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).