When looking at the organisms of the world, one might not expect that over 50% of them survive by being parasitic either in part or through their whole life. These organisms range from the mundane free-loaders like the Indian pipe flower to the exotic organ replacing tongue louse, which consumes and becomes the tongue of its host. Some even manipulate their hosts so as to allow for their transmission to more preferred hosts. Such parasites include the infamous trematode, which manipulates its intermediate host (e.g. a frog) both physically and behaviourally so as to increase its host’s risk of predation. Once eaten, the parasite breeds within its final host (e.g. a bird) and its eggs are dispersed through its host’s waste. The waste is then consumed by an initial host (e.g. a snail), initiating the start of a new cycle.
Ribeiroia ondatrae Photography Courtesy Pieter Johnson |
Photograph courtesy Dave Herasimtschuk, Freshwaters Illustrated |
The effects of trematodes have also been noted in human populations, and while they may not increase a human’s risk of predation, they can significantly affect their normal bodily functioning. For example, schitosomiasis, caused by the trematode Schistosoma, is the third most prevalent tropical disease in the world. It causes internal bleeding and organ damage, and similar to the effects of Ribeiroia ondatrae on frogs, the severity of the damage depends on the host’s developmental stage, with more severe effects seen at younger ages. Thus, while the effects of parasites have been well researched with respect to humans, their effects on other organisms have been neglected. In order to fully appreciate the role of parasites in our world we must attempt to understand how they affect not only humans, but other organisms as well. Research into parasitism in animals has provided insight into how these parasites negatively affect their hosts with respect to habitat use and survival ability, ultimately increasing their own survival. Given that frog populations are declining significantly, it is imperative that attention be paid to the role of parasites in amphibians, for it is only with this knowledge that we can hope to protect amphibian populations from such life-threatening diseases.
See Also
- Whats with the Frogs? Short Documentary on the Malformations
- Colorado University Amphibian Parasite Observatory
- Goodman, B.A., Johnson, P.T.J., 2011a. Disease and the extended phenotype: Parasites control host performance and survival through induced changes in body plan. PLoS ONE 6, 1-10.
- Goodman, B.A., Johnson, P.T.J., 2011b. Ecomorphology and disease: cryptic effects of parasitism on host habitat use, thermoregulation, and predator avoidance. Ecology 92, 542-548.
- Johnson, P.T.J., Kellermanns, E., Bowerman, J., 2011. Critical windows of disease risk: amphibian pathology driven by developmental changes in host resistance and tolerance. Functional Ecology (DOI: 10.1111/j.1365-2435.2010.01830.x).