Effects of the spatial pattern of damage on plant growth and reproduction via the male and female functions.

摘要

Different patterns of herbivory may differentially affect plant fitness because in plants, the movement of nutrients and photosynthate is less restricted within than among physiologically coherent units (determined by vasculature). Patterns of damage merit attention also because herbivores forage in specific patterns, thus imposing selection on plant responses to the pattern of damage. I assessed the impact of the spatial pattern of foliar damage on growth and reproduction via the male and female functions of plants using experimental populations of the wild, herbaceous, annual gourd, Cucurbita pepo L. ssp. texana (A. Gray) Filov. Typically, these plants produce a main axis with primary, secondary and tertiary branches. After 1–2 months of vegetative growth, plants produce one flower per node (4:1 staminate: pistillate flowers). Primary and secondary branches produce most of a plant's nodes and flowers. In a five-year study conducted at four structural levels of a plant (single nodes, primary branch, branch system, whole plant), I tested whether simulated herbivory is more detrimental to growth and reproduction when concentrated on certain leaves/branches than when dispersed throughout the plant. The pattern of damage affected pollen performance, pollen production per flower, fruit production and the proportion of pistillate nodes. Results varied depending on the structural level. Foliar damage affected few traits overall. Concentrated damage was not more detrimental to plant fitness than dispersed damage. Plants tolerated simulated herbivory consistently throughout five growing seasons. I evaluated the effects of fruit removal (opposite effect of herbivory: increase resource availability) on growth and flower production. Plants that did not produce fruits grew faster and produced more flowers than plants where fruits developed. I conducted an experiment to determine whether the negative effects of damage are due to resource reallocation or loss of photosynthetic area, but results were inconclusive because there were few treatment effects. I compared the effects of mechanical vs. herbivore damage on plant reproduction, and found no effects of either treatment. I characterized the histological development of staminate buds, and found it similar to that in common zucchini (e.g. differences in pollen wall ultrastructure). Bud size correlated closely with developmental stage.