Astronomers have just discovered two Earth-size, rocky planets around a nearby star. Though the planets are way too broilsome for life, they suggest that steady improvements in telescope technology has made the discovery of habitable planets just a matter of time.

But as astrobiologists continue to search for life in space, geo-biologists (ok, we coined that) continue to find bizarre life in strange places on Earth: in the dark ocean depths, between grains of sand, and at roasty-toasty temperatures once considered deadly.

Hot, humid, and totally alive!

Fifty years ago, nobody believed organisms could survive near the boiling point of water. When Thomas Brock started probing the hot springs in Yellowstone in the 1960s, he was not looking to overthrow a ground rule of biology. Instead, the University of Wisconsin-Madison professor, then at Indiana University, sought to study bacteria in a simplified, real-world environment.

At the time, and even today, precious little was known about how bacteria live their lives — unless they cause disease.

As Brock sampled his way up a hot stream, he approached its source in a hot spring, and the water temperature rose steadily.

At the time, biologists thought life would not tolerate temperatures near 80° C. But Brock kept finding bacteria, so he kept looking. Eventually, he found some that could live and reproduce near the temperature of boiling water — 100° C.

The prize of his collection was a bacterium he named Thermus aquaticus (for its hot-water habitat) and placed in a public repository for study by other scientists.

Over the years, T. aquaticus proved interesting indeed. For one thing, it was the first of more than 50 species of thermophilic bacteria known to tolerate or require temperatures near water’s boiling point.

For another, it was the first of the Archaea (ancient ones), primitive microorganisms that scientists now regard as a separate and highly primitive kingdom of life.

Deep roots indeed

Because thermophiles are Archaeans, and prefer the steamy conditions typical of early Earth, many scientists think they may tell us about the origin of life itself.

To any basic scientist, those contributions would be enough. But because their enzymes work in high temperatures, where chemical reactions are faster, the thermophiles have proven to be extraordinarily useful.

Today, enzymes derived from thermophiles are used to convert millions of pounds of corn (maize) into sugar to sweeten soft drinks.

But more important, at least to scientists who don’t guzzle fizzy pop at the lab bench, T. aquaticus supplied TAQ polymerase, the essential enzyme for polymerase chain reaction, AKA PCR.

PCR is an artificial technique that does what living critters do every day — replicate DNA. But PCR is the rocket ship of replication, since it allows you to multiply a piece of DNA a billion times in a few hours. That produces enough DNA to analyze to your heart’s content — for genetic engineering, biotechnology and forensic purposes.

PCR depends on TAQ polymerase.

Aware that PCR and soda pop are both billion-dollar industries, corporations and scientists around the world have frantically searched for other thermophiles that may have equally useful enzymes. They’re looking in odd places — not just hot springs and volcanoes, but also deep-sea vents, hot petroleum-bearing rock, the outflow of geothermal power plants, and smoldering piles of garbage.

Prowling for glow-in-the-dark squid

Call me Bob.

Short for bobtail squid. (Did I mention that I’m a 3-4 centimeter cephalopod, formally Euprymna Scolopes?)

Anyway, I hang out in shallow waters around Hawaii. Save your crocodile tears — somebody’s got to live in the sunny, tropical ocean. Anyway, here’s my problem: Even though I have 10 tentacles, I don’t have spines, poisons, or any other decent defense.

So I spend my days burrowed in sand at the ocean bottom, trying to keep out of mischief. Still, a fellow’s got to eat, don’tcha know, so I cruise at night, looking to grab a bite.

Here’s the snag: All sorts of nocturnal predators seem to have this thing about calamari sushi.

Light before flashlights

A long time ago, my ancestors evolved a nifty defense against their big teeth: stealth. Even their tiny squid brains figured out that predators could see them from below, as tasty dark blobs against the bright ocean surface.

Since this was before flashlights, my relatives had to improvise. So they press-ganged billions of luminescent bacteria into making light for them. The idea was to make us just as bright as the ocean surface — and hence invisible.

