Caught In The Act: Butterfly Mate Preference Shows How One Species Can Become Two

Breaking up may actually not be hard to do, say scientists who've found a population of tropical butterflies that may be on its way to a split into two distinct species.

The cause of this particular break-up? A shift in wing color and mate preference.

In a paper published this week in the journal Science, the researchers describe the relationship between diverging color patterns in Heliconius butterflies and the long-term divergence of populations into new and distinct species.

"Our paper provides a unique glimpse into the earliest stage of ecological speciation, where natural selection to fit the environment causes the same trait in the same population to be pushed in two different directions," says Marcus Kronforst, a Bauer Fellow in the Center for Systems Biology at Harvard University who received his doctor's degree at The University of Texas at Austin. "If this trait is also involved in reproduction, this process can have a side effect of causing the divergent subpopulations to no longer interbreed. This appears to be the process that is just beginning among Heliconius butterflies in Ecuador."

Heliconius butterflies display incredible color pattern variation across Central and South America, with closely related species usually sporting different colors. In Costa Rica, for example, the two most closely related species differ in color: One species is white and the other is yellow. In addition, both species display a marked preference to mate with butter-flies of the same color.

The Ecuadorian population examined by Kronforst and his colleagues shows the same white and yellow variation found in Costa Rica but has not yet reached a level of strong reproductive isolation. The entire population lives in close proximity and individuals of both colors come in contact with -- and mate with -- each other.

But, by studying the Ecuadorian population in captivity, the scientists found the two colors do not mate randomly. Despite the genetic similarity between the groups -- white and yellow varieties differ only at the color-determining gene -- yellow Ecuadorian individuals show a preference for those of the same color. White male butterflies, most of which are heterozygous at the gene that controls color, show no color preference.

"This subtle difference in mate preference between the color forms in Ecuador may be the first step in a process that could eventually result in two species, as we see in Costa Rica," says Kronforst, who began studies of Heliconius color pattern and behavioral genetics in the laboratory of Professor Lawrence Gilbert at The University of Texas at Austin.

Previous studies of species formation have focused on the characteristics of well-differentiated species, and the health and viability of their hybrids in particular, in an effort to identify how the species may have emerged and how they stay distinct.

Heliconius provides a model for a different kind of study. The researchers considered species emergence from the opposite end, studying populations that have yet to diverge into separate species in order to identify the role of mate choice in the potential emergence of new species.

Having identified color-based mate preference in Heliconius, the researchers used a battery of genetic markers to compare the genomes of the white and yellow varieties, showing that they are genetically identical except for their different colors and preferences.

Their work suggests that the genes for color and preference are very close to one another in the genome; the two traits could even be caused by the same gene. Their next step is to identify the gene (or genes) responsible for the differences in color and mate preference.

"If we can identify this gene or genes, we can say conclusively how they influence both color and mate choice," says Kronforst. "Subsequent work could elucidate exactly how changes in individual genes can, over long periods of time, lead to novel species."

"This study shows the great potential of the genus Heliconius as a model system for integrating genetics, development, behavior, ecology and evolution," says Gilbert, professor in the Section of Integrative Biology. "It is the culmination of diverse contributions of the co-authors involving insectary, field and laboratory research over more than a decade."

Co-authors on the Science paper with Kronforst are Nicola L. Chamberlain and Ryan I. Hill, both of Harvard; Durrell D. Kapan of the University of Hawaii; and Lawrence E. Gilbert of The University of Texas at Austin. Their work was funded by the National Science Foundation and the National Institutes of Health.

Biological Clocks Discovery Overturns Long-held Theory

University of Michigan mathematicians and their British colleagues say they have identified the signal that the brain sends to the rest of the body to control biological rhythms, a finding that overturns a long-held theory about our internal clock.

Understanding how the human biological clock works is an essential step toward correcting sleep problems like insomnia and jet lag. New insights about the body's central pacemaker might also, someday, advance efforts to treat diseases influenced by the internal clock, including cancer, Alzheimer's disease and mood disorders, said University of Michigan mathematician Daniel Forger.

"Knowing what the signal is will help us learn how to adjust it, in order to help people," said Forger, an associate professor of mathematics and a member of the U-M's Center for Computational Medicine and Bioinformatics. "We have cracked the code, and the information could have a tremendous impact on all sorts of diseases that are affected by the clock."

