Fitness measurement
Plant fitness was measured as total seed output per plant. For this, berries were picked fresh as they ripened on plants up until most fruiting had finished by mid-July. After this time berries were allowed to dry on the plant before a final picking in early August. Although birds were not excluded from the common garden, we did not observe any bird frugivory. All berries were dried in an oven at 80oC for 1.5 days. To estimate the total number of fertilised seeds per plant from dry berry weight, we established two regression equations; one for berries that were picked fresh (y = 0.9937x – 14.257, R2 > 0.99), and one for berries that were picked dry (y = 1.0017x – 14.423, R2 > 0.99). Berries were randomly selected across all genotypes and treatments in order to establish these equations. Only fertilised seeds were counted, which are easily visually differentiated from non-fertilised seeds (Thompson 1971). Owing to their much-reduced size, non-fertilised seeds made only a negligible contribution to dry berry weight (data not shown).