Love at First Sniff: Male Moths Go by First Impressions

Apr. 16, 2013 — An international team of researchers, including an entomologist at the University of California, Riverside, has an explanation for why we see so many hybrid moths in nature. The team closely examined the behavior and the olfactory circuitry of male moths and found an answer in female-produced pheromones -- chemicals generally consisting of a blend of two to several derivatives of fatty acids.

Male moths use pheromones to find females. To avoid mating with the wrong moth species, the pheromone blends are specific for each moth species, with only males of the same species "understanding" these volatile messages -- a result shown many times during the last 40 years of research on moth pheromones. The researchers focused on the European corn borer, a moth species in which males often mate with females from a different strain.

Strains are variants, forms of the same species. While two different species cannot mate with each other, strains, being from the same species, can.

To understand the mating behavior of the European corn borer, first, the researchers followed the flights of males to female pheromones in a wind tunnel. Each strain of the European corn borer uses a blend of pheromone components in a very specific ratio. But to their surprise, the researchers found that as the male moth flies upwind along the pheromone plume, its olfactory circuitry loses the ability to measure this ratio.

"This happens because receptors in the moth brain for each pheromone component have differential rates of sensory adaptation and each type of receptor begins to fire at a different rate, causing the input into the moth's brain to change as the moth flies along the plume," explained Teun Dekker, a former UCR graduate student and now an associate professor at the Swedish University of Agricultural Sciences, and a coauthor on the study. "To overcome this mismatch, moths rely on the ratio they detected in their first encounter with the plume."

According to the researchers, this "mental short cut" is needed for male moths to continue their orientation along the plumes which, from a sensory input viewpoint, seem to be changing in pheromone component ratio.

"Once male moths lock onto a pheromone plume, they are much less attuned to blend quality," Dekker said. "In other words, males fly even to blends that were initially unattractive, and so can mate with females of different strains that they would not have approached otherwise, explaining why we find hybrid moths in nature."

Study results appeared online April 15 in the Proceedings of the National Academy of Sciences.

Experimental details

The researchers conducted a series of behavioral experiments with overlapping pheromone plumes as well as plumes that sharply transitioned from one blend to another in a wind tunnel at the Swedish University of Agricultural Sciences. They chose the European corn borer moth to study for its narrow tuning to a binary blend of female-produced 14-carbon-chainlength acetates, called here Z11 and E11 for simplicity. Two strains exist, the Z and E strains, which produce and prefer blends of differing ratios of the Z11 to E11 pheromone components.

The researchers installed pheromone lures of each strain in the wind tunnel, as well as an intermediate, hybrid lure. Next they exposed males to the partially overlapping pheromone plumes released by these lures, thus mimicking plumes occurring in nature when a large number of moths are present.

They found that males were initially attracted to lures releasing pheromones produced by females of their own strain. But after taking flight, the males "relax their specificity," that is, they are less particular about which lures they fly to. For example, in a choice between three partially overlapping pheromone sources in one experiment, 58 percent, 38 percent and 4 percent of Z-strain males landed on Z, H and E lures, respectively.

"What we generally recognize as a distinctive smell -- the scent of a flower or the aroma of coffee -- typically consists of a mixture of many different chemicals," said study coauthor Ring Cardé, a distinguished professor of entomology who holds the Alfred M. Boyce Chair in the UCR Department of Entomology. "This is the signature of a particular bouquet -- the presence of a blend of many chemicals often in specific ratios. Our work suggests that it could be the first impression -- the first whiff of odor -- that determines the ability of an insect to recognize that odor mixture."

Next, the researchers will examine if a response specific to odor blends is altered in other moth species and organisms such as mosquitoes after their first encounter with an odor mixture.

Zsolt Kárpáti at the Hungarian Academy of Sciences and Marco Tasin at the Swedish University of Agricultural Sciences also contributed to the study. Dekker worked in Cardé's lab, graduating from UCR with a doctoral degree in 2002.

Cardé, who spent three months in 2011 in Sweden to conduct the research, was supported by a grant from the Swedish Royal Academy of Natural Sciences, Medicine and Technology.

Alternative Way to Explain Life's Complexity Proposed

Apr. 12, 2013 — Evolution skeptics argue that some biological structures, like the brain or the eye, are simply too complex for natural selection to explain. Biologists have proposed various ways that so-called 'irreducibly complex' structures could emerge incrementally over time, bit by bit. But a new study proposes an alternative route.

