Major effects of glucosinolates and minor effects of erucic acid on predation of Brassica seeds by mice

Abstract

Seeds of cultivars of the crop oil seed rape (Brassica napus) differ widely in their content of glucosinolates (GS) and erucic acid (EA), while seeds of the wild relative B. rapa have a high content of both. If mice were to distinguish between the seed types this could affect persistence of plant populations.In a choice experiment in two habitats seven seed types were offered to seed predators, mainly mice, and to captured individuals of the wood mouse Apodemus sylvaticus.Seed predators clearly distinguished between seeds of the two species and between different cultivars of B. napus. In three experiments the amount of seeds eaten had a high, negative correlation with GS content (rank correlation coefficient −0.81 to −0.91). Correlations with EA were lower (−0.33 to −0.52) and not statistically significant. When offered a choice between two seed types with similar GS content, mice chose those with the lower EA content.Double-zero (low GS and low EA) cultivars of B. napus suffer heavily from post-dispersal seed predation while cultivars with high GS and/or EA suffer less, making the latter potentially more persistent. We suggest that the consistently high GS and EA content in seeds collected in wild populations of B. rapa is an adaptation that reduces seed predation.