Integrating past and present studies on Ophrys pollination - a comment on Bradshaw et al.

Abstract

In a recent research article in the Botanical Journal of the Linnean Society Bradshaw et al. (2010) provided a detailed and richly illustrated comparative analysis of labellum micromorphology in Ophrys L. They described the variety of epidermal cell types and the different patterns of structural complexity observed in representative species in Ophrys. We agree with Bradshaw et al. that the study of the labellum micromorphology, besides its general significance for plant morphology, is also of interest in the framework of pollinator attraction, as it might influence the optical properties of the labellum and play an important role in directing male insects to the right position for collection or delivery of pollen masses during pseudocopulation. The latter aspect was discovered some 50 years ago by Kullenberg (1956a, b, 1961) and investigated further by Ågren, Kullenberg & Sensenbaugh (1984) (a key reference overlooked by Bradshaw et al.), and the detailed descriptions by the authors shed light on possible directions of phenotypic evolution in Ophrys. However, we think that Bradshaw et al. drew largely unsupported conclusions and overlooked a considerable body of literature when they discussed the role and evolution of other floral traits, including pollinator-attracting signals, patterns of reproductive isolation and speciation in this genus of sexually deceptive orchids. Their view is notably summarized in the abstract of their article, in which they argued that ‘The relative contributions of olfactory, visual and tactile cues to the sophisticated pseudocopulatory pollination mechanism that characterizes Ophrys remain unclear, but the degree of reproductive isolation achieved, and thus the speciation rate, have certainly been greatly exaggerated by most observers’. This statement echoes similar conclusions in other papers (see, for example, Bateman et al., 2003; Pedersen & Faurholdt, 2007; Devey et al., 2008, 2009). Based on a long series of independent past and present studies, we advocate that the view expressed in the last section of their article and in the other works cited below is too simplistic and speculative and misrepresents the current state of understanding of Ophrys ecology and evolution