At least, this is how my great-aunt Tentacla tells it. To tell the truth, I think it had more to do with the evolutionary advantage of being hard to see.

Anyway, my ancestors fed the bacteria, and gave them a home in two specialized light-emitting organs. These “photophores” have a reflective membrane to shine all their light down, toward the hungry predators. They use a diaphragm to control brightness, and even have a lens to spread the light.

The photophore reminds me of a backwards eye — one that makes light rather than detects it.

My folks even figured out how to switch the bacteria “on” when needed.

In return, the bacteria got room and board, in the biological deal they call “symbiosis” or “mutualism.” Sometimes I think people could learn from this cooperative spirit….

But that’s enough thinking for today. My squid brain is squashed.

As I burrow into the sand for another daytime nap, permit me to introduce somebody who considers me almost as fascinating as I do.

Seriously speaking…

Margaret McFall-Ngai, a biologist at University of Wisconsin-Madison, says the bobtail squid may pretend it’s cooperating in a symbiosis with those light-making bacteria, but the reality is more ominous.

She says there’s evidence that this may be slavery, not symbiosis, since the squid, “inhibits the growth of the bacteria to enhance their luminescence.” The bacteria, Vibrio fischeri, could make a better living drifting in the ocean, or in the gut of another marine animal, McFall-Ngai observes.

The concept of bacterial enslavement broadens our perspective on the many possible relationships in the living world.

Most people, if they think about bacteria at all, conjure up disease and decay, but people would be dead without bacteria, since the little critters play essential roles in producing vitamins and preventing disease.

Since the bacteria in our guts vastly outnumber the cells in our bodies, it helps that they’re helpful!

Nevertheless, and for understandable reasons, bacteriologists have traditionally focused on disease-causing organisms, and, for simplicity, on one species at a time. But that skews our view of how bacteria actually live, says McFall-Ngai.

Three cheers for complexity!

Complexity and subtlety may be the hallmarks of these interactions, and the complexity begins by recognizing that V. fischeri is closely related to V. cholerae, which causes the human intestinal disease, cholera.

Cholera is caused by a V. cholera toxin similar to a toxin produced by the light-emitting bacterium. But far from harming the poor little bobtail, that toxin signals it to secrete food for V. fischeri, so the toxin is really a chemical “dinner bell.”

And this raises the intriguing notion that a cholera bug secretes toxins not to kill its host but to discuss its menu. If so, our whole notion of pathogenesis may need rewriting, McFall-Ngai suggests. “Maybe when we’ve been studying cholera pathogenesis we’ve been studying an aspect of a normal conversation that’s gone wrong.”

Indeed, the traditional bacteriological view of bacteria as pathogens to be studied in pure culture may be “like trying to understand the complexity of all the cultures that lived in Paris by studying the activity of the Nazi occupiers,” McFall-Ngai suggests. “You are studying groups that don’t belong there, and have disrupted the normal activities.”

Want more on how the flashlight squid bullies its bacterial brethren?

Between the grains

(1996 story, only photos have been updated)

To zoologist Robert Higgins, small is beautiful. His infatuation with small creatures — “meiofauna” — dates to a student job in a biology lab that paid 35 cents an hour. Instead of quitting for more lucrative work, Higgins was intrigued.

He’d heard about tiny, amazingly diverse creatures, and put grains of sand and muck through a fine mesh, and used a microscope to find hundreds of organisms.

Forty-four years later, Higgins has retired from the Smithsonian Institution, but he’s still goggling at meiofauna — a complex group of animals found in most Earthly environments.

Indeed, a handful of wet sand could contain more biological diversity than a whole rain forest, Higgins says.

In the course of peering through countless microscopes, Higgins has discovered hundreds of species. With Danish biologist Reinhardt Kristensen, he found an entire phylum, called Loricifera.

