Leaky pollination barrier in edaphic vicarious alpine plants

Abstract Adaptation to siliceous versus carbonate substrates is thought to be an important driver of speciation in the alpine flora. The role of the pollination system in formation and maintenance of such species is presently unclear. Here, we chose three species pairs in the genera Gentiana, Primula, and Rhododendron which often occur in geographic proximity or even sympatry, to study the existence of pollination barriers in these lineages. Using remote camera and direct observation approaches, scent and color analyses, and morphological comparisons, we tested the hypothesis that divergent pollinator communities help to maintain genetic separation of plant populations adapted to different soil types. We found differences in frequency, diurnal activity and to some extent also community composition of flower visitors in edaphic vicarious species pairs. Floral traits like color and scent as well as plant-flower-visitor co-distributions indicate that there are divergent but overlapping pollination systems. Our results suggest a relatively small reproductive barrier function of the pollination system. While the adaptation to different soils still seems to be the main force keeping edaphic vicarious alpine plants genetically separated, pollinators might break down hybridization barriers in contact areas.