Monarch Butterflies: Seasonal Migrations Lower Infection Levels In Wild Populations

For North American monarch butterflies battling the onslaught of a lethal parasite known as Ophryocystis elektroscirrha, long seasonal migrations may be the answer to beating it, researchers from the University of Georgia have determined. 

Ophryocystis elektroscirrha (OE) is a protozoan parasite that causes wing defects in monarch butterflies. When infected, monarchs become too weak to expand their wings. The recent study revealed that long-distance migrations can lower parasite prevalence since the journeys ultimately put a greater distance between uninfected and infected individuals that are removed from wild populations throughout the course of strenuous flights, according to the university's news release.

Researchers examined wild monarch butterflies (Danaus plexippus) collected from two wintering sites in central Mexico in order to determine the potential impacts of OE on migratory success. Uninfected monarchs exhibited lower hydrogen isotope values than parasitized butterflies, which indicates the healthy individuals had traveled from more northerly latitudes to their winter homes in Mexico. Additionally, researchers noted that, among the infected butterflies, those with higher levels of the OE originated from more southerly latitudes, suggesting infected butterflies would not have been able to migrate to Mexico from farther north.

"The chemical markers allowed us to estimate where the monarchs started and how far they travelled to reach the wintering sites in Mexico, something that would not be possible using other currently available methods," Dr. Sonia Altizer, one of the study researchers from the University of Georgia, explained in the release. "We also found that monarchs with larger wings migrated farther distances on average than those with smaller wings, something that's supported by cross-population comparisons but hasn't been previously shown within North American migratory monarchs."

Their study was recently published in the journal PLOS ONE.

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