Differential survival of genetic variants in crowded populations of Phlox.
The nature of change in genetic structure during self-thinning of crowded mixtures of Phlox drummondii genotypes was investigated with (1) 10 commercial cvs comprising dwarf and normal strains, and (2) a natural Florida population having variable (white, pink and red) flower colour and eye-markers. Two nutrient levels were compared in each experiment. The cvs differed in maximum percentage germination and in the number of days required for maximum germination. After 38 days of growth the frequency of the genotypes (cvs) in both nutrient treatments did not differ significantly from the expected frequencies based on the seed germination data. However, significant differences were observed 60 and 95 days after seedling emergence. There were marked differences in survival of the different genotypes and the relative ability for survival was related to population age and soil nutrient level. With the natural population there was also genotype-specific thinning. For example, the frequency of the white flower morph was significantly lower than expected.