Social immunity, as we have defined it (Cotter & Kilner 2010 Behav Ecol), is any sort of immune defence mounted by one individual for the benefit of others. (It is different from the more familiar personal immunity, where the immune system defends only the body in which it resides).
Burying beetles have a social immune system because they smear the carcass with antimicrobials for the benefit of their offspring, as well as themselves. Female beetles modulate the potency of their social immune response in relation to the scale of the threat that microbes pose to the carcass – upregulating the production of antimicrobials only when presented with a carcass (Cotter & Kilner 2010 J Anim Ecol), and in response to a greater bacterial load on the carcass (Cotter et al 2010). They have good reasons for using their social immune system so carefully. The more potent the antimicrobial exudates they produce, the lower their future reproductive success (Cotter et al 2010). Indeed, males try to avoid sustaining these costs themselves, passing them on to their partner instead (Cotter & Kilner 2010). In addition, their personal immune function must be balanced against social immune function. Wounded beetles, with upregulated personal immune systems, are less effective at mounting a social immune response (Cotter et al 2013).
Now that we understand better the costs involved in social immunity, we are interested in the detailed way the social immune system functions. For example:
• What are the active antimicrobial agents, besides the lysozyme we identified initially (Cotter & Kilner 2010)?
• What are the effects of these antimicrobials on the microbial community that might naturally infest the carcass?
Our work on social immunity was started by Sheena Cotter, who is continuing her research on insect immune function as a Senior Lecturer at the University of Lincoln.
In our lab, research on this topic is carried out by Ana Duarte, in collaboration with Martin Welch and Peter Davenport (Department of Biochemistry, Cambridge) (http://www.bioc.cam.ac.uk/people/uto/welch)
W. J. P. Palmer, A. Duarte, M. Schrader, J. P. Day, R. M. Kilner, F. Jiggins: a gene for social immunity in the burying beetle Nicrophorus vespilloides? biorxiv.org, doi: http://dx.doi.org/10.1101/020644
Cotter, S. C., Littlefair, J. E., Grantham, P. J. and Kilner, R. M. (2013) A direct physiological trade-off between personal and social immunity. J Anim Ecol 82:846-853
Cotter, S. C., Ward, R. S. J., and Kilner R. M. (2011) Age-specific reproductive investment in female burying beetles: independent effects of state and risk of death. Funct Ecol 25:652-660
Cotter, S. C., Topham, E., Price, A. J. P. and Kilner (2010) Fitness costs associated with mounting a social immune response. Ecol Lett 13:1114-1123.
Cotter, S. C. and Kilner R. M. (2010) Personal immunity versus social immunity. Behav Ecol 21:663-668.
Cotter, S.C. and Kilner, R. M. (2010) Sexual division of antibacterial resource defence in breeding burying beetles, Nicrophorus vespilloides J Anim Ecol 79:35-43