Phenotypic Selection on Flower Traits in Food-Deceptive Plant Iris pumila L.: The Role of Pollinators

Abstract

To gain insight into the evolution of flower traits in the generalized food-deceptive plant Iris pumila, we assessed the color, size, shape, and fluctuating asymmetry (FA) of three functionally distinct floral organs—outer perianths (‘falls’), inner perianths (‘standards’), and style branches—and estimated pollinator-mediated selection on these traits. We evaluated the perianth color as the achromatic brightness of the fall, measured the flower stem height, and analyzed the floral organ size, shape, and FA using geometric morphometrics. Pollinated flowers had significantly higher brightness, longer flower stems, and larger floral organs compared to non-pollinated flowers. The shape and FA of the floral organs did not differ, except for the fall FA, where higher values were found for falls of pollinated flowers. Pollinator-mediated selection was confirmed for flower stem height and for subtle changes in the shape of the fall and style branch—organs that form the pollination tunnel. This study provides evidence that, although all analyzed flower traits play significant roles in pollinator attraction, flower stem height and pollination tunnel shape evolved under the pollinator-mediated selection, whereas achromatic brightness, size, and symmetry of floral organs did not directly affect pollination success.