Rapid wing size evolution in African fig flies (Zaprionus indianus) following temperate colonization.

Invasive species often encounter novel selective pressures in their invaded range, and understanding their potential for rapid evolution can offer insight towards evolutionary processes and the factors that drive invasion success. Zaprionus indianus is an invasive drosophilid native to Africa that reached Florida in 2005 and likely re-establishes temperate North American populations each year. We addressed two evolutionary questions in this system: first, do populations evolve phenotypic changes in the generations immediately following colonization of temperate environments? Second, does Z. indianus evolve directional phenotypic changes along a latitudinal cline? We established isofemale lines from wild collections and measured twelve ecologically relevant phenotypes, using a reference strain as a control. Z. indianus evolved smaller wings following colonization, and we found evidence of significant post-colonization evolution when considering all phenotypes simultaneously. We found little evidence for latitudinal clines. However, we documented substantial laboratory evolution and large effects of the laboratory environment across multiple phenotypes, emphasizing the importance of controlling for both possibilities in common garden studies. Our results demonstrate the potential for rapid evolution in Z. indianus, which could contribute to its ongoing expansion, and offer insights towards the types of rapid evolutionary changes that might occur in invasive insects.