Tadpoles don’t cry to get their way. But some of them sure can beg.

Each bout of hungry-baby drama among mimic poison frogs (Ranitomeya imitator) occupies both parents for hours. The tadpoles get so crazy-frantic that researchers wanted to know whether the begging is an honest call for help or a histrionic scam.

Frogs can lay globs of eggs by the thousands and leave them to fend for themselves. But the two-to three-egg clutches of mimic poison frogs (the only known monogamous frogs) get coddled, says Kyle Summers of East Carolina University in Greenville, N.C. Dad repeatedly checks in, sitting on the eggs and shedding some paternal pee if they’re drying out.
When the eggs hatch, dad gives each tadpole a piggyback ride to its own private pool. To find a little rainfall cupped between a leaf and stem, he’ll haul youngsters four meters or so. “A bit of a hike,” Summers says, since dad is only about a centimeter or two long himself.

These baby pools are pretty empty: home to only some algae, maybe some small insects. “The good news is that your offspring are not likely to get eaten; the bad side is that they don’t have anything to eat,” Summers says.
This is where the begging comes in. Frogs can’t make milk like mammals or regurgitate bugs like birds. But this species is one of the rare frogs whose moms, after considerable persuading, will lay an unfertilized egg for the tadpoles’ breakfast.
When parents show up on their weekly visit, a youngster stops regular swimming, noses up to a parent and goes into a frenzy of vibrating its tail. “The parent cannot miss a hungry tadpole,” Summers says.

Bouts of persuasion go on for several hours as the tadpole begs, stops, begs more and then more. Mom often makes several false starts, entering the pool but leaving it without any egg action. During all this, “dad will be the cheerleader,” calling in trills and stroking her, Summers says.

Analyzing tadpole frenzies in the lab, Summers’ then-student Miho Yoshioka found that tadpoles on short rations begged more as hungry weeks dragged on. Parents fed these hungrier tadpoles more reliably than the babies that researchers slipped treats to, Yoshioka, Summers and Casey Meeks report in the March Animal Behaviour. Overall, the researchers conclude, the relentless frenzy shows honest need, not tadpole greed.

A mushroom whose genes have been edited with molecular scissors known as CRISPR/Cas9 doesn’t need to be regulated like other genetically modified crops, the U.S. Department of Agriculture said April 13 in a letter to the mushroom’s creator. The edible fungus is the first CRISPR-edited crop to clear USDA regulation.

Yinong Yang, a plant pathologist at Penn State University, used CRISPR/Cas9 to snip out a tiny bit of one gene from the mushroom Agaricus bisporus. The edit reduces browning when the mushroom is sliced.

Because the gene editing left no foreign DNA behind, the USDA’s Animal and Plant Health Inspection Service determined that the mushroom poses no risk to other plants and is not likely to become a weed.

Yang says he plans to submit data about the mushroom to the U.S. Food and Drug Administration. FDA clearance isn’t required but, says Yang, “we’re not just going to start marketing these mushrooms without FDA approval.”

Smartphone-toting pilgrims regularly stream into northern Cambodia from all over the world. Their destination: Angkor Wat, a medieval temple that’s famous for massive towers and majestic stone carvings of Hindu gods, spirits and mythological battle scenes. The site, considered the world’s largest religious monument, drew more than 2.3 million visitors in 2014.

Angkor Wat’s sightseers encounter a study in contrasts. This architectural wonder of human civilization ascends skyward, on the verge of being engulfed by nature below. Tourists walk along a path that crosses over a moat and through the temple’s western side, the one entrance cleared of vegetation. Lush forest stops just short of the rest of the structure. Outside the moat, trees, thick ground cover and ponds dominate the landscape.
While adventurous visitors snap pictures, scientists are using high-tech approaches to uncover Angkor Wat’s hidden side, long obscured by all that vegetation. After more than a century of research on the parts of Angkor Wat that are visible with the naked eye, many scientists assumed that the site was a sacred city contained within the bounds of a square moat. But even though its name roughly translates as “temple city,” new finds show that Angkor Wat was not a sacred city at all. It was a gigantic temple connected to residential districts, canals and other structures that stretched beyond the moat and blended into a sprawling city called Greater Angkor, which covered about the same area as Berlin or Columbus, Ohio.
Angkor Wat’s unveiling by modern laser technology began in April 2012. Archaeologist Damian Evans of Cambodia’s Siem Reap Center and several colleagues made daily helicopter flights for almost two weeks over a 370-square-kilometer area around the temple. The helicopter carried $250,000 worth of special equipment that fired millions of laser pulses every few seconds at the forest below. A small percentage of those pulses zipped in between trees and foliage to the forest floor. The Earth’s hard surface bounced those laser shots back to a sensor on the helicopter. This technique, known as light detection and ranging, or lidar for short, picked up differences in the contours of the land now obscured by jungle. With the findings, researchers could draw a picture of city blocks, residential areas, dried-out ponds and other archaeological remains. Results gleaned from lidar and from new ground-based investigations appeared in the December 2015 Antiquity.

Lidar has been around since the early 1960s. Scientists have used it to measure pollutants in the atmosphere, map shorelines and guide robotic and manned vehicles around obstacles. Lower costs over the last decade have made the technology accessible to archaeologists.

With their laser eye in the sky, Evans and colleagues uncovered big surprises at Angkor Wat. Just beyond one side of the roughly 1.3-kilometer-square moat surrounding the temple, the researchers found six massive and mysterious lines of earth arranged in precise coils — as well as adjacent areas where later canal construction had apparently destroyed two more coiled mounds. These Khmer creations resemble the spiraling paths of labyrinths. Lidar-guided excavations within the moat’s boundary upended ideas about who lived on temple grounds. Rather than religious or political bigwigs, residents were workers who kept the place running. And on-the-ground research found evidence of unexplained towers, built and then demolished during Angkor Wat’s construction, as well as defensive platforms used, perhaps, to fight off invaders.
SUBSCRIBE
“It’s an embarrassingly exciting time for archaeologists who study Angkor Wat,” says University of Sydney archaeologist Roland Fletcher. “Researchers have driven and walked over many of these new discoveries for a century.” Fletcher directs the Greater Angkor Project, which combines remote sensing technology with archaeological digs.

