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01 Apr 09 How do they do it?

Each year one hundred million monarchs migrate one thousand miles up and down North America, from Canada to the Mexican Sierra Madre Mountains. There are few other greater biological marvels than that of the Monarch Butterfly and its incredible migration. They fly 50 miles a day and stop only for water and nectar. They fly over the great lakes and scorching deserts. They have a four-inch wingspan and a weight of less than 1/5 of an ounce. How do they do it?

Scientists have studied these amazing creatures for years in an attempt to unravel the mystery of this insect, and are just now discovering some of the mechanisms that work together to accomplish this feat that staggers the mind.

Monarch butterflies fly south in the fall and spend the winter in Mexico. In the spring, they migrate northwards, breeding as they go. Unlike summer butterflies, fall Monarchs are not active reproductively, which allows them to live longer than summer butterflies and prevents them from laying eggs during their fall migration south. This happens because their bodies produce less JH (juvenile hormone). Pretty good plan, if you ask me.

In 2005, a research team out of University of Massachusetts Medical School studied the brain and eye tissues of the Monarch, and determine that light was necessary to the function of the biological clock in the brain of the butterfly. They learned that Monarchs had special photoreceptors in their eyes specifically for the ultraviolet band of light. Ultraviolet, or UV, light determined the butterfly’s metabolic cycles and activated the signal in the brain to “migrate”, and when butterflies were put under a UV light filter, they lost their orientation. Further studies revealed that the photoreceptors in the butterfly’s eyes where specifically wired to the navigation system in its brain, and together, these amazing systems worked to guide the butterflies in their migration.

Wow! It is incredible to think that this beautiful, yet lowly creature has such intricately designed pieces in its nervous system. Furthermore, neither system would work without the either, and this also requires exact sensory data from the light of a star a million light years away. But it gets better.

Scientists, again from the University of Massachusetts, have recently uncovered 40 genes that are linked to the butterflies’ ability to migrate a thousand miles. Their research explains that the genes compel the butterfly to orient itself to the sun by an internal “sun compass”. One mutation off, and the butterfly ends up in Portugal!

So you have the JH system, which controls the butterfly’s reproduction so it can migrate, and then you have this crazy “sun compass” system, which directs the butterfly – no, “compels” the butterfly, to migrate 1,000 miles to an exact destination. And then you have the light of the star that they orient to, and lastly, you have their destination, a forest of broad-trunked trees that effectively retain warmth and keep out rain- factors that are essential for the Monarchs’ survival.

I have a hard time thinking that this all evolved by “chance”. But that’s just me.

BMC Biology (2009, March 31). Genetic Basis For Migration In Monarch Butterflies Uncovered

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