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Prognosticator.
E. coli may be able to predict an upcoming oxygen deficit based on temperature cues.

Credit: USDA

We've all heard of Pavlov's dogs, the famous canines trained by Russian physiologist Ivan Pavlov to associate food with the sound of a bell. Now, scientists have found that bacteria may be capable of similar behavior--an ability never seen in such simple organisms.

Researchers already know that microbes can mount simple responses to changes in their environment, such as acidity fluctuations, by altering their internal workings. If the changes are regular enough, bacteria can respond ahead of time. But systems biologist Saeed Tavazoie of Princeton University wondered if microbes were capable of more sophisticated reasoning. Could they, for example, learn to match a signal that didn't occur regularly to a probable future event? If so, the bacterium could improve its chances of survival by turning on a preemptive response to that event.

Tavazoie and colleagues first ran a computer simulation to determine if a simple system could evolve such behavior. They created an environment inhabited by evolving virtual bugs. The organisms garnered more energy if they could "learn" that certain signals preceded the arrival of food and launch a preemptive metabolic response. Even when the signal combinations grew more complex, the population was able to evolve the correct responses, the team reports online this week in Science.

The researchers then looked for evidence of this ability in the bacterium Escherichia coli. Because E. coli gets warmer when it enters a human mouth--ferried in on some old meatloaf, perhaps--and then must soon contend with low oxygen levels as it passes into the large intestine, the team reasoned that the bacterium might use temperature as a cue to prepare for the upcoming lack of oxygen. Indeed, when the researchers turned up the heat in a dish of E. coli, the bugs dialed down activity in genes that normally operate in high-oxygen conditions. But the true test came when the team flipped the normal association, growing the bacteria in conditions in which high oxygen levels followed temperature increases. Less than 100 generations later, the bacteria stopped turning on their low-oxygen response after exposure to high temperatures, suggesting that they had evolved to break the association.

The study is the "first convincing demonstration" that bacteria can use environmental cues to anticipate events, says Michael Travisano, an evolutionary biologist at the University of Minnesota, Twin Cities. The work could open up new ways to explain puzzling behavior of microbial pathogens, which might use predictive signals to change their cell surfaces and avoid a host's impending immune attack. "If it does something you don't understand, maybe it's anticipating an environmental shift," he says.

Related sites

• More on E. coli
• More on Pavlov's dogs

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Getting duller.
In these three species, males (second column) retained the ancestral wing patterns (first column), whereas females (third column) now mimic toxic butterflies (fourth column).

Credit: Krushnamegh Kunte

There's no confusing male and female mallard ducks. The male's emerald head stands in stark contrast to the female's dull brown coloring. Males evolved their sheen in order to attract the opposite sex. At least that's what Biology 101 tells us. But a new study suggests that, in some species, once-colorful females were the ones to change, sometimes dulling down as a protective measure.

Charles Darwin was the first to propose sexual selection, the idea that evolution could drive males and females to look and act very differently to attract the opposite sex. But his contemporary rival, Alfred Russel Wallace, took a different tack: He argued that such differences could arise because females face different risks than males, being burdened with motherhood. He noticed that in certain swallowtail butterflies, females, but not males, had changed their coloration to mimic a toxic species, presumably because females carrying eggs were less able to make quick escapes and needed a different way to avoid being eaten. For the most part, the idea was ignored.

In the past 5 years, however, a few studies of birds and lizards have suggested Wallace might have been on to something. Now, Krushnamegh Kunte, an evolutionary biologist at the University of Texas, Austin, has taken a comprehensive look at swallowtail butterflies--genus Papilio--to explicitly test Wallace's hypothesis. The 200 species of Papilio include species with bright males and females as well as with dull females and bright males. The group also includes some species in which both sexes mimic a toxic species, as well as some in which only the female depends on mimicry for defense.

Kunte mapped the relevant traits--wing color and pattern differences, mimicry, etc.--onto a family tree showing the ancestral relationships among more than 50 Papilio species. In most species, males and females looked the same and were not mimics of any sort. But in the species in which males and females looked different, females, not males, had evolved the new look. And in these species, the females were mimicking a toxic butterfly, supporting the idea that they changed their color for protection. Female Eastern tiger swallowtails, for example, traded bright yellow wings still evident in males and close relatives for a darker wing more like that of the toxic pipevine swallowtail.

