VARIATION IN A POPULATION OF PLANTAGO-LANCEOLATA ALONG A TOPOGRAPHICAL GRADIENT

Patterns of variation were studied in a pasture population of Plantago lanceolata. Four subsites could be distinguished along a riverside gradient ranging from a dry ridge towards a wet depression (a former river-bed). A reciprocal-transplant experiment revealed differences between sites in mortality patterns, plant growth and reproduction. At some sites the native plants performed best; differences in survival in particular were observed during extreme abiotic circumstances, drought at the highest site and inundation at a low site. However, native and alien plants did not differ in seed yield; many spikes were grazed before seed set and environmentally induced variation in seed yield between plants was high. Local adaptation to conditions at the four subsites appeared limited. However, different clones from the same subsite showed significant genetic variation in morphology, survival and reproduction. Apparently the scale of genetic varition did not coincide with major environmental factors that distinguish the four sites. Progenies from crosses between plants from the four sites were reared in the greenhouse. Significant genetic variation in morphology was found between sites but, again, predominantly within sites. Canonical variate analysis of variation between all crosses revealed no strong interdependence of traits, that might have been due to pleiotropic effects of genes or linkage. When associations between traits existed, e.g. for traits related to growth habit, they appear to be brought together by selection; however, at least in P. lanceolata trait associations are easily modifiable by selection. Selection in the most common microsite - where plants also have the highest survival and seed production - appears to dominate patterns of adaptation and genetic variation in this population of P. lanceolata.