Instead of starting from simpler precursors and becoming more intricate, say authors Dan McShea and Wim Hordijk, some structures could have evolved from complex beginnings that gradually grew simpler -- an idea they dub "complexity by subtraction."       Computer models and trends in skull evolution back them up, the researchers show in a study published this week in the journalEvolutionary Biology.

Some biological structures are too dizzyingly complex to have emerged stepwise by adding one part and then the next over time, intelligent design advocates say. Consider the human eye, or the cascade that causes blood to clot, or the flagellum, the tiny appendage that enables some bacteria to get around. Such all-or-none structures, the argument goes, need all their parts in order to function. Alter or take away any one piece, and the whole system stops working. In other words, what good is two thirds of an eye, or half of a flagellum?

For the majority of scientists, the standard response is to point to simpler versions of supposedly 'irreducibly complex' structures that exist in nature today, such as cup eyes in flatworms. Others show how such structures could have evolved incrementally over millions of years from simpler precursors. A simple eye-like structure -- say, a patch of light-sensitive cells on the surface of the skin -- could evolve into a camera-like eye like what we humans and many other animals have today, biologists say.

"Even a very simple eye with a small number of parts would work a little. It would be able to detect shadows, or where light is coming from," said co-author Dan McShea of Duke University.

In a new study, McShea and co-author Wim Hordijk propose an alternative route. Instead of emerging by gradually and incrementally adding new genes, cells, tissues or organs over time, what if some so-called 'irreducibly complex' structures came to be by gradually losing parts, becoming simpler and more streamlined? Think of naturally occurring rock arches, which start as cliffs or piles of stone and form when bits of stone are weathered away. They call the principle 'complexity by subtraction.'

"Instead of building up bit by bit from simple to complex, you start complex and then winnow out the unnecessary parts, refining them and making them more efficient as you go," McShea said.

A computer model used by co-author Wim Hordijk supports the idea. In the model, complex structures are represented by an array of cells, some white and some black, like the squares of a checkerboard. In this class of models known as cellular automata, the cells can change between black and white according to a set of rules.

Using a computer program that mimics the process of inheritance, mutation, recombination, and reproduction, the cells were then asked to perform a certain task. The better they were at accomplishing the task, the more likely they were to get passed on to the next generation, and over time a new generation of rules replaced the old ones. In the beginning, the patterns of black and white cells that emerged were quite complex. But after several more generations, some rules 'evolved' to generate simpler black and white cell patterns, and became more efficient at performing the task, Hordijk said.

We see similar trends in nature too, the authors say. Summarizing the results of previous paleontological studies, they show that vertebrate skulls started out complex, but have grown simpler and more streamlined. 

"For example, the skulls of fossil fish consist of a large number of differently-shaped bones that cover the skull like a jigsaw puzzle," McShea said. "We see a reduction in the number of skull bone types in the evolutionary transitions from fish to amphibian to reptile to mammal." 

In some cases skull bones were lost; in other cases adjacent bones were fused. Human skulls, for example, have fewer bones than fish skulls.

Computer simulations like Hordijk's will allow scientists to test ideas about how often 'complexity by subtraction' happens, or how long it takes. The next step is to find out how often the phenomenon happens in nature.

"What we need to do next is pick an arbitrary sample of complex structures and trace their evolution and see if you can tell which route they proceeded by, [from simple to complex or the opposite]. That will tell us whether this is common or not," McShea added.

Self-Medication in Animals Much More Widespread Than Believed

Apr. 11, 2013 — It's been known for decades that animals such as chimpanzees seek out medicinal herbs to treat their diseases. But in recent years, the list of animal pharmacists has grown much longer, and it now appears that the practice of animal self-medication is a lot more widespread than previously thought, according to a University of Michigan ecologist and his colleagues.

Animals use medications to treat various ailments through both learned and innate behaviors. The fact that moths, ants and fruit flies are now known to self-medicate has profound implications for the ecology and evolution of animal hosts and their parasites, according to Mark Hunter, a professor in the Department of Ecology and Evolutionary Biology and at the School of Natural Resources and Environment.

In addition, because plants remain the most promising source of future pharmaceuticals, studies of animal medication may lead the way in discovering new drugs to relieve human suffering, Hunter and two colleagues wrote in a review article titled "Self-Medication in Animals," to be published online today in the journal Science.

