Incomplete partitioning of pollinators byLinum suffruticosumand its coflowering congeners

Abstract

AbstractPremiseLinum suffruticosumshows variations in pollinator fit, pollen pickup, and local pollinators that predict pollen deposition rates. The species often coflowers with otherLinumspecies using the same pollinators. We investigated whetherL. suffruticosumtrait variation could be explained by local patterns of pollinator sharing and associated evolution to reduce interspecific pollen transfer.MethodsPollinator observations were made in different localities (single species, coflowering with other congeners). Floral traits were measured to detect differences across populations and from coflowering 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 after natural pollination in allopatric and sympatric localities.ResultsThe size and identity of the most important pollinator ofL. suffruticosumand whether there was pollinator sharing with coflowering species appeared to explain floral trait variation related to pollinator fit. The morphological overlap of the flowers ofL. suffruticosumwith those of coflowering species varied, depending on coflowering 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 coflowering with congeners, conspecific pollen‐tube formation was lower than at single‐species localities.ConclusionsTrait variation inL. suffruticosumappears to respond to the most important local pollinator. Locally, incomplete pollinator partitioning might cause interspecific pollination, imposing reproductive costs. These reproductive costs may generate selection on floral traits for reduced morphological overlap with coflowering congeners, leading to the evolution of pollination ecotypes.