  Handedness in humans - better performance using either the left or right hand
- is personally familiar, moderately heritable, and regulated by many genes,
including those involved in general body symmetry. But behavioral handedness,
i.e. lateralization, is a multifaceted phenomenon. For example, people display
clockwise or counter-clockwise biases in their walking behavior that is
uncorrelated to their hand dominance, and lateralized behavioral biases have
been shown in species as disparate as mice (paw usage), octopi (eye usage), and
tortoises (side rolled on during righting). However, the mechanisms by which
asymmetries are instilled in behavior are unknown, and a system for studying
behavioral handedness in a genetically tractable model system is needed. Here
we show that Drosophila melanogaster flies exhibit striking variability in
their left-right choice behavior during locomotion. Very strongly biased
"left-handed" and "right-handed" individuals are common in every line assayed.
The handedness of an individual persists for its lifetime, but is not passed on
to progeny, suggesting that mechanisms other than genetics determine individual
handedness. We use the Drosophila transgenic toolkit to map a specific set of
neurons within the central complex that regulates the strength of behavioral
handedness within a line. These findings give insights into choice behaviors
and laterality in a simple model organism, and demonstrate that individuals
from isogenic populations reared under experimentally identical conditions
nevertheless display idiosyncratic behaviors.
