Isozyme variation within and between Dutch populations ofClosterium ehrenbergiiandC. moniliferum(Chlorophyta, Conjugatophyceae)

The isozyme banding patterns of up to 43 strains of Closterium ehrenbergii isolated from two populations and up to 51 strains of C. moniliferum isolated from five populations were examined for shikimate dehydrogenase (SDH), tetrazolium oxidase (TO), malate dehydrogenase (MDH) and NADH dehydrogenase (NADH-DH). Breeding experiments were also attempted. Genetic variability was found both within and between populations for both species tested. The phenotypic identity (Ip) between species was 0·674 which is consistent with their current classification as congeneric species. The breeding experiments indicated that Dutch populations of these two species may be sterile, which may account for observed nonrandom associations between genotypes within populations. These data indicate that C. moniliferum may have a higher level of genetic variation than C. ehrenbergii. This is one of the few quantitative studies of genetic variability and differentiation of freshwater algal populations.