A chimpanzee grooms another

Parasites of primates like the chimpanzee are also likely to disappear if their host goes extinct. Image ©Shutterstock / Scandium

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Extinction of primates threatens greater diversity loss than first thought

The loss of the world's primates will lead to a greater loss of diversity than first thought, as their parasites also risk extinction. 

While the end of these parasites may not seem to be such a loss, their extinction will see millions of years of evolution gone forever, with potentially important scientific knowledge fading away.  

New research by scientists from Duke University suggests that hundreds of specialist parasites, from viruses to worms, may be lost forever as their mammalian hosts die out. 

It could also lead to the parasites changing and becoming more aggressive, which could lead to more infectious diseases in primates and potentially spread to humans too. 

Dr Natalie Cooper, a mammologist at the Museum who was not involved with the study, says, 'We don't necessarily know what will happen if some parasites are wiped out. Some could become more virulent, and might be able to be passed into humans.  

'We really don't know what removing some of these things will do and what the knock-on effects will be.' 

The new paper has been published in the journal Philosophical Transactions B

Ringtailed lemurs sit in palms.

95% of lemur species are threatened with extinction. Image © Shutterstock / Romet6

Arms races 

Primates, which includes lemurs, monkeys and apes, are one of the most threatened mammalian groups on Earth.  

Of the 500 or so species which can be found across many of the tropical and subtropical regions of the world, it is currently thought that at least 50% are either classed as Vulnerable, Endangered or Critically Endangered. This includes some of our closest living relatives, the chimpanzees and bonobos. 

The biggest threat to these animals is that of land-use change and deforestation, as growing human populations and demand of land encroaches on the few remaining wild places. But they also face significant pressure from hunting and the pet trade. 

This means that if things don't change, many species of primate are at risk of extinction. But it is not only the primates that may be lost forever. 

Each primate species is host to a whole range of parasites. While many of these are generalists which can infect a range of species, others are specialists which only target small groups or individual species. When the host thrives, specialist parasites continue to grow and spread in their populations. But when the host is threatened, the parasites may be too well adapted to switch to a different target. 

For instance, rhino botflies are adapted to lay eggs on rhinos as the larvae burrow into the animal's stomach to grow. But as rhinos have been targeted by poachers, the flies have also seen their populations crash as their increasingly rare hosts have become harder to find. 

But this high degree of specialisation by the parasite can create its own problems. If its host eventually becomes extinct, then the parasite can often go extinct with it, in what is known as a secondary extinction. The chances of the parasite's extinction depend on just how specialist it is, and how integral its host is to the wider ecosystem. 

'If you knock out a host and that host has a couple of completely exclusive parasites, then those will go extinct,' says Natalie. 'But if the host is peripheral to the network it may be not such a big deal for the wider community.  

'If you knock out the hosts in the middle, however, then the whole network can end up collapsing.' 

This new study looked at primates, which are known to be infected by over 1000 parasites, including everything from viruses to mites and intestinal worms. 

Previous research has shown that threatened primates have fewer parasites than the non-threatened, suggesting that some of these parasites may already be going extinct. 

After modelling the relationship between over 200 primates and 763 parasites that affect them, the researchers began to gradually remove the threatened species from the model, as if they had gone extinct. They found that over 250 parasites would be affected, of which 176 have no known other hosts and would be threatened with extinction. 

A mountain gorilla sits in the forest.

Parasites such as Covid could make the jump into other species, and even humans © Shutterstock / Onyx9

What have parasites ever done for us? 

The loss of these parasites would see a unique part of evolutionary history disappear, in many cases without ever have being known about. A 2020 study using the Museum's database of worm-like parasites called helminths estimated that up to 95% may be unknown to science. 

In certain areas of the world, the impacts may be greater. Madagascar is home to all the world's lemurs, of which 95% are threatened of extinction. Two thirds of their parasites live in just one host, and will vanish without protection. 

'We should be protecting them because they're unique organisms and contribute to biodiversity,' Natalie says. 'Of all the organisms in the world, it shouldn't be our responsibility to decide what is useful and what is not.' 

But there is also the possibility that some of these parasites could become more virulent, or make the jump to other primates, including humans. 

'For example, gorillas have a small population size and are under stress,' Natalie says. 'If they catch something very infectious, that parasite will have a greater chance of spreading through the population and perhaps wiping it out. This has been a worry for many years with diseases such as Ebola, and now for Covid.' 

The Duke University researchers have called for new research to investigate the consequences of these parasites going extinct, and how the surviving parasites may change and adapt to new species.