Symbionts unmask the latent trade-off between reproduction and survival

Reproductive trade-offs are fundamental to life history evolution, yet their expression is often obscured by individual variation in quality. Symbionts represent a critical environmental factor that may alter these trade-offs, but their impact on the link between reproductive effort and somatic maintenance remains poorly understood. Using burying beetles (Nicrophorus nepalensis) and their phoretic mite (Poecilochirus carabi), with a split-brood design to control for genetic background, we show that mite presence shapes both the magnitude and success of reproductive attempts. Brief physical exposure to mites alone was sufficient to trigger a plastic shift toward higher fecundity, even when mites are subsequently removed, producing brood sizes matching those of permanently mite-associated females. Crucially, survival analysis revealed that mites unmasked a latent trade-off between reproduction and longevity. These findings demonstrate how symbiotic interaction can both induce anticipatory life history shifts and reveal reproductive costs that remain hidden.