By Rachel Baxter
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| "Pantal flavescens at Kavadoor"
© 2010 Jeevan Jose
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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.