I went to a fantastic departmental seminar yesterday by Associate Professor Mark Thomas about how parasites are able to manipulate the behaviour of their unfortunate host, usually as a means of enhancing transmission or to enable the parasite to reach the next phase of its life cycle. I wanted to share some of the fantastic examples Mark talked about, starting with suicidal crickets.
A few years ago, FrÃ©dÃ©ric Thomas and colleagues described (1) how crickets infected with hairworms (Nematomorpha) commit suicide by jumping into water. This is necessary behaviour on the part of the hairworm as the parasites spend their adult lives free-living in aquatic environments where they mate and produce eggs.
During a field study, the authors collected crickets either from the forest or around a swimming pool, and found very different rates of infection: 15% (5/33) for forest-caught crickets compared with 95% (36/38) for those collected around the swimming pool. Furthermore, when all the crickets were placed near the swimming pool, almost half of infected crickets entered the water within 15 minutes, compared to less than 14% of uninfected crickets. Infected crickets that had been rescued immediately returned to the edge of the swimming pool and jumped in again.
FrÃ©dÃ©ric Thomas and colleagues have used a proteomics approach to identify proteins expressed by infected crickets and grasshoppers and their infecting hairworms to find the cause of the suicidal behaviour (2). Turns our hairworms synthesise two proteins from the Wnt family of signalling molecules that are homologous to insect proteins involved in the development of the central nervous system (CNS). Similarly, infected grasshoppers also show higher synthesis of two Wnt proteins in their CNS.
So there you have it. Parasitic worms can control the brains of crickets. Whatever next?!
1. Thomas, F. , Schmidt-Rhaesa, A. , Martin, G. , Manu, C. , Durand, P. and Renaud, F. (2002), Do hairworms (Nematomorpha) manipulate the water seeking behaviour of their terrestrial hosts?. Journal of Evolutionary Biology, 15: 356—361. doi: 10.1046/j.1420-9101.2002.00410.x
2. Biron, D.G. , MarchÃ©, L. , Ponton, F. , Loxdale, H.D., GalÃ©otti, N., Renault, L., Joly, C. and Thomas, F. (2005), Behavioural manipulation in a grasshopper harbouring hairworm: a proteomics approach. Proc. R. Soc. B, 272: 2117-212. 6doi: 10.1098/rspb.2005.3213.