Larval development under continuous and dynamic light pollution alters sexual dimorphism in a moth species

Abstract Larval development under artificial light at night (ALAN) can affect adult body mass, often in a sex‐specific way. However, it is still unclear whether ALAN also affects other morphological traits. In this experimental study, we tested for differences in flight and fecundity‐related morphology and wing melanization in the noctuid moth Agrotis exclamationis , originating from populations under contrasting skyglow levels, and whose offspring were reared under either a dynamic ALAN, continuous ALAN or control dark treatment. In response to ALAN, adult body mass and wing size were affected in a sex‐specific way, resulting in altered sexual‐size dimorphism. Wing aspect ratio was lower in populations originating from higher skyglow levels, but only in males. Under ALAN conditions, relatively more mass was allocated to the abdomen and less to the thorax. Sexual colour dimorphism was stronger in populations originating from higher skyglow levels as males from these populations had lighter coloured wings and females had darker wings compared to populations from lower skyglow levels. We provide evidence for alterations of sexual dimorphism under ALAN. Different developmental effects of ALAN on males and females are likely to contribute to the significant though complex impacts of this type of sensory pollution in a wider range of moth and other insect species.