Mechanical fit between flower and pollinators in relation to realized precision and accuracy in the hummingbird-pollinated Dolichandra cynanchoides

The adaptive accuracy of flowers in the context of pollination can be used to address the relationships between flower phenotype (fundamental pollination accuracy and precision) and realized accuracy and precision (interaction of floral parts with a pollinator). Here we tested whether effectiveness (number of pollen grains transported per visit) and realized male and female accuracy and precision differ between two hummingbird pollinator species (Heliomaster furcifer and Sappho sparganura) that pollinate the ornithophilous liana Dolichandra cynanchoides. Although the hummingbird species did not differ in the frequency of flower visitation, H. furcifer carried pollen on a narrower spot of the head and deposited significantly more pollen on a restricted zone of artificial stigmas − representative of the true stigma − compared with S. sparganura. Flower structure exhibited similar accuracy with regard to pollen deposition on and retrieval from pollinators. Functional flower depth matched significantly with the bill of the hummingbird exhibiting the highest precision and accuracy. This suggests that mechanical reciprocal fit may be responsible for the better pollination performance of H. furcifer. In this study we show that differences in realized accuracy and precision may explain evolutionary responses to pollinator specialization in a single pollinator species within functional groups.