research highlights

MODEL ORGANISMS Drosophila’s outdoor schedule

Fly rhythms under natural light and erally been labeled ‘crepuscular’(meaning temperature differ from those in the lab. most active in twilight), this finding indi- A fruit fly in a lab does not sense the cates that these insects would be better sunrise. There are no lengthening days, classified as diurnal, says Costa. cool mornings or hot afternoons. Under As the weather got hotter, the flies’ typical laboratory conditions, lights are morning burst of activity came earlier and flicked on or off every 12 hours; temper- the evening burst grew later, correlating ature is a constant 25 °C. These are not with the lengthening days. English sum- the most natural conditions for studying mer days have 3–4 hours’ more daylight the 24-hour cycles of behavior known than the corresponding Italian days fur- as circadian rhythms, but they are what ther south, but the timing of the English researchers have used for decades. and Italian flies’ activity was largely Flies’ daily rhythms differ in lab and outdoors In the lab, flies have a sharp burst of dependent on average temperatures. This activity that starts just before the lights shows, says Costa, “the dominance of morning burst of activity at the same time, turn on in the morning; a second burst in temperature over photo-period in nature, but their afternoon and evening activities activity comes in the evening, just before a result at odds with most laboratory stud- were different, with the ‘short’ mutants’ the lights go off. Aberrations in these ies.” However, temperature is not the only activity bursts occurring earlier and ‘long’ patterns were crucial to discovering sev- factor: if flies were covered up so that they mutants’ bursts occurring later. eral ‘clock genes’ that govern rhythms for could not sense the coming dawn, their Costa’s team was able to replicate pat- sleep-wake-activity patterns. morning bursts in activity were delayed. terns observed under outdoor conditions In light of these long-established obser- Some mutant flies with off-sync behav- in the laboratory by simulating natural vations, flies are thought to be adapted ior in the lab showed regular patterns out- daylight and temperature variations, but

© 2012 Nature America, Inc. All rights reserved. America, Inc. © 2012 Nature for activity bursts around dawn and dusk. doors and generally behaved similarly to doing so was difficult. An electronics whiz There is even a set of neuronal clusters their wild-type counterparts. Circadian designed a panel of programmable white- that determines morning activity and rhythms are thought to help organisms light LEDs that can vary light intensity another that controls evening activity. tailor activities to the most suitable times over six or more orders of magnitude. npg But new research shows that flies living of day as well as adapt to gradual seasonal Also, if the temperature changes were outdoors keep a different schedule. changes. Internal cues may be particularly not very smooth, the flies’ behavior was From spring to autumn, research teams important for regulating internal organs, affected. led by Rodolfo Costa at the University whereas other activity can take its cue Experiments in animal behavior could of Padova in Italy and Charalambos from external factors, says Costa. “Our benefit from conditions closer to animals’ Kyriacou at the University of Leicester in study suggests that behavior, which is the natural environments, says Costa. Not the UK kept flies outdoors, where they brain’s way of changing its environment, only will these adjustments provide bet- were exposed to daily light and tem- doesn’t necessarily need to anticipate reg- ter interpretation of what behaviors are perature fluctuations at 46° and 52° lati- ular environmental changes; it can simply adaptive, they could also improve animal tude, respectively. In addition to bursts react to them.” welfare. “The results of our experiments of activity around dusk and dawn, flies Whereas temperature and twilight cues could help make animals’ environments maintained al fresco have a third burst, in get flies up in the morning, internal clock- healthier and more comfortable through the afternoon. More than half of the flies derived cues seem to regulate afternoon simple measures like changing light levels perked up in the afternoon at average daily and evening behavior. The PERIOD gene and temperatures gradually.” temperatures of 20 °C; nearly all did at 27 affects timing of circadian rhythms: the Monya Baker °C. In fact, when total daily levels of activ- ‘long’ mutants have more time between Research papers ity were considered, less than a quarter of their morning and evening activity peri- Vanin, S. et al. Unexpected features of Drosophila the flies’ activity occurred around dawn ods, whereas the ‘short’ mutants have less. circadian behavioural rhythms under natural and dusk. Although fruit flies have gen- Outdoors, both types of mutants had their conditions. Nature 384, 371–375 (2012).

nature methods | VOL.9 NO.6 | JUNE 2012 | 529