"When we watch animals foraging for food in nature, we now have to ask, are they visiting the grocery store or are they visiting the pharmacy?" Hunter said. "We can learn a lot about how to treat parasites and disease by watching other animals."

Much of the work in this field has focused on cases in which animals, such as baboons and woolly bear caterpillars, medicate themselves. One recent study has suggested that house sparrows and finches add high-nicotine cigarette butts to their nests to reduce mite infestations.

But less attention has been given to the many cases in which animals medicate their offspring or other kin, according to Hunter and his colleagues. Wood ants incorporate an antimicrobial resin from conifer trees into their nests, preventing microbial growth in the colony. Parasite-infected monarch butterflies protect their offspring against high levels of parasite growth by laying their eggs on anti-parasitic milkweed.

Hunter and his colleagues suggest that researchers in the field should "de-emphasize the 'self' in self-medication" and base their studies on a more inclusive framework.

"Perhaps the biggest surprise for us was that animals like fruit flies and butterflies can choose food for their offspring that minimizes the impacts of disease in the next generation," Hunter said. "There are strong parallels with the emerging field of epigenetics in humans, where we now understand that dietary choices made by parents influence the long-term health of their children."

The authors argue that animal medication has several major consequences on the ecology and evolution of host-parasite interactions. For one, when animal medication reduces the health of parasites, there should be observable effects on parasite transmission or virulence.

For example, when gypsy moth caterpillars consume foliage high in certain toxic compounds, transmission of viruses between the caterpillars is reduced, facilitating moth outbreaks.

In addition, animal medication should affect the evolution of animal immune systems, according to Hunter and his colleagues. Honeybees are known to incorporate antimicrobial resins into their nests. Analysis of the honeybee genome suggests that they lack many of the immune-system genes of other insects, raising the possibility that honeybees' use of medicine has been partly responsible -- or has compensated -- for a loss of other immune mechanisms.

The authors also note that the study of animal medication will have direct relevance for human food production. Disease problems in agricultural organisms can worsen when humans interfere with the ability of animals to medicate, they point out.

For example, increases in parasitism and disease in honeybees can be linked to selection by beekeepers for reduced resin deposition by their bees. A reintroduction of such behavior in managed bee colonies would likely have great benefits for disease management, the authors say.

The first author of the Science paper is Jacobus de Roode of Emory University. The other author is Thierry Lefevre of the Institut de Recherche pour le Developpement in France.

Goosefish Capture Small Puffins Over Deep Water of Northwest Atlantic

Apr. 10, 2013 — A recent study has shown that bottom-dwelling goosefish, also known as monkfish, prey on dovekies, a small Arctic seabird and the smallest member of the puffin family. To understand how this deep-water fish finds a shallow-feeding bird in offshore waters, researchers looked at when, where, and how these animals were most likely to be in the same place at the same time.

Remains of fourteen dovekie were recovered from the stomachs of 14 goosefish caught during the winters between 2007 and 2010. The goosefish were captured in gillnets deployed at depths between 275 and 495 feet in waters 65 to 95 miles south of Chatham, Mass. The Cape Cod Commercial Hook Fishermen's Association collected the specimens and provided them for the research study.

Researchers from NOAA's Northeast Fisheries Science Center (NEFSC) in Woods Hole, Mass. and the USGS Patuxent Wildlife Research Center in Laurel, Md., wanted to know how the birds could be captured so far from shore by a fish that lives on the ocean bottom in deep water. Their findings, recently published online in the Northeastern Naturalist, suggest that it is all a matter of timing.

Goosefish (Lophius americanus) are highly opportunistic predators. Distributed from the Gulf of Maine to Cape Hatteras, N.C., the fish are typically partially buried on soft bottom habitats and attract a variety of prey by using a modified dorsal fin ray that resembles a fishing pole and lure.

Dovekies, a small black and white puffin species, breed along the Arctic coast and head south in the winter, typically as far as New England. The dovekie (Alle alle), also known as little auk, is the smallest of the auks. It lives in the open ocean and can dive to depths of more than 100 feet to prey on small fish, crustaceans, and zooplankton.

Study co-author Anne Richards of the NEFSC says tagging studies that she and colleagues have conducted reveal that goosefish swim considerable vertical distances from the bottom to near the surface, especially during their spring and fall migrations onshore and offshore in response to water temperatures and related factors.

