The Scar of Rebuilding: Limb Regeneration Triggers Asymmetric Melanisation and Developmental Trade-Offs

Abstract

Melanisation is a key insect immune response activated by injury, yet its role as a long-term indicator of regeneration costs is unclear. This study examined whether limb regeneration in the ladybird beetle (Cheilomenes sexmaculata) leads to persistent immune investment, seen as increased cuticular melanisation, and what trade-offs emerge. Larvae amputated in each instar showed that regeneration triggered a systemic immune response, with significantly elevated melanisation specifically on the contralateral elytra. This was accompanied by prolonged development and, after fourth-instar amputation, larger elytra size. These findings reveal that regeneration imposes organism-wide costs, permanently altering immune status, development, and morphology, with melanisation serving as a visible signature of these physiological trade-offs.