"I hope that the current male-centered view of evolutionary change ... will give way to more balanced research" that recognizes that it's not just males who evolve to look different, says Kunte, who reports his findings today in Proceedings of the Royal Society B.

"This study contributes to a fuller understanding of the diversity in sexual traits," says Alex Badyaev, an evolutionary biologist at the University of Arizona, Tucson. It shows "Wallace got it right after all," adds Felix Sperling, an evolutionary biologist at the University of Alberta, Edmonton.

Related sites

• More about Alfred Russel Wallace
• More on swallowtail butterflies

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Premodern?
The shell of this fossil turtle may predate the ancestor of modern turtles.

Credit: (fossil) Juliana Sterli/Biology Letters (turtle) Jorge A.Gonzalez (2008)

As reptiles go, turtles are old--no question. They evolved before snakes and crocodiles and preceded dinosaurs. But establishing when the common ancestor of modern turtles first appeared has recently become controversial. Now a new fossil is backing the idea that modern turtles evolved more recently than previously thought.

Living turtles are divided into two main groups--the Cryptodira and the Pleurodira--based on where on the skull the muscles that close the lower jaw are attached. In the 1970s, paleontologist Eugene Gaffney of the American Museum of Natural History (AMNH) in New York City conducted the first modern analysis of turtle evolution. He proposed that almost all fossil turtles belonged within one or the other of these two modern, or crown, groups. That meant that the common ancestor of these turtles first appeared in the Late Triassic, some 210 million years ago.

Last year, paleontologist Walter Joyce of Yale University outlined a major revision of this classification. After reviewing all of the anatomical features, called characters, of the fossil turtles, he argued in the Bulletin of the Peabody Museum of Natural History that many of the fossil taxa were so different from modern turtles that they don't belong in either the Cryptodira or the Pleurodira groups. The implication is that these two groups only evolved about 150 million years ago. "Joyce's picture of turtle evolution is totally different," says James Parham of the California Academy of Sciences, who is based in Santa Barbara.

The new fossil backs this picture, say Joyce and Parham. It comes from Argentina and was discovered in central Patagonia by a joint expedition of the Museo Paleontológico Egidio Feruglio in Trelew and AMNH. About 35 centimeters long, the fossils of a shell and skull were found in ancient lake rocks, dating to between 160 million and 146 million years old--a period in which turtle fossils are few and far between. Juliana Sterli, a Ph.D. student at the Museo de Historia Natural de San Rafael in Mendoza, Argentina, set about describing and analyzing the fossil, which has been named Condorchelys antiqua. Sterli says her research shows that Condorchelys doesn't belong to the Cryptodira or Pleurodira and fits Joyce's hypothesis that the modern groups are at least 60 million years younger than previously thought.

"It's an important fossil," Gaffney says. "A discovery like this gives an important ... glimpse of early Jurassic turtles" in South America. But Gaffney thinks that the turtle fits within his original classification scheme--as a primitive Cryptodira--and is not evidence for Joyce's reinterpretation of turtle evolution. Sterli disagrees, based on analyses of anatomical details. If Joyce and Sterli are correct, Parham notes, then modern turtles would have taken much less time to evolve.

Related site

• Overview of Gaffney's history of turtle evolution

Tooth decay.
In red deer and other ungulates, larger males have relatively smaller teeth and shorter life spans.

Credit: Sebastián J. Hidalgo-de-Trucios

Being the buffest guy on the block is often one of the surest ways to score a mate in the animal kingdom. But new research indicates that brawniness can have a serious downside. Bucks, bulls, and other large hoofed males have relatively small teeth, which wear out quickly and impair their ability to digest food.

Researchers have long puzzled over the shorter life span of larger male ungulates, or hoofed mammals. Two years ago, Juan Carranza, a behavioral ecologist at the University of Extremadura in Cáceres, Spain, and colleagues showed that molars in male red deer were relatively smaller than those in the more petite females, and that this difference was correlated with a shorter life. Researchers had assumed that the size difference was due to the fact that male and female teeth wore down at different rates, perhaps because of different eating habits between the sexes. But Carranza's work suggested that male teeth were never that big to begin with.

