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Tuesday, July 22, 2014

The Dragonfly as Nature's Drone, Both Pretty and Deadly

Fiery Skimmer Dragonfly ?
Fiery Skimmer Dragonfly ? (Photo credit: aussiegall)
Dragonfly. Libelulă
Dragonfly. Libelulă (Photo credit: Cost3l)
A Dragonfly.
A Dragonfly. (Photo credit: Wikipedia)
English: Emperor Dragonfly (Anax imperator). F...
English: Emperor Dragonfly (Anax imperator). Français : Un Anax empereur en vol. (Photo credit: Wikipedia)
English: Dragonfly
English: Dragonfly (Photo credit: Wikipedia)
Dragonfly (Photo credit: Wikipedia)

by Natalie Angier

African lions roar and strut, but they're lucky to catch 25 percent of the prey they pursue. Great white sharks have 300 slashing teeth, and still nearly half their hunts fail.

Dragonflies, by contrast, look dainty, and they're often grouped with butterflies and ladybugs on the short life of Insects People Like. Yet they are also voracious aerial predators, and new research suggests they may well be the most brutally effective hunters in the animal kingdom.

When setting off to geed on other flying insects, dragonflies manage to snatch their targets in midair more that 95 percent of the time, often wolfishly consuming the fresh meat without bothering to alight.

"They'll tear up the prey and mash in into a glob, munch, munch, munch," said Michael L. May, an emeritus professor of entomology at Rutgers University in New Jersey.

"It almost looks like a wad of snuff in the mouth before they swallow it," he said.

Next step: grab more food. Stacey Combes, who studies dragonfly flight at Harvard University, once watched a laboratory dragonfly eat 30 flies in a row. "It would have happily kept eating," she said, "if there had been more food available."

In recent papers, scientists have pinpointed key features of the dragonfly's brain, eyes and wings that allow it to hunt so unerringly. One research team has determined that the nervous system of a dragonfly displays an almost human capacity for selective attention, able to focus on a single prey as it flies amid a cloud of similarly fluttering insects, just as a guest at a party can attend to a friend's words while ignoring the background chatter.

Other researchers have identified a kind of master circuit of 16 neurons that connect the dragonfly's brain to its flight motor center in the thorax. With the aid of that neural package, a dragonfly can track a moving target, calculate a trajectory to intercept that target and subtly adjust its path as needed.

The scientists found evidence that a dragonfly plots its course to intercept through a variant of "an old mariner's trick," said Robert M. Olberg of Union College in Schenectady, New York, who reported the research with his colleagues in Proceedings of the National Academy of Sciences. If you're heading north on a boat and you see another boat moving, say, 30 degrees to your right, and if as the two of you barrel forward the other boat remains at that 30-degree spot in our field of view, vector mechanics dictate that your boats will crash: better slow down, speed up or turn aside.

In a similar manner, as a dragonfly closes in on a meal, it maintains an image of the moving prey on the same spot. "The image of the prey is getting bigger, but if it's always on the same spot of the retina, the dragonfly will intercept its target," said Paloma T. Gonzalez-Bellido, an author of the new report who now works at the Marine Biological Laboratory in Woods Hole, Massachusetts.

As a rule, the hunted remains clueless until it's all over. "Before I got into this work, I'd assumed it was an active chase, like a lion going after an impala," Dr. Combes said. "But it's more like ambush predation. The dragonfly comes from behind and below, and the prey doesn't know what's coming."

Dragonflies are able to hover, dive, fly backward and upside down, pivot 360 degrees with three tiny wing beats, and reach speeds of nearly 50 kilometers per hour. In many insects, the wings are simple extensions of the thoracic box and are moved largely as a unit, by flexing the entire thorax. In the dragonfly, the four transparent, ultraflexible wings are attached to the thorax by separate muscles and can each be maneuvered independently, lending the insect an extraordinary range of flight options.

Their eyes are the largest and possibly the keenest in the insect world, a pair of giant spheres each built of some 30,000 pixel-like facets that together take up pretty much the entire head.

Dragonflies can't really hear, and with their stubby antennas they're not much for smelling or pheromonal flirtations.

Perhaps not surprisingly, much dragonfly research is supported by the United States military, which sees the insect as the archetypal precision drone.

Some dragonfly species migrate long distances. Recent studies have shown that green darner dragonflies migrate in sizable swarms each fall and spring between the northern United States and southern Mexico, while the globe skimmer dragonfly lives up to its name: it has been tracked crossing between India and Africa, a round-trip, multigenerational pilgrimage that may exceed 16,000 kilometers.

Dragonflies migrate to maximize breeding opportunities, to find warm freshwater ponds in which they can safely lay their eggs. From those eggs hatch dragonfly larvae: astonishing gilled predators that will spend weeks to years hydro-jetting through water and shooting their mouthparts after aquatic prey, until they're ready to spread their wings and take the hunt to the sky.