Goosefish leave the bottom to use the currents during migration periods or to spawn at the surface. If prey items are encountered during their vertical movements, the goosefish take advantage. Hence, timing may be the key factor in bringing dovekies and goosefish together in the same place.

"Given the common name 'goosefish', it is not surprising to find birds in goosefish stomachs, but it is surprising to find that this predation occurs over deep water, "Richards said. "Goosefish do not actively seek out the dovekies, but when such tasty morsels are available in the water column, the fish are going to consume them."

Another source of data used in the study is the NOAA NEFSC food-habits database, which contains decades of predation information collected from the stomachs of fish that are caught during regular research vessel surveys. While not a particularly good measure of how often or how many birds are eaten by fish, these data confirm that not only goosefish, but also spiny dogfish, Atlantic herring, pollock, Atlantic cod, red hake, and fourspot flounder will eat birds.

Lead author Matthew Perry, a research wildlife biologist at the USGS Patuxtent Wildlife Research Center, says he became interested in goosefish predation when he learned from a sea scalloper on Nantucket that Chatham gillnetters were finding birds inside goosefish stomachs.

"I was studying long-tailed ducks and thought, to avoid being eaten, these birds fly 30 to 50 miles to Nantucket Sound each night and return to the ocean in the morning," said Perry, who studies several species of seaducks. "People ask why don't dovekies fly to Nantucket Sound at night like the long-tailed ducks to avoid goosefish? My explanation is that dovekies have small wings and can't make the routine flight."

"One thing we know is that dovekies cannot dive to the bottom in 300 to 400 feet of water," Perry said. "Goosefish probably come up from the ocean bottom to within 10 to 20 feet of the water surface at night. As dovekies dive for amphipods, small crustaceans, in the morning at first light, goosefish seize the opportunity and might use their 'fishing lure' to simulate one of these prey species by attracting the dovekies with their typical 'sit and wait' behavior."

The magnitude of fish predation on seabirds is poorly understood. Perry says most food habit studies for goosefish have been conducted during summer when the dovekies have migrated north to their Arctic breeding areas; thus, they seldom have been recorded as prey. Perry hopes more telemetry tracking of goosefish will be done in winter when birds are in the area and are potential prey.

As for what's ahead, Richards says ongoing use of electronic tags on goosefish will provide more information on their vertical movements.

New Genus of Bat Discovered in South Sudan

Niumbaha superba

Apr. 9, 2013 Researchers have identified a new genus of bat after discovering a rare specimen in South Sudan.

 With wildlife personnel under the South Sudanese Ministry of Wildlife Conservation and Tourism, Bucknell Associate Professor of Biology DeeAnn Reeder and Fauna & Flora International (FFI) Programme Officer Adrian Garside were leading a team conducting field research and pursuing conservation efforts when Reeder spotted the animal in Bangangai Game Reserve.

"My attention was immediately drawn to the bat's strikingly beautiful and distinct pattern of spots and stripes. It was clearly a very extraordinary animal, one that I had never seen before," recalled Reeder. "I knew the second I saw it that it was the find of a lifetime."

After returning to the United States, Reeder determined the bat was the same as one originally captured in nearby Democratic Republic of the Congo in 1939 and namedGlauconycteris superba, but she and colleagues did not believe that it fit with other bats in the genusGlauconycteris.

"After careful analysis, it is clear that it doesn't belong in the genus that it's in right now," Reeder said. "Its cranial characters, its wing characters, its size, the ears -- literally everything you look at doesn't fit. It's so unique that we need to create a new genus."

In the paper, "A new genus for a rare African vespertilionid bat: insights from South Sudan" just published by the journalZooKeys, Reeder, along with co-authors from the Smithsonian Institution and the Islamic University in Uganda, placed this bat into a new genus -- Niumbaha. The word means "rare" or "unusual" in Zande, the language of the Azande people in Western Equatoria State, where the bat was captured. The bat is just the fifth specimen of its kind ever collected, and the first in South Sudan, which gained its independence in 2011.

"To me, this discovery is significant because it highlights the biological importance of South Sudan and hints that this new nation has many natural wonders yet to be discovered. South Sudan is a country with much to offer and much to protect," said Matt Rice, FFI's South Sudan country director. FFI is using its extensive experience of working in conflict and post-conflict countries to assist the South Sudanese government as it re-establishes the country's wildlife conservation sector and is also helping to rehabilitate selected protected areas through training and development of park staff and wildlife service personnel, road and infrastructure development, equipment provision, and supporting research work. || Read more about FFI's conservation efforts in South Sudan here.

