Australasian Science: Australia's authority on science since 1938

Should Ecologists Save Parasites?

By Stephen Luntz

Dr Melinda Moir of the Centre of Excellence for Environmental Decisions has challenged her fellow ecologists to consider when parasites deserve saving.

It is not easy to inspire donations towards the rescuing of parasitic invertebrates, but Moir uses the example of a plant relocation program to save threatened species in the south-west of Western Australia, where two out of three plants to be relocated were hosting parasites that could not feed on any other species.

“It was clear that if we took the plants and left the bugs behind, the bugs would become extinct if the plants failed to survive at their original location, as they were specially adapted to live on those plants and no others,” Moir says.

“This brings up the question of whether we are merely trying to salvage a few species that we think are important or attractive – or to preserve as much of the Earth’s biodiversity as possible through what many scientists now consider to be the sixth mass extinction driven by human activity.

“It also goes to the question: what is the real ‘value’ of a species? People may not have much time for parasites, especially ‘low-life’ bloodsuckers like ticks, but they may often play an important though largely invisible role, such as priming the immune system of their host or keeping its numbers under control.”

Moir says these questions are not widely debated. “Until the late 1990s, even on rare animals and plants, parasites were removed when they were relocated. It was thought they were detrimental to the chances of the host’s survival.”

However, we now know that parasites can play a role in priming the hosts’ immune system against disease, while some species considered parasitic have turned out to be pollinators. Parasites are also an important food source for other animals.

Moreover, Moir argues that “a world with no dependent species would be a biologically impoverished world. We ignore their fate at our own peril.”

Nevertheless there are costs involved, as it is necessary to ensure that the parasites really are exclusive to the host species and will not become pests in their new environment. Moir says that such studies can be quite expensive.

“Conserving most of the world’s biodiversity is a monumental task. But rather than be overwhelmed, we can begin to address the problem with small steps,” she says.