Friday, 18 March 2016

Flight of the Dragonfly

By Rachel Baxter

"Pantal flavescens at Kavadoor" 
© 2010 Jeevan Jose 

Commonly known as the “globe skimmer”, it is no surprise that Pantala flavescens, a unique species of dragonfly, can travel long distances. Despite being less than 2 inches long, these tiny insects have the ability to fly across oceans, making some of the greatest migratory journeys on Earth.

However, only recently have scientists had an insight into just how often these voyages are occurring. A recent study, by biologists at Rutgers University, published in the journal PLOS One, has shown that Pantala dragonflies all over the world are genetically very similar. This is unusual in nature, as geographically segregated populations of the same species tend to vary genetically to some extent.

Jessica Ware, one of the paper’s authors, explains, "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.”

Nevertheless, in the case of the Pantala dragonfly, highly similar genetic profiles have been found in individuals across the world, ranging from the USA and South America, to Japan, India and Korea. The fact that they seem to share one common global gene pool suggests that individuals from different continents are not only interbreeding, but doing so on a regular basis. This would mean that they are travelling around the world annually, if not more often.

The purpose of the vast migrations of these dragonflies is simple; they follow the weather, allowing them to reproduce in the ideal environment. For example, when the dry season hits India, they will move across to Africa for the wet season, as they require moisture to breed.

So, how do they do it? Pantala dragonflies have specialised wings that are perfectly adapted to long-distance travel, with minimum energy expenditure. They have relatively large wings that enable them to fly high up in the air, and glide in the wind. This mechanism is what allows them to cross entire oceans, and is referred to as “passive dispersal”, as they rely on the wind to do most of the work for them. Furthermore, as they are so small, weight is not a problem.

However, their size does cause a problem to the scientists studying them. Genetic analyses were used in the recent study because the dragonflies are too small for researchers to attach GPS trackers or tagging equipment to them. The weight of any existing technologies would be too overpowering, reducing their abilities to fly. Therefore, scientists thus far have no way of tracking the exact routes of the dragonflies, to assess exactly how long they are travelling for and where exactly they are travelling to and from.

Perhaps future technologies will provide trackers light enough to attach to the back of the minute dragonflies, allowing scientists to unlock further information about them. Until then, many key details of one of the greatest migrations on the planet will remain a mystery.