Carb loading: It’s not just for runners anymore—because apparently parasitic wasps are able to force their host caterpillars to seek out the sweet stuff.
This research comes out of the 2016 annual conference of the Society for Integrative and Comparative Biology, where a team from Wesleyan University presented their findings.
The researchers were interested in how parasites and parasitoids might influence feeding behavior and diet of their hosts—as a parasite might need different nutrients than its host, it seems only logical they would manipulate the host’s feeding patterns to suit their needs. Up until now, though, the topic has been little-studied, and there is nothing conclusive regarding its existence.
“There hasn’t been much evidence,” said Melissa Bernardo, a PhD student at Wesleyan University who studies how parasites and parasitoids manipulate their hosts, in a statement.
Bernardo and the rest of the Wesleyan team may have found just the proof they were looking for for their hypothesis, though. They decided to put their focus on the wooly bear caterpillar—which, unlike most other kinds of caterpillars, grazes on more than 80 plant species. That amount of variety gives a parasitoid the potential to force any number of different diet changes, meaning it’s a good place to search for diet manipulation.
In the case of the caterpillars, it usually lives 14 days after the wasp lays eggs inside of it. After that, the wasp larvae emerge, killing the wooly bear, and usually consuming it. In between the egg-laying and the hatching is where things got interesting for the team.
After a series of experiments in which the team granted caterpillars access to both a protein- or carbohydrate-rich diet, they discovered that the unparasitized caterpillars selected the protein diet, whereas the egg-burdened caterpillars went for a…sweeter fare.
“The wasps are making their hosts carb-load,” said Bernardo.
Carb-loading caterpillars have much bigger larvae
And the more carbs the caterpillars ate before day 14, the larger the larvae were that emerged. Apparently, though, the carbs aren’t exactly what the larvae want.
“When these parasitoids are older larvae living in the host, they switch from feeding on host blood to feeding on specific host tissue,” explained Bernardo.
And the emerging larvae grow in size thanks to the tissue they eat in order to emerge—and grow even larger in carb-loaded caterpillars, as the ingestion of carbs leads the caterpillars to store them as lipids (fat). The more carbs the caterpillars eat, the more lipids accumulate in their tissues, and the more the larvae eat on their way out. This serves the wasps nicely, as they cannot produce lipids themselves—so they need to get it elsewhere.
And there is evidence a similar process could happen in humans, too. “There are hypotheses out there that predict that our feeding behavior would be altered depending not only on the parasites in our gut, but our gut microbiome in general,” Bernardo said. Lovely.
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Feature Image: Thinkstock
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