Seed mucilage – a coating on seeds that becomes sticky and slimy when wet - is a widespread plant trait that has evolved convergently many times. One consequence of seed mucilage is that sand and dirt particles stick to wet mucilage and remain tightly bound to the seed surface after drying. Despite its common occurrence, little work has investigated the ecological costs and benefits of sand entrapment on mucilaginous seeds. Here, we explore the hypothesis that mucilage-bound sand coatings protect the seed from seed predators, either physically or through reduced apparency (i.e. background matching). To investigate this hypothesis, we placed bare and mucilage-bound sand-coated seeds of 53 plant species from 13 families in feeding “depots” near harvester ant nests in California’s Central Valley and measured seed removal.
Results/Conclusions
Consistent with the defensive hypothesis, sand coating reduced predation on seeds in 48 of the 53 species examined. To test whether this striking benefit was due to reduced apparency (i.e., camouflage), we factorially manipulated background substrate color and sand coating color in a targeted experiment using flax seeds. Our results did not support reduced apparency as a mechanism; seeds coated in sand that matched the background were removed at the same rate as seeds coated in un-matched sand. Our results demonstrate that seed mucilage is a phylogenetically widespread, but poorly studied defensive trait, and should be further investigated in the context of evolution and ecology of seed defense more broadly.