Counteracting selective pressures: Museum collections show declining Aglais io wing size

Hollens-Kuhr, H.; Buchholz, S.

Abstract

Global environmental change is affecting insect biodiversity, yet long‐term morphological responses remain poorly understood. Using museum specimens, we tested whether wing size in the butterfly Aglais io changed over time in north‐western Germany between 1953 and 1984. We measured forewing and hindwing length in 124 specimens from three populations and analysed temporal variation using generalized linear models with year and locality as explanatory variables. Temperature trends were assessed using linear regressions based on regional climate data. Both forewing and hindwing length declined significantly over time (forewing: R ² = 0.58, p < 0.01; hindwing: R ² = 0.51, p < 0.01), with similar patterns across all populations. Only the mean temperature of the warmest month increased significantly during the study period. These results indicate a long‐term reduction in wing size in Aglais io , potentially linked to environmental change. Our study highlights the value of museum collections for detecting subtle morphological trends across decades.