Quantitative Trait Loci responsible for variation in sexually dimorphic traits in Drosophila melanogaster. R.M. Graze 1, A. Kopp 2, S. Xu 3, S.V. Nuzhdin 1. 1) Section of Evolution and Ecology, University of California Davis, Davis, CA 95616; 2) Howard Hughes Medical Institute and Laboratory of Molecular Biology, University of Wisconsin - Madison, Madison, WI 53706; 3) Department of Botany and Plant Sciences, University of California at Riverside, Riverside, CA 92521.
In many groups of animals, sexually dimorphic characters can differ dramatically among closely related species, suggesting that these characters evolve at a faster rate than most other morphological traits. Presumably, interspecific differences in secondary sexual traits evolve as a result of divergent selection on genetic variation present in natural populations. Unfortunately, little is known about intraspecific variation for sexually dimorphic characters.
We have combined our knowledge of Drosophila development with a quantitative genetic approach in an attempt to identify genes responsible for variation in sexually dimorphic traits. D. melanogaster owes its name to the male-specific dark pigmentation of the last two abdominal segments. This pattern is controlled by the bab gene, which in turn is jointly regulated by dsx and the homeotic gene AbdB. In females, bab expression in the abdomen is required to prevent the development of male-specific pigmentation. In males, bab is repressed by AbdB in posterior abdominal segments, allowing dark pigmentation to develop. In other Drosophila species, the pattern of bab expression in the abdomen correlates with the presence or absence of dimorphic pigmentation, suggesting that changes in bab regulation have played a key role in the evolution of this trait.
We mapped QTLs for female abdominal pigmentation segregating in a natural population, and show that most of this variation is accounted for by segregation of at least 3 alleles positioned at the tip of 3L. We use quantitative complementation tests to show that these alleles are natural variants of bab.