The team's research in South Sudan was made possible by a $100,000 grant that Reeder received from the Woodtiger Fund. The private research foundation recently awarded Reeder another $100,000 dollar grant to continue her research this May and to support FFI's conservation programs.

"Our discovery of this new genus of bat is an indicator of how diverse the area is and how much work remains," Reeder added. "Understanding and conserving biodiversity is critical in many ways. Knowing what species are present in an area allows for better management. When species are lost, ecosystem-level changes ensue. I'm convinced this area is one in which we need to continue to work."

Original Article

A Poem: "The Oak Tree" by Johnny Ray Ryder Jr.

The Oak Tree

by Johnny Ray Ryder Jr.

A mighty wind blew night and day.

It stole the Oak Tree's leaves away.

Then snapped its boughs

and pulled its bark

until the Oak was tired and stark.

But still the Oak Tree held its ground

while other trees fell all around.

The weary wind gave up and spoke,

"How can you still be standing Oak?"

The Oak Tree said, I know that you

can break each branch of mine in two,

carry every leaf away,

shake my limbs and make me sway.

But I have roots stretched in the earth,

growing stronger since my birth.

You'll never touch them, for you see

they are the deepest part of me.

Until today, I wasn't sure

of just how much I could endure.

But now I've found with thanks to you,

I'm stronger than I ever knew.

Into the Unknown

Into the Unknown

(A National Geographic Article)

They were 31 men at the bottom of the world exploring uncharted territory. What followed was one of the most terrifying survival stories of all time.

By David Roberts

Photograph by Frank Hurley

Mawson heard the faint whine of a dog behind him. It must be, he thought, one of the six huskies pulling the rear sledge. But then Mertz, who had been scouting ahead on skis all morning, stopped and turned in his tracks. Mawson saw his look of alarm. He turned and looked back. The featureless plateau of snow and ice stretched into the distance, marked only by the tracks Mawson’s sledge had left. Where was the other sledge?

Mawson rushed on foot back along the tracks. Suddenly he came to the edge of a gaping hole in the surface, 11 feet wide. On the far side, two separate sledge tracks led up to the hole; on the near side, only one led away.

------------------------------

It was December 14, 1912. Thirty years old, already a seasoned explorer, Douglas Mawson was the leader of the Australasian Antarctic Expedition (AAE), a 31-man team pursuing the most ambitious exploration yet of the southern continent. Let Scott and Amundsen race for the South Pole. Mawson was determined to discover everything he could about a 2,000-mile-long swath of Antarctica that was terra incognita, and to wring from it the best scientific results—in terms of geology, meteorology, magnetism, biology, atmospheric science, and glaciology—ever obtained on a polar journey.

Having built a hut on the shore of a cove they named Commonwealth Bay, the men of the AAE had wintered over in what was later proven to be the windiest place on Earth (at least at sea level), with gusts up to 200 mph. At times, the gales were so strong they knocked the men off their feet and sent them sliding across the ice.

Setting out in November 1912, Mawson’s sledging party was one of eight three-man teams sent off on journeys in all possible directions. For his own Far Eastern Party, he chose 29-year-old Swiss ski champion Xavier Mertz and 25-year-old Belgrave Ninnis, an eager, likeable Englishman serving in the Royal Fusiliers. Hoping to connect the unmapped interior with the heights of far-off Oates Land, discovered by Robert Falcon Scott’s party only the year before, Mawson was bent on making the deepest push of all into the unknown.

------------------------------

By the morning of December 14, 35 days out, the trio had reached a point nearly 300 miles from the hut. The men had crossed two major glaciers and scores of hidden crevasses—deep fissures in the ice camouflaged by thin snowbridges. Just after noon that day, Mertz had held up his ski pole, signaling yet another crevasse.

Mawson judged it to be only a minor nuisance, as his sledge glided smoothly across the bridge. He called out the usual warning to Ninnis, and, in a last glance back, saw that his teammate had corrected his path to cross the crevasse head-on rather than diagonally.

Now Mawson and Mertz cut away the fragile lip of the open crevasse, roped up, and took turns leaning over the abyss. What they saw appalled them.

One hundred fifty feet down, a husky lay moaning on a snow shelf, its back evidently broken. Another dog, apparently dead, lay beside it. A few pieces of gear lay scattered on the same shelf.

