Woolly Bear Caterpillars
Michael Singer at Wesleyan University discovered that, when healthy, tiger moth larvae, also known as woolly bear caterpillars, focus their diet on nutrient-rich food, but switch to eating plants with high levels of toxic substances when infected with parasites. The basis for this preference, Singer learned, has to do with taste. Parasitic infection by tachinid flies, for example, increased the firing rate of caterpillar taste cells in response to toxic pyrrolizidine alkyloides (PA), compared to uninfected caterpillars, enhancing their preference for PA-rich food. Eating such food, Singer found, improved infected caterpillar survival.
When experiencing stomach upset, chimpanzees turn to noxious plants, such as the bitter leaf plant, to help handle any intestinal parasites that might be causing their symptoms. “They remove the bark and leaves like a banana,” explains Michael Huffman of the University of Kyoto. “Once they suck out the juice, the chimps spit out the fiber”—receiving no nutritional benefit from the plant, but giving the nematodes in their gut a toxic bath.
Gibbons, Macaques, and More
A number of primate species, including chimpanzees, Japanese macaques, gibbons, and bonobos, sometimes choose plant material for its physical characteristics. A behavior called “leaf swallowing,” wherein a chimp picks a rough leaf, folds it carefully, and swallows it whole. Covered in tiny stiff hairs, the leaves sweep through the chimps’ intestines undigested, carrying parasites with them.
Capuchin monkeys have been spotted frantically rubbing their fur with citrus fruits, fuzzy terciopelo pods, clematis stems, and marigold pepper leaves—all plant materials rich in aromatic compounds known to have microbicidal effects. Capuchins don’t restrict themselves to plant matter, however. Millipedes and insects, too, have their place on a well-anointed capuchin. Researchers hypothesize that benzoquinones secreted by millipedes repel mosquitos, and that ant-derived formic acid also helps keep capuchin fur free of irritating insects.
Honey bees were recently shown to self-medicate, and perform the task as a whole colony. When challenged with the fungus Ascophaera apis, which causes a larval disease called chalkbrood, researchers at North Carolina State University and the University of Minnesota found that the worker bees sought out more propolis and less pollen than usual. Propolis, sticky resins bees forage from a variety of plants, are rich in antimicrobial activity. Adding propolis to hives decreased fungal infections by A. apis.
Sheep learn to increase consumption of foods that alleviate symptoms associated with parasitic nematode infection. They also learn to eat moderate amounts of tannin-rich alfalfa when suffering from nematode infections, which helps reduce parasite burdens.
The protozoan parasite Ophryocystis elektroscirrha forms spores on adult monarch butterflies, which get transferred to the milkweed plant as the monarch mother lays her eggs. Once the caterpillars hatch, they’ll eat the parasite spores and stay infected for the rest of their lives. An adult monarch can’t cure its own infection, but she can protect her offspring by choosing the right species of milkweed—one rich in cardenolides that may be toxic to the protozoan.
Drosophila melanogaster larvae are extremely resistant to alcohol’s toxic effects, but the parasitic wasps that lay their eggs in fruit fly larvae are not. As a result, parasitized D. melanogaster larvae fed a diet rich in alcohol live longer than their booze-free compatriots. Not surprisingly, fruit fly larvae actively seek out alcohol-laced food when parasitized.
On Lake Ontario, scientists observed double-crested cormorants eating small stones. Birds commonly eat stones to aid digestion, but these stone-eating birds were less plagued by nematode parasites, and those in areas with higher parasite infestation tended to eat small stones more often.
Female sifaka lemurs in Madagascar choose food that’s rich in tannins during pregnancy, while males and non-pregnant females avoid plants high in these astringent compounds. In what may be the first demonstration that self-medication can improve reproductive fitness, scientists found that eating tannins correlated with more successful births.
Read the full story.