Variation in ribosomal DNA within and between populations of Isotoma petraea and Macrozamia riedlei

Abstract

Restriction fragment length polymorphisms in ribosomal DNA were observed within and between populations of Isotoma petraea and Macrozamia riedlei. 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-pollinated cycad with high levels of gene flow throughout its population system. Variation in rDNA was observed within and between populations of both species. In I. petraea the level of variation was low with most individuals having one length variant, except in populations with fixed hybridity, whereas in M. riedlei high levels of variation were observed with an average of eight variants per individual. The pattern of variation in I. petraea showed homogenization of length variants within individuals and populations with divergence of length variants between populations. The pattern of variation in M. riedlei showed mixing of length variants and maintenance of various length variants within individuals and populations. The different patterns of variation are consistent with the different breeding systems of the two species.