Pollination failure in Tritoniopsis parviflora (Iridaceae): New insights into the ecology and anatomy of this oil- and nectar-producing species

Abstract

Pollination in the South African species Tritoniopsis parviflora is of particular interest as it is the only oil-producing member of Iridaceae outside the Americas and the only species in the family known to secrete both floral oil and nectar. We evaluated oil and nectar secretion dynamics of T. parviflora, identified floral visitors and characterized their foraging behavior, and quantified reproductive success. Chemical and anatomical analyses suggest temporal segregation in rewards offered in male and female phases of the protandrous flowers. The diacetin amount was vestigial and none of the bees observed on flowers were specialist oil-collecting bees. Fruit set in the four studied populations was very low (c. 16 % of flowers). These results suggest that the T. parviflora pollination may be ensured by different functional bee groups and the visits by nectar-feeding and pollen-collecting bees may have been supplementary for seed production in the study period in conditions of low abundance of oil bees. The diversity of rewards in T. parviflora may serve as a form of bet-hedging that allows for pollination by generalist bees in the face of unreliable pollination service by specialist oil-collecting bees.