ISOZYME VARIATION IN NEW-ZEALAND POPULATIONS OF MYRIOPHYLLUM AND POTAMOGETON SPECIES

Isozymes of six freshwater angiosperm species were examined as a measu re of genetic variation within and between populations. Five species ( Myriophyllum triphyllum Orchard, Myriophyllum propinquum A. Cunn., Myr iophyllum pedunculatum Hook. f., Potamogeton cheesemanii A. Benn., and Potamogeton ochreatus Raoul) are native to New Zealand, while Potamog eton crispus L., is adventive. Species were collected from a wide geog raphic range of lakes and rivers throughout New Zealand. Myriophyllum triphyllum, Myriophyllum propinquum and Myriophyllum pedunculatum were sampled from 23, 18 and five lakes respectively, while Potamogeton ch eesemanii, Potamogeton ochreatus and Potamogeton crispus were collecte d from a total of 12, nine and four water bodies, respectively. The pl ants were grown under uniform conditions prior to analysis and analyse d by starch ,eel electrophoresis for the following enzyme systems: PGM , PGD, MDH, GPI, AAT, EST, and IDH. All species studied showed little isozyme genetic diversity between populations and even less variabilit y within populations. On a relative scale, Myriophyllum propinquum dis played the largest degree of genetic differentiation, Myriophyllum ped unculatum and all three Potamogeton spp. were moderately variable, and Myriophyllum triphyllum showed the lowest level of diversity. There w as a close correlation between the amounts of intra- and interpopulati on genetic variability in all species. No association between geograph ic and genetic distances between populations could be found for any of the species examined, and the patterns of distribution of isozyme phe notypes and genotypes over populations suggest that populations are of ten started by a single colonising propagule, or several propagules of identical genotype, and then predominantly grow through vegetative pr opagation. The apparent lack of genetic variability indicated by the r esults of this study is consistent with low levels of variability obse rved amongst aquatic macrophytes in other countries.