Introduction
Methods
Results
Conclusion
Each day organisms go through a rhythm of
activities, a routine, involving waking, working, eating, and sleeping
at specific times. When these periods are structured around the 24-hour
period they are referred to as circadian rhythms. These rhythms are
controlled by internal timing mechanisms called biological clocks that
occur in all eukaryotic organisms. Biological clocks are produced
by the suprachiasmatic nucleus in the hypothalamus. Rhythms are normally
synchronized by cues in the surrounding environment. One very important
cue is light. Changes in light are an indicator for most animals
to wake and sleep. It is during this cycle that these animals eat and are
most active. Contradictions between biological clocks and the surrounding
cues cause feelings of fatigue and other psychological problems (Biological
Timekeeping).
The golden hamster, Mesocricetus auratus,
is a nocturnal burrowing mammal. Its biological clock is set up for
activity during the dark hours and inactivity during the light hours.
In this lab we will look at the Mesocricetus auratus in three different
photoperiods and by measuring the daily activity demonstrate the effects
that the surrounding environment will have on their circadian rhythms.
Hamsters exposed to altered photoperiods will
in initially alter behavior, but will readjust after an acclimation period.
I predict that in the beginning all the hamsters will vary in their activity
due to difference in the photoperiods, but after a set amount of time they
will readjust and continue on their normal circadian rhythms.
“Biological Timekeeping”. Journal of Neuroendocrinology, Oct2000, Vol. 12 Issue 10, p935.
There will be six hamsters
divided up into three aquariums. One group will be the control group;
B, and the other two groups will the variable groups; A and C. The
hamsters will all be under normal conditions for one week to develop a
set pattern for each group. The will be on three different photoperiod
cycles for thirty days with each cycle balanced during the day, (light:dark):
LIGHT
DARK
Group A: 4:20 cycle
7am 8 9 10 11 12pm 1 2 3 4 5 6
7 8 9 10 11 12am 1 2 3 4 5 6 7am
Group B: 12:12 cycle
7am 8 9 10 11 12pm 1 2 3 4 5 6 7
8 9 10 11 12am 1 2 3 4 5 6 7am
Group C: 20:4 cycle
7am 8 9 10 11 12pm 1 2 3 4 5 6 7 8 9 10
11 12am 1 2 3 4 5 6 7am
To achieve the photoperiod cycles, the aquariums
will be placed in a box with a nightlight in it. The nightlight will
be attached to a timer that will turn the light on and off.
There will be a hamster wheel with a digital
counter will be placed in each aquarium to record the daily activity of
the hamsters. These results will be recorded each day at 7am and
7pm. The actives from the wheels will be recorded and analyzed using
averages, standard deviations, and t-tests to determine if there is a significant
difference between the three groups.
The following tables and graphs
illustrate the results discovered from this lab. The table shows
the data recorded each day and the calculations for average, standard deviation,
and t-tests. The 30 days that the hamsters were under cycles was
divided in to 10-day increments.
A t-test was computed within
each group between the 1st and 2nd 10 days, the 2nd and 3rd 10 days, and
the 1st and 3rd 10 days. For group A, 4:20 (L:D), there was no significant
difference between the 1st and 2nd 10 days; however there was a significant
difference between the 2nd and 3rd 10 days as well as the 1st and 3rd 10
days with p-values of .17, 2.7x10-4, and .001 respectively for the 7pm
–7am hours. Additionally the results were the same for the 7am-7pm
hours with p-values of .12, .02, and 3.2x10-3 respectively.
Within group B, 12:12, there was no significant difference between any
of the day divisions with p-values of .50, .82, and .46 respectively for
7pm-7am, and p-values for 7am-7pm of .66, .18, and .09 respectively.
Group C, 20:4, showed no significant difference with in the 7pm-7am hours
between the 1st and 2nd 10 days as well as the 2nd and 3rd 10 days with
p-values of .15, and .55 respectively; however there was a significant
difference between the 1st and 3rd 10 days with a p-value of 3.2x10-4.
Additionally there was no significant difference between any of the day
divisions for the 7am-7pm hours with p-values of .14, .76, and .08 respectively.
T-tests were also calculated
for the different day divisions between the control group and the variable
groups. For the 1st 10 days neither of the groups showed any differences
between them, with p-values for the 7pm-7am hours of 1.4x10-7 for A&B,
and 5.9x10-3 for B&C, and with values of .01 and .03 respectively for
the 7am-7pm hours. For the 2nd 10 days in the 7pm-7am hours there
was no difference between A&B with a value of 6.1x10-7, however there
was a difference between B&C with a value of .76. As for the
7am-7pm hours there was no difference for A&B with .12, but for B&C
there was a difference with a value of 2.8x10-4. Lastly, during the
3rd 10 days there was no difference between A&B with .07, but there
was a difference between B&C with a value of .05 for the 7pm-7am hours.
The results were the same for the 7am-7pm hours with values of .77 and
6.0x10-5 respectively.
The first graph shows a representation
of the total activity per day. It illustrates the increase and decrease
of activity for each group during the 30 days. The second and third
graphs illustrate the averages and standard deviations for the groups divided
into 10 days increments.
Based on the results of this
lab I can conclude that altered photoperiods have an effect on the daily
activities of the hamsters. My predictions were correct and proven
by the results.
Group A, 4:20, altered their
behavior, but towards the end of the 30 days readjusted to normal activity.
For this group I looked heavily at the 7am-7pm hours. As nocturnal
mammals, hamsters should sleep during these hours, but when introduced
to a different photoperiod they altered their activity and were more active
than the norm. The t-tests confirm that they resumed their normal
activity by the end of the 30 days. With a p-value of .12 between
the 1st and 2nd 10 days shows that there was a difference, however between
the 2nd and 3rd 10 days there was no difference with a value of 3.2x10-3.
To tell that the hamsters returned to their normal cycles I had to look
at the difference between this group and group B, the control group.
For the first 10 days there was a significant difference with a p-value
of .01, and by the end of the 30 days there was no difference between group
C and the norm with values of .12 and .77 respectively.
The outcome for group C, 20:4,
was the opposite of what was expected. They did differ from the norm,
but in the opposite way of what should happen to nocturnal mammals when
offered more light. For this group I looked heavily at the differences
between this group and the control, group B during the 7am-7pm hours.
For all three 10-day increments there was a significant difference with
p-values of .03, 2.7x10-4, and 6.0x10-5 for the 1st 10 days, the 2nd 10
days and the 3rd 10 days respectively. However, this group did not
return to complete normal activity after the 30 days. During the
7pm-7am hours the hamsters returned to normal activity with a p-value of
3.2x10-4 between the 1st and 3rd 10 days, but they did not reach normal
activity during the 7am-7pm hours with a value of .07. I do believe
though that given extra time group C will reach normal activity since the
p-values decrease as you move further away from the start of the 30 days.
By looking at these two outcomes
I can say with some certainty that hamsters in altered photoperiods will
alter their activity, but will resume normal activity after a set amount
of time. However, I do feel that more tests need to be run for a
more exact answer to this hypothesis. I also feel that given more
time the hamsters will all have returned to normal activity.