Contagion in real social networks: insights from social insects

1. Contagion in real social networks:insights from social insects Michael Otterstatter Zachary Jacobson

2. What is a social network? Influence Disease Information Resources

3. Disease spread in social networks Meyers et al. 2005. J. Theor. Biol. WHO 2005

4. Problem: disease spread is unobservable A possible solution: study transmission of observable proxies for contagious disease • infectious spread of behaviour (behavioural contagion)

5. 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?

6. 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

7. Lifecycle of bumble bees

8. Bumble bees in the lab ‘bee-movie’

9. Automated tracking of bee behaviour 5 cm behavioural tracking software Example of movement traces from a single colony video camera flight cage colony

10. Three analyses of bee mobility behaviour

11. 1. Analysis of isolated bees Do isolated inactive bees ‘activate’ spontaneously after a fixed interval?

12. 2. Analysis of interacting bees mobility behaviour z z z contact rates Are inactive bees ‘activated’ by contacts from mobile nestmates?

13. 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?

14. Results of bee behaviour analysis

15. 1. Mobility behaviour of isolated bees Isolated bees show no inherent rhythm of activity

16. 2. Mobility behaviour of interacting bees z z z Inactive bees receiving many contacts from mobile nestmates tend to become mobile themselves

17. 2. Mobility behaviour of interacting bees z z After a ‘refractory’ period, contacts from nestmates increase a bee’s probability of becoming mobile (logistic regression) z P = 0.03 P = 0.001

18. 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) (summary results from multivariate time-series analysis)

19. Predicted dynamics of groups When individuals behave as we observed: We expect group behaviour like this: Simulated activity of social group (Goss & Deneubourg, 1988)

20. Observed dynamics in bee hives In bee hives, activity level showed stable cycles as predicted

21. Observed dynamics in bee hives Also, average rates of contact within hives showed stable cycles

22. 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):

23. 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

24. Acknowledgements Technical assistance: Kieran Samuk, Athena Fung Funding: Health Canada Postdoctoral Fellowship Program