptions for sinusitis, Streptococcus pneumoniae and Haemophilus influenzae common upper respiratory tract bacterial species

• 1992: 13 million prescriptions for sinusitis• 1985: 15 million prescriptions for middle ear

infections, Streptococcus pneumoniae bacteria1992: 23.6 million prescriptions for middle ear infections

23

Feedlot Use of Antibiotics

• 19 million pounds of antibiotics per year are fed to farm animals, and 88 percent of that amount was fed at low doses, which favor evolution of antibiotic resistance because they do not kill all bacteria in a colony.

• 36 million antibiotic prescriptions at 1.5 grams per prescription.

• (36 million scripts) (1.5 g) = 54 million grams• 8.6 trillion grams in feedlots vs 54 million grams in

prescriptions

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Man-made alteration of the environment by industrial pollution changes natural selection on white and black color morphs of the moth, Biston betularia.

Man-made alteration of the environment by use of antibiotics to combat disease in humans and domestic animals changes natural selection on sensitive and resistant morphs ofStaphylococcus aureus

25

Environmental Variation and Genetic Trade-offs

• Together, environmental variation and a genetic trade-off means that more than one genetic kind of individual will be maintained in the population.

• More than one environment, More than one Genetic Strategy for Survival.