Phyla are the broadest categories of organisms, based on structure, and according to the International Association of Meiobenthologists, “The majority of recognized phyla have meiofaunal representatives. Currently, 20 phyla considered to be meiofaunal from the 34 recognized phyla of the Kingdom Animalia. Out of these 20 phyla, five are exclusively meiofaunal in size.”

Photo: Giulio Melone, department of biology, Milan University.

A bdelloid (a type of meiofauna) shrinks when it undergoes anhydrobiosis. The dormant, dehydrated bdelloid has greater resistance to environmental stress but is ready to spring back to the active form in conducive conditions.

Meiofauna living between grains of sand have made some fancy adaptations to their harsh environment. Some have hooks on their feet, used to grab the sand. Others have hooked mouthparts, also useful for locomotion.

Beyond freeze-dried

To survive a difficult environment, meiofauna called tartigrades have evolved an amazing adaptation called “anhydrobiosis.” In this form of suspended animation, the animals replace water in their cell membranes with sugar, protecting the membrane from destruction through radiation and freezing. Microorganisms die when their cell membrane ruptures.

During anhydrobiosis, organisms are rather like plant seeds or bacterial spores, Higgins explains. “They can dry up for 100 years, and be rewetted, and come right back to active metabolism.”

Fun is fun. But what is the practical importance of studying stuff that can hardly be seen, doesn’t seem to cause disease, and is — at least to some — utterly ugly?

In other word, who cares about microscopic beach crud?

Meet the beach-cleaning crew

Anybody who likes to hang on the sand should be interested, Higgins says. “This is the system that helps keep our beaches clean.” Plankton, bacteria, all sorts of dead material is continually washing ashore, and a lot of people love to sit on beaches.

There’s a public-health angle here. Hookworms occur on beaches where dogs defecate, but meiofauna may consume hookworms, along with other nematodes. “So if we upset that, we could upset beach cleanliness,” Higgins says.

Higgins notes that meiofauna comprise a basic part of the food web, and disturbing them could have unforeseen consequences for the entire system.

Still, it’s hard to escape the notion that most of the motivation here is the pure scientific urge to discover, to classify, to understand. Meiofauna, Higgins notes, were seen under the microscope Anton van Leeuwenhoek invented in 1683.

The key to finding these things, Higgins indicates, in patience, technology, curiosity — and institutional support. “If you stare through a microscope for hour after hour, you have a chance of finding these things, but if you need to get out a certain number of papers each year, you have to take shortcuts and you won’t find as much.”

Fantastic freak show

If you drop a worker ant from an Amazonian treetop, what happens? In the species Cephalotes atratus, 87 percent of the time, that ant will wind up back where it started — a few meters lower down the same tree. Drop things that drift down at random, and only 5 percent of them will hit the tree.

In other words, these ants are controlling their flight — even though they don’t have wings.

That finding, which Stephen Yanoviak, Robert Dudley and Michael Kaspari¹ reported in 2005, provides a great starting point for untangling one of the mysteries of biology:

When and how did so animals take to the air?

Fly high

Flight is pretty common — among critters with wings, or something that resembles them, like a stretched membrane of skin. Birds, bats, moths and butterflies can fly. Even some lizards, snakes, fish and squirrels can glide under control toward the ground, which is not the same thing as falling.

Studies of ants in South America provide good data on “controlled aerial descent,” says Dudley, a professor of integrative biology at the University of California at Berkeley. In the course of some rather entertaining research, he and his colleagues have found that Cephalotes atratus ants:

During the controlled descent, at speeds above 4 meters per second, the ants perform “rapid postural adjustments,” Dudley says. “The limbs are moving, it’s not like a paper airplane.”

Dudley, an expert in the biomechanics of flight, says hundreds of species of tree-living ants in tropical Amazonian forests have evolved controlled gliding. Dropping to the forest floor can make them a meal for a mean and hungry ground-dwelling ant.

Looking at evolution

Perhaps the coolest part of the story is its evolutionary angle. Previously, scientists intrigued by the origin of flight have looked for evidence of wings and feathers, which appear more than 100 million years back in the fossil record.

