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Monarch Butterflies: Females More Efficient Fliers Than Males, Researchers Say

Nov 04, 2015 10:57 AM EST

There are just some things female monarch butterflies do better than their male counterparts – flying and migrating, say researchers from the University of Georgia (UGA). They compared the physical traits of the two sexes and concluded that females possess thicker wings that make them more efficient fliers and ultimately better migrators.

"Both of these elements would play important roles in determining the outcome of the migration," Andy Davis, lead author of the recent study and a research scientist in UGA's Odum School of Ecology, said in a news release. "Until now, we had no idea why females were better flyers than males, but this study definitely helps to answer that question."

Female monarch wings are generally smaller than those of males, and their flight muscles are also smaller than those of males; however, their wings' superior thickness makes up for these shortcomings. A thicker wing allows females to bear less weight per square inch, making it less daunting to fly long distances to their winter homes in California and Central Mexico. 

For their study, researchers measured wings and body parts of 47 male and 45 female monarchs in order to better compare their physical features. They were most interested in examining three characteristics responsible for flight: the ratio of wing size to body size, the size of flight muscles and wing thickness.

"We expected we'd find that females have bigger flight muscles, but it was the opposite," Michael Holden, co-author of the study and an undergraduate ecology student at UGA, explained in the release. "Males had the largest muscles." (Scroll to read more...)

(Photo : Sonia Altizer/University of Georgia)
Monarchs migrate to their winter homes in Central Mexico and California annually.

But larger muscles aren't always better. That is, muscles add weight to one's body, so having lighter bodies in relation to wing size pays off for female monarchs, essentially making females more efficient fliers.  

"The way I think about it is that per flap of their wings, females use less energy to move their bodies relative to males," Holden added.

Thicker wings are also stronger, so female wings are less likely to break or tear. Those are key factors in determining a monarch's chances of survival during migration.

"We believe this work will be important for improving scientific understanding of the migratory cycle," Davis said in a statement, "and it will also serve as a reference point for future studies aimed at flight characteristics of monarch butterflies."

The findings were recently published in the Journal of Insects.

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