University of Minnesota
The Asota caricae moth, an agricultural pest, is found from Taiwan to Australia.
Photo: Lauren Helgen, Smithsonian Institution
Insect DNA reveals species' hidden histories
By Deane Morrison
What if checkout clerks had to consult an expert halfway around the world to identify the electronics we wanted to buy? And another expert to identify the housewares?
That's how it used to be with tropical insects. Researchers often had to send samples to experts in the far corners of the globe and hope they arrived in good enough condition to name.
But just as clerks now identify items with a single swipe of the barcode, scientists have a new way to tell what species they've dropped in the collection jar. University of Minnesota researcher George Weiblen and his colleagues report that the technique, called DNA barcoding, is used to quickly identify insects, making it easier to track the distributions and habits of species.
The work is published online in Proceedings of the National Academy of Sciences.
The moth went over the mountain
Rapidly evolving DNA barcodes can reveal the history of migration. Weiblen points to a moth found on either side of the New Guinea mountains. Did the mountains, when they appeared millions of years ago, split a population of the moth in two? Or, after the mountains had formed, did moths cross them to colonize the other side?
"If ancient populations were split by the uplift of the mountains, we would expect to find different DNA barcodes on either side of the barrier," says Weiblen. "But when we find the same barcode on both sides, it suggests recent movement of moths across New Guinea."
Insect ID card
In DNA barcoding, a species' identity is revealed by a unique sequence in one short stretch of DNA. Weiblen uses these sequences, called DNA barcodes, to identify moths and butterflies in Papua New Guinea, which has 100 times as many Lepidopteran species per square mile as does North America.
But the country is developing rapidly, and researchers are in a race against time to document the biodiversity so it can be effectively managed and protected.
"For instance, we don't know, at this point, how many protected areas would be sufficient to preserve the butterfly diversity of New Guinea or where they should be located," Weiblen explains.
Some species are different but look alike, and others migrate large distances. DNA barcoding reduces the uncertainty in sorting out who's who and how species came to be distributed the way they are (see sidebar).
"You can't put a radio transmitter on a moth, so how do you figure out how far it can travel across the Pacific?" says Weiblen. "We don't have a fossil record for these species, so instead we use a molecular clock to trace their history."
Because DNA barcodes evolve rapidly, they can be used to separate populations of the same species that have been isolated for many generations. Therefore, barcodes may help pinpoint the source of invasive insects like the emerald ash borer, which came from Asia and was recently found in Minnesota.
"We need to understand the history of migration in order to combat the pests that threaten our forests and crops," notes Weiblen.
Little insects, big questions
Weiblen's work is part of a larger push to learn how many species share our planet. One thing is for sure: Insects and the plants they feed on make up a large piece of global biodiversity.
"But," says Weiblen, "we know very little about the geographic distribution of tropical insects."
Published in 2010