But if flight really originated in arthropods that could not survive a fall from a tree or a cliff, that could wind the evolutionary clock back a good deal further. (Arthropods are animals with external skeletons and jointed legs, including spiders, insects and crustaceans like the horseshoe crab.)

Gliding under control is neither rare nor constrained to ants, Dudley says. “There are wingless aphids and flat spiders that live under the bark that can glide at a 45° angle. Controlled aerial descent has hundreds or thousands of independent origins in terrestrial arthropods.”

As old as the hills?

Over all, Dudley says, directed descent probably originated about 280 million years. If jumping like a flea or grasshopper is also deemed a form of flight, the origin could date back more than 400 million years.

The gliding hypothesis would not only help explain the origin of a common and cool behavior, but could take wind out of the sails for a favorite anti-evolutionary argument. Creationists, Dudley notes, have long demanded to know how wings evolved by asking, “What good is half a wing?” But according to the gliding hypothesis, wings unable to hold an animal airborne could still have evolved to help control a descending behavior that had long been in existence.

Flight of the control freaks?

Controlled gliding, Dudley says, “preceded the origin of wings, and so the evolution of flight is more about control than about the formation of wings.”

The new analysis “addresses qualms about the [supposed] lack of intermediate forms in the fossil record,” Dudley says. “Here is a viable intermediate form. There are lots of behavioral and ecological contexts where stubby, partial airfoils are useful.”

– David J. Tenenbaum

Since they were discovered 200 years ago, the plesiosaurs have posed a riddle. Long, brawny, toothy, their skeletal architecture was unsuited to laying eggs and sitting on a nest — and yet, there was no evidence that these reptiles gave birth to live young.

Until now.

In the journal Science tomorrow, a pair of paleontologists will describe a stunning fossil that shows a maturing plesiosaur inside its mother’s abdomen.

The fossil, dating to 78 million years ago, had lain in a museum basement for many years, says first author F. Robin O’Keefe, professor of biological science at Marshall University in Huntington, West Virginia. “Finding a pregnant animal fossil is always really rare, for any group of aquatic reptiles, and finding an undisturbed specimen is very unusual.”

O’Keefe collaborated with Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles, in studying the fossil, which is part of a new dinosaur-era exhibit at the museum.

Common, but curious

The plesiosaurs were monsters of the deep, says O’Keefe, having lived from roughly 200 million years ago until they went extinct along with the dinosaurs 65 million years ago. “These were apex predators, killer-whale size, and there is a very long, diverse fossil record.”

The specimen in question was complete, except for the head and some neck vertebrae, and was about 4.65 meters long.

Although the fetus was no midget – at 1.5 meters long — it was not ready to be born, O’Keefe says. “It’s really a guesstimate, but we think it is maybe two-thirds developed, definitely not ready for prime time. We have a bit of the back of its skull, and it’s poorly ossified [hardened]. If it was born like that, it would be like having your head made of Play Doh. It had no teeth, tiny flippers, and could not move around.”

The Cretaceous ocean, with its range of giant predators, was “not a place to be that helpless.”

Pride of the plains?

The pregnant plesiosaur was excavated in 1987 by Kansas landowner Charles Bonner. “He knew at the time that this was something interesting, but when it comes out of the ground, it’s inside a plaster jacket,” O’Keefe says. Removing a 15-foot specimen embedded in rock “is a time-intensive and expensive operation.”

But when the natural history museum decided to mount a new paleontology exhibit, the plesiosaur seemed a logical display, and director Luis Chiappe contacted O’Keefe. “He knew it was something interesting, thought it’s maybe a baby,” says O’Keefe. “Would I be interested in working on the specimen?”

A question answers itself

Would any paleontologist not be? And so O’Keefe found himself handling ancient evidence of reptilian motherhood. “My first thought was not some great scientific thought: ‘It’s really cool, you don’t often see fossils that neat.’”