There was no sign of Ninnis or the sledge.

For three hours, Mawson and Mertz called into the depths, hoping against hope for an answering cry. They had far too little rope to lower themselves into the crevasse to search for their companion. At last they accepted the inevitable. Ninnis was dead. Gone with him were the team’s most valuable gear, including their three-man tent, the six best huskies, all the food for the dogs, and nearly all the men’s food.

The two men might have perished the first night if they hadn’t improvised a shelter. With the temperature just above 0°F, they pitched a spare tent cover over a frame concocted of sledge runners and Mertz’s skis. Inside this gloomy cave, they laid their reindeer-skin sleeping bags directly on the snow. So cramped and flimsy was their “tent” that only one man could move at a time, and neither could rise higher than a sitting position.

In the first days of their homeward dash, driven by adrenaline, they made excellent mileage. But during the next two weeks, the dogs gave out one by one. When George, then Johnson, then Mary could no longer pull, they were loaded on the sledge and carried to that night’s camp, where the men shot them with the rifle. Desperate to hoard their tiny supplies of pemmican, biscuits, raisins, and cocoa, the men ate the tough, stringy dog meat, then threw the bones and skin to the remaining huskies, which fought ravenously over every scrap.

Navigating with a theodolite and dead reckoning, Mawson steered a homeward course as much as 25 miles south of their outward track, hoping to skirt the worst of the crevasses and the heads of the two big glaciers. He tried to bolster his partner’s spirits, promising him a safe return to Australia. At 1 a.m. on December 25, Mawson woke Mertz to wish him a merry Christmas. “I hope to live to share many merry Christmases with my friend Mawson,” Mertz wrote in his diary.

By now, only Ginger, the pluckiest of the surviving dogs, could haul. The two men put on their chest-and-hip harnesses and pulled the sledge alongside her, exhausting themselves after only a few miles’ run. Crossing wind-carved ridges of hard snow known as sastrugi as high as three and a half feet, they repeatedly fell down and often capsized the sledge. To save weight, they threw away gear—their alpine rope, the rifle, the extra sledge runners, and, most painfully, Mawson’s camera and the film packs that held the visual record of the trio’s pioneering journey.

Something was wrong with Mertz. He was rapidly losing strength. Too weak to move on January 2, he could manage only five miles the next day before giving up, forcing Mawson to pitch the tent. In disbelief that his fingers had been frostbitten, Mertz surprised Mawson by biting off the tip of one. Mawson knew that their only hope was to keep moving, but on January 5, Mertz refused. It would be suicide, he said.

Though racked with pain himself, Mawson persuaded Mertz to ride the sledge. Summoning extraordinary powers, Mawson pulled the terrible load by himself for two and a half miles. In his diary that night, he wrote, “If he cannot go on 8 or 10 m[iles] a day, in a day or two we are doomed. I could pull through myself with the provisions at hand but I cannot leave him.”

------------------------------

By January 7, the men had covered some 200 miles of their return trek, with 100 still to go. But as they tried to pack up that morning, Mawson discovered that his teammate had “fouled his pants.” As a nurse might tend a baby, Mawson undressed Mertz, cleaned up the mess, and put him back in his sleeping bag. That afternoon, he tried to lift Mertz to a sitting position to drink cocoa and weak beef broth, but the man started raving deliriously and again soiled himself.

At 8 p.m., Mertz pulled himself half out of his sleeping bag and flailed about in a wild frenzy, breaking one of the tent poles. For hours he raved in German. Mawson held him down, hoping to calm him, then stuffed him back into his bag. At 2 a.m. on January 8, Mertz died in his sleep.

Mawson buried his friend, still in the sleeping bag, beneath a mound of snow blocks atop which he fixed a rude cross made of discarded sledge runners. Many years later, some researchers speculated that Mertz’s debilitation was caused by poisonous overdoses of vitamin A from the huskies’ livers. But if so, why did the condition affect Mertz so much more drastically than it did Mawson? Other experts suggested that Mertz’s collapse was due simply to hypothermia, overexertion, and near starvation.

Whatever its cause, Mertz’s death now threatened Mawson’s survival as well. The food was almost gone, and his own physical state was deplorable, with open sores on his nose, lips, and scrotum; his hair coming out in clumps; and skin peeling off his legs. And he still had a hundred miles to go. “I am afraid it has cooked my chances altogether,” Mawson wrote in his diary. But he added, “I shall do my utmost to the last.”

