A small species of dragonfly has been crowned as the most prolific traveller of the insect world. Pantala flavescens, also known as the globe skimmer, is found across almost every continent, inhabiting most parts of Australia, Japan and Korea and in some areas of India, South America and Texas.
Biologists at Rutgers University-Newark, led by assistant professor Jessica Ware, have studied these far-flung flying cousins to figure out just how diverse the gene-pool gets from one continent to the next.
The DNA comparisons reveal the dragonflies are genetically very closely related, which means the populations originated from the same group, and the species inter-breeds across different continents.
This means the aptly named globe skimmer, which measures just 4.5 centimetres, flies thousands of kilometres to breed.
Senior author Jessica Ware says this is the first time scientists have studied the genes of the species to determine their travel habits.
"If North American Pantala only bred with North American Pantala, and Japanese Pantala only bred with Japanese Pantala, we would expect to see that in genetic results that differed from each other," explains Ware. "Because we don't see that, it suggests the mixing of genes across vast geographic expanses."
So, why the long trips?
This species of dragonfly has particularly fragile larvae, which are incredibly sensitive to changes in weather. The migration probably mirrors a change in seasons, for example, the species might leave India in the dry season, heading for moist conditions in Africa.
Although the journey is treacherous, and many dragonflies don't make it, there is enough success rate to further the species.
Thanks to these results, the globe skimmer has surpassed a species of butterfly previously believed to be the world's most intrepid traveller.
"Monarch butterflies migrating back and forth across North America were thought to be the longest migrating insects," says researcher Daniel Troast, who analysed the DNA samples of the dragonflies.
Monarch butterflies are thought to travel about 4,000 kilometres each way, says Troast, "but Pantala completely destroys any migrating record they would have," flying over 7,000 kilometres, which is more than the distance between Sydney and Kuala Lumpur.
The stamina of the species is helped along by its evolutionary traits, say researchers.
"These dragonflies have adaptations such as increased surface areas on their wings that enable them to use the wind to carry them," says Ware. "They stroke, stroke, stroke and then glide for long periods, expending minimal amounts of energy as they do so."
While the dragonflies' process of migration is still up for discussion, researchers suspect there may be variance among their itineraries.
While some dragonflies are thought to fly direct to their destination, using air currents and even hurricane winds to catch a ride, others might stop along the way if they spot an appropriate place to lay their eggs, such as a puddle or freshwater pool.
The hatching process takes a few weeks, after which the young dragonflies will continue their parents' journey across the globe, creating travel habits that cross generations.
More research is needed to understand the specifics of the species' mode of migration, however the researchers say the tracking technology will need to be particularly innovative, given the diminutive size of the passengers.
The study was published this month in the journal PLOS ONE.
Amy Middleton is a Melbourne-based journalist.
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