Explained: Why the Monarch Butterfly never loses its 2000-mile long migration

The monarch butterfly has an internal, genetically-encoded compass which allows it to navigate from the USA to Central Mexico. A team of researchers discovered that the monarch butterfly’s compass incorporates the sun’s position at the horizon as well as the day of the week so it can determine the southern direction. Researchers have been wondering for years how Danaus plexippus, the monarch butterfly (Danaus perilis), knows where it is going each fall as it flew south. Researchers from three universities, including the University of Washington and Massachusetts, have published a paper in Cell Reports that claims they know the secrets of the amazing butterfly’s navigation system. Scientists have created a model of how the brain of the monarch butterfly integrates time and the position of the sun in the sky. (Image: washington.edu. Credit to Eli Shlizerman. The compass combines two pieces of data Eli Shlizerman is a University of Washington assistant professor. He explained that the compass incorporates the sun’s position in the sky with the time of the day. Previous studies have revealed the nature of this ability. But, no one has yet to understand how the butterfly’s brain processes and receives this data. Professor Shlizerman and his colleagues worked together to create a model of how the monarch’s brain organizes its compass. Professor Shlizerman was the lead author of this paper. He said, “We wanted to know how the monarch processes these different kinds of information to yield the constant behavior – flying Southwest each fall.” A 3-D visualization of Monarch butterflies brain, with neuropils related sun compass integration, has been highlighted. Image: cell.com. The Monarch butterfly processes information about the Sun’s location and the time of the day. This is thanks to its complex, large eyes that track the Sun’s position. It cannot, however, determine the direction of the Sun by its position. To determine where it is going, the data must be combined with the times of day. Like most mammals, the internal clock of monarchs is based on rhythmic expressions of key genes. The clock keeps track of daily behaviours and physiological patterns. Its antennae is the center of the monarch’s clock, which transmits information via neurons to its brain. Researchers have studied previously the rhythmic patterns in the antennaes of monarchs, which control their internal clock. They also study how compound eyes interpret the Sun’s position in the sky. Professor Shlizerman and Steven Reppert (Chair of the Department of Neurobiology, University of Massachusetts Medical School), and their colleagues captured signals from the antennae nerves of monarchs, as they sent clock information to brains and light data from the eyes. National Geographic reports that millions of these fragile insects fly south every fall as the cold weather draws near. They fly until they reach Southern California and central Mexico. This is more than 2 ,000 mile (3 ,200 km) from their home range. Professor Shlizerman stated that they created a model to incorporate this information, which is how antennae and antennae send data to the brain. The researchers had an identical system to determine the Sun’s location based on signals received from the eyes. This balance would allow the brain to determine which direction is southwest. Arizona State University says that there are four stages to the butterfly’s life cycle. These stages are egg, larvae, pupae, and adults. The entire process is called complete metamorphosis.” (Image: askabiologist.asu.edu) Monarch never crosses ‘separation point’ Based on their model, it also appears that during course corrections the butterflies do not simply make the shortest turn to get back onto the right route. The unique aspect of their model is a separation point. This would determine which direction the monarch turns (left or right), and direct it to the southwest. Professor Shlizerman stated that the location of the separation point changes in the visual field of the monarch butterfly throughout the day. Our model predicts the monarch won’t cross this point if it has to make a course change to go back south. Further studies will be required to verify that the model matches monarch butterfly behavior, brain anatomy and physiology. The separation point and other aspects of the model have been consistent with observations. Professor Shlizerman stated that there are times when the turns of monarch butterflies in course corrections can be unusually slow, long or meandering. This could indicate that they are unable to make a faster turn as it would involve crossing the separation line. Their model provides a straightforward explanation for why monarch butterflies can reverse their course and travel northeast from Central Mexico to Canada and the United States. It would be simple for the four neural mechanisms transmitting data about the Sun’s location and the clock to operate in the opposite direction. in reverse direction. Professor Shlizerman stated that when this happens, the compass of their butterflies points to northeast rather than southwest. This simple and robust system explains how the butterflies migrate – each generation by generation. Citation: “Neural integration underlying a time-compensated sun compass in the Migratory Monarch Butterfly,” Eli Shlizerman and James Phillips Portillo. Cell Reports. 14 April 2016. DOI: http://dx.doi.org/10.1016/j.celrep.2016.03.057. Video: Video of Monarch Butterfly’s time-compensated compasses: Midday

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