Stronger Antipredatory Vigilance of Prey to Olfactory Cues From Injured Vulnerable Conspecifics

Predation risk is a key evolutionary force shaping prey behaviors and life-history strategies across taxa. Predators often target vulnerable life stages of prey, but how prey females adjust their reproductive strategies in response to cues from injured conspecifics of these stages remains unclear, particularly in haplodiploid species, where mothers can adjust offspring sex ratios in response to social environments. Using the predatory mite <i>Phytoseiulus persimilis</i> and its prey, the spider mite <i>Tetranychus ludeni</i>, we first investigated the stage-specific vulnerability by exposing <i>T. ludeni</i> eggs, deutonymphs, and female adults to <i>P. persimilis</i> for choice. We then tested whether ovipositing <i>T. ludeni</i> females adjusted reproductive performances and survival when exposed to potential predatory cues from those injured conspecifics. Results show that <i>P. persimilis</i> significantly preferred <i>T. ludeni</i> eggs for feeding, indicating their higher vulnerability to predators. <i>T. ludeni</i> females responded most strongly to potential predatory cues from injured eggs, reducing fecundity and producing smaller eggs, but without trading off their longevity. Additionally, when exposed to injured adult cues, <i>T. ludeni</i> females adjusted offspring sex ratios, producing more dispersing daughters by fertilizing more smaller eggs, an evolved strategy to escape from the risky environments. In contrast, egg hatching and immature survival were unaffected by conspecific cues. Our results demonstrate that <i>T. ludeni</i> females may discriminate among cues from injured conspecifics of different life stages, with the strongest vigilance elicited by cues from the most vulnerable stage (i.e., eggs). This study highlights the role of indirect, life stage-specific cues in shaping antipredator strategies and reveals that non-consumptive effects of predation risk could influence prey population dynamics in ways beyond direct predation. Our findings provide a mechanistic understanding of reproductive plasticity in haplodiploid systems, offering new insights into how prey balance current and future reproductive investments under predation pressure.