Sexual dimorphism and between-year variation in flowering, fruit set and pollinator behaviour in a boreal willow

• In Salix myrsinifolia-phylicifolia, males and females produced approximately the same number of catkins per individual, but males produced more flowers per catkin. Females had a higher concentration of sugars in the nectar than males, but the standing crop of nectar did not differ between sexes. Females had a hexoserich nectar, males a sucrose-dominated nectar. Bumblebees discriminated between male and female willows, but their preference changed during the day and differed between bumblebees with different tongue length. The relative abundance of different species of bumblebees varied considerably between years. Hand-pollination in 2 populations significantly increased both fruit and seed set per catkin. Production of flowers in female plants showed a large between-year variation. Both average fruit set and seed set per fruit were <50% during 1981-1985. Fruit set showed greater variation than did seed set per fruit. The early time of flowering and the strongly female biased sex ratios commonly observed in populations of this willow (60-80% females), increase the risk of pollen limitation. The production of many more flowers than fruist may represent a bet-hedging strategy to match the uncertainty in the conditions for fruit maturation, although it may also be of value as it potentially allows the plant to selectively mature fruits of a high genetic quality. -from Authors

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NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

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