Wing shape heritability and morphological divergence of the sibling species Drosophila mercatorum and Drosophila paranaensis

The fruit-flies Drosophila paranaensis and Drosophila mercatorum pararepleta are sibling species belonging to the repleta group. Females of these two species are normally considered to be morphologically indistinguishable while males only differ consistently in the morphology of their genitalia. These species are sympatric throughout a large area of their geographic distribution. In this study, we investigated the degree of morphological divergence between D. paranaensis and D. mercatorum pararepleta based on morphometric analysis of their wings. The ellipse method was used to describe the placement of the longitudinal and transversal wing veins as well as the size of the wing and the shape of its outline. The heritability under laboratory and field conditions was also estimated from the parameters generated. Multivariate analysis showed that wing morphology possessed sufficient differences to discriminate between the two species with a successful classification rate of 95-98% for females and 82-87% for males. The results of the autoclassification were confirmed by a cross-validation test for females (92-96%). Most measurements possessed significant natural heritability (a mean of 0.48 for D. mercatorum and 0.88 for D. paranaensis), indicating that the variation observed was related to differences in genes acting additively. The principal difference between the two species was in the placement of the posterior transverse wing vein. However, the pattern of morphological variation in the wings of both species was similar, possibly because of shared restrictions in wing development pathways.