Reactions of Heracleum Lanatum to Floral Herbivory by Depressaria Pastinacella
1984
Hendrix, Stephen D.
Heracelum lanatum, an andromonoecious perennial plant, reacted to herbivorous destruction of its primary (first) umbel by Depressaria pastinacella by an increase in the proportion of hermaphroditic flowers in late—developing umbels and a subsequent increase in seed set on these umbels. However, these reactions were not sufficient to offset completely the damage sustained; control plants produced 40% more seeds than damaged plants and seed biomass was 53% greater. Plant size (measured by basal stem diameter of the flowering stalk) was significantly correlated with total flower production, seed number, and seed biomass in both control and damaged plants. Plant size was also significantly correlated with the number of hermaphroditic flowers in the primary umbel of control plants and secondary umbels of damaged plants. Hermaphroditic flower production by the secondary umbels of control plants was negatively correlated with flower number in these umbels. Pastinaca sativa, another andromonoecious host plant of D. pastinacella, shows the same type of reactions as H. lanatum, but in P. sativa, compensation, at least in terms of seed number, is complete. The difference between the two species in replacement of lost offspring is interpreted in terms of frequency of reproduction. The interoparous h. lanatum may maximize reproduction in later seasons by increasing vegetative growth rather than by replacing all lost offspring. In contrast, the semelparous P. sativa maximizes replacement of destroyed offspring during its single reproductive bout.
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