Before I even explain the topic of today’s post, I have to tell you that the papers that I’m blogging about today use the best and most hilarious piece of field equipment that I have ever seen. Project budgets may never be the same. I may even need to change study systems. Read on, if you dare.
The literature on parasites and animal personalities is ever-growing, perhaps because personalities have palpable consequences for transmission dynamics: the likelihood of direct transmission between infected and susceptible hosts often depends on host behavioral tendencies and their impacts on social interactions. I’ve blogged about this in the past: aggressive Tasmanian devils are more likely to transmit facial tumor disease to non-aggressive conspecifics and house finches that dominate the use of artificial feeders are more likely to acquire and transmit conjunctivitis. Similarly, in a world (er, Africa) where spiders live together in a shared web and cooperatively capture and share prey, bold spiders are more likely to transmit cuticular bacteria to shy spiders than shy spiders are to bold spiders (Keiser et al. 2016a). And what’s more, spider social networks are behaviorally disassortative, where bold spiders were more likely to rest in contact with shy spiders than they are with their own personality types. Thus, it appears that this system might be poised for rapid transmission of microbes, depending on the personality composition of the susceptible spiders in the colony.
These South African social spiders (Stegodyphus dumicola) live in colonies of a few dozen to over a thousand individuals. The ability to capture a large amount of large prey items is key to a colonies’ success, and colonies attack faster when they contain a mixture of bold and shy personality types in the group (Keiser et al. 2014). Furthermore, the execution of this important collective behavior is often based on the behaviors of one or a few important “keystone individuals” or leader spiders (Pruitt & Keiser 2014). These keystone individuals are so important in this system – and probably in many other systems, too – that we have to wonder: what happens when the keystone individuals take a sick day or even die from infection?
It turns out that increased bacterial load on colonies’ keystone individuals can impair the collective behavior of their entire society (Keiser et al. 2016b). Specifically, groups whose keystone individual are exposed to bacteria attack prey stimuli more slowly, and fewer individuals participate in the attack. Interestingly, the keystone’s participation in the task is not altered, suggesting that increased bacterial load alters the way keystones influence their colony-mates’ behavior.
Perhaps you find yourself wondering how, exactly, one might measure a spider group’s response to prey stimuli. Do you sit around and wait all night for some prey to get caught in the web? Boring. Do you try to throw a moth into the web and watch what happens? Rude. No, what you do is you attach a “hand-held vibrator” (Model: Flamenco Purple no. 4, Golden Triangle; do not Google if you’re at work) to a wire and then attach a piece of paper to the other end of that wire, and you use that vibrating piece of paper as your simulated prey. This is brilliant, and I HAVE SO MANY QUESTIONS. Why that model? How awkward is international travel for field work? I must know!
Anyways, social spiders are awesome, their personalities influence pathogen transmission, and their pathogens influence the role that individuals’ personalities play in colony behavior. Cool stuff!
Keiser, C.N., Jones, D.K., Modlmeier, A.P. & Pruitt, J.N. (2014) Exploring the effects of individual traits and within-colony variation on task differentiation and collective behavior in a desert social spider. Behavioral Ecology and Sociobiology, 68, 839-850.
Keiser, C.N., Pinter-Wollman, N., Agustine, D.A., Ziemba, M.J., LingranHao, J.G.L., and Pruitt, J.N. (2016a). Individual differences in boldness influence patterns of social interactions and the transmission of cuticular bacteria among group-mates. Proceedings of the Royal Society B, 283, 20160457.
Keiser, C.N., Wright, C.M. & Pruitt, J.N. (2016b) Increased bacterial load can reduce or negate the effects of keystone individuals on group collective behaviour. Animal Behaviour, 114, 211-218.
Pruitt, J.N. & Keiser, C.N. (2014) The personality types of key catalytic individuals shape colonies’ collective behaviour and success. Animal Behaviour, 93, 87-95.