hat genetic changes underly the evolved
differences in behavior between related strains and species? A number
of classic fly behavior papers (Dobzhansky et al., 1974; Levene et
al., 1976) showed that natural populations of Drosophila pseudoobscura
could be artificially selected for positive and negative phototaxis over a small
number of generations.
This genetic plasticity likely has mediated the strain and
species-level differences in phototaxis we have observed using a number of assays.
We are currently using quantitative trait
localization to identify the genetic loci responsible for the behavioral
differences between several pairs of Drosophila species and strains.
hat underlies the behavioral differences between genetically identical individuals?
One can consider behavioral diversity at a number of scales. Arthropods may on
average behave differently than vertebrates - sister species differ behaviorally
either by drift or selection for mating isolation - the behavior of strains within
a species may vary due to differential allelic frequencies or phenotypic plasticity -
and genetically identical siblings display non-heritable behavioral differences. In
humans, this is called personality.
We have found that even in isogenized stocks of fruit flies, individuals display
idiosyncratic behaviors in a number of paradigms. In all strains tested, whether they
prefer on average to run toward light or darkness when startled, some individuals are more
photo-positive or photo-negative than their clonal siblings. While not showing a
species-level bias, individual flies prefer to choose either left or right turns in
branching mazes. These idiosyncrasies are not heritable, but last the lifetime of the
flies, and therefore constitute a form of personality.
s there a basic behavioral vocabulary?
The modularity of developmental signaling pathways appears to be
essential for the generation of diverse animals forms through evolution by natural
selection. Rather than evolve new genes and signaling pathways to generate a wing
or antenna from scratch, it is sufficient to reuse the modular signaling pathways
that generate limbs, particularly since each insulated pathway typically controls
an independent physical parameter of development, such as limb length, width, or
number of segments. Could behavioral modularity be analogously utilized in the
generation of behavioral diversity?
We are addressing this question using dimension-reducing analytic methods on
high-resolution temporal and spatial data of single flies performing spontaneous
walking behavior on floating balls.