Egg-sac-brooding wolf spiders show flexible hatchling emergence and context-dependent escape performance.

Egg-sac brooding is a costly maternal strategy for which evolutionary persistence hinges on clear offspring benefits and effective maternal tactics to offset those costs. Using the wolf spider Pardosa pusiola, we examined (1) whether hatchling emergence depends on the presence of a conspecific mother, (2) whether egg sac opening is a flexible response to embryonic cues, and (3) how mothers modulate locomotor performance under different ecological risks (sun exposure, flooding, predation). Conspecific foster mothers matched biological mothers in synchronizing egg-sac opening with embryonic development, whereas interspecific foster mothers (Pardosa astrigera) mistimed opening in most cases. Motherless egg sacs contained fully developed but un-emerged hatchlings, confirming that maternal presence is indispensable for emergence, not for hatching itself. Under moderate sun exposure, egg-sac-carrying females escaped slower than non-carrying females. Under high sun exposure or predator stimulus, carrying females escaped as fast as or faster than non-carrying females. Under simulated flooding, carrying females suffered higher mortality, yet survivors showed no difference in escape speed compared to non-carrying females. These results demonstrate flexible egg-sac management coupled with adaptive maternal locomotion, illustrating how costly parental care can be maintained when parents adjust their behavior according to environmental risk.