Genetics of wing size asymmetry in Drosophila buzzatii

Abstract

Abstract Contemporary approaches that use fluctuating asymmetry (FA) as a possible target for natural and sexual selection are based on the premise that FA is a quantifiable expression of developmental instability (DI) that is inherited. Previous work with Drosophila buzzatii found that male mating success was correlated positively to body size (wing length) and negatively to FA, but these relationships seem to be environmentally induced. Heritability of FA was low and not significantly different from zero, but statistical power was also estimated to be very low and, hence, no conclusive evidence could be obtained. A large half-sib mating design is used here to examine the relationships of different aspects of development for wing size. Consistently with previous findings, I found high heritabilities for wing length (WL) and wing width (WW), and positive correlations between both traits. Heritabilities of FA (FAWL, FAWW) were low (0.037) but significantly different from zero, and the genetic correlation between FAWL and FAWW was estimated as −1 because the absolute value for the genetic covariance was similar in magnitude or even larger than the estimated genetic variances of both traits. This suggests that these two traits should be considered to be the same character. The between-trait phenotypic correlation in FA, which reduces to the repeatability in this situation, was positive and statistically significant thus rendering an estimate of heritability for DI in D. buzzatii of . Nevertheless, the fact that left/right wing sizes were found to be determined by the same set of genes is difficult to reconcile with the presence of special genetic mechanisms that stabilize left/right development in this species. A qualitatively different pattern for asymmetry was observed when the nonlinear composite character wing area (WA ≈ WL × WW) was used, and . Although the results could be made compatible with the existence of a diallelic locus with antagonistic pleiotropic effects on FAWL and FAWW that combine multiplicatively to produce overdominance for FAWA, the available evidence is extremely weak at best. Finally, a test to the null hypothesis of a nongenetic basis of FA, particularly relevant to those situations when directional asymmetry may be heritable, is suggested.