The sweet path of Hansel and Gretel: pollination system of Masdevallia hortensis (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 this group (44 genera and over 5100 species) and the relatively limited number of available studies (pollination ecology has been assessed 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. The few known associations of pleurothallid orchids with a large assortment of fly taxa further support the assumption of generalized pollination by deception. We investigated the natural pollination system of Masdevallia hortensis, a strictly endemic species of cloud forests in the Western Andes of Colombia. This species exhibited a sophisticated and unique 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 significantly decreased after pollinaria removal. Visiting fruit flies appeared to be guided towards a chamber between the mobile lip and the column, by dotted lines in the lateral sepals. During visitations, individuals of the most abundant species in our observations (Drosophila sp. 1) 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 be thoroughly evaluated before making generalizations. In this way, we urge integrative ecological studies to understand the reproductive evolutionary patterns in this group of orchids.