Signal selection in a desert lily, Pancratium sickenbergeri

Hypothesis: The optimum height of an inflorescence is expected to be the result of costs and benefits for the plant, where the benefit is pollination and the costs are herbivory and allometric growth. Thus, plants with more resources will have taller flower stalks, will provide a greater reward to pollinators, and will be preferred by pollinators. However, in populations subject to stronger herbivory, mean stalk height will be shorter. Organism: We studied populations of a hysteranthous and tall-stalked geophyte, the Negev desert lily (Pancratium sickenbergeri), subject to varying levels of herbivory by dorcas gazelles (Gazella dorcas). Field site: Sandy habitats in Makhtesh Katan and Makhtesh Ramon, in the Negev Desert, Israel. Methods: We measured the survival and frequency distribution of floral stalk height, bulb size and condition (by artificially simulating bulb herbivory), pollinator preference, rewards for the pollinators (pollen grains per plant and the energetic value of the nectar per flower), and fruit and seed production. We then compared stalk height between populations and correlated stalk height, pollen and nectar, and seed production. Results: Lilies in populations with high herbivory produced shorter inflorescences than in populations with low herbivory. The condition of the bulb affected stalk production, but not its height or seed production. The pollinator preference results were inconclusive. Taller inflorescences produced more rewards for pollinators. We observed variability in fruit and seed production due to the size of the flower stalk and this variability differed among the populations with different levels of herbivory.