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Parasite Prejudice
Parasite researcher and blogger Tommy Leung sees beauty in the most villainized creatures on earth.
Posted on April 16, 2018
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In 1987, the California condor (Gymnogyps californianus) was on the brink of extinction. In an attempt to save the largest bird in North America, the 23 remaining individuals were placed in a captive-breeding program.  That program eventually saved the condor and now more than 400 California condors, a magnanimous turkey-like bird, are gliding back in the wild. Success story, right?

There was a largely invisible downside to rescuing the condor in this way, as Tommy Leung, a parasite ecology researcher at University of New England, points out.  A certain louse that only lives on that species went extinct during the captive-breeding program when the birds were deloused.

The California condor was saved, but the parasite that lived on it was not.

“Our conservation efforts are biased.” he says, “there’s no other organism on Earth that evokes as much apathy in people as parasites.”

Leung sees injustice in saving one animal over another, points out that parasites play a role in maintaining ecosystem health and ensure the livelihood of other species as well. He is the self-described Lorax of parasites. It’s not a role he ever intended to fill, but Leung has become an advocate for some of the most villainized creatures on Earth. “Parasites are fascinating organisms in themselves,” he explains. “They deserve to be viewed through the same lens as any other organism.”

Ever since Leung was a university student, he’s been fascinated with parasites. Now he shares that fascination with his own students at the University of New England and the world at large. On his blog Parasite of the Day, Leung showcases different parasites by highlighting what makes each one unique and interesting. Leung and his co-blogger, Susan Perkins, have used the blog to profile over 500 parasites to date.

Pretty much every animal and plant on earth has a parasite that infects it. The parasites are as varied as the hosts and can range from worms to fungi to plants. This diverse appearance and lifestyle keeps Leung inspired in his research and his art.  On Parasite of the Day, he also shares colourful anime portraits of parasites that he draws himself (see the complete collection here.)The goal is to show parasites as complex organisms with more to offer than meets the eye.

Tommy Leung re-imagines parasites as anime superheros, like Cassandra the dodder monster girl — inspired by a type of parasitic plant. (Credit: Tommy Leung)

The most commonly known parasites are animals like ticks and tapeworms, because they infect humans. “People tend to find parasites gross and creepy. They have this idea that ‘they’re going to infect me!’ But most of these parasites want nothing to do with you,” he says. “They want to leave you alone and for you to leave them alone too so they can get on with their lives.”

The huge diversity among parasites is a result of the unique evolutionary hurdles they’ve overcome, explains Leung. One of the biggest hurdles for parasites is completing their life cycle and reaching the reproductive stage.

Many parasites require multiple hosts over their lifetime, which means jumping from host to host at key life stages. Take the trematode worms (Acanthoparyphium sp.) that live out their adult lives in the guts of seabirds, such as seagulls (Laridae sp.) and oystercatchers (Haematopodidae sp.). In order to lock onto those birds, however, they first have to navigate through the food chain. First, the worms infect several other hosts, like marine snails (Zeacumantus subcarinatus). At this initial larval stage, the worm looks like a tadpole and reproduces asexually inside the snails until it almost fills up the whole body.

At this stage, known as cercaria, the worm swims out of the snail in search of a cockle clam (Austrovenus stutchburyi). When it finds a suitable cockle, the cercaria embeds itself in the soft foot of the clam. Then the cercaria turn into little marble-like cysts that make it impossible for the clam to use its foot to burrow down into the sand. This forces the clam to remain high on the sand where they become easy prey for birds — the parasite’s ultimate host.

Trematode cercaria forming cysts in the foot of a cockle clam

The trematode worms are undeniably bad news for the snail, the cockle and the seabird they infect. But, argues Leung, they create broader biodiversity on the mudflats they inhabit. The hard cockle shells they force to the sandy surface create space for barnacles and limpets to attach themselves (normally sandy surfaces would be off-limits to such animals).

This is a form of ecological engineering, explains Leung, with parasites altering the physical habitat to the benefit of other species. “Because of the effect they have on keystone species, they almost become a keystone species themselves,” he says.

While the thought of parasites and infection may seem spooky to some, Leung encourages his students and readers to look beyond the label and marvel at the ingenuity and tenacity of these parasitic organisms. “Parasites have stories to tell and there are things we can learn from them about evolution and ecosystems and life in general,” he urges. Leung’s love for parasites is about an equal approach to conservation. Whether we like parasites or not, we can’t deny the role they play in the ecosystem.

Megan Bull is studying Environmental Science at the University of British Columbia and writing for Ocean Wise’s Aquablog.

 


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