If Angkor Wat blended into Greater Angkor’s 1,000 square kilometers of urban sprawl, so did hundreds of other temples and shrines of lesser grandeur built by rulers of Southeast Asia’s Khmer Empire from the ninth to 15th centuries, he says.

“There was nothing like Greater Angkor until the advent of 19th century industrial cities,” says Fletcher, who estimates it held about 750,000 residents in the 12th and 13th centuries. Cities of around 1 million people arose in China by the ninth century, but those metropolises covered one-half or less the area of Greater Angkor. Spread-out cities in the mold of Greater Angkor became more common in the 1800s as trains and cars made long-distance travel easier. But discoveries at Greater Angkor shatter a long-standing assumption that urban sprawl was impossible without mechanical forms of transportation, he says.
City sprawl
Lidar technology revealed new structures in and around the Angkor Wat temple complex.
Tap red dots for details
Big grids
Carved inscriptions at Angkor Wat describe the structure as the pet project of Suryavarman II, who ruled the Khmer Empire from 1113 until his death in 1149. Serving first as a temple dedicated to the Hindu god Vishnu, Angkor Wat also became a mausoleum for Suryavarman II when he died.

The temple hosted Hindu ceremonies into the 13th century. In the 14th or 15th century, it became a Buddhist temple. Like tourists and scientists, Angkor Wat’s modern-day Buddhist monks had no idea that the site was once so extensive.

Lidar revealed a grid of pathways forming four rectangular blocks, each the size of a small town, that encircle the main temple inside the moat. Earthen mounds and an estimated 250 to 300 ponds — now dried-out depressions on the forest floor — dotted these gridded areas.

Excavations in 2010 and 2013, the latter guided by lidar findings, uncovered remains of modest wooden dwellings and household goods, such as pots and a ceramic cooking device, in the mounds. Archaeologist Miriam Stark of the University of Hawaii at Manoa in Honolulu led that work.

Radiocarbon dating conducted by Stark’s team indicates that houses situated around the ponds appeared at least as early as the sixth century near the eventual site of Angkor Wat. Other residences date to after the 15th century, supporting evidence — including a 17th century Japanese map of the Angkor Wat temple — of the structure becoming a Buddhist religious center.
No more than 4,500 people lived within Angkor Wat’s moated boundary in the 12th century, Fletcher estimates. His calculation is based on the account of a 13th century Chinese emissary to Greater Angkor, who wrote that one to three families shared each pond in the area around the tample.

Stone inscriptions at nearby Ta Prohm, a late–12th century Greater Angkor temple, record a workforce of 12,640 people that included only about 2,000 on-site residents. Another 66,625 people were described as being “in service” to the temple, delivering food and other supplies.

At roughly twice the size of Ta Prohm, Angkor Wat probably relied on a workforce of about 25,000, Fletcher suspects. An additional 125,000 people must have shuttled in supplies. Each Greater Angkor temple apparently supported a vast economy.

If that’s true, it makes sense that crisscrossing roads forming residential blocks fan out far beyond Angkor Wat’s moat on the 2012 lidar map. “Urban grids stretched beyond temple walls into the hinterlands,” Evans says.

Lidar data showed a comparable street network at a nearby 12th century temple, Angkor Thom. Here too, “to our complete surprise, the layout of houses and streets continues beyond the moated confines of the temple,” says archaeologist Charles Higham of the University of Otago in New Zealand. He studies Greater Angkor and is familiar with the lidar results.

Religious and political big shots lived somewhere in the urban sprawl outside Angkor Wat and other temples, Fletcher suspects. Why they did so is unclear.

Mystery coils
Finding that Angkor Wat extended far beyond its moat was unexpected. But a discovery just south of the temple’s moat was unprecedented.

Lidar unveiled long banks of earth that formed six well-preserved coiled or spiral-shaped patterns. Each formation is roughly 1 kilometer long and 0.5 kilometers wide, or about 10 times the length and width of a football field. The precise alignment of these earthworks with the moat suggests they were assembled around the time of Angkor Wat’s construction.
A ground survey in late 2012 and early 2013 determined that the coils consisted of 18-meter-wide sandbanks separated by 12-meter-wide channels. After using laser maps to locate the spirals on the ground, investigators walked through the channels searching for signs of human activity. They found no pottery or other artifacts to suggest that anyone had lived or worked there.

“Nothing like the shape and design of these spirals has been seen anywhere else,” Fletcher says.

Suryavarman II’s reasons for building the coils are unknown. These mounds might have served as raised fields for growing herbs used in temple rituals. Or the coils might have been sites of formal gardens that would have been unrivaled in size and complexity until the construction of 18th century palace gardens in Europe, Evans suggests.

Rainwater could have flowed through channels between the coils. Evans doubts, however, that enough water collected to support farming.

It’s also possible that Angkor Wat’s spiral structures held special spiritual meaning for Khmer people and had no practical use. Yet Fletcher says that nothing resembling these coiled forms appears in Hindu writings and art.
After what must have been several decades of construction coinciding with work on the temple, “the spirals may never have been completed and might never have become operational,” Evans says.

Researchers are now examining fossilized pollen recovered from the coils for signs of cultivation or gardening.

Buried towers
Another surprising discovery at Angkor Wat comes not from lidar but from ground-penetrating radar. While lidar reveals characteristics of the ground’s surface covered by vegetation, ground-penetrating radar can detect objects buried deep under several dozen meters or more of soil.

