Water stress is one of the most significant challenges limiting insect survival and reproduction. To cope with water-limited environments, insects have developed various mechanisms, such as depressing metabolic rate to reduce water loss or increasing the consumption and catabolism of nutrients (e.g., proteins) to enhance water intake and availability. These water-stress coping mechanisms may alter the intake and usage of macronutrients necessary for growth and reproduction. In this study, we worked with the widespread cabbage white butterfly (Pieris rapae), a species that experiences a wide range of humidity conditions in its habitats. During mating, P. rapae females obtain a nitrogen-rich nuptial gift that they use for egg production. Given that more than 70% of the nuptial gift is water, females may also use it to increase water intake in dry environments. Here, we tested whether P. rapae can overcome water stress by consuming the nuptial gift and how this affects the use of nuptial gift-derived amino acids. To do this, we exposed mated females to either a dry or a wet environment and used stable isotopes to track the metabolic fate of nutrients from the nuptial gift. Additionally, we measured the physiological hydration state of females in both environments and compared it to that of virgin females without nuptial gifts. Our results revealed that the nuptial gift supports both metabolism and egg production, and allows females to cope with dry environments. Future research should explore how challenging environmental conditions impact male investment in this critical resource for females.
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