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

The establishment of laboratory populations provides an opportunity to document rapid phenotypic changes across generations, although the processes underlying these changes may be difficult to disentangle. Using geometric morphometrics, we investigated changes in wing size and shape in the Neotropical drosophilid Drosophila sturtevanti. We compared field-collected males (Field) with descendants from 12 isofemale lines established independently from field-collected females, in the first (F1) and tenth (F10) laboratory generations. Wing size showed heterogeneous responses in F1, followed by a consistent reduction across all lines by F10, possibly reflecting differences among founders and developmental conditions, including larval density and temperature. Wing shape changed significantly in every line between Field and F1 and between F1 and F10. Changes in wing shape followed broadly similar directions from Field to F1 but became more heterogeneous among lines from F1 to F10. Total shape variance increased significantly between Field and F1. Within-line shape variation was not significantly lower in F1 or F10 than the variation observed in Field, while between-line shape variance increased from F1 to F10. These patterns are consistent with the possible expression of previously cryptic genetic variation following environmental change and the exposure of phenotypic effects of pre-existing genetic variation as homozygosity increases within isolated lines. Our results demonstrate that substantial morphological changes can be detected within the first laboratory generation and continue during subsequent maintenance, highlighting the potential of geometric morphometrics of insect wings for documenting rapid phenotypic change.