Flight behaviour diverges more between seasonal forms than between species inPierisbutterflies

Abstract

AbstractIn flying animals, wing morphology jointly evolves with flight behaviours. Whether seasonal polymorphism in butterfly wing morphology is linked to divergent flight behaviour is however not known. Here we compared the flight behaviour and the morphology between the spring and the summer forms of two closely related, temperate species,Pieris napiandP. rapae. We first quantify three-dimensional flight behaviour by reconstructing individual flight trajectories using stereoscopic high-speed videography in an experimental cage. We then measure wing size and shape characteristics assumed to influence flight behaviours in butterflies. We show that seasonal, but not interspecific, differences in flight behaviour might be associated with divergent forewing shapes, either elongated or rounded wings. InPierisspring forms, individuals are small and have elongated forewings, which are significantly correlated with low speed and acceleration, but with high flight curvature. LargePierissummer individuals exhibit rounded forewings, which are correlated with high flight speed, turning acceleration, and advance ratio. We interpret such results as potentially adaptive flight behaviours inPieris. Curvy flight trajectories in the spring forms may be a specialised foraging behaviour evolving in response to newly emerging feeding and oviposition resources. In contrast, the summer forms’ high flight speed and flight efficiency may be advantageous for dispersal to new habitats. Further, the recorded higher acceleration capacities of the summer form could have evolved in response to higher predation pressure. Our study provides quantitative evidence of divergent flight behaviours between seasonal forms ofPierisbutterflies correlated with differences in wing morphology. Seasonal flight behaviour could be adaptive, possibly driven by the interaction of various seasonal selection pressures, including resource distribution (nectar and larval food plants), predator and parasitoid pressure, and thermoregulation.