Study shows salt encouraged 'decoy species'.

The presence of pollutants in water may have an influence in whether biodiversity decreases disease spread, a study has suggested.

The research, conducted by the University of Wisconsin-Madison, investigated whether high biodiversity in amphibian eco-systems had differing effects on disease spread in polluted or non-polluted water.

The experiment used newly hatched wood frogs (Rana sylvatica), spring peepers (Pseudacris crucifer) and American toads (Anaxyrus americanus), splitting the tadpoles into groups that either lived in unpolluted water or salted water.

The tadpoles were then moved into water with parasites called trematodes, often called flukes, which are known to infect each of the species in the wild and disrupt their growth and development.

The results indicated that each species of tadpole had similar susceptibility to the parasites when in unpolluted water. However, in the water with salt the woodfrogs and peepers were more susceptible to infection, while toads remained unaffected.

The researchers continued the experiment by creating artificial communities with differing levels of biodiversity.

In the unpolluted water, high biodiversity communities had similar susceptibility to trematodes to low biodiversity communities.

In the polluted water, despite the salt making peepers and wood frogs more susceptible when they lived alone, the total infections among these species was cut almost in half when living in a high biodiversity community.

This indicates that the toad tadpoles, which had previously been unaffected by the trematodes, were acting as a ‘decoy species’, drawing the parasites away from the more susceptible wood frogs and peepers when living in the salt water.

The study suggests that, where ecosystems are becoming polluted, biodiversity is more important to protect species from diseases. Future research may investigate these interactions with new species and pollutants.

Jessica Hua, a professor of forest and wildlife ecology at the University of Wisconsin-Madison, said: “The idea that biodiversity can dampen disease outbreaks is an exciting idea because it provides a clear benefit and great reason for protecting biodiversity,”

“Our research suggests that whether biodiversity protects communities from disease depends on environmental conditions. We cannot understand the role of biodiversity on disease without considering how environmental factors like pollutants change host susceptibility.”

The full study can be found in the Journal of Animal Ecology.

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