Friday, August 10, 2007

PS 72-177: Nectar composition and corolla size variation in an endangered plant species, Sidalcea pedata

Marry Jones, Sean X. Liu, and Joan M Leong. California State Polytechnic University, Pomona

      Sidalcea pedata is a federally endangered gynodioecious species confined to montane meadows in Southern California. Previous studies indicate that insect pollinators visit hermaphrodite flowers of S. pedata more frequently than females. One potential reason for the preference of pollinators may be due to differences in nectar quality between the two floral morphs. The objectives of this study were to determine: (1) if there is a difference in the corolla diameter between the two floral morphs of S. pedata, (2) if a difference exists in the relative nectar sugar composition between the two morphs, and (3) if the amount of nectar sugars differs between floral morphs. Floral measurements and nectar samples were collected from two sites: a large meadow near the western end of Big Bear Lake, and a meadow fragment in the city of Big Bear. HPLC was used to extract sugars from the nectar samples. Standard curves of glucose and fructose were generated using pure samples and the respective sugar concentrations were extrapolated from the graphs. The corolla diameter of hermaphrodite flowers was larger than females. However, no difference exists in the relative nectar sugar composition between the two floral morphs. Analysis of variance revealed a significant effect of floral morph on the average amount of nectar sugars. Nectar of hermaphrodites had nearly twice the amount of glucose and fructose per volume than nectar of females. Consequently, pollinator preference for a particular sexual morph may be related to variation in nectar rewards. Site also had a significant effect on the average amount of nectar sugars. There was a significant site by sex morph interaction. However, no significant interactions were found between sex morph and type of sugar, or site and type of sugar.

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