Tilioideae-Anthophila interactions in the Cenozoic of Europe

Bees of Europe are known to visit Tilia flowers of the subfamily Tilioideae
and pollen grains of this plant genus are frequently found on the bee’s exterior, especially in their corbiculae and scopae. To unravel the origin and history of Tilioideae-Anthophila relationships through the geological history of Europe, we studied flowers and insects from four Paleogene localities in France and Germany, including Menat (middle-late Paleocene, SelandianThanetian, 61–56 Ma), Messel (middle Eocene, early Lutetian, c. 48 Ma), Eckfeld (middle Eocene, middle Lutetian, c. 44 Ma), and Enspel (late Oligocene, late Chattian, c. 24 Ma), focusing on Tilioideae flowers and fossil bees with in-situ and/or adhered Tilioideae type pollen. Additionally, we also investigated living wild bees from different regions of present day Austria and screened them for Tilioideae pollen. Today, the Tilioideae consists of three genera; Craigia (2 spp.), Mortoniodendron (16 spp.), and Tilia (31 spp.). Craigia is restricted to S. China and Vietnam, Mortoniodendron ranges from S. Mexico to Colombia, but Tilia has a wide Northern Hemispheric distribution. All three genera are generally insect pollinated, some taxa are also wind pollinated, and all groups are known to be visited by both Anthophila (e.g., bees, bumblebees) and Diptera (e.g., hoverflies, blowflies).Our study revealed a close relationship between bees and Tilioideae flowers in Europe already during the Paleocene and spanning more than 55 million years until present day. We have identified bees with adhering Tilioideae
pollen from all investigated localities. In addition, we have discovered several fossil flowers from Eckfeld and Enspel with in-situ Tilioideae type pollen enabling a morphological/anatomical comparison with extant flowers of the subfamily. Our findings suggest that in Europe bees visited Mortoniodendron flowers during the Paleocene and Eocene, then Craigia and Tilia from the Oligocene to Miocene, and then continued visiting Tilia until present times.