As I’ve mentioned previously, I really like predators of parasites (like this and this). And I’m interested in how predators of parasites alter parasite transmission and foodwebs (like this and this). Today, I’m blogging about how Daphnia can be predators of Bd, the causative agent of chytridiomycosis in amphibians, and how that predation can reduce transmission of Bd to tadpoles. The scientific community is currently desperately looking for ways to reduce transmission of Bd, because chytrid is causing extinction of amphibian species all over the world. Daphnia are being considered as one potential biocontrol option.
The paper that I just read was by Searle et al. (2013) – it’s an Ecology and Evolution paper that you can find here FO FREE. Searle et al. (2013) explored how Daphnia (=predator) density, algae (=alternative prey) density, and grazing period affected the presence and abundance of Bd in water samples and on exposed tadpoles. They found that Daphnia reduced Bd both in water samples and on tadpoles, but the effect of Daphnia on Bd was context-dependent – the outcome depended on the Daphnia species, Daphnia abundance, algae abundance, and grazing period.
Here are three things I found really interesting about this paper:
- Daphnia magna and Daphnia dentifera, which are different sizes, both reduced the amount of Bd spores in the water, but only D. magna reduced tadpole infection. Searle et al. (2013) suggested that the two species had similar consumption rates of Bd, but that zoospores were filtered through D. magna more times and thus became less infectious in that treatment group. Coooooool.
- When Daphnia weren’t present, algae reduced the transmission of Bd. But when Daphnia were present, the reverse happened – more algae resulted in higher Bd transmission. There are some cool older papers that found that algae and habitat complexity can reduce the transmission of free-swimming aquatic parasites. This brings up some interesting questions about transmission of parasites with free-living stages in eutrophic environments.
- And finally, the amount of zoospores in water didn’t always relate to the presence/amount on tadpoles. This suggests that at these Bd densities, there isn’t a dose-response effect on tadpole infection. Interesting!!
Soooo… would Daphnia be a good biocontrol option? Maybe. Maybe not. It depends on the context. Biocontrol is tricky!
C. L. Searle, J. R. Mendelson, L. E. Green, and M. A. Duffy. 2013. Daphnia predation on the amphibian chytrid fungus and its impacts on disease risk in tadpoles. Ecology and Evolution. (Free pdf!)