Macronutrient composition and glyphosate-based herbicide interact to influence resource allocation

Exposure to pesticides and variation in food quality are emergent features of environmental change. Therefore, decisions regarding resource acquisition (feeding) and resource allocation (investment into life-history traits) may be key to animals’ success. Here, we examined links among dietary macronutrients, glyphosate-based herbicide (GBH, the most applied pesticide worldwide), feeding, and life-history traits. Wing-dimorphic variable field crickets (Gryllus lineaticeps) were exposed to either GBH or control (tap water) drinking solutions during development and adulthood. Adult females were offered isocaloric diets in one of two experiments: choice (allowed to choose between imbalanced protein [P]-biased or carbohydrate [C]-biased diets), or no-choice (constrained to P- or C-biased diet). Resource acquisition and allocation were then determined during early adulthood. Exposure to GBH did not affect nutrient (P or C) intake targets, but it prioritized soma under good nutritional conditions (choice experiment) and reproduction under poor nutritional conditions (no-choice experiment). Further, the reproductive advantage of the high-P diet was eliminated by GBH exposure. Individuals fed a C-biased diet increased their food consumption, putatively to regulate P intake. Compared to those offered dietary choices, individuals constrained to a single imbalanced diet exhibited a much stronger bias toward investment into reproduction—that is, heavier ovaries, more food converted into ovary mass relative to somatic mass, and reduced investment into flight muscles. Together, our results indicate that feeding, diet quality, and a common pesticide can collectively modulate life-history tradeoffs among investment into reproduction, somatic tissue, and dispersal (flight) capacity.