Homostyle primroses re-visited. I. Variation in time and space

Abstract

Populations of Primula vulgaris L. generally consist of two self incompatible heterostyle morphs, but in Somerset, S.W. England, a third type, homostyle, also occurs and was studied in the 1940s and 1950s by J. Crosby and others. A more extensive mapping of the distribution and frequencies of the three morphs has now been carried out and 30 well defined local populations have been re-scored after 25–40 years have elapsed. The observed changes in morph frequency were only slight but showed a frequency dependent pattern. This is contrary to the prediction of Crosby who expected the homostyles would increase in all cases because they self fertilise and can pollinate one of the heterostyle morphs. Computer simulations of this breeding system combined with other fitness variables showed that a restricted range of values for inbreeding depression, inviability of the homozygous homostyle and gene flow between populations would give frequency dependent change of the kind which was observed.