Abstract
The extent of reproductive isolation in various organisms increases with genetic distance. It was suggested that Asplenium setoi in the Ogasawara and Ryukyu islands were genetically differentiated and it was suspected that reproductive isolation may exist between them. In this study, rbcL sequences of the plants from these two localities were determined. They were found to have a 5-bp difference out of 1,203 bp. Artificial crossing experiments were also performed between A. setoi from the two localities to elucidate the extent of reproductive isolation between them. Although hybrids were obtained, the rate of hybrid formation differed between the reciprocal crosses. Twenty-three hybrids from 80 crosses were obtained when the maternal plants were from Ogasawara and the paternal plants were from Ryukyu. In the opposite combination of 80 crosses, only two hybrids were obtained. Thus, hybrids were easily formed only when plants from Ogasawara were the maternal parent. Asplenium setoi from the Ogasawara and Ryukyu islands may be bound for speciation.
