Genetically linked, a continent apart: the rise of DNA barcoding

DNA barcoding uses a few standard genes to provide a sure-fire genetic species identification method. Conor Lawless

We’ve written previously on The Conversation about how taxonomy – the science of describing and naming species – can be quite a subjective science. But taxonomists can broadly be split into two camps:

  • “lumpers”, who tend to group different organisms together, reducing the total number of species (as well as subspecies, genera, families and so on)

  • “splitters”, who define ever more detailed physical features to separate populations, increasing the number of recognised subspecies, species, genera, etc.

This difference in philosophy has had a massive influence on how life is recognised, leading to a variable system of classification.

More recently, genetic variation has been used as a standard yard-stick to document the differences between species. In particular, DNA barcoding uses a few standard genes to provide a sure-fire genetic species identification method.

A nice demonstration of the power of DNA barcoding can be seen in a recently published article about crane flies. For those that aren’t familiar, crane flies resemble overgrown mosquitoes but generally feed on plants or small insects rather than blood.

Scientists from Russia and Finland located two populations of crane fly separated by more than 6,500km – one in Kittilä, northern Finland, and the other in Primorsky Krai in the Russian far east, just north of Korea.

Despite the vast distance between the populations, the researchers were able to use DNA barcoding to identify both groups as the same species, Tipula recondite.

Insects are the most biodiverse (an estimated 7m species or more) and, relatively speaking, the most poorly described group on the planet. With national differences in taxonomic frameworks and such a vast separation in populations it’s likely most taxonomists would have regarded the two populations as separate species.

But DNA barcoding has demonstrated that with very few genetic differences between them, these disjunct populations should be considered a single species.

Male (figures A, B and C) and female (D, E and F) crane flies (Tipula recondita). ZooKeys/Pilipenko & Salmela

Using genetic information not only clarifies species interpretation but also allows us to better understand the evolution of the species and its surrounding ecosystem. For instance, how did Tipula recondite end up with such a widely disjointed distribution?

It’s possible that in the future we will uncover that this species can be found in other locations, and we can’t rule out a recent introduction to either Kittilä or Primorky Krai.

However, other cool-adapted Eurasian species show similarly fragmented distributions, leading us to speculate that there may be factors that affecting the ecology of the entire region.

We now understand from a range of fossils and ice cores that as recently as 10,000 years ago, the northern latitudes – including Europe and Russia – were covered in extensive ice sheets due to an ice age which started around 90,000 years ago.

During the ice age, cold-adapted species would have spread across central Europe and Russia. It is possible that Tipula crane flies lived across the entire 6,500km between Scandinavia and the east coast of Russia.

Due to natural oscillations in the global climate (including the 100,000 year Milankovich cycle), the region started to warm approximately 8,000 years ago. With a warmer climate, plants and animals previously confined to southern Eurasia started to reinvade northern areas.

This might have pushed Tipula into the last remaining suitable cold habitats for its survival: rare old-growth and herb-rich forests of the Taiga (also known as boreal forest).

Global warming continues today, above and beyond historical levels, so the pressure never stops for rare, cool-adapted species such as our crane flies.

Our understanding of Earth’s climate history tells us the Milankovich cycle should be tipping the earth back into another ice age, any time in the next 10,000 years. But human impacts on the atmosphere indicate we’re likely to experience an increasingly hot climate.

While the short-term future of cool-adapted species such as Tipula recondite is uncertain, if they can hang on until the natural systems of the earth tilt the climate back in their favour, there might yet be hope on the horizon.

In the meantime it’s worth reflecting on the case of the humble crane fly as an example of effective DNA barcoding in action and how we can use these emerging technologies to gain a surprising insight in to the ecology of the past, present and future.

The authors of this piece would like to acknowledge the contribution of Judith Ware from EcoGene in writing this piece.

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