The extinction crisis looming for monkeys, primates, and their relatives could have an even greater cascading effect on the small, undervalued species that camp out on and within their bodies.
People seem more aware of the plight of threatened primates than of the intestinal worms of gorillas, or understandably more passionate about mouse lemurs than about their mites. But some depend on one another.
Our closest animal relatives face a precarious future: about half of the world’s roughly 500 primate species are threatened with extinction due to human activities such as hunting, capture, and deforestation. But the death of threatened primates around the world could trigger even more species extinctions among the parasites that live on or inside them, according to a study led by Duke University.
“If all the threatened primates really die out, they will not be the only species to go extinct,” said James Herrera, the study’s author, from the Duke Lemur Center, in a statement.
“It is an entire kingdom of biodiversity that could be going extinct without our realizing it,” Herrera said. “There is so little we know about what they do in the body, that we don’t even know what we are losing.”
An earlier study suggests that about 85% to 95% of animal parasitic worms are still unknown to science, let alone evaluated by the extinction authority ‘Red List’ maintained by the International Union for Conservation of Nature (IUCN).
Herrera acknowledges that this may seem odd to worry about, given all our efforts to deworm and decontaminate ourselves and our pets. For most people, parasites are “something we want to eradicate, rather than conserve,” Herrera noted.
The idea of alien creatures biting and nesting in the moist, warm folds of the intestines makes most people shudder. But parasites do not always cause noticeable symptoms or leave their hosts sick, says the expert. Parasites may even have some surprising benefits, such as when intestinal worms help the body avoid other infections or regulate autoimmune diseases.
To assess the potential biodiversity loss if primates go extinct, the Duke Lemur Center researchers used network-analysis techniques to measure the potential cascading effect on the parasites that inhabit or live on primate bodies. Their work appeared on September 20 in the journal Philosophical Transactions B.
In their model, species are connected in complex webs of interactions involving 213 primates — including monkeys, lemurs and galagos — and 763 worms, mites, protists, and other parasites known to infect them. When a primate host disappears, the parasites connected to it can no longer rely on it for survival. Cut many of these connections, and their loss triggers a lethal cascade where one extinction begets another.
Currently, 108 of the 213 primate species are considered threatened by the IUCN. The team found that if all these species disappeared, 250 additional parasites could also be doomed, and that 176 of these parasite species had no other suitable hosts.
The extinction cascade is likely to be worse in isolated places such as Madagascar, the study found. There, forest shrinkage, illegal hunting, and collection for the pet trade are driving 95% of lemur species closer to the brink, and more than 60% of lemur parasites inhabit a single host.
For example, at least two species of nematode worms depend on the aye-aye, a long-fingered lemur with a thick tail and beaver-like teeth. If the aye-aye dies, the worms it carries will die as well.
The researchers say they cannot predict from their analyses how many of the parasites in their dataset could potentially avoid extinction by abandoning ship and adapting to new hosts that are more abundant. But some of the most notorious diseases in humans, such as malaria, AIDS caused by HIV, and yellow fever, began in other primates before spreading to people.
The study is part of a special issue of Philosophical Transactions B devoted to the macroecology of infectious diseases.