When the rocks spoke, they revealed that this well-known reptile was, finally, in a maternal mood. “So here we have a pregnant plesiosaur, after 200 years of mystery, we have the smoking gun, we now know they gave live birth.”

To prove that, however, the scientists had to discount alternative explanations for finding an embryo inside an adult of the same species:

Does momma care?

We tend to think of reptiles as egg layers, but various flavors of birthing live young have evolved at least 80 times among marine reptiles. “The mother could retain the egg and have it develop inside her, or it could go all the way to a full-blown mammalian pattern, using a placenta to connect to the uterine wall,” O’Keefe says. “Given how big this fetus was, there probably had to be some pretty significant communication between mother and young.”

Paleontology shows structure, not behavior. O’Keefe says the new find suggests that mother plesiosaurs probably cared for their young, a rarity among modern reptiles. If one offspring “has absorbed all your reproductive energy, it makes a lot of sense to take care of it,” he points out.
In raising this possibility, he says, “We climbed out as far out on a limb as we thought we could get.”

And although there is no suggestion that the plesiosaurs nursed their young, live birth would distinguish them from many reptilian relatives and move them closer to modern, maternal marine mammals like whales and dolphins.

– David J. Tenenbaum

Can a gene that causes dwarfism also confer major health benefits? Perhaps, according to a new study showing that a group of extremely short people in Ecuador get no diabetes, even though they are unusually obese.

The 22-year study of people living in villages on the slopes of the Andes mountains also found just one case of cancer in the 99 patients it tracked, many fewer than among non-dwarf relatives.

The absence of two of the worst diseases of aging was strong evidence that the mutation that causes what’s called “Laron syndrome” has an upside, says Valter Longo, a gerontologist at the University of Southern California, and the senior author on the new study. “If you talk to anybody in the field, there is no way you can have a population with increased obesity and no diabetes. What was particularly strange was having zero deaths from cancer with 22 years of direct monitoring.”

Unfortunately, the subjects did not outlive the comparison group of relatives, due to large numbers of accidents and other alcohol-related problems.

The Laron’s patients are descendants of “Conversos,” Jews who were forcibly converted to Catholicism in Spain after 1492, and who emigrated to Latin America to escape continued persecution. Laron’s syndrome is also found in Israel and several other Middle-eastern countries.

The root of Laron’s syndrome, AKA growth hormone receptor deficiency, is a genetic mutation that disables the growth-hormone receptor, says Arlan Rosenbloom, a professor emeritus of pediatric endocrinology at the University of Florida who has long studied the Ecuadorian group but was not involved with the current report. “Growth hormone binds to its receptor on cell surfaces to stimulate production of insulin like growth factor-I (IGF-I) which is the real ‘growth hormone,’” Rosenbloom says. “Failure of the growth-hormone receptor cuts growth after birth by 50 percent. The Ecuadorians with this condition, 99 living individuals, comprise upwards of one-third of all individuals in the world with growth-hormone receptor deficiency.”

Image: Mikael Häggström

Growth hormone, secreted by the pituitary gland, travels to the liver, where it stimulates the formation of insulin-like growth factor 1, which stimulates bone growth.

The genetic angle

The new comparison of genetic differences between Laron patients and their non-dwarf relatives emerged from what Rosenbloom calls “spectacular epidemiological observations” by first author Jaime Guevara-Aguirre, an Ecuadorian endocrinologist who treats the Laron’s patients.

Working with Rafael de Cabo, a collaborator at the National Institute on Aging, Priya Balasubramanian from Longo’s research group exposed human epithelial cells, where most human cancers originate, to blood serum from control and Laron subjects. Serum is the cell-free portion of blood. “We wanted to know how this would affect the expression of dozens of genes,” says Longo, who studies cellular changes in aging.

