"Long before it's in the papers"
March 02, 2016

RETURN TO THE WORLD SCIENCE HOME PAGE


Near-suicidal trips said to make dragonfly a champion long-distance flier

March 2, 2016
Courtesy of Rutgers University-Newark
and World Science staff


A spe­cies of lit­tle drag­onfly seems to be an­i­mal world’s most pro­lif­ic long dis­tance flier—cross­ing oceans as it mi­grates from con­ti­nent to con­ti­nent, newly pub­lished re­search claims.

The jour­neys have been termed “kind of” sui­ci­dal, with many dy­ing on the way, but enough sur­viv­ing to keep the genera­t­ions go­ing.

Pantala flavescens. (Photo: Greg Lasley)


Sci­en­tists claim the inch-and-a-half (a­bout 4 cm) long in­sect, called Pan­tala fla­ves­cens, blows away any and all in­sect com­peti­tors for its trav­el­ing range. 

Such other in­sects in­clude mon­arch but­ter­flies—famed long-dis­tance fliers them­selves—and al­so oth­er drag­on­flies, some of which dwell along the same pond their whole lives.

Al­though the only di­rectly ob­served Pan­tala ocean migra­t­ions have been across the In­di­an Ocean—only the third largest—sci­en­ti­sts have mar­shaled ge­net­ic ev­i­dence to sug­gest they al­so reach as far as Tex­as and Ja­pan. That would mean they ef­fec­tively span the globe East to West.

The in­sects are too small to car­ry track­ing de­vices, mak­ing it hard to study them di­rectly. But bi­ol­o­gists who led the study found that popula­t­ions of the drag­onfly in loca­t­ions as far apart as Tex­as, east­ern Can­a­da, Ja­pan, Ko­rea, In­dia, and South Amer­i­ca, have very si­m­i­lar ge­net­ic pro­files. So sim­i­lar, they ar­gue, that con­stant in­ter­min­gling is the only likely ex­plana­t­ion: the crea­ture has built a com­mon world­wide gene pool.

“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,” said Jes­si­ca Ware, the stu­dy’s sen­ior au­thor. But “we don’t see that.”

How do they do it? “These drag­onflies have adapta­t­ions such as in­creased sur­face ar­eas on their wings that en­a­ble them to use the wind to car­ry them,” said Ware, a bi­ol­o­gist at Rut­gers Un­ivers­ity-Newark in New Jer­sey and sen­ior au­thor of the stu­dy, pub­lished in the jour­nal PLoS One. “They stroke, stroke, stroke and then glide for long pe­ri­ods, ex­pend­ing min­i­mal amounts of en­er­gy.”

Mi­grat­ing drag­onflies “are fol­low­ing the weath­er,” said Dan­iel Troast, who an­a­lyzed the DNA sam­ples in Ware’s lab while work­ing to­ward his mas­ter’s de­gree in bi­ol­o­gy, which he earned at the uni­vers­ity in 2015. “They’re go­ing from In­dia where it’s dry sea­son to Af­ri­ca where it’s moist sea­son, and ap­par­ently they do it once a year.”

Mois­ture is a must for Pan­tala to re­pro­duce, and that, said Ware, is why these in­sects would be driv­en to even at­tempt such a per­i­lous trip, which she calls a “kind of su­i­cide mis­sion.” The spe­cies de­pends on it. While many will die en route, as long as enough make it, the spe­cies sur­vives.

Flight pat­terns ap­pear to vary, said Ware and col­leagues. The har­di­est drag­onflies might make the trip non­stop, catch­ing ro­bust air cur­rents or even hur­ri­cane winds and glid­ing all the way. Oth­ers may be pud­dle jumpers: Pan­tala need fresh wa­ter to mate and lay their eggs, and if while rid­ing a weath­er cur­rent they spot a fresh wa­ter pool cre­at­ed by rain—e­ven on an is­land in the mid­dle of the ocean—Ware and Troast say it’s likely they dive earth­ward and use those pools to mate. 

Af­ter the eggs hatch and the ba­bies are ma­ture enough to fly­—which takes just a few week­s—the new drag­onflies might join the swar­m’s intercon­ti­nental and now mul­ti­-genera­t­ional trek right where their par­ents left off.

For the mo­ment, the de­tails of this ex­tra­or­di­nary in­sect itin­er­ary are an ed­u­cat­ed best guess, as are spe­cif­ic routes these migra­t­ions might take, the sci­en­tists said. Much more work is needed to br­ing many loose ends to­geth­er. But now that their work has es­tab­lished a world­wide popula­t­ion of in­ter­min­gling drag­onflies, Ware and Troast hope that sci­en­tists can work on plot­ting those routes in ear­nest. They would need to be in­no­va­tive, be­cause track­ing de­vices that can be at­tached to larg­er an­i­mals are far too big to put on in­sects.

What the Rut­gers sci­en­tists have dis­cov­ered puts this drag­onfly far ahead of any iden­ti­fied in­sect com­pet­i­tor. “Monarch but­ter­flies mi­grat­ing back and forth across North Amer­i­ca were thought to be the longest mi­grat­ing in­sects,” trav­el­ing about 2,500 miles (a­bout 4,000 km) each way, said Troast. “But Pan­tala com­pletely de­stroys any mi­grat­ing rec­ord they would have,” with its es­ti­mat­ed range of 4,400 miles or more. It al­so ex­ceeds Charles Lind­bergh’s cel­e­brat­ed so­lo flight from New York to Par­is by at least sev­er­al hun­dred miles.

