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House hunting by honey beesa study of group decision making
Thomas D. SeeleyDepartment of Neurobiology and Behavior
Cornell University
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Group decision making
Individual Inputs
Aggregation Process
Group Action
The question of social choice:
How can a group use the knowledge and opinions possessed by its members
to produce an optimal choice of action for the
group as a whole?
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• One queen bee
• ~ 10,000 worker bees
• 3-5% are active
(300-500 scout bees)
• 95-97% are quiescent
A Swarm of Bees
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Home Sweet Home
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Pioneering discovery by Martin Lindauer:scout bees report potential home sites with
waggle dances (1955)
Martin Lindauer Karl von Frisch
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1. Angle of waggle run indicates direction.
Coding location information in waggle dance
2. Duration of waggle run indicates distance.
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QuickTime™ and aDV/DVCPRO - NTSC decompressor
are needed to see this picture.
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• Initially, bees perform dances for multiple sites
• Before swarm flies away, all dances indicate one site
• The swarm flies to the consensus site, moves in
• Therefore, dances on swarm indicate nest sites
• Scouts are holding a kind of plebiscite on the swarm’s new home
Lindauer’skey findings
Lindauer (1955) Z. vergl. Physiol. 37:263-324.
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The real estate preferences of bees (1975)
(“>” means “is preferred to”)
• Entrance height: 5 > 1 m
• Entrance area: 15 > 75 sq cm
• Entrance direction: south > north
• Entrance position: bottom > top
• Cavity volume: 40 > 10 liters
• Combs: with > without
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How exactly do the scout bees conduct
their group decision making?
How does social choice (democracy) work in a honey bee swarm?
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Detailed eavesdropping on the scout bees’ “debate” on a swarm
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One 16-hour “debate”: 11 sites, 149 scouts
Seeley& Buhrman (1999) Behav. Ecol. Sociobiol. 45:19-31.
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Decision-making process:consensus building or quorum sensing?
Dancer consensus Scout quorum
at swarm? at site? What is the decision evidence?
Where is it accumulating?
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Laboratory for experiments withhouse hunting bees:
Appledore Island, Maine
(Shoals Marine Laboratory, Cornell University)
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Testing the hypothesis of quorum sensing
Critical prediction:
Delaying quorum formation at the chosen site, while leaving the rest of the decision-making process undisturbed, should delay the reaching of a decision.
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Experimental methods
Each swarm conducted its decision-making process twice, once with 1 nest box, and once with 5 nest boxes (or vice-versa).
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1 nest-box trials vs. 5 nest-box trials
• Slower buildup of scouts at each nest box• No decrease in dancing at swarm• Marked delay in time to decision!
(on average, 3.3 vs 7.4 hours, P < 0.005)
14:00 15:00 16:00 7:00 8:00 9:00 10:00 11:00
Seeley & Visscher (2004) Behav. Ecol. Sociobiol. 56:594-601.
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Conclusions
• Decision evidence: number of scouts at
each site
• Making a decision: accumulating a
threshold number (quorum) of bees at a
site
• How bees sense the quorum remains a
mystery
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Decision making by accumulation of evidence
0
2
4
6
8
10
12
14
16
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Time
No. of scout bees
Selected nest box
Nonselected nest box
Monkey brain Bee swarm
quorum
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When quorum is reached, scout bees produce an acoustical signal (“worker piping”)
to stimulate non-scouts to warm up for flight
Seeley & Tautz (2001)
J. Comp. Physiol. A 187:667-676.
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QuickTime™ and aDV/DVCPRO - NTSC decompressor
are needed to see this picture.
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Piping/warming takes 30-60+ minutes
Why quorum sensing, not consensus sensing?
Warm up starts as soon as enough scouts (not all scouts) have approved of a site: boost speed, maintain accuracy
Seeley, Kleinhenz, Bujok &Tautz (2003) Naturwissenschaften 90:256-260.
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Does a swarm choose the best of the various sites that it examines?
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Variable quality nest site
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Results (note: winner takes all)
Time of day
Scou
ts v
isib
le a
t ne s
t box
Seeley & Buhrman (2001) Behav. Ecol. Sociobiol. 49:41416-427.
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What are the behavioral processes of the individual scout bees that underlie the
rapid buildup of scouts at superior sites, and the
eventual decline of scouts at the inferior ones?
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“Friendly competition” among coalitions of committed scouts for the uncommitted scouts
Site 1
bees
Uncommitted
Scout bees
Site 2
bees
Superb site
So-so site
For each site i: dNi/dt = NiriU - Niai
Bees need this: r1 > r2 and a1 < a2
N1 N2U
r1 r2
a2a1
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0
2
4
6
8
10
0 10 20 30 40 50 60 70 80 90 100 110 120
Waggle runs per dance
Number of dances
15 liter nest box40 liter nest box
Tuning of dance duration as a function of site quality
Seeley & Buhrman (2001) Behav. Ecol. Sociobiol. 49:41416-427.
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A bee makes multiple visits to her site, but dances less and less strongly after each visit
(phasic, not tonic, coding of site quality)
Seeley (2003) Behav. Ecol. Sociobiol. 53:417-424.
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Decay function for scout’s nest-site dances
6 5 4 3 2 1 0 Remaining returns to swarm
with dancing
Seeley (2003) Behav. Ecol. Sociobiol. 53:417-424.
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Why the scout buildup is strongest at the best site
• Scouts for the best site have the highest per capita recruitment (“birth”) rate and the lowest per capita abandonment (“death”) rate.
• Population of scouts for the best site grows most rapidly, and ultimately overwhelms, all populations for other sites.
Superb site
So-so site
90+75+60+45+30+15 = 315 waggle runs
30+15 = 45 waggle runs
Remaining returns to swarm
with dancing
6 5 4 3 2 1 0
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Dynamics on swarm cluster and at nest sites that underlie swarm decision making
Seeley, Visscher & Passino (2006) Amer. Scientist 94:220-229.
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Good decision making by groups is not automatic
“The mass never comes up to the standard of its best member, but on the contrary degrades itself to a level with the lowest.”—Henry David Thoreau, Journal, 14 March 1838
“Madness is the exception in individuals but the rule in groups.”—Friedrich Nietzsche, Beyond good and evil, 1886
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Swarm Smarts!
1. Promote diversity of knowledge within
the group
–scouts search autonomously and report freely
2. Avoid tendency to conformity, rapid consensus
–scouts conduct an open competition among opinions
–scouts assess and report sites independently
3. Aggregate opinions with both speed and accuracy
–scouts use quorum sensing,with moderate quorums
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Swarm Smarts!
1. Promote diversity of knowledge within
the group
–scouts search autonomously and report freely
2. Avoid tendency to conformity, rapid consensus
–scouts conduct an open competition among opinions
–scouts assess and report sites independently
3. Aggregate opinions with both speed and accuracy
–scouts use quorum sensing,with moderate quorums
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CollaboratorsBrigitte Bujok (Würzburg)
Susannah Buhrman (Cornell)
Marco Kleinhenz (Würzburg)
Roger A. Morse (Cornell)
Kevin Passino (Ohio State)
Jürgen Tautz (Würzburg)
Kirk Visscher (UC-Riverside)
Field AssistantsSiobhan Cully
Robert Fathke
Benjamin Land
Adrian Reich
Ethan Wolfson-Seeley
Inspiration
Martin Lindauer (Würzburg)
Funding
National Science Foundation
National Geographic Society
U.S. Dept. of Agriculture