Absence of long-proboscid pollinators for long-corolla-tubed Himalayan Pedicularis species:: Implications for the evolution of corolla length

The genus Pedicularis manifests great variation in corolla morphology, including corolla tube length. Previous observations conducted during daytime have documented bumblebees to be important pollinators for short-and long-tubed Pedicularis species. However, the potential role of night-flying long-proboscid insects (moths) as selective agents for the evolution of corolla length has not been determined. Three Pedicularis species, Pedicularis densispica, Pedicularis gruinea, and Pedicularis siphonantha, in montane meadows of Yunnan Province, southwestern China, have extremely divergent corolla tube lengths of 7.1, 22.0, and 50.6 mm, respectively. We find that all three species are pollinated by similar bumblebee species. Pollination treatments indicate that seed sets of inflorescences enclosed in fine-meshed nylon nets in the night are not different from open-pollinated inflorescences, but those bagged in the day have significantly decreased seed set, indicating that moth pollinators are not important for the study species. We present anatomical evidence that the loss of nectaries in long-tubed species, and hence the loss of nectar production, is a derived trait. The loss of nectaries may be a key innovation, releasing the corolla from the mechanical constraint imposed by pollinators reaching for nectar.