Download Contagion in real social networks

Contagion in real social networks:
insights from social insects
Michael Otterstatter
Zachary Jacobson
What is a social network?
Influence
Disease
Information
Resources
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Disease spread in social networks
Meyers et al. 2005. J. Theor. Biol.
WHO 2005
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Problem: disease spread is unobservable
A possible solution: study transmission of
observable proxies for contagious disease
▫ infectious spread of behaviour (behavioural contagion)
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A novel approach
The transmission of behaviour, as a proxy
for disease, can be studied directly in
social insect networks
Here, we ask
•
does mobility behaviour spread contagiously
among bumble bees via social contact?
•
is the contagious spread of behaviour a useful
proxy for the spread of disease?
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Materials and methods
• Bumble bees (Bombus spp.)
▫ 7 colonies, reared from wild queens
▫ colonies maintained in the lab under constant light,
temperature
▫ bees allowed to forage at will in flight cage
▫ observations throughout colony cycle (3-20+ bees)
• Automated behavioural tracking
▫ Ethovision software used for 331 hr hive observations,
tracking movement and contacts between nestmates
▫ all observations and analyses are based on the
natural behaviour of bees within their hive
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Lifecycle of bumble bees
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Bumble bees in the lab
‘bee-movie’
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Automated tracking of bee behaviour
5 cm
behavioural tracking
software
video
camera
colony
Example of
movement traces
from a single
colony
flight cage
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Three analyses of bee mobility behaviour
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1. Analysis of isolated bees
Do isolated inactive bees
‘activate’ spontaneously
after a fixed interval?
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2. Analysis of interacting bees
mobility behaviour
z
contact
rates
zz
Are inactive bees ‘activated’ by
contacts from mobile nestmates?
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3. Analysis of all bees within a hive
In an active hive, is a bee’s
movement behaviour
related to its recent contact
rate with nestmates?
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Results of bee behaviour analysis
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1. Mobility behaviour of isolated bees
Isolated bees show no
inherent rhythm of activity
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2. Mobility behaviour of interacting beesz z z
Inactive bees
…that became active (n=89)
…that remained inactive (n=21)
rec’d 1.46 contacts/min
rec’d 0.14 contacts/min
Inactive bees receiving many contacts from mobile
nestmates tend to become mobile themselves
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2. Mobility behaviour of interacting beesz z z
After a ‘refractory’
period, contacts
from nestmates
increase a bee’s
probability of
becoming mobile
(logistic regression)
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3. Mobility behaviour of all nestmates
In most cases, social contacts cause
mobility behaviour to spread between bees
and mobility feeds back to cause increased
contacts (bi-directional causality)
Granger Causality Statistics
Uni-directional causality
Contact causes
Mobility
4 bees
Mobility causes
Contacts
5 bees
Bi-directional
causality
17 bees
No causality
8 bees
(summary results from multivariate time-series analysis)
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Predicted dynamics of groups
When individuals behave as we observed:
We expect group behaviour like this:
Simulated activity of social group
(Goss & Deneubourg, 1988)
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Observed dynamics in bee hives
In bee hives, activity level showed stable cycles as predicted
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Observed dynamics in bee hives
Also, average rates of contact within hives showed stable cycles
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Spread of behaviour and disease
Importantly, these results suggest that the basic
underlying ‘model’ of behavioural contagion and
disease contagion may be the same:
Behavioural contagion:
Disease contagion (SIR model):
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Conclusions
• Mobility behaviour spreads contagiously among
bumble bees through social contact
• Social transmission of mobility, like disease,
results in oscillatory dynamics at group level
• Studying observable transmission of behaviour
offers a way to understand the unobservable
spread of disease in social networks
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Acknowledgements
Technical assistance:
Kieran Samuk, Athena Fung
Funding:
Health Canada Postdoctoral Fellowship Program
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