Geographic consistency and variation in conflicting selection generated by pollinators and seed predators.
Floral traits that attract pollinators may also attract seed predators, which, in turn, may generate conflicting natural selection on such traits. Although such selection trade-offs are expected to vary geographically, few studies have investigated selection mediated by pollinators and seed predators across a geographic mosaic of environments and floral variation.



Floral traits were investigated in 14 populations of the bumble-bee-pollinated herb, Pedicularis rex, in which tubular flowers are subtended by cupular bracts holding rain water. To study potentially conflicting selection on floral traits generated by pollinators and florivores, stigmatic pollen loads, initial seed set, pre-dispersal seed predation and final viable seed production were measured in 12-14 populations in the field.



Generalized Linear Model (GLM) analyses indicated that the pollen load on stigmas was positively related to the exsertion of the corolla beyond the cupular bracts and size of the lower corolla lip, but so too was the rate of seed predation, creating conflicting selection on both floral traits. A geographic mosaic of selection mediated by seed predators, but not pollinators, was indicated by significant variation in levels of seed predation and the inclusion of two-, three- and four-way interaction terms between population and seed predation in the best model [lowest corrected Akaike Information Criterion (AICc)] explaining final seed production.



These results indicate opposing selection in operation: pollinators generated selection for greater floral exsertion beyond the bracts, but seed predators generated selection for reduced exsertion above the protective pools of water, although the strength of the latter varied across populations.
School of Life Sciences, Central China Normal University, Wuhan 430079, China.
Shi-Guo
SG
Sun
School of Biological Sciences, University of Portsmouth, Portsmouth PO1 2DY, UK Institute of Arctic Biology, University of Alaska, Fairbanks AK 99775-7000, USA.
W Scott
WS
Armbruster
School of Life Sciences, Central China Normal University, Wuhan 430079, China hsq@mail.ccnu.edu.cn.
Shuang-Quan
SQ
Huang
D000818:Animals; D001516:Bees / Q000502:physiology*; D004777:Environment; D035264:Flowers / Q000033:anatomy & histology* / Q000235:genetics / Q000502:physiology; D005843:Geography; D016014:Linear Models; D032262:Pedicularis / Q000033:anatomy & histology* / Q000235:genetics / Q000502:physiology; D010641:Phenotype; D011058:Pollen / Q000033:anatomy & histology / Q000235:genetics / Q000502:physiology; D054817:Pollination; D012639:Seeds / Q000033:anatomy & histology / Q000235:genetics / Q000502:physiology; D012641:Selection, Genetic
Corolla tube length; Pedicularis rex; cupular bract; geographic selection mosaic; phenotypic selection analysis; pre-dispersal seed predation; seed survival; stigmatic pollen load