Transcript House hunting by honey bees - University of Chicago Press

House hunting by honey bees
a study of group decision making
Thomas D. Seeley
Department of Neurobiology and Behavior
Cornell University
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?
Group decision making
Individual Inputs
Aggregation Process
Group Action
A Swarm of Bees
• One queen bee
• ~ 10,000 worker bees
• 3-5% are active
(300-500 scout bees)
• 95-97% are quiescent
Home Sweet Home
Pioneering discovery by Martin Lindauer:
scout bees report potential home sites with
waggle dances (1955)
Martin Lindauer
Karl von Frisch
Coding location information in waggle dance
1. Angle of waggle run
indicates direction.
2. Duration of waggle
run indicates distance.
QuickTime™ and a
DV/DVCPRO - NTSC decompressor
are needed to see this picture.
Lindauer’s
key findings
• 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 (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 does social choice (democracy)
work in a honey bee swarm?
How exactly do the scout bees conduct
their group decision making?
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
at swarm?
Scout quorum
at site?
What is the decision evidence?
Where is it accumulating?
Laboratory for experiments with
house 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
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.
• 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)
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
Monkey brain
Bee swarm
16
Selected
nest box
No. of scout bees
14
12
quorum
10
8
6
4
Nonselected
nest box
2
0
1
2
3
4
5
6
7
8
Time
9
10 11 12 13 14
When quorum is reached, scout bees produce
an acoustical signal (“worker piping”)
to stimulate non-scouts to warm up for flight
Seeley & Tautz (2001)
QuickTime™ and a
DV/DVCPRO - NTSC decompressor
are needed to see this picture.
Piping/warming takes 30-60+ minutes
Seeley, Kleinhenz, Bujok &Tautz (2003) Naturwissenschaften 90:256-260.
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
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
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
So-so
site
Superb
site
Site 1
r1
Uncommitted
r2
Site 2
bees
a1
Scout bees
a2
bees
N1
U
For each site i: dNi/dt = NiriU - Niai
Bees need this: r1 > r2 and a1 < a2
N2
Tuning of dance duration as a function of site quality
Number of dances
10
15 liter nest box
40 liter nest box
8
6
4
2
0
0
10
20
30
40
50
60
70
80
90
100 110 120
Waggle runs per dance
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
Superb site
90+75+60+45+30+15 = 315
waggle runs
So-so site
30+15 = 45 waggle runs
6 5 4 3 2 1 0
Remaining returns to swarm
with dancing
• 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.
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
Collaborators
Brigitte Bujok (Würzburg)
Susannah Buhrman (Cornell)
Marco Kleinhenz (Würzburg)
Roger A. Morse (Cornell)
Kevin Passino (Ohio State)
Jürgen Tautz (Würzburg)
Kirk Visscher (UC-Riverside)
Field Assistants
Siobhan Cully
Robert Fathke
Benjamin Land
Adrian Reich
Ethan Wolfson-Seeley
Funding
Inspiration
National Science Foundation
Martin Lindauer (Würzburg)
National Geographic Society
U.S. Dept. of Agriculture