Bees don't wear wristwatches, but bees can certainly tell time. They are attuned to time in relation to the sun's position in the sky throughout the day. Bees can remember the time at which flowers have nectar and can use this information to guide their foraging choices. This timekeeping ability can be seen clearly in experiments conducted by Martin Lindauer in which bees were trained to feed from an artificial flower that provided sugar syrup at a particular time of day.
The bees were able to learn to return to the feeder at that time, and while some scouts might look at the feeder at other times, a large majority of foragers returned when the time was right and the feeder was filled. Being time-sensitive is most likely an adaptation that enables bees to exploit food sources that are available during the hours of the day when nectar and pollen production is highest. An awareness of the circadian clock is involved in sensing the time as well as in navigation, the division of labor, and the bees' dance language. The movements used to communicate about the location of nectar sources would be unintelligible to nest mates if a bee had a faulty sense of time.
Young adult bees, newly emerged from their pupal stage, typically engage in behaviors associated with tending the larvae in the brood combs, and the larvae are hungry around the clock with no particular sleep-wake cycle, not unlike human newborns. Like the babies, the nursing workers do not exhibit circadian rhythms, but they acquire them as they age and integrate into the light-dark cycle of the nest. The older adult workers, the foragers, have strong cycles, based on the daily clock, that are tuned to cycles of pollen and nectar production. Guy Bloch and a team of researchers, using the honey bee genome sequence, identified a core group of "clock" genes that is responsible for circadian rhythms in honey bees. Interestingly, they found that the expression of the clock genes in the honey bee was more similar to the pattern in a mouse than in a fruit fly.
The significance of this finding raises lots of new questions to be explored about the evolution of timekeeping behaviors. Why is clock gene expression in bees more similar to the expression in a mammal than in another insect? In what other ways are insects like mammals, and what does this tell us about the evolutionary conservation of molecules in various animals? Future research will undoubtedly explore questions like these.
The development of circadian rhythms in honey bee foragers is connected to the regulation of one of the clock genes, the period gene, well known for its role in circadian rhythms. Because the level of expression of this gene varies between nurses and foragers, we know that at least part of a bee's biological clock is associated with her social role in the environment of the nest. In recent research from the Hebrew University of Jerusalem by Yair Shemesh, Mira Cohen, and Guy Bloch, using a technique regularly used to study bee behavior and physiology, the researchers manipulated the social conditions in the nest by creating a colony of bees that were all the same age.
In a process that is not well understood, some young bees adopt the behavior of the normally older foragers. Shemesh and coauthors found that the nurse bees could show sensitivity to activity cycles set by daylight when their social setting required it. They also found that the levels of gene expression in three other clock genes were lower or totally suppressed in nurses as compared to behaviorally cyclical foragers. This behavioral flexibility in the bees' circadian rhythms is associated with the organization of the internal clock on the molecular level.
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