The springboard of modern aging research is caloric restriction, because a diet with roughly 65 percent of normal calories is the only life-extension technique that works in a vast range of organisms. Although a similar group of protective genes activate under caloric restriction in yeast, fruitflies and mice, “We did not expect that a lot of the genes we study in yeast would come out as the most affected” in patients with a broken growth-hormone receptor, Longo says. “Serum from the Laron patients caused changes that we and others have shown to be highly protective in simple systems [like yeast]. We hoped for this but never really expected that many of the same genes would be coming up.”

At the molecular level, a key mechanism of aging is “oxidative stress,” damage to proteins and DNA caused by reactive molecules and fragments containing oxygen. When the researchers exposed human cells to the oxidant hydrogen peroxide, far fewer DNA breaks appeared in cells bathed in serum from the Laron patients, suggesting that they were protected against cancer.

The study found a second critical difference: When the DNA was damaged, cells in Laron serum were much more likely to commit suicide through apoptosis. Because apoptosis is a major obstacle to cancer, this suggested that cells in a Laron patient that had started on the path toward cancer would be more likely to kill themselves before going rogue.

Combined, the two phenomenon seem to explain why during the 22-year study only one of the Laron’s patients being tracked had a cancer, which was successfully treated. About 17 percent of their normal-height relatives had cancer during the same period.

Growing more confident

The study illuminates the role of insulin-like growth factor-1 (IGF-1), a growth hormone that, while required during development, may cause problems later on. “Large population studies show that people with the highest levels of IGF-I are at increased risk for certain types of cancer,” says Rosenbloom.

Longo notes that the effects of IGF-1 may depend on whether it is formed in an individual organ or distributed in blood. “Our hypothesis is that we do not need a ton of circulating IGF-1,” Longo says. Laron patients have between 0 and 10 percent of the normal level of IGF-1, “but they are fine, several made it into their 80s.”

The Ecuadorian study was more evidence that IGF-1 formation requires a functioning growth-hormone system. A drug that blocks the growth-hormone receptor has been approved for treating acromegaly, or gigantism, which is caused by excessive production of growth hormone.

You don’t have to be a hypochondriac to wonder if such a drug could prevent cancer and diabetes in adults, but the new study shows correlation, not proof, and Longo advocates a more modest first step in clinical trials. Return to caloric restriction for a moment: Studies in mice show that fasting reduces IGF-1 and protects healthy cells — but not tumor cells — from damage during chemotherapy, and some cancer patients have begun fasting to reduce collateral damage during chemo. “I think that soon enough, we will start with a clinical trial of this growth-hormone receptor antagonist to protect cancer patients against chemotherapy toxicity,” Longo says.

The new study is further proof, that, up and down the line from yeast to mice to people, similar “conserved” biochemical mechanisms influence aging, cancer and diabetes, Longo says. “The conservation hypothesis is something I am very convinced of, but I did not expect what we saw. Maybe we would see major reductions in cancer and insulin resistance [a marker of diabetes], but to see not one case of diabetes, not one cancer death, and to see the genetic matches with the simple systems that we study, that was as good as we could hope for.”

Photo: Vince Panzano

A hungry fruit fly (Drosophila melanogaster) extends its proboscis to feed on a droplet of sugar water. The proboscis contains sensors that detect irritating chemicals such as the ones in wasabi. Quite similar sensors occur inside the human mouth.

Whether you are a cobra or a cocker spaniel, a raccoon or a raconteur, lots of natural, reactive chemicals will cause pain and possibly damage your cells. Even fruitflies quickly learn to shy away from sugar water that contains caffeine or chemicals found in cinnamon, cigarette smoke, onion and horseradish.

These chemicals trigger activity at receptors on cell surfaces which eventually results in an “ouch” signal being sent brain-ward.

In a study published in Nature this week, a group lead by Paul Garrity, an associate professor of biology at Brandeis University, showed that a major class of pain receptors have ancient roots. We are talking older than yesterday: the report shows that TRPA1 (transient receptor potential A1) receptor was found in the critter that spawned both vertebrates (green tree snakes, bullfrogs, dinosaurs and talk-show guests) and invertebrates (horse flies, crabs, quahog clams and talk-show hosts) at least 500 million years ago.

