Drosophilid species (Insecta, Diptera) in the Brazilian savanna are more symmetric in the dry season

Abstract

The development of an organism is a controlled process, which can be disrupted by genetic or environmental stress. Although fluctuating asymmetry is widely used as an indicator of developmental instability, its effectiveness has been questioned due to the contradictory results produced by this technique which, at least in part, probably reflects methodological inappropriateness. Here, we investigated if wing asymmetry of drosophilids increases when they develop during the dry season in the Brazilian savanna, considered a stressful season for these insects. Using protocols designed to avoid methodological problems, we analysed the wings of Zaprionus indianus and three species of the genus Drosophila (D. mercatorum, D. simulans, and D. sturtevanti). Surprisingly, the flies were more asymmetrical in the rainy season than in the dry season, although this difference was not always significant. It is suggested that the wings of these insects are submitted to strong natural selection throughout the dry season, when the asymmetric individuals would have less chance of surviving. During the wet season, on the other hand, selective pressures would be more relaxed. Therefore, the results of this study suggest that asymmetry of the wings is not a good indicator of natural environmental stress in drosophilids. Future research should focus on selectively neutral characters.