In December 2009, a team led by archaeologist Till Sonnemann of Leiden University in the Netherlands dragged a wheeled device reminiscent of a lawn mower over Angkor Wat’s vast outer section for two weeks. High-frequency radio waves emitted by the contraption bounced off buried objects, signaling locations of possible archaeological remains.

Sonnemann was looking for remnants of houses or administrative buildings from the 12th century or later. Something far more intriguing turned up.

At Angkor Wat’s western entrance, where visitors enter the grounds of the temple, the radar machine identified what looked like the foundations of eight towers. Excavations in 2010 and 2012 confirmed their existence. Foundation remains lie roughly 21 meters belowground, about 10 times as deep as an Olympic swimming pool.

Each cross-shaped foundation, held in place by walls made of a reddish rock called laterite, had a square central section bound by porches jutting out on each side. Intact shrine towers from other Khmer Empire sites, which were dedicated to various gods, feature side porches.

Angkor Wat’s former towers were intentionally destroyed, Sonnemann says. Radiocarbon dating of burned wood from the foundations suggests the towers were built around the time that work started on Angkor Wat. Demolition occurred when Angkor Wat’s outer wall and western gate were completed, Sonnemann suspects.

Perhaps 12th century residents of Greater Angkor used the gateway towers as a temporary religious shrine to the Hindu god Vishnu while erecting Suryavarman II’s temple, which was dedicated to the same deity, Sonnemann says. Of the eight towers, four formed a square that stood within a larger square formed by the four others. Angkor Wat itself features four towers arranged in a square around a central tower.

The gateway towers may have served as an outline of Angkor Wat’s permanent towers, Sonnemann speculates. But they were not identical. Remote sensing identified no remnants of a central tower at the western entrance.
Wall defenses
Tourists and researchers have long gazed at Angkor Wat’s impressive stone outer wall without realizing it holds clues to warfare between the Khmer Empire and regional foes, says archaeologist David Brotherson of the University of Sydney.

Archaeologist Christophe Pottier of the Bangkok Center in Thailand first noticed holes that had been intentionally carved in parts of the wall constructed later. When Brotherson took a closer look, he speculated that those openings once supported wooden platforms and fences.

Angkor Wat’s defenders stood on the platforms and positioned themselves between the fences to repel attacks by nearby Thai kingdoms, Brotherson proposes. Those confrontations probably took place sometime between the late 13th and early 17th centuries.

Brotherson studied 6,257 wall cavities. Most consist of groups of seven square holes, at the same height, running across the inside of the wall near its top. Sets of holes, notches and grooves also run across adjacent areas on top of the wall.
These alterations appear at spots where six nearly 20-meter-wide gaps in the wall — which probably framed wooden gates — were later filled in with stone blocks. Differences in detailing and finish distinguish original masonry from filled-in sections.

Holes on the inner part of the wall held wooden beams that supported platforms about 3.5 to 4 meters above the ground that must have had stairs at each end, Brotherson says. Angkor Wat’s fighters would have stood on platforms while raining down arrows or other weapons on attackers. Wall-top holes probably held fence posts for additional protection, he suspects. Yet researchers have found no arrowheads or other weapons and no evidence of military damage to Angkor Wat, such as wall marks from catapulted boulders or remnants of torched wooden buildings.

Still, it’s more likely that the wall’s inside holes held platforms for temple defenders to stand on than wooden roofs that sheltered people or animals underneath, Brotherson says. Gateway spaces would not have been filled in simply to construct shelter roofs, he contends. And roofs would not have required holes carved on top of the wall.

“There are no historical references to defensive fortifications at Angkor Wat,” Fletcher says. “Sometimes archaeology tells us things that history cannot.”

Tropical trajectories
Lidar’s bird’s-eye view of forest floors has guided archaeologists not only to lost parts of Angkor Wat, but to a greater appreciation of similarities between Greater Angkor and other ancient tropical cities.

Lidar surveys of west-central Belize in 2009 and 2013 showed that the ancient Maya city of Caracol sprawled across now-forested landscape much as Greater Angkor did. A dense urban area, incorporating agricultural fields into a planned city, spread 10 kilometers in all directions from central Caracol in 650. Researchers estimate that more than 140,000 people lived at Caracol (SN: 12/15/12, p. 14).

Laser maps revealed farming terraces, housing tracts and roads leading to public plazas that ranged far beyond Caracol’s urban center. Anthropologists Arlen and Diane Chase of the University of Central Florida in Orlando directed lidar research at Caracol.

At 1,000 square kilometers, Greater Angkor covered a much larger area than Caracol. “Lidar surveying has just begun, but we now know that Maya cities were shrimps compared with mighty Angkor,” says Yale University anthropologist Michael Coe, a long-time investigator of the Maya and other ancient American civilizations.
Nothing like Angkor’s street grids stretching with geometric precision toward the horizon appears at Caracol, adds Coe, who is familiar with work at both sites.

Still, common factors inspired the rise and fall of Greater Angkor, Maya urban centers such as Caracol and the tropical city of Anuradhapura in Sri Lanka between the ninth and 16th centuries, Fletcher and two colleagues concluded in the October 2015 Antiquity.

Rulers in each region directed the construction of reservoirs and canals that allowed spread-out cities to flourish. Effective water management cemented the power of kings by enabling masses of farmers to make a steady living.

Severe periods of drought, indicated by analyses of tree rings and lake sediments, strained water supplies in each tropical setting, Fletcher says. Periodic monsoon rains in Southeast Asia and Sri Lanka added insult to injury, overwhelming reservoirs and damaging canals.

Unable to supply enough water, political systems at Greater Angkor and other tropical cities crumbled, Fletcher argues. But societies didn’t vanish. Farmers reorganized into smaller communities based near coasts and along major rivers. Cultivation continued in fields that had once been part of massive cities.

