Scholarship & CreativityTime of day tempers tadpoles' response to predators
To a tiny tadpole life boils down to two basic missions: eat and avoid being eaten. But there's a trade-off. The more a tadpole eats, the faster it grows big enough to transform into a frog; yet finding food requires being active, which ups the odds of becoming someone else's dinner.
Scientists have known that prey adjust their activity levels in response to predation risk, but new research by a U-M graduate student shows that internal factors, such as biorhythms, temper their responses.
Michael Fraker, a doctoral student in the laboratory of ecology and evolutionary biology professor Earl Werner, studied tadpoles of the green frog (Rana clamitans), which normally feed more at night, to see whether their responses to predatory dragonfly larvae differed with time of day.
"Green frog tadpoles, like many other aquatic animals, assess predation risk indirectly by sensing chemicals released by their predators into the water," Fraker says. Typically, the tadpoles respond to such cues by swimming down to the bottom, seeking shelter and remaining still. In his experiments, Fraker exposed tadpoles in a tank to the chemical signatures of dragonfly larvae for one hour during the day and one hour at night. Then he recorded their swimming and feeding activity during and after exposure. Both during the day and at night, the tadpoles initially responded similarly to the chemical cues, showing the typical plunge in activity. But at night they returned to feeding more quickly than during the day.
"My interpretation of these results is that green frog tadpoles behave more conservatively in response to a predator chemical cue during the day because predation risk may still be fairly high and the tadpoles are going to feed very little anyway. That means the growth rate-to-predation risk ratio is low. At night, the ratio is higher because that's when the tadpoles do most of their feeding. This favors a quicker return to their pre-cue activity levels.
"The main implication of my results is that prey behavior can be influenced by both external factorsthe chemical cues released by the predatorsand internal factors such as circadian rhythms."
Stigma of suicide perceived the same for blacks, whites
Blacks and whites are similar in their perceptions about how suicide can stigmatize their respective communities, according to a new study co-authored by a U-M researcher.
The finding is contrary to other published studies indicating that suicide is more stigmatized in the Black community.
"When African Americans are seriously suicidal in response to difficult life events, family or friends who believe that life's difficulties do not warrant a suicidal act may not respond or intervene actively," say co-authors Rheeda Walker of the University of South Carolina, David Lester of the Richard Stockton College of New Jersey and Sean Joe of U-M.
Researchers examined cultural beliefs of suicide among African Americans and whites. They found that prevention and intervention efforts often are compromised, as Blacks are reluctant to disclose suicide-related thinking or planning. If the Black community helps those exhibiting warning signs for suicidal tendencies, the number of deaths and severe suicide attempts can be reduced, says Joe, an assistant professor in the School of Social Work.
The study also indicates Black people believe God controls life and that suicide cannot be attributed to life stressors. Whites are more likely to believe suicide attempts are triggered by conflict, work stress or experiencing a broken home, and that the individual or government is responsible for life.
"This means whites are more likely to blame themselves, thus increasing the propensity for the onset of depression and other psychiatric disorders associated with an increased risk for suicide," Joe says.
In another study written by Joe and published in the same journal, the suicide rate for Blacksmainly among malespeaked in the early 1980s as unemployment, decaying communities, family disruption and the proliferation of firearms might have caused many to take their lives.
This period coincided with social change and upheaval, including post civil rights movement reactions, such as the elimination of social services. The high suicide rates, especially among younger Blacks, continued for nearly 10 years.
"Although the rates of suicide have declined since 1993, non-fatal suicidal behavior among Black males continues to rise," Joe says. "Black rates now parallel whites, thus all groups declined, but we are not sure what has caused this decline."
Younger Blacks are more susceptible to suicidal forces because they are more likely to accept taking their lives as a solution to life problems than previous generations.
Intervention and prevention efforts should target this group, as well as the elderly, who face health challenges that often increase their chances to consider suicide, Joe says.
Want to lose weight? Sleep more.
In a new article appearing in the current issue of Obesity Reviews, U-M researcher Michael Sivak presents calculations showing that replacing one hour of inactive wakefulnesssuch as watching televisionwith sleep can result in a 6 percent reduction in caloric intake.
"Caloric consumption in a society with readily available food is likely to be approximately proportional to the number of hours of being awake," says Sivak, head of the Human Factors Division at the Transportation Research Institute. "By replacing one hour of being awake with sleeping, we forgo a significant consumption of food because of the resulting reduction in the opportunity to eat."
Sivak says that a person who sleeps seven hours a night and consumes 2,500 calories during the remaining 17 hours of the day can cut 147 calories simply by sleeping an extra hour instead of watching TV. He calculated that such a decrease in caloric intake would result in a body-weight reduction of about 14 pounds per year.
"Recent research has suggested that the levels of the hormones leptin and ghrelin mediate an association between lack of sleep and weight gain. But this may turn out to be only part of the story," he says. "The behavioral, non-hormonal relationship between sleep and weight is another possible connection.
"To the extent that a large proportion of the population is both overweight and voluntarily sleep-deprived, replacing some sedentary activity with sleeping might offer a practical behavioral solution for a large segment of the overweight population."
How can identical twins be genetically different?
They sleep together, eat together, and most people find it impossible to tell them apart. Identical twins who grow up together share just about everything, including their genes. But sometimes only one twin will have health problems when genetics predicts both of them should.
Scientists at the Medical School are just beginning to understand how two biologically similar people can be so different when it comes to development of diseases like rheumatoid arthritis.
