I examine pollination ecology and evolution in floral features of the 13 species of western Lilium. I present a model for factors determining nectar concentration in angiosperms.;Multivariate morphometric analyses revealed four flower morphologies. Large tubular Lilium species are pollinated by sphingids, small tubular by hummingbirds or bird/bees, and large and small turk's-cap by large butterflies (chiefly Papilio) and/or hummingbirds. Usually nectar rewards pollinators. Pollination patterns are somewhat independent of flower morphology: small tubular-flowered lilies and some turk's-cap species are hummingbird-pollinated. Instead, the temporal pattern of nector secretion, and size of reward offered (not nectar concentration) interact to determine animal visitation. Flower anatomical details include the location and amount of nectariferous tissue, and influence flower-visitor behavior and pollen transfer effectivness. Sepal nectar secretion encourages butterflies to remain on the corolla tube periphery, where they contact exserted stamens and stigma. Tubular-flowered lilies have evolved petal nectar secretion too, and sphinx moths, bees, and hummingbirds are directed inside the floral tube where they contact included stamens and stigma.;A cladistic analysis employed morphological and cytological characters and permitted evolutionary interpretation of floral features. In L. rubescens the small metacentric chromosome has been replaced by a long acrocentric; all other Lilium possess two metacentrics and ten acrocentrics.;The two large tubular-flowered moth-pollinated lilies evolved independently from turk's-cap ancestors, and likewise the three small tubular-flowered hummingbird or bird/bee-pollinated species. The evolution of floral characteristics--morphology, flower orientation, color, scent, and nectar secretion timing, amount, and location--is strongly parallel in like-pollinated, independently derived species. This validates Stebbins's "most important pollinator principle". Initial evolutionary steps during floral transformations involved floral reward changes (sugar secretion timing/amount); morphological modification and flower color fine-tuning eventually evolved to complement major pollinators' sensory and behavioral characteristics. Floral morphology evolved to maximize pollen deposition by most effective pollinators, not to reduce floral parasitism; physical exclusion of non-pollinators is a by-product of selection for proper pollen placement.;Lilium pollen exines evolved convergently in eastern and western North American bird-pollinated species, probably in response to selection for adherence to the different surface materials of birds and insects.
展开▼
