A University of Georgia study has found that monarch butterflies that migrate long distances have evolved significantly larger and more elongated wings than their stationary cousins.

As part of the study, researchers in the Warnell School of Forestry and Natural Resources and the Odum School of Ecology examined the size and shape of monarchs from migratory and non-migratory populations using sophisticated computer imaging that was able to measure precise details about the insects' wings.

Warnell doctoral candidate Andy Davis and Odum associate professor Sonia Altizer compared migratory monarchs from the eastern and western US to those in Hawaii, Costa Rica, South Florida and Puerto Rico that do not migrate.

They also measured the wings of lab-grown monarchs to rule out environmental causes of differences in size and shape, and to demonstrate a genetic basis for variation in wing traits among individual monarchs.

The findings in monarchs were consistent with previous studies comparing migratory and non-migratory bird species, which indicate that the best shape for long-distance flight involves long wings with a narrow tip to help reduce drag.

In addition to their findings on wing size and shape, the team also found that monarchs from the two migratory populations in the US differed in body size, suggesting that each population could have adapted to the demands of migration in subtly different ways.

Larger bodies might help eastern monarchs, with their much longer migration, carry fat deposits to fuel the long journey and five-month overwintering period in Mexico.

"Second, Mallorca appears to be particularly well suited to the task, because neither tectonics nor isostasy- geological forces of crustal motion - over-complicate the record. It's really close to the ideal scenario," he added.