POPULATION GENETICS AND GEOGRAPHICAL DISTRIBUTION OF CAFFEIC ACID ESTERS IN LEAVES OF PLANT AGO MAJOR IN DENMARK.

(1) This paper deals with the geographical distribution of two sugar esters of caffeic acid determined by a single gene difference in populations of Plantago major ssp. pleiosperma in Danish plant communities. (2) A pronounced skewness in the frequency of the recessive phenotype, an ester with rhamnose, has been verified in two independent sets of plant samples with decreasing frequency of the rhamnose ester towards the west. (3) The existence of polymorphism in these phenolic compounds is shown to be advantageous to the taxon in relation to herbivory by slugs and snails. (4) Selective feeding on the most frequent phenotype has been shown in the population samples as well as in controlled experiments. (5) This mechanism is discussed in relation to a stable polymorphism in the populations and is, so far. one of the very few examples of frequency-dependent selection in favour of the rarest genotype, i.e. pro apostatic selection. [ABSTRACT FROM AUTHOR]