Macronutrient Balance Modulates the Temperature-Size Rule in an Ectotherm

Area of Science:

• Ecology
• Nutritional Physiology
• Insect Biology

Background:

• The temperature-size rule (TSR) describes ectotherms maturing larger at colder temperatures.
• Existing TSR hypotheses lack a nutritional perspective.
• Dietary composition's role in TSR remains understudied.

Purpose of the Study:

• Investigate how dietary protein:carbohydrate (P:C) balance affects the TSR in Spodoptera litura.
• Determine if nutrient imbalances modify the thermal reaction norm for body size.
• Explore the role of nutrient selection in modulating temperature-body size relationships.

Main Methods:

• Fed final-instar Spodoptera litura caterpillars controlled diets varying in P:C ratio.
• Analyzed the thermal reaction norm for body size under different dietary conditions.
• Assessed changes in body lipid storage and nutrient preference at varying temperatures.

Main Results:

• Dietary P:C balance significantly altered the slope of the thermal reaction norm for body size.
• A balanced diet resulted in a near-flat slope, while imbalanced diets (especially excess carbohydrates) yielded negative slopes.
• Temperature-driven shifts in caterpillar preference for carbohydrates helped buffer body size changes.
• Nutrient-dependent effects on body size were primarily linked to changes in lipid storage.

Conclusions:

• Macronutrient balance is a critical factor modulating the temperature-size rule in ectotherms.
• Nutrient selection behavior can buffer the impact of temperature on body size.
• This study offers a novel nutritional framework for understanding the TSR.