Interpopulation variation and optimal mating in the perennial herb, Polemonium brandegeei

Abstract

Generalist pollinated plants receive pollination services from a wide range of animals, but pollinator effectiveness varies. More effective pollinators in generalist systems optimize pollen transfer by promoting outcrossing between more distant plants. This leads to increased pollinator mediated selection by these pollinators on floral traits and variation in pollinator abundance may therefore cause population genetic and phenotypic differentiation across the range of a species. However, variation may also be caused by plastic responses to variable environmental conditions. Here, I analyze the prevalence and potential causes of interpopulation variation as well as optimal mating distance in generalist pollinated Polemonium brandegeei. I compared morphology and floral scent (1) among four field populations and (2) between field and greenhouse grown plants sourced from the same populations. Populations varied in morphology and floral scent profile and the southernmost population was most distinct with floral traits consistent with increased selection by hawkmoths or hybridization events. All major among population differences were preserved in the greenhouse which suggests a genetic component to phenotypic variation but there was an overall increase in flower size and total scent emission in the greenhouse. Field hand crosses indicated that mating in P. brandegeei was optimized provided crosses were made between plants at least 1 – 3.5m apart, and that environmental variability influenced mating success. These findings may reflect differences in pollinator abundance and/or pollinator mediated selection among populations or hybridization events and offer support for past selection by more effective pollinators (hawkmoths and hummingbirds) which transport pollen over larger distances. ii

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