The sweet path of Hansel and Gretel: pollination system of Masdevallia hortensis Luer & R. Escobar (Orchidaceae: Pleurothallidinae) in a cloud montane forest of the Cordillera Occidental, in Colombia

Abstract

Pollination by deception is assumed as the general rule among pleurothallid orchids. However, considering the exceptional diversity of these orchids (44 genera and over 5100 species) and the relatively limited number of available studies (pollination ecology has been assesed in only 17 genera), generalized trends about their pollination systems might disregard a wide variety of specific life-history traits and inconspicuous honest signals/rewards for pollinators. Known associations of pleurothallid orchids with a large assortment of fly taxa further support this assumption. We investigated the natural pollination system of Masdevallia hortensis, a strictly endemic species of cloud forests in the Western Andes of Colombia. Masdevallia hortensis exhibited a sophisticated and customized pollination mechanism, producing sugary secretions in the lateral sepals along purple dotted patches, fed upon by different visiting species of fruit flies (Drosophilidae). The sucrose concentration in these secretions varied throughout the day and was significantly lower after removing the pollinaria. Visiting fruit flies appeared to be guided towards a chamber between the mobile lip and the column by the dotted lines in the lateral sepals. During visitations, individuals of the most abundant species in our observations (Drosophilidae sp. 1 [AO]) were singly entrapped in the chamber until eventually freeing themselves with the pollinaria attached to their bodies. We also demonstrated that M. hortensis is strictly self-incompatible, which makes fly pollination an essential process for the maintenance of natural populations of the species. The flowers of M. hortensis offer rewards for visiting insects, an aspect that should also be evaluated among congenerics. In this way, we urge integrative ecological studies to understand the evolutionary patterns of this group of orchids.