Mating System and Hybridity in Eucalyptus pauciflora

Abstract

Allozyme polymorphisms at 4 loci expressed in seeds, and 3 other loci expressed in seedlings, were used to determine the outcrossing rate in 3 natural subalpine populations of snow gum (E. pauciflora). Based on the seed loci data, an estimated 37% of seed was derived from self-fertilization and 63% from random outcrossing. In the most elevated population the estimate after germination was similar. However, at lower elevations the frequency of effective self-fertilization estimated at the seedling stage was only 16%. The less elevated populations also showed a greater average heterozygosity and a larger increase in heterozygosity in the adult over the progeny stages. Heterosis apparently operated differentially in these populations. It was more intense at the lower altitudes. Selection in favor of outcrossed individuals may be an important factor in checking the spread through the population of genes which promote self-fertilization, and which would otherwise enjoy and evolutionary advantage.