Arquivo da tag: Temporalidade

Time flies: Breakthrough study identifies genetic link between circadian clock and seasonal timing (Science Daily)

Date: September 4, 2014

Source: University of Leicester

Summary: New insights into day-length measurement in flies have been uncovered by researchers. The study has corroborated previous observations that flies developed under short days become significantly more cold-resistant compared with flies raised in long-days, suggesting that this response can be used to study seasonal photoperiodic timing. Photoperiodism is the physiological reaction of organisms to the length of day or night, occurring in both plants and animals.

Sunrise. Photoperiodism is the physiological reaction of organisms to the length of day or night, occurring in both plants and animals. Credit: © tomaspic / Fotolia

Researchers from the University of Leicester have for the first time provided experimental evidence for a genetic link between two major timing mechanisms, the circadian clock and the seasonal timer.

New research from the Tauber laboratory at the University of Leicester, which will be published in the academic journal PLOS Genetics on 4 September, has corroborated previous observations that flies developed under short days become significantly more cold-resistant compared with flies raised in long-days, suggesting that this response can be used to study seasonal photoperiodic timing.

Photoperiodism is the physiological reaction of organisms to the length of day or night, occurring in both plants and animals.

Dr Mirko Pegoraro, a member of the team, explained: “The ability to tell the difference between a long and short day is essential for accurate seasonal timing, as the photoperiod changes regularly and predictably along the year.”

The difference in cold response can be easily seen using the chill-coma recovery assay — in which flies exposed to freezing temperatures enter a reversible narcosis. The recovery time from this narcosis reflects how cold-adaptive the flies are.

The team has demonstrated that this response is largely regulated by the photoperiod — for example, flies exposed to short days (winter-like) during development exhibit shorter recovery times (more cold adapted) during the narcosis test.

Dr Eran Tauber from the University of Leicester’s Department of Genetics explained: “Seasonal timing is a key process for survival for most organisms, especially in regions with a mild climate. In a broad range of species, from plants to mammals, the annual change in day-length is monitored by the so-called ‘photoperiodic clock’.

“Many insects for example, including numerous agricultural pests, detect the shortening of the day during the autumn and switch to diapause — a developmental arrest — which allows them to survive the winter.

“Despite intensive study of the photoperiodic clock for the last 80 years, however, the underlying molecular mechanism is still largely unknown. This is in marked contrast to our understanding of the circadian clock that regulates daily rhythms.”

The team has tested mutant strains in which the circadian clock is disrupted and has found that the photoperiodic clock was also disrupted, providing the first experimental evidence for the role of the circadian clock in seasonal photoperiodic timing in flies.

The new research is based on an automated system, allowing the monitoring of hundreds of flies, which paves the way for new insights into our understanding of the genes involved in the photoperiodic response and seasonal timing.

Professor Melanie Welham, Executive Director for Science, at the Biotechnology and Biological Sciences Research Council (BBSRC), said: “This study shows an interesting genetic link between the circadian clock and the seasonal timer. The ubiquity of these clocks across so many species makes this an important discovery which will lead to a better understanding of these essential processes.”


Journal Reference:

  1. Mirko Pegoraro, Joao S. Gesto, Charalambos P. Kyriacou, Eran Tauber. Role for Circadian Clock Genes in Seasonal Timing: Testing the Bünning Hypothesis.PLOS Genetics, September 2014 DOI: 10.1371/journal.pgen.1004603

Why Animals Compare the Present With the Past (Science Daily)

May 30, 2013 — Humans, like other animals, compare things. We care not only how well off we are, but whether we are better or worse off than others around us, or than we were last year. New research by scientists at the University of Bristol shows that such comparisons can give individuals an evolutionary advantage.

The ‘contrast effect’ has been reported in a number of living things, including bees. (Credit: © Daniel Prudek / Fotolia)

According to standard theory, the best response to current circumstances should be unaffected by what has happened in the past. But the Bristol study, published in the journalScience, shows that in a changing, unpredictable world it is important to be sensitive to past conditions.

The research team, led by Professor John McNamara in Bristol’s School of Mathematics, built a mathematical model to understand how animals should behave when they are uncertain about the pattern of environmental change. They found that when animals are used to rich conditions but then conditions suddenly worsen, they should work less hard than animals exposed to poor conditions all along.

