LAUSR

PREMISE OF THE STUDY Linum suffruticosum shows variation in pollinator fit, pollen pick up, and local pollinators that predict pollen deposition rates. The species often co-flowers with other Linum species using the same pollinators. We investigated whether L. suffruticosum trait variation could be explained by local patterns of pollinator sharing and associated evolution to reduce interspecific pollen transfer. METHODS Pollinator observations were made in different localities (single species, co-flowering with other congeners). Floral traits were measured to detect differences across populations and from co-flowering species. Reproductive costs were quantified using interspecific hand-pollinations and measures of pollen-tube formation, combined with observations of pollen arrival on stigmas and pollen tube-formation under natural pollination in allopatric and sympatric localities. KEY RESULTS The size and identity of the most important pollinator of L. suffruticosum, and whether there was pollinator sharing with co-flowering species, appeared to explain floral trait variation related to pollinator fit. The morphological overlap of the flowers of L. suffruticosum with those of co-flowering species varied, depending on co-flowering species identity. A post-pollination incompatibility system maintains reproductive isolation, but conspecific pollen-tube formation was lower after heterospecific pollination. Under natural pollination at sites of co-flowering with congeners, conspecific pollen-tube formation was lower than at single-species localities. CONCLUSIONS Trait variation in L. suffruticosum appears to respond to the most important local pollinator. Locally, incomplete pollinator partitioning might cause interspecific pollination, imposing reproductive costs. This may generate selection on floral traits for reduced morphological overlap with co-flowering congeners, leading to the evolution of pollination ecotypes. This article is protected by copyright. All rights reserved.