house hunting by honey bees a study of group decision making thomas d. seeley department of...

House hunting by honey beesa study of group decision making

Thomas D. SeeleyDepartment of Neurobiology and Behavior

Cornell University

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?

• One queen bee

• ~ 10,000 worker bees

• 3-5% are active

(300-500 scout bees)

• 95-97% are quiescent

A Swarm of Bees

Home Sweet Home

Pioneering discovery by Martin Lindauer:scout bees report potential home sites with

waggle dances (1955)

Martin Lindauer Karl von Frisch

1. Angle of waggle run indicates direction.

Coding location information in waggle dance

2. Duration of waggle run indicates distance.

QuickTime™ and aDV/DVCPRO - NTSC decompressor

are needed to see this picture.

• 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.

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

How exactly do the scout bees conduct

their group decision making?

How does social choice (democracy) work in a honey bee swarm?

Detailed eavesdropping on the scout bees’ “debate” on a swarm

One 16-hour “debate”: 11 sites, 149 scouts

Seeley& Buhrman (1999) Behav. Ecol. Sociobiol. 45:19-31.

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?

Laboratory for experiments withhouse hunting bees:

Appledore Island, Maine

(Shoals Marine Laboratory, Cornell University)

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.

Experimental methods

Each swarm conducted its decision-making process twice, once with 1 nest box, and once with 5 nest boxes (or vice-versa).

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.

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

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

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.

QuickTime™ and aDV/DVCPRO - NTSC decompressor

are needed to see this picture.

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.

Does a swarm choose the best of the various sites that it examines?

Variable quality nest site

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.

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?

“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

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.

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.

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.

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

Dynamics on swarm cluster and at nest sites that underlie swarm decision making

Seeley, Visscher & Passino (2006) Amer. Scientist 94:220-229.

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

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

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

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