Hatchling morphology and adaptation to host plants during juvenile stages in the butterfly Pieris napi

Abstract

AbstractThe adaptations of young insect larvae to factors causing mortality may not depend on whole‐body size but may instead depend substantially on the size of specific body parts. Using two closely related plant species, Arabis flagellosa, which has leaves that are tougher and difficult to digest, and A. gemmifera, which has leaves that are softer and difficult to convert, we showed that larvae of the butterfly Pieris napi exhibit specific adaptations through changes in body‐part size based on different traits of their host plants. For a given egg size, the head widths of hatchlings from eggs collected from A. flagellosa were significantly larger than those of hatchlings from eggs collected from A. gemmifera. In addition, larger heads were accompanied by smaller abdomens in hatchlings originating from A. flagellosa, whereas the opposite pattern was observed in hatchlings from A. gemmifera. The time to completion of the first feeding on leaves of A. gemmifera was not affected by either egg or head size regardless of the original food plant. However, the time to completion of the first feeding on A. flagellosa decreased with increasing head size of hatchlings, regardless of the original food plant. Furthermore, even though egg sizes did not differ between treatments, larvae originating from A. gemmifera and A. flagellosa exhibited similar weight gain on leaves of A. flagellosa, whereas larvae originating from A. gemmifera gained more weight than larvae from A. flagellosa when reared on leaves of A. gemmifera. These results suggest that selection in young larvae for adaptations to environmental conditions may operate on specific larval body‐part sizes.