Pollination biology of a disjunct population of the endangered sandhills endemic <Emphasis Type="Italic">Penstemon haydenii</Emphasis> S. Wats. (Scrophulariaceae) in Wyoming,USA |
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Authors: | Vincent J Tepedino Trent R Toler Brosi A Bradley Jessica L Hawk Terry L Griswold |
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Institution: | (1) USDA ARS Bee Biology & Systematics Lab, Department of Biology, Utah State University, Logan, UT 84322-5310, USA;(2) Department of Biology, Utah State University, Logan, UT 84322-5305, USA;(3) Present address: HDR Engineering Inc., 3995 S 700 E, Suite 100, Salt Lake City, UT 84107-2594, USA;(4) Juniata College, 1700 Moore Street, Box 1071, Huntingdon, PA 16652, USA;(5) 1016 Clouet St., New Orleans, LA 70117, USA |
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Abstract: | We studied the breeding system and flower visitors of the endangered plant, Penstemon haydenii, at several south-central Wyoming, USA occurrences. In agreement with earlier studies of the species 300 km to the east in
Nebraska, we found Wyoming plants to be self-incompatible and pollinator-dependent for sexual reproduction. Flower visitors
were several species of native bees in the families Apidae (particularly bumblebees), Halictidae (small sweat bees), and Megachilidae
(especially in the genus Osmia); and the masarid wasp Pseudomasaris vespoides. Especially important was Osmia brevis, an abundant megachilid bee, and one of only two species (the sweat bee Lasioglossum (Dialictus) pruinosum was the other) present at all five sites. As in Nebraska, fruit set did not differ between our experimental cross-pollination
treatment and an open-pollinated control. However, unlike Nebraska, open-pollinated treatments in Wyoming produced significantly
fewer seeds per fruit than the experimental out-crossing treatment. We discuss several possible explanations for seed limitation:
(1) a scarcity of pollinators early in the flowering season; (2) resource competition for developing ovules on open-pollinated
inflorescences but not on experimental inflorescences; (3) the deposition of self pollen through intra-inflorescence and intra-genet
pollinator movements; (4) few S-alleles and mating types in the Wyoming metapopulation compared to the Nebraska metapopulation,
from which it likely derives. |
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Keywords: | Breeding system Reproductive limitation Bees Pollinators Beardtongue Rare Conservation |
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