Variation in the breeding system of two sympatric Dombeya species on La Reunion island

The high frequency of dioecy on oceanic islands has attracted a great deal of attention in plant evolution. In this study we quantify variation in the breeding system of two sympatric Dombeya species on La Reunion island. Bot h Dombeya species are cryptically dioecious, each sex retaining non-functio nal morphological structures of the other sex. One species is strictly dioe cious, whilst the other shows leaky dioecy, with 8/13 males producing fruit during two years of study. Males that set fruit did so following outcrossi ng but not after self-pollination despite the growth of self-pollen tubes i n the style. This suggests the occurrence of a late-acting self-incompatibi lity system. Several morphologically intermediate individuals are recognize d and suggested to be a result of interspecific hybridization. These purpor ted hybrids are hermaphrodite rind self-compatible, consistent with a compl ementary breakdown in dioecy and self-compatibility.