Molecular Genetics of Insect Behavior - Insect Molecular Genetics - page 476

important in associative learning. The conditioned stimulus must be presented
before the unconditioned stimulus, and the unconditioned stimulus must follow
the conditioned within a relatively brief interval. It was thought that the per +
gene could be involved in learning, based on the observation that males with
the per L allele in one experiment did not exhibit normal experience-dependent
courtship behavior. However, males with the wild type per + or the per S and per 0
alleles could be conditioned normally ( Gailey et al. 1991 ).
Although the above-described analyses of Drosophila circadian behavior have
informed us about the genetics of circadian rhythms, Vanin et al. (2012) discov-
ered that the behavior of flies under natural conditions is different from that
observed in artificial laboratory conditions with constant temperatures and
light-dark cycles without dawn- or dusk-lighting regimes. Vanin et al. (2012) rec-
ommended that studies of circadian rhythms be conducted in the future using
more-natural temperature and light regimes in the laboratory. Under artificial
laboratory conditions, where lights were either on or off, flies anticipated lights
turning on by increasing their locomotor activity about two hours before that
event. However, under field conditions, the flies did not behave in this manner.
In fact, their sleep-wake cycle was quite different when temperature, sunlight,
moonlight, and humidity varied. Instead of sleeping during the middle of the day, as
they did in the laboratory, they became active. Instead of anticipating dawn, they
reacted to changing light during twilight, but did not respond to dawn. In addition,
moonlight had no effect on behavior under field conditions, although it does
under artificial laboratory conditions.
Sandrelli et al. (2008) note that the mammalian genes Clock and Period share
a common evolutionary origin with that of insects, although the mammalian-
clock components consist of multiple gene copies, increasing complexity and
redundancy. They also reviewed what has been learned about circadian clock
genes in insects (Diptera, Lepidoptera, and Orthoptera) other than Drosophila .
Sandrelli et al. (2008) note that peripheral clocks are common in insects and
can be entrained by light in extraretinal photoreceptors, but these have not yet
been studied.
11.5.2 Learning in Drosophila
It is difficult to produce a single definition of learning ( Meller and Davis 1996,
Tully 1996, Waddell and Quinn 2001 ). Learning can be defined as a change in
behavior with experience, but this definition would not exclude responses such
as growth and maturation, or other processes that are triggered by events such as
mating or feeding. Another definition is a reversible change in behavior with