The body's main time-keeper resides in a region of the central brain called the suprachiasmatic nuclei, or SCN. For decades, researchers have believed that it is the rate at which SCN cells fire electrical pulses---fast during the day and slow at night---that controls time-keeping throughout the body.

Imagine a metronome in the brain that ticks quickly throughout the day, then slows its pace at night. The rest of the body hears the ticking and adjusts its daily rhythms, also known as circadian rhythms, accordingly.

That's the idea that has prevailed for more than two decades. But new evidence compiled by Forger and his colleagues shows that "the old model is, frankly, wrong," Forger said.

The true signaling mechanism is very different: The timing signal sent from the SCN is encoded in a complex firing pattern that had previously been overlooked, the researchers concluded. Forger and U-M graduate student Casey Diekman, along with Dr. Mino Belle and Hugh Piggins of the University of Manchester in England, report their findings in the Oct. 9 edition of Science.

To test predictions made by Forger and Diekman's mathematical model, the British scientists collected data on firing patterns from more than 400 mouse SCN cells. The U-M scientists then plugged the experimental results into their model and found that "the experimental data were almost exactly what the model had predicted," Forger said.

Though the experiments were done with mice, Forger said it's likely that the same mechanism is at work in humans, since timekeeping systems are similar in all mammals.

The SCN contains both clock cells (which express a gene call per1) and non-clock cells. For years, circadian-biology researchers have been recording electrical signals from a mix of both types of cells. That led to a misleading picture of the clock's inner workings.

But Forger's British colleagues were able to separate clock cells from non-clock cells by zeroing in on the ones that expressed the per1 gene. Then they recorded electrical signals produced exclusively by those clock cells. The pattern that emerged bolstered the audacious new theory.

"This is a perfect example of how a mathematical model can make predictions that are completely at odds with the prevailing views yet, upon further experimentation, turn out to be dead-on," Forger said.

The researchers found that during the day, SCN cells expressing per1 sustain an electrically excited state but do not fire. They fire for a brief period around dusk, then remain quiet throughout the night before releasing another burst of activity around dawn. This firing pattern is the signal, or code, the brain sends to the rest of the body so it can keep time.

"The old theory was that the cells in the SCN which contain the clock are firing fast during the day but slow at night. But now we've shown that the cells that actually contain the clock mechanism are silent during the day, when everybody thought they were firing fast," Diekman said.

Piggins said the findings "force us to completely reassess what we thought we knew about electrical activity in the brain's circadian clock." In addition, the results demonstrate the importance of interdisciplinary collaborative research, he said.

"This work also raises important questions about whether the brain acts in an analog or a digital way," Belle said.

Learning To Talk Changes How Speech Is Heard: 'Sound Of Learning' Unlocked By Linking Sensory And Motor Systems

Learning to talk also changes the way speech sounds are heard, according to a new study published in Proceedings of the National Academy of Sciences by scientists at Haskins Laboratories, a Yale-affiliated research laboratory. The findings could have a major impact on improving speech disorders.

"We've found that learning is a two-way street; motor function affects sensory processing and vice-versa," said David J. Ostry, a senior scientist at Haskins Laboratories and professor of psychology at McGill University. "Our results suggest that learning to talk makes it easier to understand the speech of others."

As a child learns to talk, or an adult learns a new language, Ostry explained, a growing mastery of oral fluency is matched by an increase in the ability to distinguish different speech sounds. While these abilities may develop in isolation, it is possible that learning to talk also changes the way we hear speech sounds.

Ostry and co-author Sazzad M. Nasir tested the notion that speech motor learning alters auditory perceptual processing by evaluating how speakers hear speech sounds following motor learning. They simulated speech learning by using a robotic device, which introduced a subtle change in the movement path of the jaw during speech.

To assess speech perception, the participants listened to words one at a time that were taken from a computer-produced continuum between the words "had" and "head." In the speech learning phase of the study, the robot caused the jaw to move in a slightly unusual fashion. The learning is measured by assessing the extent to which participants correct for the unusual movement.