Laser quest
Fletcher’s rise-and-disperse scenario for ancient tropical cities is being put to a broader test. From March to May 2015, a second set of lidar flights expanded laser mapping of northern Cambodia to a total area of 2,000 square kilometers. Researchers want to see if, like Angkor Wat, other ancient temples in the region sat in the center of dispersed settlements tied together by reservoirs, canals and ponds. Archaeological investigations based on the new lidar data are under way. Evans plans to announce initial findings in June.

Over the next 10 to 15 years, lidar technology will become smaller and cheaper, Evans predicts. Laser-wielding drones will replace lidar-toting helicopters. But laser mapping is already a game changer for tropical archaeology.

Around Angkor, “the impact of lidar data is like turning on a light after groping in the dark for over a century,” says archaeologist John Miksic of the National University of Singapore.

Suryavarman II, a politically ambitious warrior who tried to expand his kingdom by launching wars and allying himself with Imperial China, would surely celebrate Angkor Wat’s laser revival if he was around today. It’s a revival of sorts for the once-mighty king, as well.

Venus flytraps (Dionaea muscipula) make carnivory look cool. But the genes that make it possible have roots in herbivory.

Though modern flytraps eat insects, their ancestors probably didn’t. In search of clues to this transition, Rainer Hedrich of the University of Wurzburg in Germany and his colleagues looked at protein production patterns in in different parts of the plant.

Unstimulated traps seem to decode genes for similar proteins to those found in leaves, which supports the theory that traps originally evolved from foliage. Glands inside the trap, which help with digestion, share common gene expression patterns with roots — perhaps because both process nutrients.

Sensory hairs signal traps to close on prey. When an unsuspecting spider trips those trap hairs, gene expression patterns shift dramatically. Traps start producing signaling hormones and digestive enzymes. Some of these same protein pathways also help plants heal wounds inflicted by herbivores. Venus flytraps may have rewired traditional plant defense machinery to eat insects in nutrient-poor soils, Hedrich’s team writes May 4 in Genome Resarch.

Giraffes’ genes tell a not-so-tall tale about growing necks to great lengths.

Tweaks to genes important for development may account for both the giraffe’s stature and turbocharged cardiovascular system, researchers report May 17 in Nature Communications.

Researchers compiled the genetic instruction book, or genome, for both the giraffe and the okapi, its short-necked closest living relative. Those two species’ most recent common ancestor lived about 11.5 million years ago, says Douglas Cavener, a geneticist at Penn State University. Overall, giraffes and okapis still have very similar genes, with 19.4 percent that are identical.
The researchers compared giraffe, okapi and cattle genomes to see what sets giraffes and okapis apart from other ungulates. About 400 genes differ between those species and cattle.

Further comparisons of those genes with DNA from other animals revealed 70 genes in which giraffes had DNA differences from all other mammals. Those uniquely tweaked genes could be responsible for giraffes’ unusual height and physiology, the researchers reasoned.

Among the giraffe’s most distinctively altered genes are some that are well known to regulate embryo development. For instance, the team found alterations in several genes that govern skeletal development, including the gene FGFRL1.

FGFRL1 encodes a protein that helps regulate the size of body segments. Giraffes have the same number of vertebrae in their necks as okapi and other animals do, but the bones are bigger. The giraffe version of the FGFRL1 protein contains seven amino acids that are different than those found in other mammals. Those amino acid differences may change the way the protein works and allow giraffes’ body parts to grow larger than those of other animals.

Some of the same genes that gave the giraffe its long neck — FGFRL1 included — may also be involved in strengthening the cardiovascular system in order to pump blood all the way to the giraffe’s lofty brain, the researchers found. Such multifunctional genes would have allowed coordination of giraffes’ adaptations, Cavener says.
The researchers “provide some very compelling candidates” for genes that shaped giraffe evolution, says Michael Hiller, an evolutionary genomicist at the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden, Germany. More research is needed to show that fiddling with those genes really could turbocharge giraffes’ hearts and supersize their bones. Hiller says he doubts the researchers have found all the genetic secrets to giraffes’ many evolutionary innovations.

Although giraffes have a unique appearance, the statuesque leaf eaters didn’t invent any new genetic tricks to change their hearts and necks, says Cavener. “Giraffes’ novelties almost certainly weren’t created by new genes or pathways, but by modifications of genes and pathways universal to all mammals.”

A notorious Alzheimer’s disease villain may also be a germ-busting superhero. Amyloid-beta gums up the brains of people with Alzheimer’s but also takes out dangerous brain invaders, scientists report May 25 in Science Translational Medicine.

As strong as steel, tough strands of A-beta protein imprison pathogens that threaten the body and brain, experiments in mice and worms show. Those results raise the possibility that A-beta plays a role in the immune system and its accumulation in Alzheimer’s might be prompted by an infection.
Earlier studies have shown that A-beta can bust germs in cells in dishes, but the new experiment shows A-beta protection in living mice and worms. Mice engineered to have the human form of A-beta better survived a brain infection of Salmonella bacteria than mice without the human A-beta, Robert Moir and Rudolph Tanzi, both of Harvard Medical School, and colleagues found. And in the bodies of worms, A-beta helped stave off the dangerous yeast Candida.

When researchers injected Salmonella into mice’s hippocampi, a brain area damaged in Alzheimer’s, A-beta quickly sprang into action. It swarmed the bugs and formed aggregates called fibrils and plaques. “Overnight you see the plaques throughout the hippocampus where the bugs were, and then in each single plaque is a single bacterium,” Tanzi says. That rapid response was surprising, he says. “No one expected that.”
And those prisons are probably permanent, Moir says. “In A-beta, those fibrils set like concrete and the bugs have no chance of ever getting out.”

Alzheimer’s has been linked to a host of bacterial, fungal and viral infections, says immunologist Kevan Hartshorn of Boston University School of Medicine. That work, along with the new study, raises the possibility that Alzheimer’s could be spurred by an immune response to a pathogen.

