Evolution, 4th Edition

THE GENETiCAl THEoRy of NATuRAl SElECTioN 105

studies that have been done on the genetics and ecology of the peppered moth

give us one of the most detailed understandings of evolution by natural selection

in any species. The peppered moth story also shows that evolutionary biology, like

physics and chemistry, is a rigorous science in which scientists propose and test

hypotheses.

While the peppered moth is the most famous example of evolution by natural

selection that has been directly observed, hundreds of other cases have also been

studied. One is close to home. If you’ve ever had cockroaches in your kitchen, you

may be familiar with the traps used to control them. Cockroaches are attracted to

the traps by glucose that is laced with poison. Some populations of the German

cockroach (Blattella germanica), which is found in kitchens around the world, have

evolved an aversion to glucose in just a few years. This change is caused by a single

mutation that rewires the neural receptors that cockroaches use to taste their food

[36, 42]. One type of receptor fires when a cockroach tastes something bitter, caus-

ing the cockroach to avoid it. In cockroaches that carry the mutation, the receptor

for bitter taste also fires when it is exposed to glucose (FIGURE 5.2), effectively

repelling the cockroaches from the traps.

Further evidence of the power of selection to cause rapid evolution can be seen at

your local supermarket. Almost all the food there results from the remarkable evolu-

tionary changes resulting from artificial selection, the selective breeding by humans

of animals and plants. When prehistoric farmers harvested their crops, the plants

that were most productive contributed the most seeds to the harvest. Some of those

seeds were used to plant the next year’s crop, resulting in plants that were more pro-

ductive than the previous generation. Selective breeding of domesticated animals

Futuyma Kirkpatrick Evolution, 4e
Sinauer Associates
Troutt Visual Services
Evolution4e_05.02.ai Date 12-14-2016

(A) Wild type

(B) Glucose-averse

Fructose Caffeine Glucose

Bitter

Time

Amplitude

Sweet Bitter Sweet Bitter Sweet

Fructose Caffeine Glucose

Bitter

Time

Amplitude

Sweet Bitter Sweet Bitter Sweet

FIGURE 5.2 German cockroaches have evolved an aversion to the glucose used to trap

them. (A) Cockroaches have four types of taste receptors that respond to different tastes.

The neural impulses shown here illustrate how two of these receptors respond to two

kinds of sugar (fructose and glucose) and to a bitter stimulus (caffeine). In wild-type cock-

roaches, the bitter receptor is triggered by caffeine but not by either sugar. This causes

the cockroaches to avoid caffeine. (B) In cockroaches that have the glucose-aversion

mutation, the bitter receptor is also triggered by glucose (but not fructose). This causes

the cockroaches to avoid traps that use glucose as an attractant. (After [42].)

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