In an earlier family-line study in 2006,
designed to look for an association between Dca
allelic variation and cold tolerance, we measured wing size because this trait
is long established as showing a relationship to both the thermal environment
and latitude, and because genes determining size variation map close to Dca on the right arm of chromosome
three. We found a highly significant association between wing size and Dca genotype. This observation was
repeated in 2007 on an independently collected and derived set of family lines.
The genotypes occurring at high frequency at cool-temperate latitudes
associated with larger wing length, as would be expected if Dca contributed in a causal way to the
wing-size cline. To test for a casual effect of Dca expression level on wing and body size we measured these traits
in crosses designed to over-express Dca, using
our UAS-GAL4 transformed lines. To our surprise the F1 line over-expressing Dca had shorter wings than the parental
and control lines, strongly suggesting a causal effect. Interestingly, no
effect of expression occurred for thorax length, a result consistent with the
idea that the latitudinal cline previously established for wing/thorax length
ratio could be under-pinned by allelic variation in the Dca gene. These are exciting results since recent data indicate flies with a high wing/thorax ratio
are more successful and moving longer distances to locate resources in field
release experiments, independently of ambient temperature – a trait that may be
ecologically important in some climatic regions but not others. We will follow
up on this idea, and on testing for Dca expression
differences between Dca genotypes
that vary clinally, over the next year.