• Differential survival
• Differential reproduction
• Results in changes in allele frequencies
• Selection Against Recessives

• Selection Against Recessives

• Selection Against Heterozygotes

• Heterozygote Advantage

Kettlewell’s Experimental Study of Peppered Moth: Biston betularia

Industrial Melanism:Rapid spread of melanic (dark) forms of 50 species of Lepidoptera in industrial areas of Britain.

H. D. B. Kettlewell's Experiments to Test:

• Is there advantage to black or pale on appropriate backgrounds?
• Can the4difference be evaluated?
• Do birds or other visual predators search for and eat resting moths?
• If so, are insects taken selectively, in order of conspicuousness?

Visibility Score. 2 observers

Recorded the minimum distance at which the moths could be seen. The corroborating observer was the famous behaviorist Dr. R. A. Hinde.
 

Distance Visible	Score
> 30 yds	-3	Conspicuous
20-30	-2
10-20	-1
10	+1
5	+2
2	+3	Inconspicuous

 

Distribution of Light & Dark Forms

Birmingham - Industrial
 

Typical	89% conspicuous
Carbonaria	2 % conspicuous

Devon - Rural
 

Typical	0 % conspicuous
Carbonaria	95 % conspicuous

Aviary Experiments

• Great Tits (Parus major) - predatory bird
• 18 yd X 6 yd X 7 ft enclosure
• Dark & Light tree trunks as supports
• Dark & Light moths placed on each

Mark-Release Recapture Experiments

• Moths marked with dot of paint on underside of wings
• Released into Cadbury Bird Reserve, near Birmingham & Recaptured by traps
• light traps
• pheromone traps
• tested for trap bias - no difference in capture efficiency for carbonaria vs typical

Field Release - Recapture Results - Birmingham
 

	Carbonaria	Typical
Release (marked)	447	137
Captures (total)	651	81
Recapture (marked)	123	18
Percent Recaptured	27.5	13.1

• Survival vs Conspicuousness - carbonaria males

Survival vs conspicuousness - typical males
 

	Inconspicuous			Conspicuous
Visibility Score	+3	+2	-2	-3
Percent Survival	53.6	50	52	38

Summary of Kettlewell Results

• Three sets of results
• camouflage efficiency as scored by observers
• differential survival of predation in aviary
• mark-release results
• Each show more conspicuous moths taken
• Birds act as selective agents, as postulated by evolutionary theory

Sir Cyril Clarke's data
 

Year	% Carbonaria	SO2 in air
1959	93	290
1969	92	100
1979	85	40
1989	30	40
1997	6.5	??

This page last modified Wednesday, 23-Aug-2000 17:33:10 EDT