By creating a model circuit and recording the neural activity of monarch butterflies, a team led by researchers from the University of Washington has solved one of nature’s greatest mysteries: how the insects are able to migrate more than 2,000 miles across North America each year.
According to BBC News and the Telegraph, lead investigator Professor Eli Shlizerman and his colleagues set out to recreate the internal compass of these threatened butterflies, which are able to fly southwest from Canada to Mexico annually, knowing exactly where to go without fail.
Generation after generation of monarchs make the voyage, and the researchers wanted to learn how the monarch’s innate sense of direction functions, how its neurobiological systems are set up, and what lessons we could learn from the way that its brain functions. A paper detailing their findings has been published in the latest edition of the journal Cell Reports.
So what did Shlizerman and his co-authors learn? That the monarch butterflies’ internal compass “integrates two pieces of information – the time of day and the sun’s position on the horizon – to find the southerly direction,” the UW assistant professor explained in a statement Thursday. Both mechanisms rely directly on input cues from the sun, he told BBC News.
The butterflies migrate en masse from Canada to Mexico (Credit: Thinkstock)
Model shows that both time of day, position of the sun are key
As part of their research, Shlizerman’s team developed a model of how the monarch butterflies’ brains are able to use information sent by the eyes and antennae to make it to their intended destination. The creatures use their large, complex eyes to track the position of the sun and the internal clock located in their antennae to know the correct time of day.
This information is sent to the brain via neurons, and their models used two neural mechanisms, one of which was inhibitory and another that was excitatory, to control signals sent by the antennae’s clock genes. A similar system was used to determine the position of the sun from signals sent by the eyes, and the combination of these systems helped the brains of the butterflies determine which direction was southwest.
Taking the best route, not the shortest
Furthermore, the model suggests that the monarchs do not necessarily take the shortest path to get back on the right path when course corrections are needed. Rather, the model demonstrated that they have a separation point that determines if the insects needed to take a right or left turn in order to head in a southwesterly direction. If the butterfly gets off course, it will innately turn to the direction which does not require it to cross the separation point.
“The location of this point in the monarch butterfly’s visual field changes throughout the day, and our model predicts that the monarch will not cross this point when it makes a course correction to head back southwest,” said Shlizerman. “In experiments with monarchs at different times of the day, you do see occasions where their turns in course corrections are unusually long, slow or meandering. These could be cases where they can’t do a shorter turn because it would require crossing the separation point.”
The model also indicated that the same mechanisms are reversed when the insects need to make their way back to the northeast in the spring. To make the internal compass point in the opposite direction, the neural connections that transmit information about the time and the position of the sun are flip-flopped, making it easy for the creatures to complete the migration in reverse.
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Image credit: Thinkstock
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