Sex, flies and flower trap: Trapping trichomes and their function in pollination

Trapping trichomes, a common trait found in protogynous trap flowers, are thought to enable interaction with pollinators, promoting both pollen removal and fruit set. However, this hypothesis has yet to be empirically confirmed. In this study, we experimentally tested whether trapping trichomes favour male and female functions in trap flowers. Using protogynous South American Aristolochia esperanzae trap flowers, we observed the temporal variation in both sexual functions and associated them with the wilting of the flower and trapping trichomes. Next, we described the trapping trichomes features associated with the capture, entrapment and release of pollinators. Finally, we used manipulative experiments involving trapping trichome removal to quantify their influence on pollinator entrapment, pollen removal and fruit set. While flowers wilted after the end of the female phase, the trapping trichomes only wilted some hours after pollen presentation, promoting a delay in the exit of pollinators, so they carried pollen. Trapping trichomes features, such as a density gradient towards the interior of the tube, unidirectional orientation and epicuticular waxes, may be important in the capture and entrapment of pollinators. Trapping trichome removal decreased drastically the probability of pollinator entrapment and pollen removal, leading to no fruit set. These results indicate that the evolution and maintenance of trapping trichomes in trap flowers probably occurred through selective pressures from both sexual functions and highlight their role in the functioning of this highly phenotypically specialized pollination system. Read the free Plain Language Summary for this article on the Journal blog. Resumen Los tricomas de captura son un rasgo común en las flores trampa protogínicas, se cree que estos permiten la interacción con los polinizadores, promoviendo tanto la remoción de polen como la fructificación. Sin embargo, esta hipótesis aún no ha sido confirmada empíricamente. En este estudio, probamos experimentalmente si los tricomas de captura favorecen las funciones masculina y femenina en flores trampa. Utilizando las flores trampa protogínicas de la especie Sudamericana Aristolochia esperanzae, nosotros observamos la variación temporal en las funciones sexuales y las asociamos con el marchitamiento de la flor y los tricomas de captura. Luego, describimos las características de los tricomas de captura asociadas con la captura, atrapamiento y liberación de poli