Outcrossing rates as affected by pollinators and the heterozygote advantage of Monochoria korsakowii

Monochoria korsakowii shows somatic enantiostyly as each plant bears two kinds of flowers: left- and right-handed flowers, which differ in style deflection. Since the capsules of M. korsakowii and M. vaginalis contain hundreds of seeds, we detected heterozygotes with two isozyme markers, Adh-1 and Pgi-2 locus, and measured outcrossing rates for single fruits in each of the target genotypes, Outcrossing rates were measured on an experimental population of Adh-1(1)/Adh-1(1) homozygotes, in which target plants of the Adh-1(0)/Adh-1(0) homozygote were planted at three different positions. Outcrossing rates for M, korsakowii ranged from 37% to 80% with pollinators and were 0% without pollinators. The variation in the outcrossing rates was significantly affected by the species of pollinators but was not affected by the position of target in the experimental population. When the flowers were visited by both Apis cerana japonica and Xylocopa circumvolans, the mean outcrossing rate was 72.3%, and when visited by Apis cerana japonica only, the mean outcrossing rate was 49.2%. The heterozygous seeds, detected by Adh-l locus in the present experiment, had greater weight, and produced larger seedlings than those from homozygous seeds. In a comparative experiment, the outcrossing rate for M. vaginalis, was zero because it had been self-pollinated before the flowers opened, or it was cleistogamous. (C) 1998 Elsevier Science B.V, All rights reserved.