Abstracts (first author)
Pollinator-mediated selection on floral size and color in two Iris species
Pollinator-mediated selection is considered the major drive of floral evolu-tion and the evolution of floral diversity among angiosperms. Yet, causes of selection on traits contributing to attract pollinators have rarely been tested experimentally in natural populations. We quantified phenotypic selection on floral size and color in two species of the Oncocyclus irises in two years, and experimentally assessed the contribution of pollinators for this selection. Flowers of the Oncocyclus irises are among the largest in the East Mediter-ranean flora, and are usually dark-colored, from purple to black. Floral color is utilized to absorb the morning sun rays and to increase temperature within the flower. This morning floral heat rewards the pollinators of the irises: male solitary bees that shelter overnight in the flowers. To determine whether selection on floral size and color can be attributed to interactions with pollinators, selection was quantified for both open-pollinated controls and for plants receiving supplemental hand-pollination. The latter treatment is expected to remove pollinator limitation and hence to relax pollinator-mediated selection. Supplemental hand-pollination changed the extent and direction of selec-tion, suggesting pollinator-mediated selection on these traits. Pollinator-mediated directional selection on floral size and color was detected in Iris atropurpurea, and non-linear pollinator-mediated selection was detected in Iris haynei. This study provides evidence that pollinators of these irises are the selec-tion agent on floral traits, and support the contention that pollinators can drive the evolution of floral display size and color.