ALLOZYMIC VARIATION IN LOCAL APOMICTIC POPULATIONS OF LEMNA MINOR (LEMNACEAE)

Flowering occurrence and allozymic variation were studied in eight local populations of Lemna minor in eastern Ontario, Canada. After 2 years of survey, not a single flower was observed. This absence of flowering suggests the possibility of loss of sexual reproduction. This may have had no net adverse effect on fitness given the simple life history and prolific vegetative propagation in L. minor. However, the absence of sexual reproduction may limit genotypic diversity. The allozymic analysis detected 18 loci from 13 enzyme systems. Large deviations from Hardy-Weinberg equilibrium were common because of an excess of homozygotes for several enzyme systems. The genotypic diversity within these eight populations had a mean D value of 0.973 with an average number of genotypes per population of 19.6. These results suggest that genotypic diversity within these populations is not severely limited by the rarity of sexual reproduction. The mean genotypic distance index (D₁₄ = 0.801) suggests a high degree of differentiation between populations. The mean number of populations per genotype was 1.78. Using a Mantel test, the genotypic distance matrix was not significantly related to the population-to-population distance matrix (t = -0.161, P = 0.413). Although rare events of sexual reproduction may help maintain genetic variation, somatic mutations and multiple origins of clones may be important factors maintaining genetic diversity both within and between populations of L. minor.