The investigation, spearheaded by Kyeongjin Kang in Garrity’s lab, showed that the TRPA1 receptor is so similar across the entire vert-invert realm that it must have evolved once, and then descended through countless generations without significant changes. “The fly and human proteins in this receptor appear, to a very, very high degree of significance, to be from a common ancestor,” Garrity told us.

The pain in Spain

Unlike TRPA1, many other chemical receptors, like those involved in most smell and taste, vary greatly between animals, Garrity added. “There are big families of these receptors that look quite different in different species, so there is a lot of flexibility and change, but this TRPA1 is pretty much fixed.”

When structures have remained constant over long periods, scientists conclude that the evolutionary pressures that favored them were also static. Fish retain fins because they still live in water. We retain eyes because seeing is so handy.

And the stasis of the TRPA1 receptor “suggests there has been some sort of strong evolutionary pressure in these toxic chemicals that was maintained since the receptor was invented,” says Garrity. The chemicals in question are made by plants or other organisms as self-protection, and they can damage or destroy proteins and nucleic acids, at least in high doses, and therefore are to be avoided.

Fans of horseradish and wasabi know that a nibble can be tasty but a gobble can cause an eruption of coughing.

Image: NIH

A human taste bud, shown here, contains some types of chemical receptor, but the TRPA1 receptors that first formed 500 million years ago are found elsewhere in our mouths, in structures called chemical nociceptors.

Work by study co-author Doug Theobold, also at Brandeis, suggested the original TRPA1 receptor arose after the jellyfish branched away from our lineage about 700 million years ago. The first TRPA1 receptor was apparently present in the last common ancestor of vertebrates and invertebrates, which lived between 500 million and 550 million years ago.

And that means we may have the same tastes in food as fruitflies, but not jellyfish. “It’s bad enough to think about shooing the flies away from the sushi bar, but jellyfish, well, they may be on the menu, but I don’t want to see one on the stool,” growls the resident Why Files cynic.

How they did it

To explore the responses to these reactive chemicals, Garrity and his colleagues offered sugar water to fruit flies. Some of the water was tainted with pungent chemicals derived from cinnamon or wasabi. Some of the fruit flies had genetic mutations affecting the TRPA1 receptor. In some trials, the flies touched the toxic chemical with their legs; in others, they drank it.

Flies extend their proboscis (snout) toward something they want to eat, and the scientists measured this behavior as they offered a droplet of food five times. All flies extended the proboscis at the first offering.

Curiously, when the fruitflies drank sweetened caffeine-bearing water, they turned jittery and stayed up all night, devouring junk food and cramming for a biochemistry exam. Just java jiving…

So what?

Finding such a long-term similarity in a major class of pain receptors could have broad implications, Garrity says. TRPA1 receptors exist on the aphids that spread disease to many crops and the mosquitoes that carry malaria. If compounds that trigger these receptors while sparing those of benign species can be found, they could be developed into pesticides that inflict pain and cause the nasty bugs to stay away from where they are not wanted.

A second application, which may be closer to fruition, depends on the similarity of receptors between fruit flies and mammals, Garrity says.

Compounds derived from capsaicin, the active agent in hot peppers, are already used to treat pain. Although TRPA1 receptors respond to a totally separate group of pungent compounds, drug companies are already searching for TRPA1 antagonists that might treat chronic pain, asthma, arthritis or migraine headache, Garrity says.

The TRPA1 receptor responds to oxidative stress caused by nasty compounds called free radicals. “It is a key to many aspects of pain and inflammation,” Garrity says.

- David J. Tenenbaum

The genes of an invading toad

Why do some animals steam-roll across the landscape, commanding new territory in the manner of Genghis Khan, while others skulk around a tiny patch of marsh?