That’s “an extremely provocative and interesting hypothesis,” says neuroscientist Berislav Zlokovic of the University of Southern California in Los Angeles, who says the new data are convincing. But it remains to be seen whether the results are relevant for people with Alzheimer’s. Zlokovic and colleagues recently found that the barrier between brain and blood weakens with age — a situation that could let more microbes into the brain and perhaps spur A-beta accumulation.
A-beta appears to be a general immune system fighter that’s effective against many enemies, says Moir. “This is a classical innate immune response, which means that whatever gets thrown at it, it does the same thing,” he says. “So whether it’s a herpesvirus, a spirochete or chlamydia, it’s going to generate A-beta plaques.”

Moir also raises the possibility that the amyloid’s germ-busting job might play a role in other diseases that come with amyloid accumulation, such as diabetes or heart disease. “I think we may have stumbled across an underlying theme in a lot of major diseases,” he says.

Finding this helpful role for A-beta may complicate a therapeutic approach for Alzheimer’s that attempts to reduce levels of the protein with antibodies, says molecular pharmacologist Marina Ziche of the University of Siena in Italy. “I have always been very skeptical about that approach,” and the new results suggest that people benefit from some A-beta, Ziche says.

The next step is to see whether pathogens are entombed in A-beta plaques in the human brain, Tanzi says. “Now it’s time to start looking for them in patients.” To start, he and colleagues have just begun a project to catalog the collection of microbes in healthy brains and brains with Alzheimer’s.

Finding a strong link between pathogens and Alzheimer’s could suggest new ways to prevent the disease, Tanzi says. Vaccines that fight infections, for instance, might be one way to prevent A-beta pileup.

Giant squid are the stuff of nightmares. They were even one of the deadly dangers in Jules Verne’s 20,000 Leagues Under the Sea, attacking the Nautilus in a group and carrying off one of the crew:

Just as we were crowding each other to reach the platform, two more arms lashed the air, swooped on the seaman stationed in front of Captain Nemo, and carried the fellow away with irresistible violence…. What a scene! Seized by the tentacle and glued to its suckers, the unfortunate man was swinging in the air at the mercy of this enormous appendage. He gasped, he choked, he yelled: ‘Help! Help!’ … The poor fellow was done for.

What makes Verne’s giant squid all the more frightening is that he didn’t invent the creatures; giant squid strandings had been documented in Europe since at least 1639, and scientists informally described the animals in the late 1850s.

But even if we don’t really have to worry about the huge invertebrates snatching people off boats, giant squid remain mysterious. They weren’t even photographed in the wild until 2004. And many questions remain unanswered about them. The biggest: Just how giant can the giants get? A new study has come up with an estimate — and also highlights the many reasons why it’s so difficult to come up with one.

Charles Paxton of the University of St. Andrews in Scotland starts by laying out five ways that it should be possible to estimate squid length, and why the first four aren’t great measures. Anecdotal accounts — which claim giant squid reaching lengths of 30 meters and 53 meters, not counting the two long tentacles — are often riddled with inaccuracy and exaggeration. Estimating maximum length based on squid growth rate won’t work because squid growth rates just aren’t well known. Some scientists have tried to determine lengths based on the sucker scars found on whales, but since scientists don’t know how whale growth affects the sizes of those scars, those aren’t a good measure either.

Direct measurement of dead squid would seem to be a good option, except that the two long tentacles of a squid — which extend far beyond the animal’s arms and determine its full length — are elastic and can change in length when a squid is preserved, Paxton notes. That leaves the fifth method — estimating length based on the size of the hard beak. Beak size and squid body length are related.

Paxton combined the last two methods to come up with a maximum length for a giant squid of about 20 meters, from the top of its mantle, or body, to the tip of its long tentacles. His estimate appears May 17 in the Journal of Zoology.
The longest squid ever reported was 17.37 meters long, and Paxton questions its veracity, as does another paper published last year in PeerJ. Craig McClain of Duke University and colleagues note that the “longest scientifically verified giant squid” measured a mere 12 meters. “What limits the large size of [giant squid] is unclear,” McClain and colleagues write. But metabolic demands may play a role, keeping squid from getting much bigger than what have washed up onto shore (and also keeping them in the cold depths where they’re so difficult for us to find).

But perhaps the focus on the largest and biggest of species is the wrong approach, McClain and his colleagues argue (in, ironically, a paper all about large marine species). The longest, most giant individuals are, after all, just a tiny fraction of a species — and, these researchers write, “these individuals may reach these extraordinary large sizes through developmental or genetic defects and may not represent the healthiest or, in evolutionary terms, the fittest.”

They are, though, among the most mysterious creatures to inhabit our planet.

Asteroid enthusiasts, rejoice! Thursday, June 30 is your day to remind the world that humankind is just one impact with a space rock away from annihilation (or, at the least, a very bad day).

Asteroid Day, started in 2015, brings together scientists, artists and concerned citizens to raise awareness of the hazards of asteroid impacts and build support for solutions that might avert disaster from the skies. Events are planned at museums, science centers and other locations around the world.

The date coincides with the anniversary of the most powerful impact in recorded history, when a roughly 40-meter-wide asteroid crashed near Tunguska, Siberia, in 1908. The run-in flattened about 2,000 square kilometers of forest and released about 185 times the energy of the atomic bomb detonated over Hiroshima. Estimates vary, but such collisions happen roughly once every several hundred to 1,000 years.

Homo naledi, currently the best-known and most mysterious fossil species in the human genus, may be considerably younger than previously thought, a new investigation suggests.

