Matching Messel flowers with their insect visitors via pollen

The Messel Pit, a UNESCO World Heritage site, is famous for its exceptional preservation of Central Europe’s Middle Eocene terrestrial biota. Countless findings of various fossil mammals, reptiles, amphibians, birds, insects, and plants document a species-rich and complex ecosystem thriving under a hot and humid paratropical climate. Most of the buds/flowers/inflorescences collected from this site are still not taxonomically assigned, and only little is known about their insect visitors. In order to clarify the taxonomic placement of flowers, flower-insect interactions, and the foraging and feeding behaviour of insects, we extracted in situ pollen from anthers of flowers as well as in situ and/or adhering pollen from insects. So far, we have studied 715 flowers (205 with pollen) and 1126 insect specimens (225 with pollen). Pollen from the flowers suggests they represent at least 50 different angiosperm taxa, including, among others, representatives of Anacardiaceae, Araliaceae, Arecaceae, Cornaceae, Euphorbiaceae, Fabaceae, Hamamelidaceae, Malvaceae, Nympheales, Rosaceae, Rutaceae, Sapotaceae, and Vitaceae. The insects we investigated represent the four extant main pollinator groups: Coleoptera (476 specimens/101 with pollen), Diptera (220/19), Hymenoptera
(327/78), and Lepidoptera (37/9). Pollen was discovered both internally and externally in Coleoptera, Diptera, and Hymenoptera, but only externally in Lepidoptera. Even though we managed to match many of the pollen types extracted from insects to those from flowers, there were still several pollen types associated only with insects. Some insects had only one pollen type filling their gut or adhering to their exoskeleton, while others had up to eight different pollen types. Using the pollen, we inferred oligolectic or polylectic behaviour for visiting insects, as well as, generalized versus specialized pollination syndromes for the flowers. For example, Parthenocissus (Vitaceae) pollen was discovered in situ or adhering to various insects from all four major pollinator orders, implying a generalist pollination syndrome for this plant genus.