The predictions from the model closely match findings from classic laboratory experiments in the 1940s, in which rats were trained to run along a passage to gain food rewards. The rats ran more slowly for small amounts of food if they were used to getting large amounts of food, compared to control rats that were always rewarded with the smaller amount.

This so-called ‘contrast effect’ has also been reported in bees, starlings and a variety of mammals including newborn children, but until now it lacked a convincing explanation.

Dr Tim Fawcett, a research fellow in Bristol’s School of Biological Sciences and a co-author on the study, said: “The effects in our model are driven by uncertainty. In changing environments, conditions experienced in the past can be a valuable indicator of how things will be in the future.”

This, in turn, affects how animals should respond to their current situation. “An animal that is used to rich conditions thinks that the world is generally a good place,” Dr Fawcett explained. “So when conditions suddenly turn bad, it interprets this as a temporary ‘blip’ and hunkers down, expecting that rich conditions will return soon. In contrast, an animal used to poor conditions expects those conditions to persist, and so cannot afford to rest.”

The model also predicts the reverse effect, in which animals work harder for food when conditions suddenly improve, compared to animals experiencing rich conditions all along. This too has been found in laboratory experiments on a range of animals.

The Bristol study highlights unpredictable environmental fluctuations as an important evolutionary force. “Rapid changes favour individuals that are responsive and able to adjust their behaviour in the light of past experience,” said Dr Fawcett. “The natural world is a dynamic and unpredictable place, but evolutionary models often neglect this. Our work suggests that models of more complex environments are important for understanding behaviour.”

Journal Reference:

  1. J. M. McNamara, T. W. Fawcett, A. I. Houston. An Adaptive Response to Uncertainty Generates Positive and Negative Contrast EffectsScience, 2013; 340 (6136): 1084 DOI: 10.1126/science.1230599

Maya Long Count Calendar Calibrated to Modern European Calendar Using Carbon-14 Dating (Science Daily)

Apr. 11, 2013 — The Maya are famous for their complex, intertwined calendric systems, and now one calendar, the Maya Long Count, is empirically calibrated to the modern European calendar, according to an international team of researchers.

Elaborately carved wooden lintel or ceiling from a temple in the ancient Maya city of Tikal, Guatemala, that carries a carving and dedication date in the Maya calendar. (Credit: Courtesy of the Museum der Kulturen)

“The Long Count calendar fell into disuse before European contact in the Maya area,” said Douglas J. Kennett, professor of environmental archaeology, Penn State.

“Methods of tying the Long Count to the modern European calendar used known historical and astronomical events, but when looking at how climate affects the rise and fall of the Maya, I began to question how accurately the two calendars correlated using those methods.”

The researchers found that the new measurements mirrored the most popular method in use, the Goodman-Martinez-Thompson (GMT) correlation, initially put forth by Joseph Goodman in 1905 and subsequently modified by others. In the 1950s scientists tested this correlation using early radiocarbon dating, but the large error range left open the validity of GMT.

“With only a few dissenting voices, the GMT correlation is widely accepted and used, but it must remain provisional without some form of independent corroboration,” the researchers report in today’s (April 11) issue of Scientific Reports.

A combination of high-resolution accelerator mass spectrometry carbon-14 dates and a calibration using tree growth rates showed the GMT correlation is correct.

The Long Count counts days from a mythological starting point. The date is composed of five components that combine a multiplier times 144,000 days — Bak’tun, 7,200 days — K’atun, 360 days — Tun, 20 days — Winal, and 1 day — K’in separated, in standard notation, by dots.

Archaeologists want to place the Long Count dates into the European calendar so there is an understanding of when things happened in the Maya world relative to historic events elsewhere. Correlation also allows the rich historical record of the Maya to be compared with other sources of environmental, climate and archaeological data calibrated using the European calendar.

The samples came from an elaborately carved wooden lintel or ceiling from a temple in the ancient Maya city of Tikal, Guatemala, that carries a carving and dedication date in the Maya calendar. This same lintel was one of three analyzed in the previous carbon-14 study.

Researchers measured tree growth by tracking annual changes in calcium uptake by the trees, which is greater during the rainy season.

The amount of carbon-14 in the atmosphere is incorporated into a tree’s incremental growth. Atmospheric carbon-14 changes through time, and during the Classic Maya period oscillated up and down.

