Developmental Nutrition Affects the Structural Integrity of a Sexually Selected Weapon.

Area of Science:

• Evolutionary Biology
• Animal Behavior
• Insect Physiology

Background:

• Sexual selection drives the evolution of animal weapons for combat.
• Weapon size is known to be nutrition-dependent, but other attributes' sensitivity is less understood.
• Narnia femorata males use spiny hind legs as weapons in fights for mating access.

Purpose of the Study:

• To investigate how natural dietary variation affects weapon structural integrity in Narnia femorata.
• To assess the influence of cactus fruit phenology on weapon size and puncture resistance.
• To determine if nutrition affects weapon performance beyond just size.

Main Methods:

• Examined Narnia femorata adults from two cohorts (June and July) feeding on ripening prickly pear cactus fruit.
• Compared weapon size and puncture resistance between insects fed early green fruit, mature green fruit, and ripe red fruit.
• Analyzed the relationship between body size, cuticle properties, and weapon structural integrity.

Main Results:

• Insects fed mature green fruit had significantly larger weapons (71% increase) and higher puncture resistance (4.4x) than those fed early green fruit.
• Insects fed ripe fruit showed moderate size and high puncture resistance, with minimal phenotypical change between cohorts.
• Increased weapon structural integrity correlated with larger body size and superior nutrition, with effects on puncture resistance independent of size.

Conclusions:

• Cactus fruit phenology strongly influences Narnia femorata weapon development and performance.
• Nutrition affects weapon structural integrity and puncture resistance, with effects that can transcend body size.
• Weapon size may be an unreliable indicator of fighting performance when nutritional conditions vary.