Fluctuating Asymmetry in Drosophila: Hybrids are as Stable as Parents

In most of the animals, as per general body plan there is bilateral symmetry for different morphological traits. However, it may get disturbed in the presence of genetic and environmental stresses which results in either increase of developmental noise or decrease of developmental stability. When bilateral symmetry is disturbed in the organism, it is known as fluctuating asymmetry which is defined as subtle differences between left and right sides of a trait. It is considered as an ability of organisms to cope with genetic and environmental stress during development. Developmental instability is most often estimated by fluctuating asymmetry, the right and left side differences in shape, size or number in a single trait across the population. Thus, fluctuating asymmetry is a pattern of developmental instability resulting from perturbations during development which gives rise to imprecise expression of developmental pathways. Because of this reason, it has been used as a measure of individual quality and also as an indicator of environmental as well as genetic stress. It is interesting to mention that even Aristotle observed the regular patterns of bilateral asymmetries in animals such as crayfish, lobsters, and crabs. Fluctuating asymmetry has been investigated in different species of Drosophila and interesting findings have been reported. In this article, a study is reported which shows that fluctuating asymmetry in two sibling species of Drosophila and their hybrids are similar when different morphological traits were used. Further, the hybrids of D. ananassae and D. pallidosa are as stable as their parents. And also, the effect of hybridization on FA appears to be sex and trait specific.