Biology Reference
In-Depth Information
The truth is rarely pure and never simple.
Oscar Wilde (1854-1900)
The rotation of the Earth produces the cycles of day and
night that are of immense importance to all living
organisms. Organisms that can anticipate these daily
rhythms and adapt to them have a selective advantage.
For example, the leaves of certain plants alternate
between horizontal daytime and vertical nighttime
positions, efficiently harvesting light during the day and
protecting against radiative cooling at night. Many small,
otherwise defenseless animals are largely nocturnal,
sleeping during the day when sharp-eyed carnivores are
active. Many desert-dwelling animals are also nocturnal,
avoiding the daytime's intense heat and desiccating air.
Most birds are diurnal, active and feeding during the day
and returning to their roosts at night.
Chapter 11
DETECTING RHYTHMS
IN CONFOUNDED
DATA
These daily biological cycles lasting approximately 24
hours are called circadian rhythms—from the Latin circa
(about) and dies (day). A fascinating example of the
importance of understanding circadian rhythms comes
from the field of parasitology. Elephantiasis, a disease
marked by the enormous swelling of parts of the body, is
usually caused by the filarial worm Wuchereria bancrofti.
This worm lodges in lymphatic vessels and hampers the
return of lymph to the circulatory system, causing
edema and swelling. The larvae of W. bancrofti, called
microfilariae, exhibit a circadian rhythm with regard to
their appearance in the bloodstream. In Africa, Asia,
and parts of South America and the Caribbean, the
microfilariae are present in large numbers during the
night, but absent from the bloodstream during the day.
The microfilariae of the South Pacific strain of
W. bancrofti, on the other hand, are present in the
bloodstream in the greatest numbers during the afternoon
(Fontes et al. [2000]). Because the disease is diagnosed by
observing microfilaria in a blood smear, these findings
indicate the importance of knowing when to draw blood
samples for testing.
Biological Clocks
Example: Simulation of the Effects of
SCN Ablation and Transplantation on
Free-Running Locomotor Activity
Fundamentals of Rhythmic Data
and Time Series
Data Preprocessing Strategies
Methods for Rhythm Analysis
and Analytical Strategies
Preprocessing Before Analysis
Example Analysis: Simulation of the
Effects of SCN Ablation and
Transplantation on Free-Running
Locomotor Activity
Internal timekeeping mechanisms, often called biological
clocks, are what give organisms the ability to anticipate
such periodicities. By far, the best-studied of these
biological clocks are those responsible for circadian
rhythms. Circadian rhythms provide a survival
advantage, and organisms with no circadian rhythms, or
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