Scientists think they have modeled the brain mechanisms that let monarch butterflies, year after year, migrate thousands of miles in one direction: south, to Mexico.
While researchers already knew from prior analyses that the winged wonders use two primary bits of input data to navigate – time of day and position of the sun on the horizon – they had no answer for how the butterfly's brain gathers and processes that information.
Until now, say researchers from the universities of Washington, Michigan and Massachusetts.
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In a paper published in the journal Cell Reports, a team from those institutions says it has modeled the neural control mechanisms at work in the butterfly's brain.
"We wanted to understand how the monarch is processing these different types of information to yield this constant behavior - flying southwest each fall," said study co-author Eli Shlizerman, an assistant professor at the University of Washington, in a statement.
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Monarchs watch the sun, but that's not enough to get them where they need to go. They also need the time of day. Monarchs, just like people, have a kind of internal clock that keeps track of the daily go-round. Unlike people, though, their clock is centered in the antennae (an appendage humans have so far disdained).
Shlizerman and his colleagues recorded neural signals coming from monarch antenna nerves, to keep track of the clock information, as well as information coming from the insect's eyes, to account for sun position.
Then they used that data to create a circuit model to show the neural control mechanisms – for the "clock" and "sun position" – that help the butterfly point itself southwest.
The scientists' model even accounts for how the butterflies get back on course if they stray.
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And what about when it's time to head back north? The team's model suggests that the neural mechanisms just reverse direction.
"And when that happens, their compass points northeast instead of southwest," said Shlizerman. "It's a simple, robust system to explain how these butterflies - generation after generation - make this remarkable migration."
The scientists say more study will be needed to fully ensure their model matches up with the butterfly's brain, body structures, and behavior. For now, though, they say the model they've created appears to be consistent with behavior seen in the legendary migratory creatures.