title: Selection on Polemonium brandegeei (Polemoniaceae) flowers under hummingbird pollination: in opposition, parallel, or independent of selection by hawkmoths?
abstract: Particular floral phenotypes are often associated with specific groups of pollinators. However, flowering plants are often visited, and may be effectively pollinated by more than one type of animal. Therefore, a major outstanding question in floral biology asks: what is the nature of selection on floral traits when pollinators are diverse? This study examined how hummingbirds selected on the floral traits of Polemonium brandegeei, a species pollinated by both hummingbirds and hawkmoths. In array populations of P. brandegeei, we measured pollen movement, and female (seeds set) and male (seeds sired) fitness under hummingbird pollination. We then compared the patterns of selection by hummingbirds with our previous study examining selection by hawkmoths. We documented contrasting selection on sex organ positioning through female function, with hummingbirds selecting for stigmas exserted beyond the anthers and hawkmoths selecting for stigmas recessed below the anthers. Furthermore, hummingbirds selected for longer and wider corolla tubes, and hawkmoths selected for narrower corolla tubes. Therefore, contrasting selection by hawkmoths and hummingbirds may account for variation in sex organ arrangements and corolla dimensions in P. brandegeei. We documented how floral traits under selection by multiple pollinators can result in either an intermediate "compromise" between selective pressures (sex organs) or apparent specialization (corolla tube length) to one pollinator.
authors.affiliation: Department of Biological Sciences, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada. umkulbam@cc.umanitoba.ca
authors.forename: Mason W
authors.initials: MW
authors.lastname: Kulbaba
authors.forename: Anne C
authors.initials: AC
authors.lastname: Worley
mesh_terms: D000818:Animals; D001717:Birds; D035264:Flowers; D019684:Magnoliopsida / Q000033:anatomy & histology* / Q000235:genetics*; D009036:Moths; D054817:Pollination; D012641:Selection, Genetic
keywords: Floral selection; herkogamy; hummingbirds; male fitness; pollen movement; selection gradients