Pollination Syndromes in Mediterranean Orchids—Implications for Speciation, Taxonomy and Conservation

Abstract

The Mediterranean flora is spectacularly rich in orchid species that have evolved remarkable adaptations to their environment. Orchids have complex and delicate interactions with their pollinators, which makes them particularly prone to local extinction. Conservation actions should be encouraged for a range of endangered Mediterranean orchid species, but the current taxonomic confusion in several genera and the apparent disagreement among orchid taxonomists make the situation particularly confusing from a conservation perspective. In this review, we document how the different pollination syndromes of Mediterranean orchids (nectar reward, shelter offering, food deception and sexual deception) can have a profound impact on the type of reproductive barriers among species, on floral phenotypic variation as we perceive it, on potentially related processes of species sorting and extinction and, consequently, should have a strong influence on the related conservation management programs. We also highlight that the majority of Mediterranean orchids are pollinated by specialised bees often occupying otherwise narrow ecological niches (e.g. pollen specialisation, brood cell parasites, specific nesting site). This condition makes the orchid-pollinator interactions very fragile and several orchid species prone to local extinction. We illustrate this phenomenon by a selection of case studies that show how the adequate integration of the ecological requirements/traits of the orchids and their associated pollinators into conservation actions could help protect endangered species and ensure the sustainability of the often complex local pollination web.

Pollinator sharing by the sexually deceptive Green-comb Spider Orchids, Caladenia phaeoclavia, C. parva and C. villosissima (Orchidaceae: Caladeniinae): taxonomic considerations

“…Other potential pre-zygotic isolation mechanisms are also absent including differences in pollen position on the vector and flowering times. Hybrids are considered to be relatively common in Caladenia (Backhouse and Jeanes 1995) suggesting that postzygotic reproductive barriers to hybridisation in the genus are weak or absent, which is also characteristic of sexual deception in general (Peakall et al 1997, Stökl et al 2008, Vereecken et al 2010, Xu et al 2011, Whitehead and Peakall 2104. The distribution of C. villosissima overlaps extensively with that of C. parva in western Victoria, and the distributions of C. phaeoclavia and C. parva meet in southern Victoria and the Grampians, indicating there is a high likelihood of introgression between the three taxa.…”

Ecological interactions of the sexually deceptive orchid Orchis galilaea

“…The majority of species within the family have highly specialized adaptations to enhance pollination by insect pollinators (Vereecken et al 2010;Kindlmann and Roberts 2012).…”

“…In fact, many orchid species from the Mediterranean region do not possess nectar, attracting pollinators through food deception (Dactylorhiza genus), shelter deception (Serapias genus), or sexual deception (Ophrys genus) (Dressler 1993;Vereecken et al 2010;Kindlmann and Roberts 2012).…”

“…Consequently, they are highly vulnerable to local extinction (Kindlmann and Roberts 2012). Such intricate plant-pollinator interactions are prevalent in the Mediterranean region, which highlights the importance of targeted approaches for the conservation of endangered species (Vereecken et al 2010). Studies investigating the population ecology of threatened and vulnerable species have the potential to enhance our understanding of how species should be managed.…”

Reproductive success and pollination of the Tuncurry Midge Orchid (Genoplesium littorale) (Orchidaceae) by Chloropid Flies

“…Up to one third of orchid species deceive pollen vectors by promising non-existent rewards (van der Pijl and Dodson 1966). It is well known that orchid pollen vectors may respond to false offers of nectar (food deception) or a mate (sexual deception) (Vereecken et al 2010). …”