Armoured for battle: amino acids, cuticle toughness, and the outcome of male-male combat in leaf-footed bugs (Coreoidea)

Supervisor: Christine Miller

Project Summary (MPhil):

Male-male combat in insects is rarely a contest of size alone. In leaf-footed bugs and their relatives (superfamily Coreoidea), males wield enlarged hindlegs studded with spines and use them to grapple, crush, and pierce rivals in fights over territory and access to females, sometimes inflicting injuries severe enough to maim or disable a competitor outright. Winning such contests depends not just on having the biggest weapon, but on whether that weapon, and the body that wields it, can withstand the forces of combat without fracturing or puncturing. Amino acids such as tyrosine are key building blocks for cuticle sclerotisation, the cross-linking process that hardens and toughens the insect exoskeleton. This raises a simple but largely untested question: if a developing male does not receive enough dietary tyrosine, does he grow up with a softer, more vulnerable weapon, and does this cost him fights?

This project will answer that question through two complementary, hands-on experiments over the course of an MPhil.

Type of Work:

Project one: manipulating cuticle chemistry through diet. The student will rear young Coreoidea nymphs  on one of two controlled diets: a tyrosine-restricted diet and a tyrosine-supplemented diet, with appropriate control groups. Insects will be reared through to adulthood, allowing the student to assess whether dietary tyrosine availability during development measurably affects weapon growth, cuticle colouration (since tyrosine-derived melanin often darkens sclerotised regions), and overall body condition.

Project two: testing the consequences for fighting and injury resistance. Adult males from each dietary group will be used in two simple, direct assays. First, staged in vivo contests will pit tyrosine-restricted males against tyrosine-supplemented males of matched body size, with fights scored for outcome, fighting duration, and visible injury. Second, cuticle injury resistance will be measured directly in specimens after they die, using a penetrometer, applying controlled, incremental force to the weaponised hindleg (and a non-weaponised control region) to determine the puncture force required to breach the cuticle in each dietary group.

Importance of the area of research concerned: 

Arthropods are the most diverse phylum on Earth, accounting for approximately 90% of animal species. The cuticular exoskeleton has played a vital role in their evolutionary success, but we know surprisingly little about the external factors influencing its development, structure and biomechanical properties. This omission is critical because cuticle is involved in almost every biological function in this massive group of organisms.

References: 

Greenway EV, Woodman T, Emberts Z, Chen S, Federle W, Miller CW. 2026 Adult nutrition strongly affects insect cuticle thickness and injury resistance. Journal of the Royal Society Interface 23: 20250919.Woodman TE, Chen S, Emberts Z, Wilner D, Federle W & Miller CW.  Developmental nutrition affects the structural integrity of a sexually selected weapon. Integrative and Comparative Biology 61: 723-735. Miller CW, Kimball RT & Forthman M (2024). The evolution of multi-component weapons in the superfamily of leaf-footed bugs. Evolution 78: 635–651.