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Effects of the parasite, Ophryocystis elektroscirrha, on wing characteristics important for migration in the monarch butterfly

Davis, Andrew K., de Roode, Jacobus C.
Animal Migration 2018 v.5 no.1 pp. 84-93
Danaus plexippus, Protozoa, color, flight, migratory behavior, overwintering, parasites, pigmentation, tensile strength, wings, Mexico
There is mounting evidence that the longterm declines of overwintering monarchs in Mexico are exacerbated by losses during the fall migratory journey. Infection with the protozoan, Ophryocystis elektroscirrha (OE), is known to negatively impact migration success. Here we examine how infections affect specific wing traits of monarchs that are important for migratory success. We used a collection of infected and uninfected monarchs reared under identical conditions, and from the (deceased) specimens, measured wing area (larger monarchs are known to have greater migratory success), wing color (the shade of orange pigmentation in monarchs is a known predictor of migration and flight ability), and the physical density of wings (a measure of wing mass per unit area). We also measured the tear-resistance of wings, using an apparatus that measured the force needed to cause a tear in the wing. Results showed no effect of OE on overall wing size, nor on the shade of orange pigmentation, but a clear effect on measures of physical density and tensile strength. Wings of infected monarchs weighed less per unit area (by 6%), and there was a 20% reduction in tear-resistance of wings. All results were qualitatively similar in a follow-up investigation using freshly-killed specimens. Collectively, this indicates infected monarchs are more prone to wing damage, which would be costly during long-distance migration. As such, this would be one more way in which OE infections reduce migratory success. Given the toll of OE to the monarch population, especially during migration, it would be prudent to focus conservation efforts on mitigating human activities that spread this disease.