Taken from TODAY Saturday Edition, April 13, 2013

Saturday, July 19, 2014

Ancient Strait Is Clue To Origin of Wolf

Falklandwolf (Dusicyon australis) (Original de...
Falklandwolf (Dusicyon australis) (Original description: Canis antarcticus) (Photo credit: Wikipedia)

by Sindya N. Bhanoo

The Falkland Islands wolf, long extinct, is the only land-based mammal native to the islands. European explorers in the 17th century were puzzled by the presence of this lone mammalian species, as was Charles Darwin.

Now, researchers writing in Nature Communications suggest that the wolf traveled across a thin, shallow strait from the mainland to the islands during the last glacial maximum.During this period, about 18,000 to 25,000 years ago, the strait would periodically freeze over.

"This wolf was likely tracking penguins, seals and sea birds that were hauling out onto the ice," said Dr. Alan Cooper, an evolutionary biologist at the University of Adelaide in Australia.

The scientists believe the wolf crossed the strait from what is now Argentina. "The question is, how did this great big mammal get over when rodents didn't?" he said.

Dr. Cooper and his colleagues compared DNA samples from the wolf with those of one of its closest mainland relatives, an extinct foxlike species called Dusicyon avus. They found that the two species separated about 16,000 years ago, coinciding with the last glacial maximum and the frozen marine strait.

Previously, it had been theorized that the wolf was semi-domesticated and brought to the island by humans.

The last Falkland Islands wolf was spotted in the late 19th century.

Taken form TODAY Saturday Edition, April 06, 2013

Thursday, July 17, 2014

Solutions to the Puzzles of Mimicry in Nature

Mimicry in Butterflies Is Seen here on These C...
Mimicry in Butterflies Is Seen here on These Classic “Plates” Showing Four Forms of H. numata, Two Forms of H. melpomene, and the Two Corresponding Mimicking Forms of H. erato. This highlights the diversity of patterns as well as the mimicry associations, which are found to be largely controlled by a shared genetic locus [15]. (Photo credit: Wikipedia)
This is an article lifted from TODAY's Science and Technology section, 06-April-2013; I have kept for the purpose of posting in this blog at a later date (which turns out to be more than a year later...)

by Sean B. Carroll

Perhaps no destination has inspired more great naturalists than Brazil. Charles Darwin first made landfall at Bahia in 1832; Alfred Russel Wallace and Henry Walter Bates arrive at Para in 1848. Wallace roamed the Amazon for four years, and the indefatigable Bates for 11.

In 1852, a naturalist named Fritz Muller arrive from Germany. While Darwin and Wallace would conceive of the theory of evolution by natural selection, its acceptance was aided by Bates and Muller. And thanks to Bates and Muller, no creatures contributed more to the early growth of evolutionary science than butterflies.

Bates noticed species whose wing patterns resembled those of other butterfly families in the area. In puzzling this out, he realized that harmless butterflies were mimicking noxious species that were unpalatable to birds and lizards, and therefore, not attacked by predators.

A few years after Darwin published "On the Origin of Species," Bates suggested that this sort of mimicry - now called "Batesian" - was proof of the principle of natural selection.

Muller crucially observed that unpalatable butterflies were also mimicking other species of unpalatable butterflies. If they were already unpalatable, he wondered, what added advantage was there to mimicking other species?

It dawned on him that unpalatable mimics would enjoy strength in numbers: Their unpalatability had to be learned by predators, and species would share the cost of those lessons, whereas a uniquely patterned unpalatable species would bear the full cost.

Natural selection thus explained why different species' wing patterns would converge. But how were such similar but complex wing color patterns generated by different species? The answer eluded scientists for nearly 150 years, until an international team of researchers recently revealed mimicry's innermost secrets.

There are two ways in which what is still called "Mullerian mimicry" could evolve: Either each species independently evolved mutations that led to very similar wing patterns, or patterning genes were exchanged among species.

Several genes controlling the production of the wing patterns have now been identified, enabling researchers to distinguish between these alternatives. The answers? Both mechanisms have been at work.

By analyzing the DNA sequences in two mimicking Heliconius species in South America, researchers could determine that each species had independently evolved up to 20 different patterns that were nearly identical in each species. But in more closely related mimicking species, they found that color-controlling genes had been exchanged.

It is astonishing that so many patterns could be independently generated and replicated in different species. And it is surprising to have species swapping genes. After all, the inability to breed successfully with other groups has long been an operational definition of species.

Even if such interspecies matings are rare, a gene that confers a strong advantage, like mimicry, can spread quickly through a population.

Darwin referred to Muller as the "prince of observers," and although they never met, Muller considered Darwin a second father.

Lifted from TODAY Saturday Edition, April 6, 2013; The New York Times International Weekly