Pan­tala leaves many of its fel­low drag­onflies even far­ther be­hind. The mys­ter­ies of ev­o­lu­tion are such that while Pan­tala and its cous­in the Green Darn­er (An­ax ju­nius) have de­vel­oped in­to world trav­el­ers, Ware said that by con­trast, oth­er mem­bers of the family “don’t ev­er leave the pond on which they’re born—trav­el­ing barely 36 feet away their en­tire lives.”


* * *

Send us a comment on this story, or send it to a friend











y Sign up for
e-newsletter

   
 
subscribe
 
cancel

On Home Page         

LATEST

  • Scient­ists pro­pose: let’s search part of sky where al­iens could have seen us

  • G­o-slow can­cer treat­ment might actually work bet­ter, stu­dy sug­gests

EXCLUSIVES

  • Study links global warming, war for first time—in Syria

  • Smart­er mice with a “hum­anized” gene?

  • Was black­mail essen­tial for marr­iage to evolve?

  • Plu­to has even cold­er “twin” of sim­ilar size, studies find

MORE NEWS

  • F­rog said to de­scribe its home through song

  • Even r­ats will lend a help­ing paw: study

  • D­rug may undo aging-assoc­iated brain changes in ani­mals

A species of little dragonfly seems to be animal world’s most prolific long distance flier—crossing oceans as it migrates from continent to continent, newly published research claims. The journeys have been termed “suicidal,” with many dying on the way, but enough surviving to keep the generations going. Scientists claim the inch-and-a-half (about 4 cm) long insect, called Pantala flavescens, blows away any and all insect competitors for its traveling range. These rivals include monarch butterflies—famed long-distance fliers—and also other dragonfly species, some of which dwell along the same pond their whole lives. Although the directly observed Pantala ocean migrations are limited to the Indian Ocean—only the third largest—scientists have marshaled genetic evidence to suggest they also reach as far as Texas and Japan. That would mean they effectively span the globe East to West. The insects are too small to carry tracking devices, making it hard to study them directly. But biologists who led the study found that populations of the dragonfly in locations as far apart as Texas, eastern Canada, Japan, Korea, India, and South America, have very similar genetic profiles. So similar, they argue, that constant intermingling is the only likely explanation: the creature has built a common worldwide gene pool. “If North American Pantala only bred with North American Pantala, and Japanese Pantala only bred with Japanese Pantala,” said Jessica Ware, the study’s senior author, “we would expect to see that in genetic results that differed from each other.” But “we don’t see that.” How do they do it? “These dragonflies have adaptations such as increased surface areas on their wings that enable them to use the wind to carry them,” said Ware, a biologist at Rutgers University-Newark in New Jersey and senior author of the study, published in the journal PLoS One. “They stroke, stroke, stroke and then glide for long periods, expending minimal amounts of energy as they do so.” Migrating dragonflies “are following the weather,” said Daniel Troast, who analyzed the DNA samples in Ware’s lab while working toward his master’s degree in biology, which he earned at the university in 2015. “They’re going from India where it’s dry season to Africa where it’s moist season, and apparently they do it once a year.” Moisture is a must for Pantala to reproduce, and that, said Ware, is why these insects would be driven to even attempt such a perilous trip, which she calls a “kind of suicide mission.” The species depends on it. While many will die en route, as long as enough make it, the species survives. Flight patterns appear to vary, said Ware and colleagues, whose findings appear in the journal PLoS One. The hardiest dragonflies might make the trip nonstop, catching robust air currents or even hurricane winds and gliding all the way. Others may be puddle jumpers: Pantala need fresh water to mate and lay their eggs, and if while riding a weather current they spot a fresh water pool created by rain—even on an island in the middle of the ocean—Ware and Troast say it’s likely they dive earthward and use those pools to mate. After the eggs hatch and the babies are mature enough to fly—which takes just a few weeks—the new dragonflies might join the swarm’s intercontinental and now multi-generational trek right where their parents left off. For the moment, the details of this extraordinary insect itinerary are an educated best guess, as are specific routes these migrations might take, the scientists said. Much more work is needed to bring many loose ends together. But now that their work has established a worldwide population of intermingling dragonflies, Ware and Troast hope that scientists can work on plotting those routes in earnest. They would need to be innovative, because tracking devices that can be attached to larger animals are far too big to put on insects. What the Rutgers scientists have discovered puts this dragonfly far ahead of any identified insect competitor. “Monarch butterflies migrating back and forth across North America were thought to be the longest migrating insects,” traveling about 2,500 miles (about 4,000 km) each way, said Troast. “But Pantala completely destroys any migrating record they would have,” with its estimated range of 4,400 miles or more. It also exceeds Charles Lindbergh’s celebrated solo flight from New York to Paris by at least several hundred miles. Pantala leaves many of its fellow dragonflies even farther behind. The mysteries of evolution are such that while Pantala and its cousin the Green Darner (Anax junius) have developed into world travelers, Ware said that by contrast, other members of the family “don’t ever leave the pond on which they’re born—traveling barely 36 feet away their entire lives.” long-distance flier