Differences in pollen viability in relation to different deceptive pollination strategies in Mediterranean orchids

Abstract

Background and aims: To date, current research involving pollen viability has been evaluated in a relatively low number of orchid species. In the present study, we focused on five related Mediterranean orchid genera (Anacamptis, Orchis, Dactylorhiza, Ophrys and Serapias) that are characterized by different types of deceptive pollination.

Methods: The in vitro germination ability of increasingly aged pollinaria of eight food-, seven sexually and two shelter-deceptive species was evaluated. Pollination experiments on two food-, one sexually and one shelter-deceptive species were also performed and the percentage of embryonate seeds derived from the increasingly aged pollinaria was checked.

Key results: All of the examined species showed long-term viabilities (=50 % pollen tube growth) that ranged from 8 to 35 d. Species with the same deceptive pollination strategies exhibited the same pollen viability trends. Interestingly, pollen viabilities of species groups with different deception types have shown significant differences, with sexually and shelter- deceptive species exhibiting a shorter life span than food-deceptive species.

Conclusions: This study confirms the prolonged germination and fertilization capacities of orchid pollinaria, and to our knowledge is the first report demonstrating a clear relationship between pollen viability and pollination system. It is proposed that this relationship is attributed to the different types of reproductive barriers, pre- or post-zygotic, that characterize Ophrys and Serapias and the food-deceptive species, respectively.

Fig. 1

Relationships between pollen germinability and pollen age for food-deceptive orchids. Black and white arrows indicate 50 and 10 % pollen germinability, respectively.

Fig. 2

Relationships between pollen germinability and pollen age for sexually deceptive orchids. Black and white arrows indicate 50 and 10 % pollen germinability, respectively.

Fig. 3

Relationships between pollen germinability and pollen age for shelter-deceptive orchids. Black and white arrows indicate 50 and 10 % pollen germinability, respectively.

Fig. 4

Relationships between percentage of seeds with embryos and pollen age for Anacamptis papilionacea and Orchis italica (food-deceptive species), Ophrys lutea (sexually deceptive species) and Serapias vomeracea (shelter-deceptive species).