Self-compatibility provides little reproductive assurance in the summer-flowering Aloe reitzii var. reitzii

Abstract

Floral adaptations, notably floral design and display, enable plants to govern their mating opportunities through pollinator attraction and pollen dispersal. However, large floral displays, together with multiple simultaneously open flowers in an hermaphroditic plant, increase the potential for geitonogamous self-pollination. Many angiosperms have evolved self-incompatibility that prevents self-fertilization, instead requiring outcrossing by pollen vectors for successful seed set. We investigated the reliance of the summer-flowering Aloe reitzii var. reitzii on pollinators for reproduction and by using controlled hand-pollination experiments to determine whether Aloe reitzii var. reitzii is self-compatible. Contrary to most aloes, Aloe reitzii var. reitzii is shown here to be partially self-compatible, but reliant on pollinators to transfer pollen between flowers within the same raceme or plant, as well as to other plants. Aloe reitzii var. reitzii appears incapable of autonomous self-pollination and pollinator-mediated geitonogamy causes reduced fecundity in Aloe reitzii var. reitzii. However, hand-selfed treatments produced viable seeds capable of germinating, suggesting that the partial self-compatibility in Aloe reitzii var. reitzii does provide some reproductive advantage and may have evolved due to its restricted distribution and increasing population fragmentation – possibly due to anthropogenic change.