Evolutionary trees of ancient hominids statistically reconstructed from skull and tooth measurements indicate that H. naledi lived around 912,000 years ago, say paleoanthropologist Mana Dembo of Simon Fraser University in Burnaby, Canada, and her colleagues. That’s a provisional estimate, since researchers have yet to date either H. naledi’s bones or the sediment in which some of its remains were excavated.
The new statistical age estimate, described by Dembo’s group in the August Journal of Human Evolution, challenges proposals that H. naledi’s remains come from early in Homo evolution. Researchers who first studied H. naledi bones retrieved from an underground cave in South Africa noted similarities of the skull and several other body parts to early Homo species dating to between 2.5 million and 1.5 million years ago (SN: 10/3/15, p. 6).

A comparison of H. naledi skull measurements to those of 10 other hominid species, conducted by paleoanthropologist J. Francis Thackeray of the University of the Witwatersrand in Johannesburg, reached the same conclusion. H. naledi lived roughly 2 million years ago, Thackeray proposed in the November/December 2015 South African Journal of Science.

Dembo disagrees. Her team tested which of 60,000 possible evolutionary trees best fit skull and tooth measurements of H. naledi, 20 other hominid species, gorillas and chimpanzees. The new analysis keeps H. naledi in the genus Homo. But it’s still unclear which of several hominid species — including Homo sapiens, Homo floresiensis (or “hobbits”) and Australopithecus sediba (SN: 8/10/13, p. 26) — is most closely related to the South African species.

Dembo’s team found no signs that bones assigned to H. naledi represent a variant of Homo erectus, as some scientists have argued. H. erectus originated about 1.8 million years ago in Africa and rapidly spread to West Asia. But Dembo’s statistical model assumes that H. erectus skulls and teeth vary in shape throughout Africa and Asia much less than they actually do, says paleoanthropologist Christoph Zollikofer of the University of Zurich. Bones assigned to H. naledi most likely represent a form of H. erectus, he argues.

Further statistical comparisons that include measurements of limb and trunk bones may help to clarify H. naledi’s evolutionary relationships, Dembo says.
Based on geological dates for all hominids except H. naledi, the researchers also calculated the rate at which each species’ skull and tooth features evolved over time. Those results enabled the researchers to estimate H. naledi’s age.

“Homo naledi might be less than a million years old,” Dembo says. She considers that estimate “reasonably robust,” since ages calculated for other hominids in the analysis often fell close to dates gleaned from fossil and sediment studies. In a few cases, though, statistical and geological age estimates differed by 800,000 years or more.

A relatively young age for H. naledi expands the number of Homo species that survived well into the Stone Age, Dembo says. Small-brained H. naledi would have existed at the same time as larger-brained Homo species in Africa, just as small-brained H. floresiensis lived at the same time as larger-brained H. sapiens and H. erectus in Southeast Asia (SN: 7/9/16, p. 6).

If that scenario holds up, H. naledi may have made roughly 1-million-year-old stone tools that have been found in southern Africa, Dembo says.

“A young date for Homo naledi shouldn’t be unexpected,” says paleoanthropologist Matthew Tocheri of Lakehead University in Thunder Bay, Canada. At least some H. naledi bones appear not to have fossilized, he notes, consistent with a more recent age.

While Dembo’s statistical approach to hominid evolution shows promise, “a good geological date for H. naledi will trump the new date,” Tocheri adds.

Paleoanthropologist Bernard Wood of George Washington University in Washington, D.C., doesn’t think Dembo’s approach can accurately date H. naledi. But humanlike hands, feet and teeth of the South African hominid support the possibility that it lived about 1 million years ago, Wood says.

Two H. naledi researchers — John Hawks of the University of Wisconsin–Madison and Witwatersrand’s Lee Berger — still suspect the South African species lived at least 1.8 million years ago, based on its skeletal similarities to H. erectus. But a possible age of about 900,000 years for the cave finds, as proposed by Dembo, would be consistent with H. naledi or closely related species having survived in Africa for a million years or more, Hawks and Berger write in the current Transactions of the Royal Society of South Africa.

The scene was stranger than it looked, even by Las Vegas standards: Two young men pull up in a U-Haul truck to a motel outside the city. They check in and move a cooler into their room. They appear to be handling something of importance, and look to see if the ice needs replenishing. Inside the cooler is not the makings of epic hangovers but instead an experiment in eternal youth.

Tucked within, protected from the desert heat, are more than a hundred tiny pond invertebrates. One of the men, Daniel Martínez, with a Ph.D. in ecology and evolution a month or so old, is rearing these little organisms to test a claim that they somehow stay young all their lives, no more likely to die as years go by as they are early on. They can die, however, from high temperatures or starvation. Leaving the animals on their own for more than a day invites disaster, so if Martínez travels, even stopping for sightseeing with his brother in Las Vegas, all the animals in the aging experiment travel, too.
Their road trip was in 1993, when the “dogma,” as Martínez recalls, was that evolution would not allow any multicelled organism to escape aging. Just as humans age, the thinking was, other organisms also decline in health as time goes by, with death becoming more and more likely. Yet few people at the time were bothering to document aging in any creatures other than a few standard lab residents.
Biologists have long tracked aging in fruit flies and lab mice (SN: 7/23/16, p. 16), but a bloom of recent data from more diverse organisms is stirring up discussion about how aging could have evolved — and if it’s inevitable. The ongoing studies of Martínez’s pampered pond invertebrates and a massive effort to study aging in a roadside weed are good examples of these provocative approaches. They’re shaking up basic assumptions of a long-standing theory and inspiring new thinking to explain why there’s so much crazy variety in how life deteriorates — or maybe doesn’t.
Old ideas
Deciding whether an organism is aging can get tricky. For humans, the slowing and graying, the wrinkling and creaking are all too obvious. But what about plants? Or fungi? For a metric that applies across many species, evolutionary biologists often focus on how the number of deaths in a population changes over a particular period of time. If this death rate increases as time passes, the organism ages. (In this scheme, life span is irrelevant. A hypothetical species that lives for just a few months but keeps its death rate flat until the end would still be considered “biologically immortal.”)