Using only the serrated blade of his knife, he cut the sledge in half. Then he fashioned a makeshift sail by sewing Mertz’s jacket to a cloth bag. Three days after Mertz’s death, Mawson discovered to his horror that the soles of his feet had completely detached from the skin beneath them, which spurted pus and blood. He taped the dead soles to his feet, and put on six pairs of wool socks. Every step thereafter was an agony.

Mawson was now in a race against time, as well as miles. The expedition’s relief ship Aurora was scheduled to arrive at Commonwealth Bay on January 15 to pick up the men and steam toward home in Australia. But as the days ticked by, Mawson was still more than 80 miles from the hut, and he was growing weaker by the hour.

One day, plowing through deep snow, he broke through a snowbridge covering a hidden crevasse. Suddenly he was falling unchecked through space. Then a fierce jolt halted his plunge. The 14-foot harness rope attaching him to the sledge had held, but now Mawson was sure that his weight would pull the sledge in on top of him. He thought, So this is the end.

Miraculously, the sledge stuck fast in the deep snow, anchoring him. But as his eyes adjusted to the semidarkness, Mawson saw how hopeless his predicament was. He dangled free in space, the crevasse walls too far away to reach even with the wild swing of a boot. His first thought came as a searing regret that he had not had the chance to eat the last ounces of his food before he died.

His only chance to escape was to pull himself hand over hand up the harness rope. Providentially, he had tied knots in the rope at regular intervals. He seized the first knot and pulled himself upward, then lunged for the next. Even for a fit, healthy man, such a feat would have been barely possible; yet Mawson pulled, rested, and lunged again. He reached the lip of the crevasse and tried to roll onto the surface above.

That effort broke loose the overhanging lip. Mawson fell all the way to the end of his harness rope. Despair overwhelmed him. He pondered slipping out of the harness to plunge to the bottom of the crevasse, ending things at once rather than by strangling or slowly freezing. At that moment, a verse from his favorite poet, Robert Service, flashed through his mind: “Just have one more try—it’s dead easy to die, / It’s the keeping-on-living that’s hard.”

The words spurred him to “one last tremendous effort.” As he reached the lip, he thrust his legs out first, then pulled the rest of his body free from the crevasse. He rolled over and passed out, waking an hour or two later to find his body covered with a dusting of new-fallen snow.

Mawson was now convinced he had no chance to survive. Besides, the deadline to reach the hut had come and gone. For all he knew, the Aurora had steamed away with all the other AAE hands on board. What drove him onward was the hope of leaving his diary, along with Mertz’s, in a place where searchers might eventually find them and learn the story of the doomed Far Eastern Party.

Yet on January 29 a minor miracle occurred. Just north of his track, Mawson saw something dark loom through the haze. It was a snow cairn covered with a black cloth. Inside, he found a message from three teammates who had been out searching and a bag of food—blessed food! From the note, Mawson learned that he stood only 28 miles from the hut.

It would take him ten days to cover that short distance, as he waited out a prolonged blizzard. At last, on February 8, he began the last descent. Before he could see the hut, he caught sight of a distant speck on the horizon. As he feared, it was the Aurora, leaving Commonwealth Bay for good. Was he alone? Then the hut sprang into view, and outside it, three men working at some task. Mawson stopped in his tracks and waved for 30 seconds. The men were too far away to hear his shouts. At last one of them glanced up and saw the apparition on the horizon.

Mawson had missed catching the Aurora by a mere five hours. Instead, he and six men deputized to stay on to search for Mawson’s party were condemned to spend another year in the windiest place on Earth. Now the men at the hut rushed up the icy slope to embrace their leader. The first to arrive was Frank Bickerton, a stalwart 24-year-old British engineer who had been in charge of another of the exploring parties. From 50 yards off, Mawson recognized Bickerton. And from the startled look on Bickerton’s face as he beheld the gaunt, ravaged countenance of the man staggering toward him, he knew exactly what Bickerton was thinking: Which one are you?

Another ten months passed before the Aurora returned. When Mawson finally reached Australia in February 1914, he was greeted as a national hero and knighted by King George V. He spent the rest of his career as a professor at the University of Adelaide. Although he would lead two more Antarctic expeditions, his life’s work became the production of 96 published reports that embodied the scientific results of the AAE.

When Mawson died in 1958, all Australia mourned its greatest explorer.