To confirm this hypothesis, Carranza and Javier Perez-Barberia, an evolutionary ecologist at The Macaulay Institute in the United Kingdom, combed the literature for information on body size in ungulates and obtained measurements of the chewing surfaces of molars and premolars from museum specimens. They compared 123 species--almost half of the known ungulates--studying some in which males and females were the same size, such as roe deer, as well as species in which males were bigger than females, including Barbary sheep and the Nilgai, an antelope.

When males and females were about the same size, so were their teeth. But in species in which larger males evolved, tooth size increased relatively little. Thus, females ended up with larger chewing surfaces for their size than did males, the researchers report in the September issue of American Naturalist. The team concludes that teeth probably didn't grow at the same rate as body size because males can successfully compete for females only in their prime. Once teeth wear down, they become ineffective, and the animal gets weaker and more susceptible to disease or injury. But that doesn't matter to these males, as once they are too old to beat out rivals for mates, there's no need to live a long life. When it comes to how many offspring a male can father, "it seems that compared to body mass, tooth size is relatively unimportant," says Joanne Isaac, a mammalogist at James Cook University in Townsville, Australia, who was not part of the study team.

The large size of the survey "is simply impressive and exciting," says Atle Mysterud, a mammalogist at the University of Oslo in Norway. And Dan Nussey, a vertebrate evolutionary ecologist at the University of Cambridge, U.K., thinks the work makes an important contribution to understanding aging: "There are few comparative analyses of aging rates taking an ecological perspective in the way that Carranza's work does."

Related site

• More on ungulates

Bee's company.
A complex social life makes bees and other bugs better at fighting disease.

Credit: John Foxx/Getty Images

Social bees have surprisingly strong body armor against microbes, researchers have found. And the more gregarious the bees--the larger their colonies and the more closely related--the better they are at beating disease. The discovery is the first clear link between the evolution of immune systems and social behavior, and it dangles a new hope for bioprospectors on the trail of the next generation of antibiotics.

Insects, like humans, face greater risks of catching and spreading infectious diseases when they're crowded together. Scientists have long suspected that bees and other bugs combat the added risk that being social incurs by evolving stronger disease defenses, such as secreting antimicrobial agents to cover their bodies. The theory is that bigger colonies with more crowded conditions would require insects to evolve better immune defenses, which in turn enable the insects to evolve still-bigger colonies.

To test the idea, biologists Adam Stow, Andrew Beattie, and their colleagues at Macquarie University in New South Wales and the South Australian Museum in Adelaide collected bees from across the social spectrum: blue-banded bees and teddy bear bees, which are solitary and live in their own nests without partners or workers; semisocial reed bees that partner with their sisters and their offspring in small colonies; and Australian native honey bees, which form large colonies of closely related individuals with sophisticated divisions of labor. The scientists then washed the protective coatings from the bees' bodies and applied the resulting solution to the notorious Staphylococcus aureus (staph) bacterium.

By measuring how much of each solution it took to stop the staph's growth, the researchers determined the strength of each kind of bee's body coating. All the coatings killed bacteria, but the social bees' antimicrobials proved much more powerful than expected, says Stow. Antimicrobial armor from the most social bees was 314 times stronger than that from the most solitary bees, the team reports online this week in Biology Letters, and even the most mildly social bees were 10 times more protected than their solitary counterparts.

The mysterious bacteria-busting secretions of bees and other insects could someday offer an alternative to today's antibiotics, says Stow. "If you're going to look in nature for antibiotics," he says, "this tells you where to look."

For Oxford ecologist Robert May, the finding is crucial and long overdue. "While the idea isn't new, the demonstration is clear, elegant, and the first,” he says. "It's just very nice."

Related site

• News and information on bees

Net decrease.
Trawling for big cod has led to slim pickings, researchers say.

Credit: Jeffrey L. Rotman / CORBIS

For Atlantic cod, overfishing is the bad gift that keeps on giving. Once a mainstay of fishing fleets, cod began to thin out in the 1960s. Today, their numbers--and the fish themselves--remain small, despite a moratorium on fishing established in 1993. Now, a study of the Gulf of St. Lawrence in Canada might explain why. Researchers report that because the largest and fastest-growing fish were harvested, cod have evolved to grow slowly--an adaptation that haunts them to this day.

