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Milkweed Toxin Aids in the Survival of Monarch Butterflies
Journal of Parasitology – Parasites are some of the most common and diverse organisms in the world. Studying the relationship parasites have with their hosts gives insight into their effects on wildlife, domestic animals, agriculture and humans. By observing parasites through their life stages, researchers are able to identify how they use their morphological changes to their advantage. This understanding may assist in reducing the effects parasites have on their hosts.
Researchers from Emory University in Atlanta, Georgia, recently published a study in the current issue of The Journal of Parasitology in which they took an innovative approach to studying host–parasite interactions. Realizing that many species will use a medicinal approach to combat parasite infiltration, they observed how the monarch butterfly utilizes toxins in milkweed plants as a form of resistance to parasites. By focusing on the spore stage of the parasite life cycle, the researchers were able to track the effects of the milkweed on the morphology of the parasite.
Forty-one monarch butterflies and three different types of milkweed plants were used in the experiment. The researchers measured the concentration of cardenolide (a type of steroid) in each plant type. During the butterfly larvae stage, parasite spores were introduced into the butterfly’s development. The goal was to study the effect that the host’s diet had on the morphology of the parasite.
The researchers found that higher concentrations of cardenolide reduced parasite spore sizes, which left them more unprotected against their host’s defences. For the host, this increased its overall fitness by increasing its tolerance to the parasite. The researchers state, “While we’d known for some time that milkweed toxins could help monarch butterflies combat their parasites, we were surprised to discover that medicinal milkweeds could change the morphology of monarch parasites. As far as we know, this mechanism hasn’t been observed previously, and it provides a new avenue for research on the effects of self-medication on parasite fitness.”
Studying how the host’s diet affects the morphology of the parasite shows that this type of medicinal approach can greatly increase the tolerance of the host and help combat the parasite. The researchers suggest further study to compare the effects of reduced- and normal-sized parasites on the monarch butterfly–parasite interaction.
Full text of the article, “Host Diet Affects the Morphology of a Butterfly Parasite,” Journal of Parasitology, Vol. 103, No. 3, 2017, is available here.
About Journal of Parasitology
The Journal of Parasitology is the official journal of the American Society of Parasitologists (ASP). The journal reports on all aspects of animal and human parasites, and is widely recognized for publishing content that has a long-term impact on the field of parasitology. The journal is intended for all with interests in basic or applied aspects of general, veterinary, medical parasitology, and epidemiology. For more information, visit us.
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