"Its like being handed a two-pound weight for the first time and being asked to make a movement, it's uncomfortable at first, but after a while, the movement becomes natural," said Ostry. "In growing children, the nervous system has to adjust to moving vocal tract structures that are changing in size and weight in order to produce the same words. Participants in our study are learning to return the movement to normal in spite of these changes. Eventually our work could have an impact on deviations to speech caused by disorders such as stroke and Parkinson's disease."

"Our study showed that speech motor learning altered the perception of these speech sounds. After motor learning, the participants heard the words differently than those in the control group," said Ostry. "One of the striking findings is that the more motor learning we observed, the more their speech perceptual function changed."

Ostry said that future research will focus on the notion that sensory remediation may be a way to jumpstart the motor system.

The team previously found that the movement of facial muscles around the mouth plays an important role not only in the way the sounds of speech are made, but also in the way they are heard.

Haskins Laboratories was founded in 1935 by the late Dr. Caryl P. Haskins. This independent research institute has been in New Haven, Connecticut since 1970 when it formalized affiliations with Yale University and the University of Connecticut. The Laboratories' primary research focus is on the science of the spoken and written word.

Short Heels Make Elite Sprinters Super Speedy: Longer Toes, Unique Ankle Structure Aid Sprinters

Longer toes and a unique ankle structure provide sprinters with the burst of acceleration that separates them from other runners, according to biomechanists.

"At the start of a sprint the only way a runner can speed up is through the reaction force that results from the action of leg muscles pushing on the ground," said Stephen Piazza, associate professor of kinesiology, Penn State. "Long toes provide sprinters the advantage of maintaining maximum contact with the ground just a little bit longer than other runners."

Piazza and his colleague Sabrina S. M. Lee, former Penn State graduate student now a post-doctoral fellow at Simon Fraser University, Vancouver, Canada, studied the muscle architecture of the foot and ankle to look at the differences between sprinters and non-sprinters.

They matched 12 collegiate sprinters with 12 non-athletes of the same height. They measured the distance between the heel and the end of the toes and used ultrasound imaging to measure the sliding of the Achilles tendon during ankle motion, from which the leverage of the tendon can be calculated.

"What we found was that the lever arms (distance between the tendon and center of rotation of the ankle) were significantly shorter -- about 25 percent shorter -- in sprinters," said Piazza, whose findings appeared recently in the Journal of Experimental Biology. "This difference might be explained by a tradeoff between leverage and muscle force-generating capacity."

Because the lever arms are shorter, the muscles shorten less for the same joint rotation. If muscles shorten less, they shorten more slowly, which helps them to produce greater force that more than compensates for the reduced leverage.

While there is little published work on foot shapes and sprinting, previous work on animals suggests that ostriches, greyhounds and cheetahs have feet built for sprinting.

To understand the kind of human foot that would produce a similar sprinting advantage, the researchers developed a simple computer model that could analyze the physiological data they had collected earlier.

"We wanted to see how much acceleration we could get out of the model when we changed the tendon lever arm and the length of the toes," said Piazza. "What we found is that when the Achilles tendon lever arm is the shortest and the toes are longest, we get the greatest acceleration."

Piazza cites other recent research suggesting that shorter toes in modern humans could be an evolutionary adaptation for efficient distance running.

"Maybe our ancestors with longer toes were better sprinters. Or maybe longer toes were selected for at a time when navigating in trees was more important and our toes became shorter as endurance running became more important for our survival," he added.

The Penn State researcher cautions that while the study could be a piece of the puzzle in determining who could potentially be a good sprinter, other physiological components such as body type, cardiovascular physiology and muscle fiber types should also be taken into account.

It is also unclear whether sprinting ability is congenital or whether training can influence the shape of bones in the foot.

"It is not too far-fetched to think that training can help accentuate the shape of the bone," said Piazza. "But if sprinters' skeletal characteristics were shown to be immutable, it would support the coaches' adage that sprinters are born and not made."

The National Science Foundation funded this work.

NASA's Fermi Telescope Detects Gamma Rays From 'Star Factories' In Other Galaxies

Nearby galaxies undergoing a furious pace of star formation also emit lots of gamma rays, say astronomers using NASA's Fermi Gamma-ray Space Telescope. Two so-called "starburst" galaxies, plus a satellite of our own Milky Way galaxy, represent a new category of gamma-ray-emitting objects detected both by Fermi and ground-based observatories.

