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.

Generalized host‐plant feeding can hide sterol‐specialized foraging behaviors in bee–plant interactions

“…Other floral traits are known to support pollination specificity such as nectar and floral scent (Johnson, Hargreaves, & Brown, ; Shuttleworth & Johnson, ). Growing evidence suggests that pollination syndromes are not limited to morphological traits but convergent suites of floral chemical traits could also act as filters in host‐plant selection and therefore pollination systems (Johnson et al, ; Shuttleworth & Johnson, ; Vanderplanck et al, ; Weiner et al, ). This hypothesis is strongly supported by the bee abilities to detect pollen nutritional quality and discriminate among hosts (Vaudo, Patch, Mortensen, Tooker, & Grozinger, ).…”

Soil eutrophication shaped the composition of pollinator assemblages during the past century

“…The fact that pollinators with more diversified diets were less affected could be explained by their flexibility and ability to forage in a diverse set of habitats (Roger et al 2017), thus reducing or even excluding the contribution of plants with toxic compounds to their diets. However, larval habits are much more specialized in butterflies than bees, with non-polyphagous species frequently having strong preferences for a single plant genus; whereas a large number of non-polyphagous bees use a diverse set of plants from the same family as preferred resources (Vanderplanck et al 2017). However, larval habits are much more specialized in butterflies than bees, with non-polyphagous species frequently having strong preferences for a single plant genus; whereas a large number of non-polyphagous bees use a diverse set of plants from the same family as preferred resources (Vanderplanck et al 2017).…”

“…While there has been recent research into effects on herbivores (Nijssen et al 2017, Pöyry et al 2017, WallisDeVries and van Swaay 2017, the potential effects of soil eutrophication on those feeding on pollen and nectar (potential pollinators) are largely unexplored (Stevens et al 2018, but see Betzholtz et al 2013, Tamburini et al 2017, Ramos et al 2018. Such potential bottom-up effects could be mediated by reduction in nectar or pollen availability or quality (Petanidou et al 1999, Vanderplanck et al 2017. Also, insects may be deterred from visiting, or ovipositing, on plants whose chemical composition has been changed by nitrogen enrichment (Abbas et al 2014, Audusseau et al 2015, Kurze et al 2017.…”

Floral Metabolism of Sugars and Amino Acids: Implications for Pollinators’ Preferences and Seed and Fruit Set

“…Pollen chemistry may have a weaker influence on insect preferences, as polylectic bees, which collect pollen from plants of different species, appear to disregard the chemical composition of pollen despite the beneficial effect that blends of amino acids and polypeptide have on colony fitness (Vanderplanck et al, 2014). However, this may not hold true for oligolectic bees, for which pollen chemistry drives evolutionary host shifts (Vanderplanck et al, 2017). These studies and many others present in the literature demonstrate that pollen and nectar chemistry influence pollinators' choices but that the interaction is specific between a plant and its pollinators.…”