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PARASITE. Doesn't the word just make your skin crawl? (that's actually the worms living under your flesh... just kidding). Despite our "ick" reaction to these animals, they play important roles in their environments - and many are under threat.
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Producer, Writer, Creator, Host:
Emily Graslie

Producer, Editor, Graphics:
Sheheryar Ahsan

Producer, Camera:
Brandon Brungard

Interviews with:
Colin J. Carlson - University of California, Berkeley
Dr. Anna J. Phillips - Curator, National Parasite Collection. Smithsonian National Museum of Natural History
This episode is filmed at and supported by The Field Museum in Chicago, Illinois.
Emily: Parasite, the word sounds nasty. We think of parasites as blood sucking illness and disease carrying aliens that infect our bodies, often without even realizing we've been infiltrated. Most people's reactions to the topic is either disgust or indifference, which makes sense. If a parasite story makes the News it's usually because it has to do with threats to human health infestations and pets, or a loss of revenue from common livestock and agricultural parasites.

So what if I told you that it's time conservation efforts turn their attention towards saving wildlife parasites. It sounds weird but think about this if an endangered species goes extinct so do all of the unique mites and tapeworms that the endangered species carried with it, like in the 1980s conservationists brought the last 20 or so California condors into captivity to save the entire species. Then they were deloused which caused a harmless chewing louse that lived on California condors and nowhere else to go extinct.

And for a population like the condors this isn't great. Scientists could have learned a lot about the endangered birds by having a better understanding of how the mites could survive on the condors without harming them or contributing to the birds extinction. But I've got some questions about this so I got in touch with Collin Carlson, a Phd student at the University of California, Berkeley, Who's Part of Pearl, the Parasite Extinction Assessment and Red List, also known as the world's first parasite conservation database.

Collin: There is really little evidence on how parasites, first of all to go extinct in a baseline let alone in the face of Climate Change so, we have the idea to put together that study and see, okay you know, how are parasites responding to a little bit change? And four and a half years later, here we've done now all of this work basically fleshing out the idea that parasite conservation might actually be a viable thing even in the face of some truly terrifying extinction rates.

Emily: And you want people to get excited about this like excited about the idea of parasite conservation.

Collin: You know, if I can be sold out, I don't even know, I just do this by training I think anyone can. Parasites are incredible, they're some of the most diverse groups of life on Earth They have some of the most amazing strategies for survival. You know, there's there's a case to be made that the majority of species on Earth are parasites. We just, we know so little about that. (

Emily: Yeah) I think that's absolutely.

Emily: I mean I'm sold. I want to go learn more about parasites.

Emily: Okay, in Biology a parasite is an organism that benefits at the expense of another species, its host. Parasitism is a behavior in a relationship, it's a way of life, but it's not a single group of organisms, like how furry things with mammary glands are all mammals. They're amazingly diverse. One study estimated as many as 40% of known species are parasitic, some are visible to the naked eye and some are so tiny that you need an electron microscope to see them.

Parasites that live on the hosts body are called ectoparasites, like lice fleas and mites. There are others that occasionally feed on their hosts like mosquitoes and leeches and many that live in the body like helmints, the parasitic worms, which includes flat worms like tapeworms and flukes and nematodes, also known as round worms. Just to give you an idea of the diversity of these parasitic animals, One study determined there could be as many as 300,000 different species of parasitic worms alone.

That's possibly four and a half times more parasitic worms than all vertebrates, every bird, fish, turtle, and mammal species on the planet combined. And by estimates in a recent paper as many as thirty percent of these parasitic worms and 10% of global parasite diversity are committed to extinction due to things like Climate Change driven habitat loss by the year 2070. But despite all of this diversity only one parasite is recognized by the international union for the conservation of nature as critically endangered and that's the pygmy hog sucking louse found only on India's endangered pygmy hog.

