Leslie Griffith, M.D., Ph.D.
Volen National Center for Complex Systems
Brandeis University
Waltham, Massachusetts
March 22, 2004
Sex and the Single Fruit Fly:
Courtship Behavior and Learning
Humans have about 35,000 genes and fruit flies about
13,000, with about 60 percent of the fruit fly’s genes
having a human homologue. Many of these genes conserve
ancient behaviors, including courtship. I have defined
two kinds of learning—non-associative learning, which
is when the animal learns about a particular stimulus
and associative learning, which is a more complicated
process. Fruit fly courtship behavior appears to be
stereotyped, with a pattern that includes the following:
tapping, wing extension, the courtship song, licking,
and copulation. But the fly’s courtship behavior is
also plastic. Associative learning for courtship, prompted
by pheromones for either stimulation or aversion, can
last between hours and days. How does learning alter
behavior? I have noted an increased latency or lag-time
between flies’ meeting and the commencement of courting.
Through a series of careful experiments, I show that
associative courtship learning is mediated by a change
in sensitivity to pheromones. What is the molecular
basis of the change? The calcium-dependent protein kinase
CamKII serves as the molecular switch. Acute inhibition
of this enzyme blocks learning and memory, while increasing
enzyme actions was shown to enhance the fly’s response
during training. This enzyme is critical for setting
sensory thresholds in pheromone-driven learning in fruit
flies. Understanding how the brain forms memories and
learns from the external environment will help scientists
pinpoint what goes wrong in autism.
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