title: Specialized and Generalized Pollen-Collection Strategies in an Ancient Bee Lineage.
abstract: Iconic examples of insect pollination have emphasized narrowly specialized pollinator mutualisms such as figs and fig wasps and yuccas and yucca moths. However, recent attention by pollination ecologists has focused on the broad spectra of pollinated plants by generalist pollinators such as bees. Bees have great impact for formulating hypotheses regarding specialization versus generalization in pollination mutualisms. We report the pollination biology of six northern European species of an extinct tribe of pollen-basket-bearing apine bees, Electrapini, of early-middle Eocene age, examined from two deposits of 48 and 44 million years in age. These bees exhibit a pattern of generalized, incidental pollen occurring randomly on their heads, thoraces, and abdomens, obtained from diverse, nectar-bearing plants. By contrast, a more restricted suite of pollen was acquired for metatibial pollen baskets (corbiculae) of the same bee taxa from a taxonomically much narrower suite of arborescent, evergreen hosts with uniform flower structure. The stereotyped plant sources of the specialist strategy of pollen collection consisted of pentamerous, radially symmetrical flowers with a conspicuous gynoecium surrounded by prominent nectar reward, organized in structurally similar compound inflorescences. Pollen specialization in bees occurs not for efficient pollination but rather in the corbiculate Electrapini as food for bee larvae (brood) and involves packing corbiculae with moistened pollen that rapidly loses viability with age. This specialist strategy was a well-developed preference by the early Eocene, providing a geochronologic midpoint assessment of bee pollen-collection strategies.
authors.affiliation: Steinmann Institute, University of Bonn, Nussallee 8, 53115 Bonn, Germany. Electronic address: twappler@uni-bonn.de.
authors.forename: Torsten
authors.initials: T
authors.lastname: Wappler
authors.affiliation: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, USA; Department of Entomology, University of Maryland, College Park, MD 20742, USA; College of Life Sciences, Capital Normal University, Beijing 100048, China. Electronic address: labandec@si.edu.
authors.forename: Conrad C
authors.initials: CC
authors.lastname: Labandeira
authors.affiliation: Division of Entomology, Natural History Museum, University of Kansas, Lawrence, KS 66045, USA; Department of Ecology & Evolutionary Biology, University of Kansas, Lawrence, KS 66045, USA; Division of Invertebrate Zoology, American Museum of Natural History, New York, NY 10024, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Engel
authors.affiliation: Department of Palaeontology, University of Vienna, Althanstraße 14 (UZAII), 1090 Vienna, Austria.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Zetter
authors.affiliation: Department of Palaeontology, University of Vienna, Althanstraße 14 (UZAII), 1090 Vienna, Austria.
authors.forename: Friðgeir
authors.initials: F
authors.lastname: Grímsson
mesh_terms: D000818:Animals; D001070:Appetitive Behavior; D001516:Bees / Q000502:physiology*; D005075:Biological Evolution; D005580:Fossils; D005858:Germany; D019684:Magnoliopsida / Q000502:physiology*; D011058:Pollen / Q000502:physiology; D054817:Pollination; D013559:Symbiosis