Early evolutionary thinkers proposed that aging followed by death is a good thing, another marvel of the mindless force of natural selection. Built into individuals, this inevitable decline kept feeble parents from sapping resources from the young.

But the idea that aging evolved as a boon for the next generation “is really nonsense,” says Axel Kowald of Newcastle University in England, a biochemist who specializes in the bioinformatics of aging. Among the many objections: It’s hard to see why a lucky few that could live a bit longer and continue to reproduce wouldn’t overtake a population. With more offspring, they’d spread more of their genes. Over time, then, genes for aging should be few, fewer, gone.

One of the modern mainstream explanations of aging rests on the idea that evolutionary forces lose their power to edit as adulthood stretches on. As genes are copied generation after generation, mutations are made. Natural selection can remove from a population the typos that harm the young; disadvantaged carriers don’t pass those mistakes down to the next generation in much abundance.

Mistakes that cause trouble late in life, however, can be almost impossible to purge, argued the late zoologist Sir Peter Medawar, a Nobel laureate who titled his autobiography Memoir of a Thinking Radish. In a 1951 lecture, he explained this approach to aging by whimsically tracing the perilous lives of laboratory test tubes. The mortality rate of these hypothetical test tubes, which for the sake of explanation reproduced more than once in their lives, allowed few tubes to reach old age. Test tubes that don’t reach old age don’t reveal detrimental effects from mutations that act only late in life. Therefore natural selection didn’t have a chance to stop those mutations from being passed down to test tube babies. In a scenario now called mutation accumulation, the late-acting mutations could thus build up and cause the declines of aging, also known as senescence. Natural selection doesn’t weed out these mutations because, Medawar said, wild organisms “simply do not live that long.”

In a perverse twist on this idea, natural selection might not just allow genes that bring late-life decrepitude to accumulate but also might favor those genes. Evolutionary biologist George C. Williams, later eulogized as a quiet and deep thinker with the look of Abraham Lincoln, argued in 1957 that genes with split personalities, like Jekyll and Hyde, could help explain aging. The benefits of these genes appear early in life and the gene is thus passed to the next generation, with its downside revealed as frailty only late in life.
Till death do us part
In the 1990s, as the theories were then understood, a widespread idea was that “nothing can escape aging,” Martínez says. Yet as a graduate student at Stony Brook University in New York, he read about some tiny hydra species that had extraordinary powers. These branching bodies can reproduce by budding off clone babies, and they can rebuild themselves after dismemberment. What’s more, they didn’t appear to deteriorate with passing time. Biological immortality was a grand claim for these distant jellyfish relatives, soft translucent stalks a few millimeters tall with a tuft of tentacles wiggling from the top. But no one had done a rigorous test collecting the hydra and tracking their death rates.
Martínez eventually set up 145 Hydra vulgaris in laboratory luxury, where no predator could reach them and they could enjoy catered food all their lives. “When I started doing the experiment, I thought that I was going to prove that hydra could not escape aging,” he says. “A year and a half later I got my Ph.D. — the hydra were still with me.” The expected rise in death rate that characterizes aging organisms still hadn’t started. “I got a postdoc at University of California, Irvine,” he says, “so I crossed the country in a U-Haul truck with the hydra and all my furniture.”

The truck was supposed to be air-conditioned but wasn’t, and with a hot engine right under the cab, driving a southern route pulling a trailer, Martínez had to keep careful track of ice for the hydra cooler. Plus, there was all the changing of water, the feeding, the raising brine shrimp so the hydra had live prey. This was when the whole party visited Las Vegas.

The hydra made it. (Martínez, however, no longer even considers a hydra project without a technician to manage their care.) In 1998 he published results of four years of hydra watching. His title was cautious: “Mortality patterns suggest lack of senescence in hydra.”

“I published the paper and forgot about it,” says Martínez, now at Pomona College in Claremont, Calif.

Opinions about the inevitability of aging continued to run strong — as demographer James Vaupel of the Max Planck Institute for Demographic Research in Rostock, Germany, discovered in 2002. At a workshop on aging in nonhuman species, Vaupel stood up to say that the paper he had found most interesting was one describing mortality rates in a roadside weed. The rates appeared to drop as time passed, leading Vaupel to propose it as a possible case of what he called “negative senescence.”

“My remark was met with ululations of horror, cries of derision, hisses and boos,” Vaupel says. Eminent biogerontologists said that theorist William Hamilton had proved decades earlier that mortality, at least in repeatedly reproductive adults, universally rises with age and “there was no need for the audience to listen to a demographer who didn’t understand biology.”

Further data on the weed showed a more complex story, but the meeting outcry had a meaningful effect. As soon as Vaupel got back to his Rostock lab, he asked Annette Baudisch, then a new Ph.D. student, to “figure out why Hamilton’s proof was wrong.”

Baudisch published her critique of Hamilton in the Proceedings of the National Academy of Sciences in 2005. Hamilton’s proof could not explain the full diversity of aging, she argued. Some species that keep growing throughout adulthood, tortoises and many plants, for example, might not be included.

Though some researchers believe there’s still much truth to Hamilton’s approach, Vaupel took this conclusion as a cue to go questing for examples of prolonged youth. He talked Martínez into redoing the hydra experiment — but bigger. Instead of four years, the test ran for eight. Instead of 145 animals, the team had multiyear data from 2,256.

The resulting paper came out last year in the Proceedings of the National Academy of Sciences. Two species of hydra, with their many representatives divided between Claremont and Rostock for raising, had continued their usual low-drama lives, feeding and budding off babies but not showing any upsweep in their mortality rates. In 10 of the 12 groups, the annual probability of death stayed around 0.6 percent, and two groups held steady with an even lower annual rate of 0.09 percent.

