Floral biology of Aristolochia bianorii Sennen & Pau

Abstract

[eng] Pollination deception has been reported in the genus Aristolochia. However, the floral biology and pollination mechanism of Aristolochia bianorii Sennen & Pau, an endemic species to Mallorca and Menorca, have not been studied yet. The objective of this study was to investigate the reproductive biology of this species, more specifically i) the floral anthesis, ii) the mating system and reproductive success, iii) pollinators and iiii) the volatile organic compounds (VOCs) emitted by the flowers. All fieldwork was performed in a population located on the east coast of Mallorca, in Cala Mesquida area (western Mediterranean Basin). First, flower buds were marked and monitored daily to define reproductive stages and flower duration. The receptivity of the stigma was evaluated using Peroxtesmo® bands. Regarding the mating system and reproductive success, experimental bagging and manual pollination treatments were performed to test for autonomous self-pollination, induced self-pollination, and cross-pollination. Moreover, VOCs emitted by flowers in different stages were evaluated by means of a solid phase microextraction (SPME) followed by immediate gas chromatography-mass spectrometry (GC-MS). Finally, flowers were collected throughout the flowering period to analyze the presence and quantity of pollinators within the flowers. The results showed that the presence of pollinators was affected both by the time of flowering and by the phenological phase in which the flower was found. Aristolochia bianorii flowers last between 72 and 96 hours and that the species exhibits autonomous self-pollination. However, the fruit set in the autonomous self-pollination treatment was lower than the others pollination treatments, and the number of seeds per fruit was lower compared to the control treatment. These results contrast with other Aristolochia species, in which both protogyny and herkogamy have been reported to prevent from autonomous self-pollination. The predominant pollinator belonged to the Chloropidae family (Diptera), and the most common VOCs were cycloalkanes or saturated hydrocarbons, alkanes or saturated hydrocarbons, oximes, esters, alkens or unsaturated hydrocarbons, cyclic unsaturated hydrocarbons, isocyanates, amides, and carboxylic acids were identified, matching with a deceptive pollination by mimicking the oviposition site. Finally, there was not significant differences in VOCs diversity between the female and the male stages. All in all, this study generates huge information on the floral biology of this poorly studied and range restricted species.