Résumé
Plant-pollinator interactions are believed to play a major role in the
evolution of floral traits. Flower colour and flower size are important
for attracting pollinators, directly influencing reproduction, and thus
expected to be under pollinator-mediated selection. Pollinator-mediated
selection is also proposed to play a role in maintaining flower colour
polymorphism within populations. However, pigment concentrations, and thus
flower colour, are also under selective pressures independent of
pollinators. We quantified phenotypic pollinator-mediated selection on
flower colour and size in two colour polymorphic Iris species. Using
female fitness, we estimated phenotypic selection on flower colour and
size, and tested for pollinator-mediated selection by comparing selection
gradients between flowers open to natural pollination and supplementary
pollinated flowers. In both species, we found evidence for pollen
limitation, which set the base for pollinator-mediated selection. In the
colour dimorphic Iris lutescens, while pigment concentration and flower
size were found to be under selection, this was independent of
pollinators. For the polymorphic Iris pumila, pigment concentration is
under selective pressure by pollinators, but only for one colour morph.
Our results suggest that pollinators are not the main agents of selection
on floral traits in these irises, as opposed to the accepted paradigm on
floral evolution. This study provides an opposing example to the
largely-accepted theory that pollinators are the major agent of selection
on floral traits.