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Thursday, March 27, 2014

Internal food webs

This is the parasite food web containing 10 groups of clustered parasites, tissues, and immune responses.
Credit: Dr. Griffiths

Last year, I wrote about researchers adding parasites to food web diagrams. You can’t really understand the dynamic interactions within an ecosystem if you don’t take parasites into account. Well, that’s just as much true inside a body as out. We play host to a complex community of microorganisms. Understanding how different parasites interact with each other within our bodies could play a key roll in defeating them.

In particular, does the presence of one type of virus or fungi inhibit or promote the growth of another? Would treating a bacterial infection give protozoans free reign to roam the body?

To begin to answer those questions, Emily Griffiths, formerly at University of Sheffield but currently at North Carolina State University, and her colleagues pored through published papers to find cases of multiple infection. From those reports, the researchers constructed a network of interactions showing links between parasites, immune system components that could attack those parasites, and the host resources that the parasites could consume.

The authors found that most parasites are only indirectly linked to each other. In other words, they don’t care what other parasites are doing or even whether they are present at all. This is not different from most free-living species, who also do not care what other organisms are doing, so long as those creatures don’t try to eat them. Where parasites did interact, it was more likely to be by sharing food resources rather than by eliciting the same immune responses.

Like in real estate, the most important thing in parasitism seems to be location. The scientists found ten tightly bound communities of parasites, eight of which were associated with particular body parts. You can
see a cartoon of this finding at the top.  

Griffiths, E., Pedersen, A., Fenton, A., & Petchey, O. (2014). Analysis of a summary network of co-infection in humans reveals that parasites interact most via shared resources Proceedings of the Royal Society B: Biological Sciences, 281 (1782), 20132286-20132286 DOI: 10.1098/rspb.2013.2286.