"Starburst galaxies have not been accessible in gamma rays before," said Fermi team member Seth Digel, a physicist at SLAC National Accelerator Laboratory in Menlo Park, Calif. "Most of the galaxies Fermi sees are exotic and distant blazars, which produce jets powered by matter falling into enormous black holes. But these new galaxies are much closer to us and much more like our own."

Gamma rays are the most energetic form of light. Fermi has detected more than a thousand point sources and hundreds of gamma-ray bursts, but the satellite also detects a broad glow that roughly follows the plane of our galaxy. This diffuse gamma-ray emission results when fast-moving particles called cosmic rays strike galactic gas or even starlight.

Cosmic rays are hyperfast electrons, positrons, and atomic nuclei moving at nearly the speed of light. But, although Earth is constantly bombarded by these particles, their origin remains a mystery nearly a century after their discovery. Astronomers suspect that the rapidly expanding shells of exploded stars somehow accelerate cosmic ray particles to their fantastic energy.

"For the first time, we're seeing diffuse emission from star-forming regions in galaxies other than our own," noted Jürgen Knödlseder, a Fermi collaborator at the Center for the Study of Space Radiation in Toulouse, France. He spoke to reporters today at the 2009 Fermi Symposium, a Washington gathering of hundreds of astrophysicists involved in the Fermi mission and related studies. The meeting continues through Nov. 5.

Knödlseder revealed an image captured by Fermi's Large Area Telescope (LAT) of a star-forming region known as 30 Doradus within the Large Magellanic Cloud (LMC). Located 170,000 light-years away in the southern constellation Dorado, the LMC is the largest of several small satellite galaxies that orbit our own.

More stars form in the 30 Doradus "star factory" than in any similar location in the Milky Way. "The region is an intense source of gamma rays, and the diffuse emission we see with Fermi follows the glowing gas we see in visible light," Knödlseder explained.

The region lights up in gamma rays for the same reason the Milky Way does -- because cosmic rays strike gas clouds and starlight. But Fermi shows that the LMC's brightest diffuse emission remains close to 30 Doradus and doesn't extend across the galaxy. This implies that the stellar factory itself is the source of the cosmic rays producing the glow.

"Star-forming regions produce lots of massive, short-lived stars, which explode when they die," Digel said. "The connection makes sense."

"The tangled magnetic fields near 30 Doradus probably confine the cosmic rays to their acceleration sites," Knödlseder said.

Fermi's LAT sees diffuse emission from the starburst galaxies M82 and NGC 253, both of which were also seen this year by ground-based observatories sensitive to gamma rays hundreds of times more energetic than the LAT can detect. They do this by imaging faint flashes in the upper atmosphere caused by the absorption of gamma rays carrying trillions of times the energy of visible light.

"The core of M82 forms stars at a rate ten times greater than the entire Milky Way galaxy," said Niklas Karlsson, a postdoctoral fellow at Adler Planetarium in Chicago. He is also a member of the science team for VERITAS, an array of gamma-ray telescopes in Arizona that detected M82, which lies 12 million light-years away in the constellation Ursa Major.

"These very-high-energy gamma rays probe physical processes in other galaxies that will help us understand how and where cosmic rays become accelerated," Karlsson explained.

"Our sensitivity to gamma-rays -- both in space and on the ground -- has increased enormously thanks to Fermi and observatories like VERITAS," Digel said. "This is opening up the detailed study of high-energy processes in galaxies very close to home." NASA's Fermi Gamma Ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Newly Discovered Ankylosaur Dinosaur Is 'Biological Version Of An Army Tank'

A husband and wife team of American paleontologists has discovered a new species of dinosaur that lived 112 million years ago during the early Cretaceous of central Montana.

The new dinosaur, a species of ankylosaur, is documented in the October issue of the Canadian Journal of Earth Sciences. Ankylosaurs are the biological version of an army tank. They are protected by a plate-like armour with two sets of sharp spikes on each side of the head, and a skull so thick that even 'raptors' such as Deinonychus could leave barely more than a scratch.

