Protogyny, Self-Incompatibility and Pollination in Anthocercis gracilis (Solanaceae)

Abstract

The pollination biology of A. gracilis was examined in glasshouse plants and natural populations. The species is both protogynous and pre-zygotically self-sterile (self-incompatible). Protogyny prevents autopollination (autogamous self-pollination), and self-incompatibility avoids geitonogamous self-fertilisation. This sequence is essential because prior selfing blocks the style with pollen tubes and prevents subsequent outcrossing. Flowers have no discernible daytime odour, the pollen is clumped and not easily shaken from opened anthers, and daytime insect visitors are rarely observed in the field. However in long-established populations, mast plants carry one or a few capsules during winter-spring and seeds per capsule are generally high. Reproduction of natural populations involves reliable pollinators of unknown identity, possibly small flies, bees or moths lured by a tiny amount of sucrose-rich nectar secreted by the hypogynous disc. It is not anomalous that A. gracilis has two devices for preventing self-fertilisation, protogyny and strong self-incompatibility, as both are functional aspects of the same outcrossing system. This is the first report of self-incompatibility in the Anthocercideae which is an old and apparently basal lineage in the Solanaceae.