Who helps whom? Pollination strategy of Iris tuberosa and its relationship with a sexually deceptive orchid.

Reproductive success of plants may be affected by interactions with co-flowering species either negatively, through competition for pollinators, or positively, by means of a magnet species effect and floral mimicry. In this study, potential interactions between Iris tuberosa, a rewarding species, and Ophrys fusca, a sexually deceptive orchid, were explored in four populations in southern Italy. In each population plots showing different ratios of the examined species were arranged in the field, and in each plot the number of pollinators and fruit set were assessed. In addition, flower size and floral hydrocarbons produced by the two species were analysed. Morphological and scent data pointed out that flower size and aliphatic compounds did not differ significantly between the two species. Interestingly, both species shared tricosane and 11-nonacosene, electrophysiologically active compounds in the shared dominant pollinator Adrena. We have found that fruit production and number of pollinators in I. tuberosa varied significantly among plots, while percentage of capsules and number of pollinators of O. fusca captured showed no significant differences across plots. These results suggested, that the presence of O. fusca contributes differentially to pollinator attraction, and thus, to total reproductive success of I. tuberosa, according to a different ratio of aggregation. These findings suggest that I. tuberosa profits from the greater abundance of insects attracted by the presence of orchid specimens, and that a sexually deceptive orchid may be a magnet species in pollination strategy.