Emily: So by this point I'm pretty into this topic and I want to go check out some parasites in the collection and consider my surprise when Jochen, the Field's collection manager of invertebrates, shows me this This is it. It's like five trays in this whole collection I want to see some parasitic worms.

Anna: Hello.

Emily: Hi Anna.

Anna: Hey.

Emily: This is Dr. Anna J Phillips, she's the curator of the national parasite collection in Washington DC.

Anna: Here at the National Museum of Natural History, we have a national parasite collection and in that collection there's about a hundred and twenty thousand specimen lots, but if we consider the number of individual parasite it's hard to estimate because some of these parasites are microscopic it very small is difficult to count each and every one so we estimate this probably between 20 million individuals but we could go as high as 70 million.

Emily: We have 30 million specimens in our whole museum That's Amazing! But I was gonna ask you, so we have all of these vertebrates that come into The Field Museum and I was a little bit surprised that we here at the Field don't have more parasites and that's just not a part of the accession in process. So what are some of the complications then, in collecting these parasites?

Anna: Parasites can be a little tricky to collect sometimes and a lot of the institutions that have larger parasite collections have a tradition of that, so they've probably had a specialist at some point in their history, that's really put a focus on collecting parasites in addition to collect and host organisms. Another thing is that because they are small in a lot of these are soft bodied, so these are worms and other blood parasites. They require special methods to collect them properly to make them to be easily medium specimens, that can be used for years into the future.

Emily: In the past, the Field Museum has had a few different curators who have studied ectoparasites, the ones that live on the body, but it's been a lot of years and more research needs to be done and the collections aren't exactly accessible.

Emily: Parasite research isn't straightforward for one thing there isn't like an amateur parasite fandom or community to dip your toe Into, like, there is for birds, or insects

Emily: This is partly because parasites are small often located literally inside of another animal and difficult or messy to extract. Plus they're really challenging to identify especially if you don't have easy access to a museum collection with a lot of them. So you can make the argument that parasites are diverse and inherently interesting. But aren't they ultimately bad for their hosts?

Well these relationships are complicated. It's true that some can wreak havoc on unwitting hosts especially if that parasite isn't suited to the hosts physiology and that's because many parasites have co-evolved alongside their hosts for thousands to millions of years, and are adapted to the host-parasite relationship. But problems can arise when these co-evolved parasite host interactions become disturbed and a parasite seeks a new host environment one that it's not adapted to.

And now with Climate Change altering the distribution and habitat ranges of many wild animal populations, parasitologists are wondering how will this impact the parasites of those animals. Parasites truly are crucial to the structure and function of their ecosystems and they play important roles in the food chain. One study estimated that 60% of the endangered Japanese trouts annual diet comes from eating grasshoppers that were driven to jump into headwater streams due to a nematode parasite in the insects.

One that requires the grasshopper to seek water so the worm can complete its life cycle. For better or worse parasites can regulate wildlife populations. A species of gut tapeworm is now the leading cause of deaths in giant pandas and they've begun evolving drug resistance.

It's one that conservation scientists are actively studying to learn more about how these worms evolved, which is going to be necessary if they hope to find a treatment for the pandas. But maybe the best case in arguing for the preservation study and devilifying of wildlife parasites is that studying parasites and emerging diseases are two sides of the same coin.

Collin: You Know, parasites are, you know, up to 80% of the food web links in an ecosystem. So they're kind of puppeteers. They're interacting like, with each other, and they might be the glue that holds some ecosystems together, What we think to be happening is if parasites are going extinct in some ecosystems that might make it easier for others to invade and cause disease and generally kind of, get out of control. It's a lot like when you miss a predator, like the wolf in a ecosystem, and the deer population skyrockets.

We think similar things could happen with parasites.

Emily: Humans, even though we always do this we shouldn't pass judgment values on species. If we're working to conserve and study the diversity of life on this planet. That doesn't just go for tigers and pandas. That goes for their parasites too.

It still has brains on it.