Tapeworms protect sea monkeys from poisoning

Parasites aren’t always bad – if you’re a sea monkey, that is. Tapeworm larvae seem to protect the tiny Artemia crustaceans – also known as sea monkeys – from arsenic poisoning through a method a European research team calls “survival of the fattest”.

Sea monkeys are famous for living in inhospitable and heavily polluted water, and are a model for scientists to study the water toxicity. They’re able to survive by laying dormant eggs called cysts – the very same eggs you may have received in the post as a child.

They’re also an intermediate host for tapeworms. Tapeworm larvae infect sea monkeys which are, in turn, scooped up and eaten by primary hosts, such as flamingos.

So Marta Sanchez from the Doñana Biological Station in Seville, Spain, and colleagues took samples of sea monkeys from a heavily polluted Spanish estuary and found a whopping 98% were infected with tapeworm larvae. But they also saw the few uninfected sea monkeys were less resistant to arsenic toxicity than their infected watermates.

How could this be?

It turned out that it’s in the tapeworm’s best interests to keep its sea monkey home healthy until it’s consumed.

Infected sea monkeys had fat-rich droplets suspended inside them, along with higher levels of antioxidant enzymes. This had a two-pronged effect: the fatty drops sequestered toxins away from sensitive parts of the sea monkey, and the antioxidant enzymes mopped up free radicals.

It’s the “first empirical evidence that parasites can increase resistance to metal or metalloid pollution, rather than decrease it”, the researchers say.

The study was published in PLOS Pathogens.