Rapid changes in wing size and shape during the transition to laboratory conditions in a Neotropical drosophilid

Laboratory environments can induce rapid phenotypic changes, but the earliest responses of natural populations to laboratory conditions remain poorly understood. Using geometric morphometrics, we investigated changes in wing size and wing shape in the Neotropical drosophilid Drosophila sturtevanti. We compared field-collected males (G0) with descendants from 12 lines each established from a single female from the same native population in the first (F1) and tenth (F10) laboratory generations. Wing size showed heterogeneous responses in F1, followed by a consistent reduction by F10, possibly reflecting differences among founder females and larval density. Wing shape changed significantly in every line between G0 and F1 and between F1 and F10. Total shape variance increased significantly between G0 and F1. Within-line shape variation was not significantly lower in F1 or F10 than the variation observed in G0, while between-line variation increased as the lines diverged. These patterns are consistent with previously cryptic variation becoming expressed following environmental change, together with founder effects, drift and increasing homozygosity. Our results show that substantial morphological changes can arise within a single laboratory generation, challenging the assumption that F1 individuals provide an unaltered representation of natural populations.