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Abstract Mating systems of sympatric related alpine shrubs, Phyllodoce caerulea and P. aleutica , were compared along snowmelt gradients at three snowbed sites in the Taisetsu Mountains, northern Japan. Seed-set success under natural pollination tended to decrease at late snowmelt places in both species, but the difference between the species was not clear. A pollination experiment revealed that selfing ability differed between the species along the snowmelt gradients. Phyllodoce caerulea showed consistently low selfing ability throughout the gradients even when artificial selfing treatment was performed. Phyllodoce aleutica , whereas, showed high selfing ability at the early and middle snowmelt plots but this abruptly decreased at the late snowmelt plots at every site. These results indicate that P. aleutica is predominantly a selfer at early and middle snowmelt places and shifts to an obligate outcrosser at late snowmelt places. Therefore, variations in the mating system actually occur among neighboring populations along snowmelt gradients probably because of directional selective forces such as interspecific competition for pollinators. [ABSTRACT FROM AUTHOR]

Abstract Deceptive orchid species that offer no floral rewards to pollinators often experience pollinator limitation because they. The breeding system and fruit set were investigated in order to examine pollinator limitation for a population of a deceptive orchid, Pogonia japonica , on a floating peat mat in Mizorogaike Pond, western Japan. Fruit sets for outcross-pollinated, self-pollinated and pollinator-excluded flowers were 75%, 80%, and 0%, respectively. Thus, this species was self-compatible but neither autogamous nor apogamous. The fruit set for open-pollinated flowers was 22.9% and 17.4% in 1994 and 1995, suggesting that pollinator limitation did occur in the field. Larger flowers were more likely to develop into fruit than smaller ones in open pollination (36%vs 8%). Thus, flower size seems to affect fruiting of this species. No effective visits by major pollinators such as bees, which could carry pollinia, were observed during 16.5 h of observation during daytime. Instead, thrips were often found moving on gynostemium or pollinia and circumstantial evidence that suggests thrips may partly transfer pollen in pieces out of a granular pollinium of P. japonica was obtained. Pogonia japonica should come to use thrips as a pollinator to supplement low fruit set under limited flower visitation by major pollinators. [ABSTRACT FROM AUTHOR]