The researchers took four samples from the lintel and used annually fluctuating calcium concentrations evident in the incremental growth of the tree to determine the true time distance between each by counting the number of elapsed rainy seasons. The researchers used this information to fit the four radiocarbon dates to the wiggles in the calibration curve. Wiggle-matching the carbon-14 dates provided a more accurate age for linking the Maya and Long Count dates to the European calendars.

These calculations were further complicated by known differences in the atmospheric radiocarbon content between northern and southern hemisphere.

“The complication is that radiocarbon concentrations differ between the southern and northern hemisphere,” said Kennett. “The Maya area lies on the boundary, and the atmosphere is a mixture of the southern and northern hemispheres that changes seasonally. We had to factor that into the analysis.”

The researchers results mirror the GMT European date correlations indicating that the GMT was on the right track for linking the Long Count and European calendars.

Events recorded in various Maya locations “can now be harmonized with greater assurance to other environmental, climatic and archaeological datasets from this and adjacent regions and suggest that climate change played an important role in the development and demise of this complex civilization,” the researchers wrote.

Journal Reference:

  1. Douglas J. Kennett, Irka Hajdas, Brendan J. Culleton, Soumaya Belmecheri, Simon Martin, Hector Neff, Jaime Awe, Heather V. Graham, Katherine H. Freeman, Lee Newsom, David L. Lentz, Flavio S. Anselmetti, Mark Robinson, Norbert Marwan, John Southon, David A. Hodell, Gerald H. Haug. Correlating the Ancient Maya and Modern European Calendars with High-Precision AMS 14C DatingScientific Reports, 2013; 3 DOI:10.1038/srep01597

When Do We Lie? When We’re Short On Time and Long On Reasons (Science Daily)

ScienceDaily (Sep. 5, 2012) — Almost all of us have been tempted to lie at some point, whether about our GPA, our annual income, or our age. But what makes us actually do it?

In a study forthcoming inPsychological Science, a journal of the Association for Psychological Science, psychological scientists Shaul Shalvi of the University of Amsterdam and Ori Eldar and Yoella Bereby-Meyer of Ben-Gurion University of the Negev investigated what factors influence dishonest behavior.

Previous research shows that a person’s first instinct is to serve his or her own self-interest. And research also shows that people are more likely to lie when they can justify such lies to themselves. With these findings in mind, Shalvi and colleagues hypothesized that, when under time pressure, having to make a decision that could yield financial reward would make people more likely to lie. They also hypothesized that, when people are not under time pressure, they are unlikely to lie if there is no opportunity to rationalize their behavior.

“According to our theory, people first act upon their self-serving instincts, and only with time do they consider what socially acceptable behavior is,” says Shalvi. “When people act quickly, they may attempt to do all they can to secure a profit — including bending ethical rules and lying. Having more time to deliberate leads people to restrict the amount of lying and refrain from cheating.”

The researchers first tested participants’ tendency to lie when doing so could be easily justified: Approximately 70 adult participants rolled a die three times such that the result was hidden from the experimenter’s view. The participants were told to report the first roll, and they earned more money for a higher reported roll.

Seeing the outcomes of the second and third rolls provided the participants with the opportunity to justify reporting the highest number that they rolled, even if it was not the first — after all, they had rolled that number, just not the first time they rolled the die. Some of the participants were under time pressure, and were instructed to report their answer within 20 seconds. The others were not under time pressure, and had an unlimited amount of time to provide a response.

The experimenters were not able to see the actual die rolls of the participants, to ensure all rolls were private. Instead, in order to determine whether or not the participants had lied about the numbers they rolled, Shalvi and colleagues compared their responses to those that would be expected from fair rolls. They found that both groups of participants lied, but those who were given less time to report their numbers were more likely to lie than those who weren’t under a time constraint.

The second experiment followed a similar procedure, except that the participants were not given information that could help them justify their lies: instead of rolling their die three times, they only rolled it once and then reported the outcome. In this experiment, the researchers found that participants who were under time pressure lied, while those without a time constraint did not.

Together, the two experiments suggest that, in general, people are more likely to lie when time is short. When time isn’t a concern, people may only lie when they have justifications for doing so.

One implication of the current findings is that to increase the likelihood of honest behavior in business or personal settings, it is important not push a person into a corner but rather to give him or her time,” explains Shalvi. “People usually know it is wrong to lie, they just need time to do the right thing.”