Effectiveness of maternal egg attendance in an exclusively cave-dwelling harvestman (Arachnida: Opiliones)

Egg attendance is the most common and phylogenetically widespread form of post-ovipositional care among ectotherms. The main benefit of egg attendance is to enhance offspring survival by preventing or attenuating attacks from natural enemies. In arachnids, there are few experimental studies on the benefits of egg attendance, and they pertain to species living in few types of habitats, mainly forests. To understand how the benefits of egg attendance vary in large geographical scales, we need to include species from poorly explored habitats, such as caves. Here, we describe a case of maternal egg attendance in an exclusive cave-dwelling harvestman, Phalangodusbriareos. Using a parent removal experiment, we also assessed the benefits of egg attendance. We found that egg attendance improves egg survival because unattended clutches were almost entirely consumed by conspecifics and crickets. When females were maintained on their clutches, egg survival was always high, regardless of female body size. There was a positive effect of clutch size on egg predation, which was higher during nighttime. We suggest that larger clutches emit more chemical cues, attracting more predators in the cave habitat. Finally, we argue that the benefits of egg protection should be higher inside caves when compared to external habitats because food is scarce inside caves and the fauna consists mainly of predators and detritivores.