Warm-up could obliterate 33% of Earth’s parasites

The velvet mite, Trombidium holosericeum has a parasitic larval stage. (Credit: Björn S.../Flickr)

Changing climate around the globe could cause the extinction of up to a third of the world’s parasite species by 2070, report researchers.

Parasites are one of the most threatened groups of life—and their loss could dramatically disrupt ecosystems, experts say.

Parasites have an admittedly bad reputation. The diverse group of organisms includes tapeworms, roundworms, ticks, lice, fleas, and other pests—most of which are best known for causing disease in humans, livestock, and other animals.

But they also play important roles in ecosystems, helping to control wildlife populations and keeping energy flowing through food chains.

parasite specimens from Smithsonian
An assortment of specimens from the Smithsonian’s National Parasite Collection at the National Museum of Natural History. (Credit: Paul Fetters/Smithsonian Institution)

Because many parasites have complex life cycles that involve passing through different host species, parasite diversity can be considered a sign of a healthy ecosystem, says Anna Phillips, a research zoologist and curator of the US National Parasite Collection at the Smithsonian Institution’s National Museum of Natural History.

“Having parasites is a good indicator that the ecosystem has been stable. It means the system has a diversity of animals in it and that conditions have been consistent long enough for these complex associations to develop.”

Despite their critical contributions to ecosystems, parasites have drawn less attention from conservation biologists than more charismatic creatures. Until now, they have largely been left out of studies of climate change and its impacts, says Colin Carlson, a graduate student at the University of California, Berkeley and lead author of the study in Science Advances.

To find out how climate change is likely to affect the survival of a wide range of parasite species, researchers turned to museum collections. The US National Parasite Collection, an expansive set of worms, fleas, lice, and other parasites, provides a broad and deep record of different species’ occurrences around the world.

The still-growing collection began in 1892 and now contains millions of organisms. Most species are represented by many specimens, meaning researchers can use the museum’s records to investigate organisms’ geographical distributions and predict changes over time.

Researchers combined records from the US National Parasite Collection with additional information from specialized databases cataloging ticks, fleas, feather mites, and bee mites to enable a comprehensive global analysis.

…parasites are even more threatened than the animal hosts they rely on.

Before they could begin their analysis, researchers needed to know exactly where each specimen came from so they could understand their habitat needs. In recent years it has become standard to pinpoint a specimen’s original location with GPS coordinates in collection records, but the locations associated with older specimens tend to be less precise.

So the team, including 17 researchers in eight countries, spent years tracking down the exact geographical source of tens of thousands of parasite specimens, adding GPS coordinates to their database wherever possible—information essential for the current study that will also aid in future research.

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Nyeema Harris, a wildlife ecologist at the University of Michigan, scoured multiple parasite databases for geographic information, including records from the university’s Museum of Zoology curated by Professor Barry OConnor, whose research focuses on the evolution and ecology of parasitic and commensal mites and their hosts.

“Climate change has the capacity to alter nearly every dimension of biodiversity,” says Harris, an assistant professor of ecology and evolutionary biology. “Yet, despite being among the most diverse groups of organisms on Earth, parasites have previously been omitted from vulnerability assessments.

“Given our concerns about parasites devastating animal populations and the transmission risks to humans, it’s been surprising to discover their patterns of diversity and to understand their sensitivities to such a major environmental concern.”

“…even in the best-case scenario, we’re still looking at fairly major global changes.”

Once the geospatial information was complete, the data could be used to make predictions about how parasites will fare as the Earth’s climate changes. Using climate forecasts, the researchers compared how 457 parasite species will be affected by changes in climate under various scenarios.

The analysis determined that parasites are even more threatened than the animal hosts they rely on. The most catastrophic model predicted that more than a third of parasite species worldwide could be lost by 2070. The most optimistic models predicted a loss of about 10 percent.

“[Slowing climate change] has a really profound impact on extinction rates, but even in the best-case scenario, we’re still looking at fairly major global changes,” Carlson says.

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Parasites need to be included in conversations about conservation, and this study highlights their delicate position in complex ecosystems, the scientists say.

“Parasites are definitely going to face major extinction risk in the next 50 years,” Carlson says. “They are certainly as threatened as any other animal group.”

Researchers have shared what they’ve learned on an online parasite “Red List” that identifies the extinction threat level of each species in the study. While much of conservation biology focuses on single species, it is important to keep in mind the goal of conserving ecosystems as a whole.

“As long as there are free-living organisms, there will be parasites,” Phillips says. “But, the picture of parasite biodiversity in 2070 or beyond has the potential to look very different than it does today based on the results of these models.”

The University of California, Berkeley, and the Natural Sciences and Engineering Research Council of Canada funded the work.

Source: University of Michigan