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House hunting by honey bees a study of group decision making Thomas D. Seeley Department of Neurobiology and Behavior Cornell University.

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Presentation on theme: "House hunting by honey bees a study of group decision making Thomas D. Seeley Department of Neurobiology and Behavior Cornell University."— Presentation transcript:

1 House hunting by honey bees a study of group decision making Thomas D. Seeley Department of Neurobiology and Behavior Cornell University

2 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?

3 One queen bee ~ 10,000 worker bees 3-5% are active ( scout bees) 95-97% are quiescent A Swarm of Bees

4 Home Sweet Home

5 Pioneering discovery by Martin Lindauer: scout bees report potential home sites with waggle dances (1955) Martin LindauerKarl von Frisch

6 1. Angle of waggle run indicates direction. Coding location information in waggle dance 2. Duration of waggle run indicates distance.

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8 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 swarms new home Lindauers key findings Lindauer (1955) Z. vergl. Physiol. 37:

9 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

10 How exactly do the scout bees conduct their group decision making? How does social choice (democracy) work in a honey bee swarm?

11 Detailed eavesdropping on the scout bees debate on a swarm

12 One 16-hour debate: 11 sites, 149 scouts Seeley& Buhrman (1999) Behav. Ecol. Sociobiol. 45:19-31.

13 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?

14 Laboratory for experiments with house hunting bees: Appledore Island, Maine (Shoals Marine Laboratory, Cornell University)

15 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.

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

17 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) 14:0015:0016:007:00 8:00 9:00 10:00 11:00 Seeley & Visscher (2004) Behav. Ecol. Sociobiol. 56:

18 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

19 Decision making by accumulation of evidence Selected nest box Nonselected nest box Monkey brainBee swarm quorum

20 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:

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22 Piping/warming takes 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:

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

24 Variable quality nest site

25 Results (note: winner takes all) Time of day Scouts visible at nest box Seeley & Buhrman (2001) Behav. Ecol. Sociobiol. 49:

26 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?

27 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: dN i /dt = N i r i U - N i a i Bees need this: r 1 > r 2 and a 1 < a 2 N1N1 N2N2 U r1r1 r2r2 a2a2 a1a1

28 Tuning of dance duration as a function of site quality Seeley & Buhrman (2001) Behav. Ecol. Sociobiol. 49:

29 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:

30 Decay function for scouts nest-site dances Remaining returns to swarm with dancing Seeley (2003) Behav. Ecol. Sociobiol. 53:

31 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 = 315 waggle runs = 45 waggle runs Remaining returns to swarm with dancing

32 Dynamics on swarm cluster and at nest sites that underlie swarm decision making Seeley, Visscher & Passino (2006) Amer. Scientist 94:

33 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

34 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

35 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

36 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 Inspiration Martin Lindauer (Würzburg) Funding National Science Foundation National Geographic Society U.S. Dept. of Agriculture


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