title: The importance of pollen chemistry in evolutionary host shifts of bees.
abstract: Although bee-plant associations are generally maintained through speciation processes, host shifts have occurred during evolution. Understanding shifts between both phylogenetically and morphologically unrelated plants (i.e., host-saltation) is especially important since they could have been key processes in the origin and radiation of bees. Probably far from being a random process, such host-saltation might be driven by hidden constraints associated with plant traits. We selected two clades of oligolectic bees (i.e., Colletes succinctus group and Melitta leporina group) foraging on co-flowering but unrelated host-plants to test this hypothesis. We analyzed floral scent, floral color and chemical composition of pollen from host and non-host plants of these two clades. We did not find evidence for host-plant evolution in the Melitta leporina group driven by one of the assayed floral traits. On the contrary, hosts of the C. succinctus group display similar primary nutritive content of pollen (i.e., amino acids and sterols) but not similar floral scent or color, suggesting that shared pollen chemistry probably mediates saltation in this clade. Our study revealed that constraints shaping floral associations are diverse and clearly depend on species life-history traits, but evidence suggests that pollen chemistry may act as a major floral filter and guide evolutionary host-shifts.
authors.affiliation: Laboratory of Zoology, Research Institute for Biosciences, University of Mons - UMONS, Place du Parc 20, B-7000 Mons, Belgium.
authors.forename: Maryse
authors.initials: M
authors.lastname: Vanderplanck
authors.affiliation: Landscape Ecology &Plant Production Systems Unit, Interfaculty School of Bioengineering (EIB), Université Libre de Bruxelles, Boulevard du Triomphe CP 160/12, B-1050 Brussels, Belgium.
authors.forename: Nicolas J
authors.initials: NJ
authors.lastname: Vereecken
authors.affiliation: Département de Biologie des Organismes, Université Libre de Bruxelles, av. Paul Héger, CP 160/12, B-1050 Brussels, Belgium.
authors.forename: Laurent
authors.initials: L
authors.lastname: Grumiau
authors.affiliation: Earth and Life Institute, Biodiversity Research Centre, Université Catholique de Louvain, Croix du Sud 4 L7.07.04, B-1348 Louvain-la-Neuve, Belgium.
authors.forename: Fabiana
authors.initials: F
authors.lastname: Esposito
authors.affiliation: Unit of Analytical Chemistry, University of Liège (Gembloux Agro-Bio Tech), Passage des Déportés 2, B-5030 Gembloux, Belgium.
authors.forename: Georges
authors.initials: G
authors.lastname: Lognay
authors.affiliation: Department of Proteomic and Microbiology, Research Institute for Biosciences, University of Mons - UMONS, Place du Parc 20, B-7000 Mons, Belgium.
authors.forename: Ruddy
authors.initials: R
authors.lastname: Wattiez
authors.affiliation: Laboratory of Zoology, Research Institute for Biosciences, University of Mons - UMONS, Place du Parc 20, B-7000 Mons, Belgium.
authors.forename: Denis
authors.initials: D
authors.lastname: Michez
mesh_terms: D000818:Animals; D001516:Bees / Q000235:genetics*; D005075:Biological Evolution; D003116:Color; D035264:Flowers; D010802:Phylogeny; D010944:Plants / Q000235:genetics*; D011058:Pollen / Q000737:chemistry*; D012903:Smell