Evidence of Outcrossing in Trillium erectum and Trillium grandiflorum (Liliaceae)

Abstract

Journal of Heredity 1997:88:325-329; 0022-1503/97/S5.00 Enzyme electrophoresis was used to Investigate aiiozyme diversity and outcrossing rates In a population of Trillium erectum and T. grandiflorum from central New York. Enzyme polymorphisms were observed for 11 of 14 and 7 of 13 loci examined in T. erectum and T. grandiflorum, respectively. Percent polymorphic loci (P), mean number of alleles per locus (A), and mean expected heterozygosities («.) were greater In T. erectum {P = 78.6%; A = 2.48; H. = 0.220) than in T. grandiflorum (P = 43.6%; A = 2.18; H. = 0.130). Neither species showed a net excess nor deficiency of heterozygotes as measured by fixation Indices. These levels of aiiozyme diversity are more typical of species with outcrossing breeding systems than species with selflng breeding systems. A mating system analysis revealed that outcrossing is high In T. grandiflorum (^ = 0.761 ± 0.076; x ± SD). In contrast, the selflng rate In T. erectum was nearly 57% (^ = 0.423 ± 0.093) more typical of a species with a mixed-mating system. Nevertheless, these data strongly challenge the view that selflng breeding systems are typical of all North American species of Trillium.