Pollen aperture heteromorphism. Variation in pollen-type proportions along altitudinal transects in Viola calcarata.
Some species produce pollen grains with different aperture numbers within a single individual (pollen aperture heteromorphism). In the pansy Viola diversifolia, aperture number is positively correlated with pollen germination speed, and negatively correlated with viability. In V. calcarata, young five-aperturate pollen grains germinate faster than four-aperturate ones. Heteromorphism could thus be favoured when pollination is unpredictable, as plants produce both very competitive and long-lived pollen grains. Depending on the efficiency of the pollinators, different proportions of pollen types will be optimal. In insect-pollinated species, such as V. calcarata, pollination efficiency generally decreases as elevation increases. We therefore expect a decrease in mean aperture number as altitude increases. This was found in four transects (out of six). Pollinator activity therefore has a potential impact on pollen morphology.
Till-Bottraud
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Laboratoire de biologie des populations d'altitude, UMR CNRS 5553, université Joseph-Fourier, Grenoble, France. irene.till@ujf-grenoble.fr
Vincent
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M
Dajoz
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I
Mignot
A
A
D018521:Plant Physiological Phenomena; D010944:Plants / Q000033:anatomy & histology*; D011058:Pollen / Q000502:physiology*