Biology

Year In Science

Sunday, January 13, 2002

African Elephants Aren't All Alike
A landmark study of the DNA of African elephants by Alfred Roca and Stephen O'Brien at the National Cancer Institute last year confirmed that there are more than two species—Asian and African—of pachyderms. Elephants that dwell in Africa's rain forests were shown to be a different species from those that roam the savanna.

The study established that the two species are as different from each other as lions are from tigers. The two African species are now thought to have diverged about 2.6 million years ago. The savanna elephant, commonly seen in zoos and on safari, has large ears and long, curving tusks. The forest elephant has a smaller skull, smaller, rounded ears, and straighter, thinner tusks. Conservation programs have treated all of Africa's elephants as the same species. A better understanding of genetic differences may help scientists plan more successful protection strategies.
— Diane Martindale


Birthing Amoeba Babies

Microscopic time-lapse images show a midwife amoeba (green) disconnecting two daughter cells (blue).
Photograph courtesy of David Biron/Weizmann Institute of Science
Researchers have long observed that Amoebas reproduce through fission, but until this year no one realized the process always stalls, with the two daughter cells apparently frozen together. In March, researchers at the Weizmann Institute of Science in Rehovot, Israel, announced that not only do cells stall in mid-delivery, but they also get help. Other amoebas often make a beeline to the distressed daughters to nudge the two cells apart. "For an amoeba, which doesn't usually display much sense of direction, it was an unexpected behavioral observation, to say the least," says Elisha Moses, a biophysicist who led the research.

Rather than being an isolated case of altruism, this amoebic midwifery turns out to be routine. The distressed cells release a chemical attractant, says Moses, which signals nearby members of the species to come to the rescue. Understanding this fission phenomenon may give researchers an idea of how to deter it. "If there's a way to interfere with this process, then there may be a way to limit their growth rate," says Moses—as well as prevent a lot of human misery. These amoebas cause human dysentery and death among AIDS patients, particularly in the third world.

"You have to look at a slow sequence of events for a long time before you realize what you're seeing," says Moses. But such patience is rare these days. "Everybody has moved on to genetics, which involves slicing and dicing organisms," he says. "Simply watching them under the microscope is out of fashion."
— Curtis Rist


Older, Wiser Elepants
Elephants don't forget—at least, female elephants don't. Elephant families are matriarchal. And the social knowledge acquired by the oldest females is the key-stone of a familial group's survival, according to a study published in April by Karen McComb, a biologist at Sussex University in England.

Elephants announce their presence by rumbling loudly, a practice referred to as contact calling. An unfamiliar call may mean that an elephant from outside the family group is nearby. A stranger can cause trouble, disrupting feeding or harassing young calves. So an elephant matriarch signals the family to bunch around her; then they all lift their trunks in the air to smell the unidentified caller. False alarms can create stress for the group and take time and energy away from feeding, so survival may depend in part on getting it right.

Working with Cynthia Moss, who founded the Amboseli Elephant Research Project in Kenya 30 years ago, McComb tested the social knowledge of 21 Amboseli elephant families with matriarchs 27 to 67 years old. She played recordings of contact calls to each family and found that the oldest matriarchs were much better at picking out unfamiliar calls. In fact, a group with a matriarch in her fifties was several thousand times more likely to bunch upon hearing an unfamiliar contact call than when hearing a familiar call.

By contrast, families with younger matriarchs were less than twice as likely to bunch in response to an unfamiliar contact call versus a familiar call. And they tended to bunch a lot. Moreover, the social savvy displayed by older matriarchs translated into reproductive benefits for their families. Families with older matriarchs produced more calves in each female-reproductive year.

This finding underscores a predicament in protecting the oldest members of dwindling elephant herds. As elephants age, they continue to grow larger, as do their coveted tusks. So the older—and wiser—a matriarch is, the greater the risk she will be slaughtered. About 800,000 elephants have been killed by poachers in the past 20 years.
— Sarah C. Greene


Honeybee Dance
Ever since Nobel laureate Karl Von Frisch discovered in the 1940s that bees perform a dance directing other bees to the location of a food source, scientists have debated how the bees transmit that information. Some assumed that the specific scent of the location clings to a bee; then worker bees would sniff and follow. Others believed a more sophisticated means of communication exists among bees. In May it became clear that the latter camp was correct—the lowly bee has a very advanced neurological system.

Harald Esch, a professor of biology at the University of Notre Dame in Indiana, hypothesized that bees register distances to food sources by keeping track of the number of landmarks they pass, such as rocks, trees, or groupings of flowers. They then pass the information along through their dance. To test the premise, Esch and others at the Australian National University in Canberra and the University of Wurzburg in Germany tried to deceive bees into giving false information to hive mates.

