Leaky pollination barrier in edaphic vicarious alpine plants

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 the 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, we tested the hypothesis whether divergent pollinator communities exist that could 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 flower visitor co-distributions indicate that our study species have divergent but overlapping pollination systems. Our results do not suggest a strong reproductive barrier function of the pollination system. While adaptation to different soils still seems to be the main force keeping edaphic vicarious alpine plants genetically separated, pollinators might mediate hybridization in contact areas.