VARIATION IN RIBOSOMAL DNA WITHIN AND BETWEEN POPULATIONS OF ISOTOMA-PETRAEA AND MACROZAMIA-RIEDLEI

Restriction fragment length polymorphisms in ribosomal DNA were observ ed within and between populations of Isotoma petraea and Macrozamia ri edlei. Isotoma petraea is a diploid self-pollinating species which has evolved complex hybridity in response to inbreeding and exhibits high levels of genetic differentiation between its geographically isolated populations. Macrozamia riedlei is a diploid dioecious wind-pollinate d cycad with high levels of gene flow throughout its population system . Variation in rDNA was observed within and between populations of bot h species. In I. petraea the level of variation was low with most indi viduals having one length variant, except in populations with fixed hy bridity, whereas in nl, riedlei high levels of variation were observed with an average of eight variants per individual. The pattern of vari ation in I. petraea showed homogenization of length variants within in dividuals and populations with divergence of length variants between p opulations. The pattern of variation in M. riedlei showed mixing of le ngth variants and maintenance of various length variants within indivi duals and populations. The different patterns of variation are consist ent with the different breeding systems of the two species.