The average size of young adult cod has decreased by about 20% in the last 3 decades. Lab experiments have shown that harvesting mainly large fish will cause average size to shrink (ScienceNOW, 5 July 2004). But in the wild, other factors can also influence size, such as temperature and population density.

To control for these variables, Douglas Swain, a fisheries biologist at the Gulf Fisheries Center in Moncton, Canada, and colleagues looked back over data on fishing intensity, cod population, fish size, and environmental variables from 1977 to 1997. Temperatures were warm, which should have stimulated growth, and prey was abundant. So why didn't the cod recover to full size? The team found that the change in average length of 4-year-old cod correlated with the size selection exerted on their parents--which suggests that younger generations inherited their small size from small parents, because larger fish had been caught. This makes sense, Swain says; slow-growing fish would have an advantage, as they have a greater chance of reproducing before they're caught in nets.

"It is the best demonstration that the growth rates of fish themselves have been reduced in this stock," says David Conover of Stony Brook University in New York. "This nails it." But not everyone is convinced. "I am a real skeptic of this result," says Ray Hilborn of the University of Washington, Seattle. Hilborn has analyzed 73 fish stocks and found no relationship between fishing intensity and growth rate. Swain says that the impact could vary depending on fishing methods and the nature of the fish stock. Although the strong selection pressure of fishing can quickly slow down growth rate, he says, it will likely take much longer for nature to speed it up again.

Related site

• More about cod

Kaboom.
Spiral gingers have evolved in part through bursts of genetic change.

Credit: Mark W. Skinner

For some biologists, "punctuated equilibrium" is a radical idea. The term was coined in the 1970s to describe an uneven pace of evolution in the fossil record. But because it posits that evolution happens in bursts, punctuated equilibrium goes against the notion that evolution inches forward in tiny steps guided by natural selection. Now evolutionary biologists have shown that evolution in the genome also has fast and slow speeds, and that natural selection isn't always governing genetic change.

Mark Pagel from the University of Reading, U.K., and his colleagues searched for telltale signs of punctuated evolution in a hodgepodge of family trees. They culled DNA data from 122 papers about various plants and animals. For each set of organisms, they used differences in the number of mutations in certain genes to determine where each organism sat in its particular group's tree. In many cases, they examined clusters of closely related organisms, such as tiger beetles or a group of tropical plants called spiral gingers that belong to one genus. But they also looked more broadly, at a family of snails and an order of frogs, for example.

The researchers counted the branch points--each point represents a new species--and measured the evolutionary distance from the root to the tips of all the branches to estimate how much evolution had occurred. Pagel's earlier work had suggested that if evolution occurs in bursts, then the number of genetic changes over time should be greater in trees with more branch points.

According the genetic analysis, bursts occurred in some trees, Pagel and his colleagues report in 6 October Science. More than a quarter of the evolution of spiral gingers took place during periods of accelerated genetic change. Evolution revved up during speciation in many of the plants and fungi examined as well. However in others, such as certain neotropical butterflies, the total number of changes in the genes indicated that evolution had been more gradual.

Pagel attributes the bursts of genetic change not just to natural selection, but also to an additional phenomenon called genetic drift, in which some genetic changes become incorporated into the genome even if they are not beneficial. Drift is likely to happen in the small populations that typically characterize an incipient species. As a new species settles into its new niche and its population grows, drift becomes less common, and the rate of genetic change slows. As a result, "We think species change very rapidly at first, and then they slow down," says Pagel.

The work is causing a stir. "This study supports the idea that punctuated equilibria exist but also suggests a limit to its overall effect on genetic change," comments Don Waller, an evolutionary biologist at the University of Wisconsin, Madison. But, despite the precautions Pagel took, Brian Charlesworth from the University of Edinburgh, U.K., worries that multiple changes at the same base in species that have been around a long time might have skewed the results.

Related site

• More on punctuated equilibrium

Two years after being checkmated by proponents of intelligent design (ID), supporters of evolution are set to win back control of the Kansas state board of education. Their victory paves the way for the revoking of the state's science standards, which are widely seen as being favorable to the teaching of ID.

