Preliminary evidence that the long-proboscid fly, Philoliche gulosa, pollinates Disa karooica and its proposed Batesian model Pelargonium stipulaceum

Abstract

Long-proboscid flies have been documented as the primary pollinators in several long-tubed floral guilds in southern Africa. These specialized pollination systems have become models for studying floral mimicry, adaptation, and coevolution. In this study we document a previously unknown pollinator of Pelargonium stipulaceum (L.f.) Willd. (Geraniaceae) and Disa karooica Johnson & Linder, a species within the Disa draconis complex (Orchidaceae), and propose the occurrence of a new floral model-mimic system in the semiarid interior of South Africa. We find that Philoliche gulosa Wiedemann (Tabanidae) is a pollinator of the putative floral model, Pelargonium stipulaceum and its floral mimic, Disa karooica. We document similarities in floral spur/tube length, spectral reflectance, absence of scent, presence of nectar guides, and overlapping phenology and distribution in these two sympatric plant species. We use colour spectrum analyses to test the idea that divergence in flower colour in the D. draconis complex is driven by adaptation to model Pelargonium species of different colours.