Themes in the Study of Life

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Henry Bates hypothesized that this mimicry evolved in harmless species as an evolutionary adaptation that reduces their chances of being eaten

Slide 108

This hypothesis was tested with the poisonous eastern coral snake and its mimic the nonpoisonous scarlet kingsnake

Both species live in the Carolinas, but the kingsnake is also found in regions without poisonous coral snakes

If predators inherit an avoidance of the coral snake’s coloration, then the colorful kingsnake will be attacked less often in the regions where coral snakes are present

Slide 109

Fig. 1-25

South Carolina

North Carolina

Key

Scarlet kingsnake (nonpoisonous)

Scarlet kingsnake (nonpoisonous)

Eastern coral snake (poisonous)

Range of scarlet

kingsnake only

Overlapping ranges of

scarlet kingsnake and

eastern coral snake

Slide 110

Field Experiments with Artificial Snakes

To test this mimicry hypothesis, researchers made hundreds of artificial snakes:

An experimental group resembling kingsnakes

A control group resembling plain brown snakes

Equal numbers of both types were placed at field sites, including areas without poisonous coral snakes

Slide 111

Fig. 1-26

(a) Artificial kingsnake

(b) Brown artificial snake that has been attacked

Slide 112

Fig. 1-26a

(a) Artificial kingsnake

Slide 113

Fig. 1-26b

(b) Brown artificial snake that has been attacked

Slide 114

After four weeks, the scientists retrieved the artificial snakes and counted bite or claw marks

The data fit the predictions of the mimicry hypothesis: the ringed snakes were attacked less frequently in the geographic region where coral snakes were found

Slide 115

Fig. 1-27

Artificial kingsnakes

Brown

artificial snakes

83%

84%

17%

16%

Coral snakes

absent

Coral snakes

present

Percent of total attacks

on artificial snakes

100

80

60

40

20

0

RESULTS

Slide 116

Designing Controlled Experiments

A controlled experiment compares an experimental group (the artificial kingsnakes) with a control group (the artificial brown snakes)