Bill and Kris Parsons, Research associates of the Buffalo Museum of Science, found much of the skull of the newly described Tatankacephalus cooneyorum resting on the surface of a hillside in 1997. Because the skull was 90% complete, it was possible to justify this fossil as a new species.

"This is the first member of Ankylosauridae to be found within the Early Cretaceous Cloverly Geologic Formation," said Bill Parsons, who characterized the fossil as a transitional evolutionary form between the earlier Jurassic ankylosaurs and the better known Late Cretaceous ankylosaurs.

The skull is heavily protected by two sets of lateral horns, two thick domes at the back, and smaller thickenings around the nasal region. "Heavy ornamentation and horn-like plates would have covered most of the dorsal surface of this dinosaur" said Bill Parsons.

"For years, Bill and Kris have been collecting fossils from a critical time in Earth's history, and their hard work has paid off," said Lawrence Witmer, professor of paleontology at Ohio University who was not involved with this study. "This is a really important find and gives us a clearer view of the evolution of armored dinosaurs. But this is just the first; I'm sure, of what will be a series of important discoveries from this team."

Parsons also illustrated the dermal armour of this new species based on the theory by Museum of the Rockies paleontologist John R. Horner that there was an outer keratinous sheathing on it as found in modern turtle shells and bird beaks. In his new reconstruction, Parsons suggests that Tatankacephalus exhibited complex and colorful patterns rather than the dull appearance suggested in earlier ankylosaur portraits. "According to Horner's theory, many other dinosaurs also had this kind of sheathing and also may have been diversely colored," said Parsons.

As to its name, the broad, short horns on the back of its skull resemble the horns found on a modern buffalo skull and Tatankacephalus loosely translates as 'Buffalo head.' Parsons also noted, "of course any further allusions to the city of Buffalo are completely intentional as well."

New Analyses Of Dinosaur Growth May Wipe Out One-third Of Species

Paleontologists from the University of California, Berkeley, and the Museum of the Rockies have wiped out two species of dome-headed dinosaur, one of them named three years ago -- with great fanfare -- after Hogwarts, the school attended by Harry Potter.

Their demise comes after a three-horned dinosaur, Torosaurus, was assigned to the dustbin of history last month at the Society of Vertebrate Paleontology meeting in the United Kingdom, the loss in recent years of quite a few duck-billed hadrosaurs and the probable disappearance of Nanotyrannus, a supposedly miniature Tyrannosaurus rex.

These dinosaurs were not separate species, as some paleontologists claim, but different growth stages of previously named dinosaurs, according to a new study. The confusion is traced to their bizarre head ornaments, ranging from shields and domes to horns and spikes, which changed dramatically with age and sexual maturity, making the heads of youngsters look very different from those of adults.

"Juveniles and adults of these dinosaurs look very, very different from adults, and literally may resemble a different species," said dinosaur expert Mark B. Goodwin, assistant director of UC Berkeley's Museum of Paleontology. "But some scientists are confusing morphological differences at different growth stages with characteristics that are taxonomically important. The result is an inflated number of dinosaurs in the late Cretaceous."

Goodwin and John "Jack" Horner of the Museum of the Rockies at Montana State University in Bozeman, are the authors of a new paper analyzing North American dome-headed dinosaurs that appeared this week in the public access online journal PLoS One.

Unlike the original dinosaur die-off at the end of the Cretaceous period 65 million years ago, this loss of species is the result of a sustained effort by paleontologists to collect a full range of dinosaur fossils -- not just the big ones. Their work has provided dinosaur specimens of various ages, allowing computed tomography (CT) scans and tissue study of the growth stages of dinosaurs.

In fact, Horner suggests that one-third of all named dinosaur species may never have existed, but are merely different stages in the growth of other known dinosaurs.

"What we are seeing in the Hell Creek Formation in Montana suggests that we may be overextended by a third," Horner said, a "wild guess" that may hold true for the various horned dinosaurs recently discovered in Asia from the Cretaceous. "A lot of the dinosaurs that have been named recently fall into that category."

The new paper, published online Oct. 27, contains a thorough analysis of three of the four named dome-headed dinosaurs from North America, including Pachycephalosaurus wyomingensis, the first "thick-headed" dinosaur discovered. After that dinosaur's description in 1943, many speculated that male pachycephalosaurs used their bowling ball-like domes to head-butt one another like big-horn sheep, though Goodwin and Horner disproved that notion in 2004 after a thorough study of the tissue structure of the dome.

