Evolution and maintenance of pollen-colour dimorphisms in Nigella degenii: habitat-correlated variation and morph-by-environment interactions.
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.
Jorgensen
Tove Hedegaard
TH
Department of Ecology, Section of Plant Ecology & Systematics, Lund University, Sweden. Tove.Hedegaard@sysbot.lu.se
Andersson
Stefan
S
D005075:Biological Evolution; D017753:Ecosystem; D004777:Environment; D005828:Genetics, Population; D006115:Greece; D008954:Models, Biological; D031844:Nigella / Q000235:genetics*; D010858:Pigmentation / Q000235:genetics; D011058:Pollen; D011110:Polymorphism, Genetic