Evolution, development, and aerodynamics of wing morphology in the genus Drosophila

Abstract

The evolution of wing morphology in three clades of Drosophila was investigated using a method of mapping a complex of continuous characters developed for landmark configurations. In the melanogaster subgroup, a rate test for morphological characters was applied using the mutation-drift equilibrium (MDE) model under a range of evolutionary scenarios. The results indicate that wing morphology has evolved at a slower rate than genital morphology. The rate test under the MDE model suggested that genital morphology has evolved at a neutral rate while wing morghology has been under stabilizing selection. In the cactophilic species of the repleta group endemic to the Sonoran desert, wings have evolved in response to two factors: adaptation to the density of rots in the host cacti and adaptation to Sonoran desert conditions. Aerodynamic parameters of the wing were calculated based on a steady-state aerodynamic model. Flies using larger host cacti tend to have wings of greater aspect ratio which are better suited for long range dispersal. Flies adapted to Sonoran desert conditions tend to have wings with broader bases and narrower tips, suggesting greater efficiency at fast forward flight. The evolution of wing pigmentation patterns in the Hawaiian picture-winged Drosophila was examined in a phylogenetic context. Four specific hypotheses were tested: (1) has the overall degree of pigmentation evolved from more lightly to more heavily pigmented wings; (2) has the evolution of pigmentation patterns proceeded through a process of elaboration resulting in patterns of greater complexity; (3) are the fundamental symmetries in pigmentation pattern the same for all species in this group; and (4) are the patterns of symmetry related to what is known about wing development in Drosophila melanogaster? The pattern of evolutionary changes in the level of pigmentation was not consistent with a hypothesis of gradual increase. Based on a measure of complexity derived from Shannon's information content, there is no compelling evidence to support the hypothesis of evolutionary elaboration of pattern. There is evidence for one major evolutionary shift in the pattern of symmetry. A model linking fundamental symmetries in pigmentation pattern to wing development is presented.