Many insects undertake seasonal migrations, the most famous of them being the monarch butterflies of southern Canada and the United States. Hoverflies are also migratory, with billions of them moving southwards from northern Europe each year, to spend the winter in warmer climates. However, not all individuals go along for the ride – some stay home and take their chances. This has given scientists an opportunity to study the genetic differences between migratory and non-migratory individuals in an attempt to identify the genetic basis of migratory behavior.
On their autumn journey southwards, the hoverflies cross the Pyrenees Mountains in dense concentrations, making use of narrow mountain passes. A team of researchers at the University of Exeter was able to capture samples of these hoverflies as they flew through a pass, and take them back to the laboratory for DNA analysis. The genetic information was then compared with DNA from non-migratory hoverflies.
“It is an amazing spectacle to witness, an endless stream of hundreds of thousands of individuals through a 30-meter pass,” said Dr. Karl Wotton, research fellow in the College of Life and Environmental Sciences.
“We identified 1,543 genes whose activity levels were different in the migrants,” said lead author Toby Doyle, of the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall. “What really struck us though was the remarkable range of roles these genes play.”
“Migration is energetically very demanding, so finding genes for metabolism was no surprise but we also identified genes with roles in muscle structure and function, hormonal regulation of physiology, immunity, stress resistance, flight and feeding behavior, sensory perception and for increasing longevity.”
When the researchers categorized the genes by function, they found that suites of genes were being activated in concert in the migratory hoverflies. These included genes for insulin signaling for longevity, pathways for immunity, and those leading to octopamine production, the insect equivalent of the fight or flight hormone adrenaline, for long-distance flight.
“These pathways have been integrated into migratory hoverflies and modified by evolution to allow for long-distance movement,” Dr. Wotton said.
The work provides a powerful genomic resource and theoretical framework to direct future studies into the evolution of migration in other species.
“Our research has already indicated several genes that have previously been associated with migration in butterflies, suggesting the existence of a shared ‘migratory gene package’ that controls migration across multiple animals,” said Dr. Wotton. “It is an exciting time to be studying the genetics of migration.”
The study is published today in the journal Molecular Ecology.