GENETIC DIVERSITY IN AN ANT-DISPERSED CHENOPOD SCLEROLAENA-DIACANTHA

Sclerolaena diacantha is a common and widespread, short-lived chenopod of arid Australia. The diaspore contains a food mass attractive to an ts and, at sites where the ant Rhytidoponera sp B is common, thousands of diaspores accumulate on the nest mounds. Bagged plants set seed, s howing that it is self-compatible. Population genetic variation was in vestigated at two levels: within and between sites, and within and bet ween seed banks accumulated on the ant nests. Electrophoretic analysis of adult plants for 17 loci at 12 sites revealed nine polymorphic loc i, but within sites only 6-18% of the loci were polymorphic. The value s for mean gene diversity (He=0.042) and total genetic diversity, (H(T )=0.088) were lower than those recorded for most other plant species. The mean fixation index of 0.52 indicated a mixed mating system with a bout 70% selfing. Most of the genetic diversity was distributed within sites (Dst=0.008) and the mean value of 0.094 for G(ST) indicated low levels of genetic differentiation. Electrophoretic analysis of seeds from 12 ant mounds at two sites showed that genetic differentiation wa s three times greater between seed banks than between the sites. Howev er, collectively the genetic diversity stored within ant mounds was si milar to the total diversity within the sites. It appears that restric ted ant-dispersal and moderate inbreeding may create a local populatio n structure that is undetected when sampling at a larger scale. Since investigations of genetic patterns on a very local scale are just begi nning, there is much to learn about the evolutionary and genetic conse quences of different seed flow patterns.