Continuing the tests until the whole study population died, which would be ideal for tracking the hydra’s entire life history, would take more than 1,000 years, researchers calculate. But eight years of data gave Martínez and Vaupel confidence. The old view that aging is inevitable, the paper declared, “is no longer tenable.”

The hydra results so far are “solid evidence” that not all species age, Kowald says. And there are other, less-studied candidates for what’s called negligible senescence, too: three-toed box turtles and bristlecone pines, for instance.

Into the wild
The lab, of course, isn’t where evolution shapes life. Biologists seeking to understand how aging evolved need to know if and how organisms age in the wild, research that is likewise challenging Medawar’s pronouncements.

The plant study that caused a ruckus for Vaupel was an early version of a test by Deborah Roach, a plant evolutionary biologist now at the University of Virginia in Charlottesville. Her results from 4,476 ribwort plantains (Plantago lanceolata), set out at a long-term research site in Durham, N.C., had suggested that this common roadside weed was escaping the supposedly inevitable decline of aging. But construction of a new art museum wiped out those plots after less than five years.

After moving to Virginia and summoning the resolve to start the experiment again, Roach selected meadows at Thomas Jefferson’s birthplace, close to Charlottesville and under the protection of local historical preservationists. During the years 2000 through 2002, an army of undergraduates set out 30,000 plantains, all of known genetic heritage and marked for individual monitoring.

After collecting seven years of data on when plants died, Roach picked up a subtle signal she hadn’t observed in Durham. At first, plantains of different ages had about the same mortality rates, all relatively low, with six-month mortality rates at less than 10 percent. But during the three years that followed, the plantains clearly struggled. Roach suspects soggy winters plus competition from neighboring foliage were to blame. Death rates rose to around 30 percent and — this was the important bit — the death rates climbed higher for the older plants. A population that had looked as if it weren’t physically declining with age showed signs of senescence when the going got tough.

The results contradict Medawar’s fundamental assumption that life is so short and brutal in the wild that the possibility of seeing frail, aged organisms there would be exceedingly rare. “Now we have a great body of literature showing that in fact there are these old animals out there, these old plants,” Roach says.
A 2013 tally by Dan Nussey of the University of Edinburgh and an international array of colleagues documented more examples of aged organisms in the wild — 175 species, in fact, including Dall sheep, antler flies and great tits, among others. A study of painted turtles published June 7 in the Proceedings of the National Academy of Sciences added that species to the list, showing that human impacts might inadvertently be nudging an Illinois population toward senescence.

Across the tree of life, aging now looks more varied than old ideas predicted. Drawing on data for 46 species, Vaupel, Baudisch (now at the University of Southern Denmark in Odense) and 12 coauthors published a paper in 2014 featuring a full page of mortality curves, which track how the number of deaths in a given group changes over time. Many of the organisms show the expected upsweep with time, but other curves are idiosyncratic. The curve of Soay sheep curls concavely downward during early adulthood before rising again to a rounded hilltop in old age. Alpine swifts’ curve looks like a side view of a lawn chair relaxed way back for a summer snooze.

With mortality data on so few of the species on Earth, it’s too early to pronounce big trends. So far, body size and life span don’t appear to dictate the shape of the curve: The curves of water fleas and lions look remarkably similar. Organisms from different kingdoms can also have similar curves: The curves for desert tortoises and netleaf oaks both tilt downward.

“We’re going to have to figure out what it is about the biology of these species that explains the variety,” Roach says. The new reports, she adds, “are putting a big, bold spotlight on the theories and saying, ‘Hey guys, we need to update.’”

Think again
Last year in Experimental Gerontology, Kowald and Thomas Kirkwood of the Institute for Ageing at Newcastle University proclaimed that Medawar’s idea about natural selection losing its power appears to be “difficult to reconcile” with new research. The discussion on that point isn’t over yet, though.

Baudisch, for her part, would like theoretical frameworks that describe aging (or its lack) as part of the whole topography of change during a life. “Theories that just deal with the end of life don’t speak to all this diversity,” she says. “Physicists don’t make theories that only apply on Sundays.”

One long-standing approach does offer more of a whole-life framework. Kirkwood proposed the approach, called disposable soma theory, back in 1977. Wild organisms have to split their limited resources between reproduction and maintaining the soma, the nonreproducing parts of the body, he noted. In many cases, the best strategy demands such liberal spending on reproduction that there’s not enough left for full upkeep of the rest of the body. Aging is, in this interpretation, the sum of deferred maintenance.
Australian Antechinus marsupials and members of two related genera offer the most dramatic example of mammals that forgo upkeep for extravagant reproduction. The climate where these marsupials live supplies a surge of insect nourishment for nursing moms only once a year. The males, roughly the size of mice or rats, grow disproportionately large testes and devote all their resources to vying for fatherhood, Diana Fisher of the University of Queensland in Australia and her colleagues reported in 2013. After healthy males reach adulthood, they stop producing new sperm , start mating and, a few weeks later, are all dead. Their immune systems collapse. A once-per-lifetime bout of intense competition leads males to what Fisher calls “suicidal reproduction.”
The hydra species in the big lab test pursue a different strategy. Because they can regenerate and reproduce through budding, there is no distinction between reproductive cells and soma. Kirkwood says that the lack of senescence in hydra fits easily with the disposable soma approach. He would bet on their immortality.

He also thinks the ideas proposed by Medawar and Hamilton still have great value, with “central relevance to understanding aging.” To explain all the recently uncovered variety in aging, researchers may simply need more than these theories. They might need to know, for example, the particulars of a species’ home, be it pond, meadow or bug-rich forest.

Understanding these details may or may not allow humankind to do much about the process of aging. But creating better theories might finally reveal how some pale brainless squiggles of pond life may have achieved perpetual youth when humankind, despite all its apparent sophistication, has not.