Reproductive ecology ofDryas integrifoliain the high Arctic semi-desert

Abstract

Flowering and fruiting of Dryas integrifolia were studied at Igloolik and Pangnirtung to analyse the importance of variation in heliotropy and flower size to seed set and weight. In addition, peduncle elongation and seed plume length were also studied to analyse variation in seed dispersal characters. At both Igloolik and Pangnirtung, most Dryas flowers were not heliotropic throughout the course of the day, but in general, pointed towards the solar noon sun. Benefits to orienting toward the sun were warmer gynoecial temperatures, heavier seeds, and more insect visitation (though not percent seed set). Flowers varied in size from 1.2 to 2.7 cm in diameter and differed in size between plants. Even though larger flowers did not point towards the solar noon sun more than smaller flowers, they had heavier and proportionally more seeds. Variation in peduncle elongation suggests the potential for conservative dispersion when a flower has produced only a few propagules: flowers with fewer or no seeds had shorter stalks. Similarly, with good seed production, a bet hedging strategy is apparent: seeds located at the centre of the receptacle had much longer plumes than those at the perimeter of the seed head. All seed data were from Pangnirtung; the cold summer in 1986 at Igloolik resulted in a complete seed crop failure. Despite the adversity of the arctic climate, there are moderate summers during the lifetime of perennial plants such as D. integrifolia in which adaptations like those described in this study benefit the production of sexual offspring. Keywords: heliotropism, flower stalk elongation, basking insects, seed dispersal, insolation, bet hedging.