Why We Should Worry About Parasites If Primates Go Extinct

It’s easy to care about endangered primates. More than half of the world’s 504 primate species are threatened with extinction.

But when chimps, gorillas, and lemurs are threatened, the parasites that live on them could also go extinct, according to a new study.

It’s not admittedly as appealing as worrying about cute animals, says first author James Herrera, research scientist and program coordinator of the Duke University Lemur Center.

“It is hard to get general audiences as excited as I am, most people get very grossed out hearing about all the parasites out there,” Herrera tells Treehugger. “But some parasites are so cool it is possible to change their minds. Disease ecologists, on the other hand, are all too excited to talk about the creatures living on and inside of us!”

For the study, researchers created a model to analyze the possible effects that the loss of primates would have on parasites. They set up a network with 213 primates and 763 parasites and then removed 114 threatened primate species in order to simulate the effects of extinction. The results were published in the journal Philosophical Transactions B.

If a primate host disappears, the parasites that live on it can no longer rely on it for survival. If enough of these relationships end, there’s a domino effect where one extinction leads to another.

Herrera likens it to the classic game, KerPlunk, where there’s a tube of marbles perched on top of crisscrossing sticks. If one or two sticks (or primates, in this case) are removed, then the marbles are still secure. But as fewer sticks are left, it’s more difficult to stop the marbles from falling.

“I am concerned because these parasites have many roles in the ecosystem, and so many we don't even know. Many have co-evolved with their hosts for millions of years,” Herrera says.

“Many don't cause any noticeable symptoms or disease in the hosts, and may have positive effects when the infection intensity isn't too high. and if you think about the diversity of hosts, and that many hosts have specialist parasites, that would suggest there are far more species out there than we know about. We know we're losing that biodiversity faster than ever in earth's history.” 

Of the 213 species studied, 108 are considered threatened by the International Union for the Conservation of Nature (IUCN). The researchers found that if those species disappeared, 250 parasites could also be doomed. And of those species, 176 have no other potential hosts.

The study found that the ripple effect would likely be heightened in isolated places like Madagascar. On the island, 95% of lemur species are having difficulty due to shrinking habitat, illegal hunting, and poaching for the pet trade.

More than 60% of lemur parasites live on just one host. If their primate host dies out, so will the dependent parasites.

Why Parasites Matter

Herrera says he became interested in parasites when he was studying community ecology, which is focused on understanding how many species occur in a habitat and why.

“In a sense, each host is a habitat for a community of parasites, and it's fascinating to think about what drives variation in which parasites infect which hosts,” he says.

There can be a cascading effect on the ecosystem if these parasites become extinct.

“It might be hard to imagine, but some parasites play important roles for the regulation of host populations, akin to predators. In that sense, they are important to stabilize populations to prevent them from exceeding the environmental carrying capacity,” Herrera says.

“Parasites shape the population dynamics of the host like wolves in Yellowstone regulate their prey, and like we've seen with the wolves, that has downstream effects on the whole ecosystem.”

In some cases, if a host primate is no longer there, the parasites may not always disappear with them. Some may be able to switch to a new host (called spilling over) if their preferred host goes extinct.

“Viruses would have an advantage in adapting to new hosts because they have a very fast mutation rate, which allows them to evolve quickly. If a new variant has a mutation that allows them to invade a new, more abundant host, that mutation would be enormously advantageous and would likely lead to fast evolution down that path,” Herrera says.

“It's what we're seeing now with SARS-COV-2, what we see with many viruses. There are whole research groups focusing on documenting the world's viruses in an attempt to understand which may have the highest chance of spill-over to humans.”