First, they set up a cup of sugar water about 36 feet from a hive and led a honeybee to eat from the cup. Instead of letting the bee fly directly to the hive and back, they forced it to fly through a 10-foot-long plastic tunnel lined with a random pattern of half-inch black-and-white squares. According to Esch, the design was intended to trick the bee into thinking it had covered much more territory than it actually had by increasing the number of landmarks—black squares—it was exposed to.

Esch's team videotaped the bee's dance when it returned to the hive, then calculated the distance communicated based on the duration of the dance. "The bee danced as if it had traveled about 70 meters [230 feet], rather than just 11 [36 feet]," says Esch. When some 200 bees flew from the hive searching for food over the next two hours, about three-quarters of them approached a dry feeding station 230 feet away looking for nectar, rather than the loaded feeding station closer to the hive. (The bees are able to communicate not only distance but also direction.)

Based on these results, Esch says there is no question that honeybees communicate distance depending on what they see rather than how they smell. "Although I would certainly hesitate to call this a language, it certainly is an abstract form of communication," he says. "And it lays the old argument to rest once and for all."
— Curtis Rist


Cannibal Ants
In a rain forest in Madagascar last January, Brian Fisher reached into a rotting log and shortly let out a howl. "Ants swarmed all over my hands," says Fisher, a curator of entomology at the California Academy of Sciences in San Francisco. "I was screaming partly out of pain but mostly out of joy."

Fisher had good reason to smile through the pain. "It was an entire colony of ants of a genus never before seen alive," he says. And these living specimens, from the genus Adetomyrma, help reveal how ants evolved from wasps starting about 100 million years ago. Instead of the two or three body joints found in other ants, these ants have just a single connection between the thorax and the abdomen. "They've got that 'wasp waist,'" says Fisher. He nicknamed the relic species Dracula ants because of their grisly feeding habits. When hunger strikes, the adult queen and worker ants visit the colony's nursery and cut holes into their own larvae to feed on hemolymph, the equivalent of insect blood. "We call this nondestructive cannibalism," says Fisher. He believes this practice may have evolved into the more common one known as social feeding, in which adult ants, unable to digest solid food themselves, feed the larvae, then suck out digested food that the larvae regurgitate for distribution around the colony. The Dracula ant, says Fisher, gives us clues into the origins of one of the most studied insects on Earth.
— Curtis Rist


Eeny-Weeny Teeny-Tiny Bacteria Backbones
Bacteria survive without certain features that plant and animal cells require, such as a nuclear membrane and a filament of protein known as a cytoskeleton. "At least this is what the cellular biology textbooks like to point out," says Jeffery Errington, a bacteriologist at Oxford University's Sir William Dunn School of Pathology. "And every single one of them is now wrong."

In March Errington and his colleagues revealed for the first time a helix-shaped skeleton inside a species of bacterium known as Bacillus subtilis. This discovery spurred them to search further, and they were excited to find similar proteins in every other rod-shaped and spiral bacterium they looked at. "The only bacteria that don't have these proteins, in fact, are spherical ones," says Errington, adding that they probably lost the trait as they evolved. "Otherwise, there's really a good correlation between a nonspherical shape and the presence of a cytoskeleton."

Errington had long suspected that bacteria, or prokaryotic cells, contained cytoskeletons, but even electron microscopy had failed to turn up any evidence. By contrast, all eukaryotic cells, which evolved from bacteria and make up all plants and animals, have cytoskeletons that control structure and internal cellular movement.

Errington says the discovery means that the cytoskeleton evolved before bacteria and our own cellular ancestors divided into two groups. It also hints at a complexity in bacteria, "which are more highly organized than they've appeared to be," Errington says. And that, he says, reinforces the value of questioning assumptions "despite what the textbooks say."
— Curtis Rist


Hey Birder, This Phone's for You
Like rap stars who spice up their music with samples of familiar songs, many Australian birds are fond of copying noises they hear. Perhaps to prove their vocal dexterity, lyrebirds, butcher-birds, and spangled drongos often add the tick of a clock or the whir of a camera to their traditional mating calls. But bird expert Greg Czechura of the Queensland Museum in Brisbane says that last year Australian birds found a new sound to mimic: "In a national park just north of Brisbane, a group of birders was watching a satin bowerbird making its call. The bird threw in this bit of cell-phone ring. Everyone started sheepishly reaching into their bags, looking for their phones."
— Jeffrey Winters

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