Evolution and maintenance of pollen‐colour dimorphisms in Nigella degenii: habitat‐correlated variation and morph‐by‐environment interactions
2005
Jorgensen, Tove Hedegaard | Andersson, Stefan
• Dimorphism in pollen colour is rare among flowering plants, but occurs in two geographically and morphologically distinct subspecies of Nigella degenii (Ranunculaceae). We evaluated the role of genotype‐by‐environment interactions in the maintenance of two pollen morphs within each of these subspecies. • Morph frequencies in a number of populations were related to current habitat conditions, and an extensive common‐garden experiment involving both optimal and stressful conditions (drought and nutrient deficiency) was carried out. • The putatively derived (dark) pollen morph of N. degenii ssp. barbro has a higher frequency on slopes facing north or east than on slopes facing south or west. Plants of the dark morph also have a higher mortality under drought stress or nutrient deficiency. Data available for N. degenii ssp. jenny provide little evidence for habitat‐correlated variation in morph frequency or morph‐specific differences in fitness under optimal and stressful growth conditions. • Our results suggest that morph‐by‐environment interactions in mortality could contribute to the maintenance of pollen‐colour dimorphisms in N. degenii ssp. barbro.
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