POPULATION ECOLOGY OF HETEROSTYLE AND HOMOSTYLE PRIMULA-VULGARIS - GROWTH, SURVIVAL AND REPRODUCTION IN FIELD POPULATIONS

Homostyle primrose are self-fertile and are also able to fertilize heterostyles with the pin morph. In theory these characteristics should give homostyles in advantage over heterostyles and homostyly should spread. In fact primrose populations with significant numbers of homostyles are rare in Britain and the frequency of homostyles in them has not noticeably increased during 40 years of observation. In search of an ecological explanation for the homostyle handicap, growth, survival and reproduction of heterostyle (pin and thrum) and homostyle primroses were compared. A significant negative relationship between seed number capsule-1 and mean seed weight occurred in all three morphs. This could mean that in years of poor pollination when heterostyle seed set is low, heterostyle seeds will be significantly larger than homostyle seeds. If seed size is more important than seed number in determining the fitness of primrose morphs, the trade-off between seed size and seed number could handicap homostyles on the common occasions when heterostyle seed set is pollinator-limited. -from Authors