Evolution, 4th Edition

58 CHAPTER 3

We have already seen (in Chapter 1) that bacteria can evolve resistance to anti-

biotics very rapidly. Similarly, resistance to chemical pesticides has evolved in hun-

dreds of species of insects (FIGURE 3.4), and many species of weeds have evolved

resistance to herbicides within 10–20 years of field exposure. Copper, zinc, and other

heavy metals are toxic to plants, but in several species of grasses and other plants,

metal-tolerant populations have evolved where soils have been contaminated by

mine works less than 100 years old. When tolerant and nontolerant genotypes of

a species are grown in competition with other plant species in the absence of the

metal, the growth of the tolerant genotypes is often much lower than that of the

nontolerant genotypes, implying that adaptation has costly side effects [1, 32].

Commercial overexploitation has severely depleted populations of many species

of fish and has resulted in evolutionary changes as well [30]. In many species there

has been a trend toward earlier sexual maturation at a smaller size, as we predict

when larger age classes are more subject to predation (see C hapter 14). In some

species, such as Atlantic cod (Gadus morhua), these changes clearly have a genetic

basis (FIGURE 3.5A). Similarly, trophy hunting for bighorn sheep (Ovis canadensis)

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_03.04.ai Date 11-30-2016

Number of resistant pest species

1940 1950 1960 1970 1980 1990

100

0

200

300

400

500

600

DDT

Insecticide class:

Cyclodienes

Organophosphates

Carbamates

Pyrethroids

FIGURE 3.4 Cumulative numbers of arthropod Total

pest species known to have evolved resistance

to five classes of insecticides. The upper curve

shows the total number of insecticide-resistant

species. The number has increased since these

data were tabulated. (After [34].)

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_03.05.ai Date 11-28-2016

Note: I removed bullet points from the Body length (red) line in part (A) since the Maturity line (green) didn’t have data points.

Should the error bars be removed from part (B)? I left these in since it wasn’t requested.

50% maturity (age in years)

1975 1980 1985 1990 1995 2000 2005

Year

5

6

7

Mean horn length (cm)

1975 1980 1985 1990 1995 2000 2005

Year

40

50

60

70

80

Body length at 5 years (cm)

30

40

50

60

70

80

(A) (B)

Fishery closed

1992

Maturity

Body length

FIGURE 3.5 Evolutionary changes caused by human harvesting. (A) The age at which

50 percent of Atlantic cod reached maturity declined until 1994 when the fishery was

closed because of overfishing. Body length at 5 years of age also declined until 1994

(B) Mean horn length of 4-year-old bighorn sheep rams declined because of selection

imposed by hunting. (A after [38]; B after [8].)

03_EVOL4E_CH03.indd 58 3/22/17 1:19 PM