In Republican and Democratic primaries conducted on Tuesday, pro-evolution candidates won party nominations for three of the five board seats that are up for re-election in November. Three of the board's other five seats are held by moderates. The results of the primary races mean that regardless of the individual winners in the November election, the board's composition will flip from its existing 6-4 conservative tilt to at least a 6-4 majority controlled by moderates.

"This is a great day for Kansas," Sally Cauble, a moderate who won the Republican primary in western Kansas, told Science. The former elementary school teacher from Liberal, Kansas, had a tough race against incumbent Connie Morris, who has repeatedly mocked evolution as "a nice bedtime story." Cauble, who ended up winning by a margin of 54% to 46%, says she wants to vote out the pro-ID standards that were adopted last year in favor of standards issued earlier by a panel of scientists and teachers appointed by the board (ScienceNOW, 9 November 2005). Those standards, rejected by the current board, emphasize the teaching of evolution.

Jack Krebs of Kansas Citizens for Science says the victory is a significant milestone in efforts by scientists and educators nationwide to keep intelligent design out of the science classroom. "The ID movement has put a lot of effort and money into trying to convince the public that the Kansas science standards are OK," he says. "It's good to see that the voters of Kansas aren't going to buy that."

But nobody believes that the controversy will die when the new board takes over. Kansas has seen a see-saw battle over evolution since 1999, when conservatives introduced creationism into the standards. Those standards were thrown out when moderates took control of the board in 2002. Two years later, the conservatives struck back and immediately resumed their efforts to revise the standards.

"It's unfortunate that we'll now be forced to again teach evolution as the only possible explanation for the origin of life, even though it's a lame explanation with very little scientific support," says certified public accountant John Bacon, one of the two pro-ID candidates who won the primaries on Tuesday. But he promises that the issue won't be going away.

Related site

• Kansas State Department of Education

Butterfly blend.
Two different butterfly species apparently mated to create a third in the South American Andes.

Credit: Mauricio Linares, Uniandes, Colombia

Like merging two companies to create a joined venture, scientists have bred two colorful butterfly species to form an intermediate type, perhaps duplicating a feat nature has already accomplished. This speciation process, known as hybridization, may play a larger role in evolution than is currently believed, the researchers propose.

It's well-accepted that a new species will arise when a subset of an existing species breaks off and accumulates too many genetic mutations to breed with members of the original species. But many researchers have uncovered hints that two species can also merge their gene pools to come up with a third (ScienceNOW July 27, 2005). For this to happen in nature, however, the newly formed species would need to be somehow separated from the other two parental species; otherwise, it would simply get sucked back into the old populations.

A team led by evolutionary biologist Jesús Mavárez of the Smithsonian Tropical Research Institute in Panama studied that problem in three similar-looking butterfly species living in parts of Central and South America. Judged by its color pattern, a species called Heliconius heurippa appears a perfect blend of two others, H. cydno and H. melpomene. Indeed, when the researchers attempted to recreate H. heurippa in the lab by breeding the other two species together, they produced offspring that, after three generations, consistently showed the H. heurippa color pattern. DNA sequencing showed that the newly created hybrid butterflies were genetically distinct from H. cydno and H. melpomene.

The researchers also discovered how similar hybrids may have become isolated in nature. When H. heurippa males had a choice between mating with a H. heurippa female or with a H. cydno or H. melpomene female, the males were 75% to 90% more likely to choose their own kind, the researchers report in the 15 June issue of Nature. Other tests indicated that the apparent hybrids recognize other members of its own species by color pattern alone. "For Heliconius, color pattern is everything," says Marávez.

Evolutionary geneticist James Mallet of University College London in the United Kingdom says the evidence that H. heurippa is a product of hybridization is "pretty convincing." But others remain skeptical. "Maybe this is a hybrid species, but I'm not convinced from the genetic data that it is," says evolutionary geneticist Jerry Coyne of the University of Chicago in Illinois, who says much more sequencing would need to be done to prove H. heurippa is a hybrid. Coyne believes hybridization can't be common in nature because current animal family trees would reveal such mixes.

Related sites

• More on speciation
• More on Heliconius butterflies