Mammal and insect predation of chemically and structurally defended Mucuna holtonii (Fabaceae) seeds in a Costa Rican rain forest

Abstract

Abstract:To prevent seed losses from predation, plants have developed protective strategies. Seeds may utilize chemical or structural defences to deter predators. Mucuna holtonii (Fabaceae) has large seeds containing a toxic amino acid, L-dopa, and covered with a hard seed coat. Our study assessed the effectiveness of chemical and mechanical seed defences against vertebrate and invertebrate seed predators within Estación Biológica La Selva, Costa Rica. Pre-dispersal insect and fungus attack of M. holtonii seeds was low (95.7% of 1493 seeds were undamaged). Camera traps monitoring 90 marked M. holtonii seeds showed that the collared peccary (Pecari tajacu) consumed 98.6% of 69 removed seeds over 16 d. Field experiments involving 100 seeds with intact and 100 with opened seed coats found that only opened seeds had endosperm removed by Sericomyrmex amabilis ants (0.5–100% of endosperm removed). Shade-house experiments showed that seeds with high amounts of endosperm removed by ants resulted in low germination success and low seedling biomass production. Although M. holtonii seeds are rich in L-dopa, this compound is not an effective chemical defence against mammals that possess foregut fermentation. The seed coat of M. holtonii is an effective structural defence against invertebrate seed predators, preventing endosperm removal and enhancing seedling survival.