Welcome to a video tutorial on Time-memory in bees:
demonstration that organisms tell 24-hour time.
This tutorial was narrated and produced by Clara Oh, under the guidance of Dr. Ben Sheredos
and Dr. Susan Golden.
Astronomical rhythms direct predictable changes in our world.
For example, each time the earth makes a full revolution around the sun, we experience the
cycling of the seasons,
and as the moon circles the earth, there are regular rhythms of high and low tides.
Life on Earth operates by these rhythms.
Because the earth spins on its axis once every 24 hours, it is responsible for creating the
cycle of light and dark in a day.
As a result, we experience changes in temperatures and light quality throughout the day.
These changes occur in a 24-hour rhythm and in turn mediate important ecological factors,
such as how much of a food source will be available at specific times of the day and
the activity of the food chain that follows.
For example, the leaves and flower petals of some plants open during the day and close at night.
This rhythmic behavior enables plants to produce nutrients from sunlight
while also dictating the type of pollinator that will visit.
The plant accomplishes this feat by matching flower availability with the feeding times
of specific organisms who depend on nectar and pollen as a food source.
It is energetically favorable for organisms to be the most active when their food source
is most readily available.
This is true both behaviorally and at the cellular level, for regulating metabolic processes
at the optimal times of day.
For these reasons, and many others, it is necessary for organisms to be able to synchronize
their behavioral and biological routines with the daily environmental changes that favor
them the most.
So what gives organisms this ability?
An organism’s ability to coordinate its internal physiology and behavior with
environmental rhythms is made possible by what is known as the circadian clock.
Circadian means “about a day” and a rhythm can be described as circadian if
its cycle time, or period, is approximately 24 hours.
These rhythms are not driven directly by the environment, but by an internal clock that
creates the rhythms even when the organism is isolated from daily night-dark signals.
A circadian clock is a molecular mechanism that regulates an organism's daily activities,
including locomotion, sleep-wake cycles, metabolism and more.
The clock is “set” by environmental signals, so that circadian rhythms normally match the
cycles in nature.
Our understanding of our circadian clocks has revealed the importance of getting light
during the day, healthy sleep patterns, and having meals at certain times of the day.
In fact, many diseases have been linked to eating and sleeping at odd hours that disrupt
our circadian system.
However, as central as circadian rhythms are to our biology, their study began by chance
one day in 1906 when physician August Forel noticed something intriguing while having
his morning breakfast on the terrace of his summer home.
Forel observed honey bees coming to sample jam during his family’s designated breakfast
time from 7:30 to 9:30 am.
After several days of having breakfast on the terrace, an overwhelming number of
bees were taking over the Forel family’s meal time.
On the fourth day, Forel decided not to put jam on the table at breakfast to avoid having
to deal with these unwelcome visitors.
However, the same overwhelming number of bees came to inspect the table at the normal breakfast
time, from 7:30 to 9:30 am.
The bees searched all items that had been associated with jam at the same hour on
the preceding days: the plates, glasses, pots, and silverware.
This situation eliminated the possibility of smell attracting the bees to the table.
So if it wasn’t a smell, why were the bees still coming to the table, and at the same
time each day on top of that?
The hive was too far away for the bees to be able to notice the dishware on the table
each morning, and far too many bees were appearing right on schedule for it to have been the
work of a scout bee.
Did this mean that the bees had memorized what time of day food was expected to be on
the table?
Forel believed that “the bee concentrates on the hours of the day when, as its memory
tells it, it can always find something.”
He called this ability a time-memory.
These early observations certainly raised interest in the possibility of organisms possessing
a time-memory, but the question remained as to whether bees truly had an internal time-sense
or if they were using signals from their environment to tell what time of day it was.
Two researchers after Forel, Ingeborg Beling and Max Renner, were responsible for
significantly furthering Forel’s observations.
In 1929, Beling developed a method for training bees on the 24-hour clock.
She gave bees sugar water at a designated feeding place for several days and always
at the same time of day under constant conditions.
This means they were exposed to the same degree of temperature all throughout the days and
the room was kept lit at all times, so there was no distinguishing day from night by these
common cues.
The dish was empty at all other times of the day.
This is what the results of the training looked like.
After a series of training days, the dish was left empty for a day.
The bees’ visiting times were recorded on that day, and it was found that the bees arrived
within or near the training time.
This experiment showed that the bees were not using an external signal to tell the time
of day because all external factors were kept constant during the entire experiment.
This meant that the bees had to have an internal time-keeping mechanism.
Important for showing that no unrecognized daily cue signaled to the bees, Beling also
showed that the bees could not be trained outside of a 24-hour interval.
This finding supported the conclusion of a 24-h based internal clock as the source of
time-memory.
These experiments shifted the view of circadian rhythms from being just a biological
curiosity to being regarded as stemming from internal time-measuring devices.
In 1955, Max Renner wondered if Beling had accounted for other periodic external
factors, such as the gravitation of the sun and moon.
Renner used Beling’s sugar water technique to conduct a definitive experiment.
Renner first trained bees to collect sugar water at a certain time in Paris, then shipped
the bees to test the their behavior in a different time zone!
Renner trained the bees in Paris for several days to collect sugar water from 8:15-10:15 pm
French time in a closed room under constant temperature and light.
After training, the bees were flown overnight to New York.
His hypothesis for this experiment was as follows: “If environmental phenomena
are decisive, [the bees] should come to the test dish either before or after the 24-hour period,
that is, 24 hours minus or plus the difference in time between the two local zones.
If, on the other hand, their punctuality is governed by an internal clock which functions
independently of daily [external] factors, but which maintains its 24-hour rhythm,
they would come to the food as usual, that is, exactly 24 hours after the last training.”
In other words, if the bees’ time-memory ability is dependent on external cues only,
then it would be expected that the bees appear for feeding at the time of day when the environment
in the new test site, in this case New York, is most similar to the environment of the
old test site, in this case Paris.
Meaning that the bees would reset their watches.
However, if the bees’ time-memory ability is managed by an internal clock then the bees
would be expected to appear for feeding at the new test site 24-hours after they last
appeared for feeding at the old test site: in other words, 8:15-10:15 pm French time,
regardless of local time in New York.
Let’s see the results of Renner’s experiment:
When tested in New York, the bees came to the feeding place at 3:00 pm New York time,
which is 24 hrs after the last feeding in Paris.
No bees appeared at 8:15-10:15 pm New York time.
To double-check his results, Renner then trained the bees on a new feeding schedule in New York,
and then flew them back to Paris.
Again, the bees appeared 24 hours after their last feeding time, showing that they kept
time using an internal clock.
This experiment confirmed that the time-sense of bees is able to function independently
of daily external factors.
The significance of having a time-memory ability has been demonstrated time and again.
The internal circadian time system of bees enables them to remember times when flowers
are open: the plants being organisms who also operate on a circadian schedule.
This ability persists even when predictable environmental cues change, such as light and
temperature changing with the seasons.
Plants and animals all respond indirectly to the cycles in their environment induced
by the rotation of the earth, through the setting of their clocks.
The circadian clock allows organisms to establish daily routines and use their energy to their favor.
When an organism is isolated from all environmental time cues—such as light and temperature
being held constant—these rhythms still operate within the organism.
So even though the development of a mechanical tool to measure time was undoubtedly an enhancement
to the human way of life, it turns out that a 24-hour clock is actually an innate part
of biology, from plants to bees to humans.