Scientists Understand Monarch Butterfly's Internal Compass And Crack Its Migration Mystery

What is the internal compass of the monarch butterfly? It uses this tool to guide its shift towards the Rio Grande when it travels 2,000 miles to hot Mexico.

"Their compass integrates two pieces of information - the time of day and the sun's position on the horizon - to find the southerly direction," said Eli Shlizerman, a University of Washington assistant professor and lead author.

Earlier, it was discovered that the monarch butterfly factors the time of day and location of the sun into its journey. But how does its brain receive and process the information? 

"We wanted to understand how the monarch is processing these different types of information to yield this constant behavior - flying southwest each fall," Shlizerman said.

The  direction can be identified by blending information on the sun's position in the sky collected from their compound eyes, with the time of day using its internal clock. This is based on the rhythmic expression of genes.

Its clock is centered in the antennae. It gets some information here, which travels to the neurons in its brain.

"We created a model that incorporated this information - how the antennae and eyes send this information to the brain," Shlizerman said. "Our goal was to model what type of control mechanism would be at work within the brain, and then asked whether our model could guarantee sustained navigation in the southwest direction."

The new model is based on two neural mechanisms---an inhibitory and an excitatory one, that control signals from internal clock genes within the antennae. Maintaining a balance between these two mechanisms helps its brain to figure out the southwest location.

When the migration calls for corrections, they do not merely take the shortest route to come back. But they harness a separation point to determine whether they should turn left or right, in order to shift towards the southwest.

"The location of this point in the monarch butterfly's visual field changes throughout the day," Shlizerman said. "And our model predicts that the monarch will not cross this point when it makes a course correction to head back southwest."

Hence, if a monarch gets lost due to the wind, they turn in the direction that does not call for them to cross the separation point.

The findings were published in the April 14, 2016 issue of the journal Cell Reports.