Generalized food deception: colour signals and efficient pollen transfer in bee-pollinated species ofEulophia(Orchidaceae)

Abstract

Non‐rewarding plants use a variety of ruses to attract their pollinators. One of the least understood of these is generalized food deception, in which flowers exploit non‐specific food‐seeking responses in their pollinators. Available evidence suggests that colour signals, scent and phenology may all play key roles in this form of deception. Here we investigate the pollination systems of five Eulophia spp. (Orchidaceae) lacking floral rewards. These species are pollinated by bees, notably Xylocopa (Anthophorinae, Apidae) or Megachile (Megachilidae) for the large‐flowered species and anthophorid (Anthophorinae, Apidae) or halictid (Halictidae) bees for the small‐flowered species. Spectra of the lateral petals and ultraviolet‐absorbing patches on the labella are strongly contrasting in a bee visual system, which may falsely signal the presence of pollen to bees. All five species possess pollinarium‐bending mechanisms that are likely to limit pollinator‐mediated self‐pollination. Flowering times extend over 3–4 months and the onset of flowering was not associated with the emergence of pollinators, some of which fly year round. Despite sharing pollinators with other plants and lacking rewards that would encourage fidelity, the Eulophia spp. exhibited relatively high levels of pollen transfer efficiency compared with other rewarding and deceptive orchids. We conclude that the study species employ generalized food deception and exploit food‐seeking bees. © 2013 The Linnean Society of London,

The functional significance of complex floral colour pattern in a food‐deceptive orchid

“…The principle of innovative change in the outer floral colour and constraints on the central floral colour is congruent with that found by Peter & Johnson () & Peter & Johnson () in 19 food‐deceptive Eulophia species and by Heuschen, Gumbert & Lunau () in flowers of 162 food‐rewarding plant species. Together, these results suggest that unrelated food‐deceptive orchids have converged globally on a pattern of floral colour contrast, but it is hard to be certain whether this is because such contrasts elicit innate attraction by bees or because they exploit preferences of bees acquired in the context of a community of food plants with contrasting colour patterns.…”

“…). This pattern is also evident in certain deceptive orchid flowers in which the colours of the central petals, typically the lip which may have pseudopollen, nectar guides and other markings, contrast with the colours of the outer petals (Jersáková, Johnson & Kindlmann ; Peter & Johnson , ; Jersáková, Johnson & Jürgens ; Shi et al . ; Vignolini et al .…”

“…). For example, Peter & Johnson () & Peter & Johnson () found that 18 food‐deceptive Eulophia species all display strongly contrasting colour patterns comprising central ultraviolet (UV)‐absorbing patches and bright outer petals. The differences in colour between these two floral parts make them easily distinguishable to pollinating bees.…”

A pollinator shift explains floral divergence in an orchid species complex in South Africa

“…They have sympodal growth with sub-terranean tubers that produce a new vegetative shoot and an inflorescence from the base of the vegetative shoot each year. All taxa of Eulophia that we have examined, including the two forms described here, are deceptive and do not reward their pollinators (Peter and Johnson, 2013), although there is evidence that two pantropical species may reward their pollinators (Singer and Cocucci, 1997;Jürgens et al, 2009).…”

“…The pollinarium undergoes a bending movement similar to that of E. streptopetala (described by Peter and Johnson, 2013) which is thought to limit geitonogamous selfing (Peter and Johnson, 2006b). The pollinaria of these two forms are easily distinguished from those of co-ocurring congeners (E. clitellifera, E. clavicornis, E. ovalis, E. ensata and E. foliosa), all of which have obviously smaller pollinaria.…”