Many paleontologists now realize that the elaborate head ornaments of dinosaurs, from the huge bony shield and three horns of Triceratops to the coxcomb-like head gear of some hadrosaurs, were not for combat, but served the same purpose as feathers in birds: to distinguish between species and indicate sexual maturity.

"Dinosaurs, like birds and many mammals, retain neoteny, that is, they retain their juvenile characteristics for a long period of growth," Horner said, "which is a strong indicator that they were very social animals, grouping in flocks or herds with long periods of parental care."

These head ornaments, which probably had horny coverings of keratin that may have been brightly-colored as they are in many birds, started growing when these dinosaurs reached about half their adult size, and were remodeled as these dinosaurs matured, continuing to change shape even into adulthood and old age, according to the researchers.

In the new paper, Horner and Goodwin compared the bone structures of Pachycephalosaurus with that of a domeheaded dinosaur, Stygimoloch spinifer, discovered in Montana by UC Berkeley paleontologists in 1973, and a dragon-like skull discovered in South Dakota and named in 2006 as a new species, Dracorex hogwartsia.

With the help of CT scans and microscopic analysis of slices through the bones of Pachycephalosaurus and Stygimoloch, the team concluded that Stygimoloch, with its high, narrow dome, growing tissue and unfused skull bones, was probably a pachycephalosaur subadult, in a stage just before sexual maturity.

Dracorex is one of a kind, and thus unavailable for dissection, but morphological analysis indicates it is a juvenile that hasn't yet formed a dome, although the top of its skull shows thickening suggestive of an emerging dome.

"Dracorex's flat skull, nodules on the front end and small spikes on back, and thickened but undomed frontoparietal bone all confirm that, ontogenetically, it is a juvenile Pachycephalosaurus," Goodwin said.

Comparison of these skulls to other fossils in the hands of private collectors confirm the conclusions, they said. In all, they looked at 21 dome-headed dinosaur skulls and cranial elements from North America.

The key to this analysis, Horner said, was years of field work in Montana by his team and Goodwin's in search of fossils of all sizes.

"We have gone out in the Hell Creek Formation for 11 years doing nothing but collecting absolutely everything we could find, which is the kind of collecting that is required," he said. "If you think about Triceratops, people had collected for 100 years and still hadn't found any juveniles. And we went out and spent 11 years collecting everything, and we found all kinds of them."

"Early paleontologists recognized the distinction between adults and juveniles, but people have lost track of looking at ontogeny -- how the individual develops -- when they discover a new fossil," Goodwin said. "Dinosaurs are not mammals, and they don't grow like mammals."

In fact, the so-called metaplastic bone on the heads of horned dinosaurs grows and dissolves, or resorbs, throughout life like no other bone, Horner said, and is reminiscent of the growth and loss of horns today in elk and deer. In earlier studies, Horner and Goodwin found dramatic remodeling of metaplastic bone in Triceratops, which led to their subsequent focus on dome-headed dinosaurs.

"Metaplastic bones get long and shorten, as in Triceratops, where the horn orientation is backwards in juveniles and forward in adults," Horner said. Even in older specimens, such as the fossil previously named Torosaurus, bone in the face shield resorbs to create holes along the margin. John Scannella, Horner's student at Montana State, presented a paper reclassifying Torosaurus as an old Triceratops at the Society for Vertebrate Paleontology meeting in Bristol, U.K., on Sept. 25.

"In order for that huge amount of bone to move, there has to be a lot of deposition and resorption," Horner said.

Horner and Goodwin continue to search for dinosaur fossils in the Hell Creek Formation, which is rich in Triceratops, dome-headed dinosaurs, hadrosaurs and tyrannosaurs. Analysis of growth stages in these taxa will have implications for other horned dinosaurs that are being uncovered in Asia and elsewhere.

"There are other horned dinosaurs I think may be over split," that is, split into too many new species rather than being lumped together as one species, Goodwin said.

The work was supported by grants from the UC Museum of Paleontology and the Museum of the Rockies.