Phenotypic variability of natural populations of an invasive drosophilid, Zaprionus indianus, on different continents: comparison of wild-living and laboratory-grown flies.

Phenotypic variability in nature is the most important feature for Darwinian adaptation, yet it has been rarely investigated in invasive species. Zaprionus indianus is an Afrotropical drosophilid species that have recently invaded the Palearctic and the Neotropical regions. Here, we compared the variability of three size-related traits and one meristic trait the sternopleural (STP) bristle number, between wild-collected flies living under different conditions: a stressful Mediterranean environment in Egypt, and a benign tropical environment in Brazil. From each population, a F(1) generation was also grown under the stable conditions of the laboratory. Variability of size in nature had a variance 13 times greater than in the laboratory, but not affected by different climates. By contrast, STP variability was identical in nature and in the laboratory. Sexual dimorphism was also investigated with contrasting results between traits. It is suggested that the very high invasiveness of Z. indianus might be related to a better capacity to survive adverse conditions.