The question can also be applied to smaller groups of animals, like the toads. At one extreme, the spray toad lives only in the mist of one waterfall and has gone extinct in its native Tanzania. Meanwhile, the cane toad, a monster native of South America that was deliberately distributed to control insects on farms, has colonized Australia and Caribbean and Pacific islands, where it is busily crowding out native animals.

Photo: New South Wales Government

The cane toad is an ecological pest in Australia, but it carries a full set of genes that enable it to occupy new habitat.

Both species are among the 500-plus members of the family bufonidae, called the “true toads.” But what distinguishes toads that can dominate new landscapes from those that must struggle to survive, and what can that tell us about how species form from their ancestors?

In a study published this week, Ines Van Bocxlaer, of the biology department at Vrije University in Brussels, identified “range expansion” traits that would, logically, make for successful invaders:

Image courtesy Franky Bossuyt

The Common Indian Toad (Duttaphrynus melanostictus), an optimal range-expansion phenotype that originated from tropically-adapted ancestors endemic to the Western Ghats mountain range of the Indian subcontinent.

The making of a new species

“We chose characteristics that might be related to being able to disperse,” says Franky Bossuyt of Vrije University, the study’s corresponding author. “If they don’t need too much water, or are poisonous, that’s an advantage.”

Van Bocxlaer and colleagues correlated the range expansion traits with the size of habitats occupied by particular species, and concluded that all seven traits were “highly correlated” with the area occupied by the toads in their new homes, Bossuyt said.

The researchers produced a branched genetic tree that traces back to the ancestral toads in South America, which suggested that the range expansion traits were present when the toads began dispersing to new locations between about 37 million and 24 million years ago. Afterwards, these traveling toads branched into many of the species that survive today.

The species that now live in South America, however, have fewer of the range expansion traits. “We think it is the first time this was studied in this way, correlating the range-expansion characteristics and mapping them on a phylogenetic tree,” says Bossuyt.

Photo: Simeon

A sugar cane farm in Northern New South Wales, Australia. Cane toads were brought here to control insect pests, and then became pests themselves.

Traits tell tales

These results shine a beacon on a venerable evolutionary question: do new species arise before or after they begin occupying new ground? Which is more important for promoting the development of new species: new habitat, or the traits needed to occupy it?

“Links between geographic expansions and speciation have rarely been demonstrated,” says Carol Lee, an associate professor of zoology at the University of Wisconsin-Madison. “The authors first found a correlation between life history traits that might promote range expansion and current distribution, suggesting that such traits are plausible candidates for promoting range expansions.” Then they constructed a genetic tree of the apparent range-expansion traits, and found that the traits correlated with the transcontinental movements, adds Lee, who focuses on the genetics of invasive organisms.

Finally, the researchers calculated that species were forming extra-fast during the global colonization, Lee notes. “The authors argue that this coincidence suggests that range expansion itself might have been an important driver of diversification and speciation. Thus, they argue that this might be a case where dispersal ability might drive range expansions, followed by speciation.”

“Range expansion itself,” the researchers concluded, “was an important driver of diversification in bufonids.” In other words, animals that can adapt are more likely to invade and conquer new habitats.

Photo: Image courtesy Bert Willaert

The common European toad has all the talents needed to colonize new habitat, and is widespread in Europe.

Which came first?

The differentiation of newcomers into many different species is the standard explanation for the many unique species found in islands like Hawaii. Although this “adaptive radiation” is often thought to result from the availability of new ecological niches rather than the genetic talents of the arriving organism, the new study suggests that these genetic talents may need more focus.

Because the study looks at only one example of global expansion, “the co-occurrence of acceleration of speciation with global colonization could be purely coincidental,” says Lee. “Nevertheless, this study is an elegant attempt to test the links between range expansions and speciation.”

Although Bossuyt concedes that the study may not aid the battle against the pestiferous cane toad, “if people wanted to try again to introduce some other species, they could use this method to predict if it was good disperser or not, and thus whether it might be dangerous.”

David J. Tenenbaum