Researchers have discovered three genes that are over-expressed in rheumatoid arthritis, or RA, that previously were not known to be associated with the disease. They also found that non-genetic factors influenced the expression of these genes, and that expression patterns varied between identical twins when only one twin had RA. Results of the study were published in the July issue of Arthritis and Rheumatism.
There are many genetic factors that put people at a high-risk for developing RA, yet in only 15 percent of identical twins will both develop it.
"There's a lot of variability in the severity of the disease, symptoms, and the response a patient will have to treatment. Differences in the expression of genes caused by environmental factors that modify DNA have a lot to do with this variability," says Dr. Joseph Holoshitz, associate professor of internal medicine and co-author of the study.
The most significantly over-expressed of the three genes codes for a protein called laeverin, an enzyme that destroys certain types of proteins. Scientists hypothesize that laeverin promotes the tissue damage of the joint found in RA by degrading cartilage and bone. Another previously unidentified gene codes for a protein called 11*-HSD2 that helps deactivate cortisol, the hormone involved in the response to stress that also has anti-inflammatory effects. The third gene discovered codes for Cyr61, which plays a role in angiogenesis, a process that recruits new blood vessels to an area.
Lead authors were Dr. Christian Haas, research fellow in the Department of Internal Medicine, and Chad Creighton, research assistant in the Department of Pathology. Additional contributing U-M authors were Dr. Xiujun Pi, research fellow in rheumatology; Ira Maine, research associate of pathology; Dr. Alisa Koch, professor of rheumatology and internal medicine, Song Ling, research investigator in internal medicine; Dr. Arul Chinnaiyan, associate professor of pathology and urology.
In tunneling physics, a decades-old paradox is resolved
As if the concept of quantum tunnelingwhere atoms pass through barriersisn't confusing enough, one of the vexing questions within that area of physics is why particles seem to travel faster than the speed of light when passing through a barrier, but not when they travel through empty space.
Also puzzling is why the time spent by the particle in the barrier does not seem to increase as the barrier is made longer and longer.
This paradox has stirred debate in the physics community since 1932, but Herbert Winful, a professor in the College of Engineering, believes he's put an end to these questions. Winful says his theoretical results show that what's being calculated and measured isn't the time it takes the particle to go from A to B (passing through a barrier in between) "but the time it takes to empty the barrier of energy already stored in the barrier." The technical term for this time is group delay.
Imagine two tour buses, one with 100 passengers and the other with 10. The buses arrive at the same restaurant together, but the bus with 10 people empties more quickly and its diners get to eat first. If the arrival time is defined as the average time at which a passenger arrives at the dinner table, this time is shorter for the bus with fewer passengers. This also explains why the so-called group delay is the same no matter the distance traveled.
In quantum tunneling most of the particles (people on the bus) bounce off the barrier and only a tiny fraction makes it through. The presence of the barrier reduces the amount of energy that can be stored compared to the amount stored in a barrier-free region. The delay time measured is directly proportional to the stored energy and is the time it takes to release this stored energy.
The time doesn't change when the barrier is widened because the barrier has a certain energy storage capacity, which does not increase with length, just as the bus has a fixed capacity regardless of the distance traveled, Winful says.
"My result is actually in a way is a bit of a downer, because it shows that we can't do that (travel faster than light)," he says. But, he adds, it's comforting to know that Einstein was right in his theory of relativity that tells us nothing can travel faster than light, about 186,171 miles per second.
Executives continue to play dating games with stock options
While the fallout from corporate accounting scandals has curtailed backdating of stock options it is still prevalent. In fact, executives also influence their compensation by engaging in another kind of dating gameforward-dating, say researchers at the Ross School of Business.
When backdating, executives report to the Securities and Exchange Commission that they received options from their corporate board on a date prior to the actual time the board decision was madeif the stock price was rising before the board decision.
But if the stock price was falling prior to the board's decision, backdating is clearly unprofitable, since the price may end up even lower after the grant date, researchers say. The lower the stock price on the reported grant date, the greater the payoff.
"In this case managers may wait to see how the stock price behaves afterwards," says H. Nejat Seyhun, professor of finance. "If it continues to fall, they may designate a date in the future as the grant date, trading off the benefit from even lower exercise prices against the risk of getting caught. We term this form of the dating game as forward-dating."
Seyhun and colleague M.P. Narayanan examined more than 638,000 option grants from Aug. 29, 2002when the Sarbanes-Oxley Act (SOX) became effectiveuntil the end of 2004. A provision within the law requires executive stock option grants to be reported within two business days after the grants.
The researchers found that nearly a quarter of executives still report their options late in spite of potential legal sanctions. About 10 percent report more than a month late.
According to the study executives have complied more closely with SOX requirements over time. The average reporting lag has declined from nearly 18 days in 2002 to just over eight days in 2004.
The magnitude of gains for large grants from backdating can be significant, the researchers say. By reporting 30 days late, a manager receiving a grant of 1 million shares of a typical company's stock can increase the value of his or her option compensation by about 8 percent.
"By conservative estimates, this is equivalent to a windfall of $1.2 million," Narayanan says.
Seyhun and Narayanan also found that dating games are more likely to be played by smaller firms, when grants are large or unscheduled, and when senior executives are the recipients. Managers in the transportation and energy industries report most promptly, while those in public utilities and consumer services are the biggest late reporters. Dating games, however, are most prevalent in the technology sector, which accounts for nearly half of all option awards.