Limited thermal plasticity and geographic divergence in the ovipositor of Drosophila suzukii

Phenotypic plasticity has been repeatedly suggested to facilitate adaptation to new environmental conditions, as in invasions. Here we investigate this possibility by focusing on the worldwide invasion of Drosophila suzukii : an invasive species that has rapidly colonized all continents over the last decade. This species is characterized by a highly developed ovipositor, allowing females to lay eggs through the skin of ripe fruits. Using a novel approach based on the combined use of SEM and photogrammetry, we quantified the ovipositor size and 3D shape, contrasting invasive and native populations raised at three different developmental temperatures. We found a small but significant effect of temperature and geographic origin on the ovipositor shape, showing the occurrence of both geographic differentiation and plasticity to temperature. The shape reaction norms are in turn strikingly similar among populations, suggesting very little difference in shape plasticity among invasive and native populations, and therefore rejecting the hypothesis of a particular role for plasticity of the ovipositor in the invasion success. Overall, the ovipositor shape seems to be a fairly robust trait, indicative of stabilizing selection. The large performance spectrum rather than the flexibility of the ovipositor would thus contribute to the success of D. suzukii worldwide invasion.