DOI: 10.5061/dryad.63xsj3v2g
title: Global patterns in bumble bee pollen collection show phylogenetic conservation of diet

description: 1. Bumble bees (Bombus) are a group of eusocial bees with a strongly
 generalised feeding pattern, collecting pollen from many different
 botanical families. Though predominantly generalists, some bumble bee
 species seem to have restricted dietary choices. It is unclear whether
 restricted diets in bumble bees are inherent or a function of local
 conditions due to a lack of data for many species across different
 regions. 2. The objective of this study was to determine whether bumble
 bee species displayed specific patterns of pollen collection, and whether
 patterns were influences by phylogenetic relatedness or tongue length, a
 trait known to be associated with structuring floral visitation. 3. Bumble
 bee pollen collection patterns were quantified from 4,132 pollen loads
 taken from 58 bumble bee species, representing 24% of the
 pollen-collecting diversity of this genus. 4. Phylogenetic trait mapping
 showed a conserved pattern of dietary dissimilarity across species, but
 not for dietary breadth. Dietary dissimilarity was driven by collection of
 Fabaceae, with the most similar species collecting around 50–60% of their
 diet from this botanical family. The proportion of the diet collected from
 Fabaceae also showed a conserved phylogenetic signal. Greater collection
 of Fabaceae was associated with longer tongue lengths, with shorter
 tongued species focusing on alternative botanical families. However, this
 result was largely driven by phylogenetic relatedness, not tongue length
 per se. 5. These results demonstrate that, though generalists, bumble bees
 are still subject to dietary restrictions that constrain their foraging
 choices. These dietary constraints have implications for their persistence
 should their core resources decline in abundance. 02-Jun-2021 --
description: <b><i>Pollen diet
 quantification.</i></b><i> </i>Bumble bee pollen
 diets were quantified following established methodologies (Kleijn
 & Raemakers, 2008; Wood <i>et al.</i>, 2019; see
 Supplementary Methods). Briefly, dried pollen balls were removed from
 selected pinned bumble bee specimens taken from museum and private
 collections in order to achieve the greatest possible taxonomic
 representation. Use of museum material is necessary for species such as
 <i>B. cullumanus</i> that have declined to extinction across
 large parts of their range (Williams <i>et al</i>., 2013), and
 therefore cannot easily be studied in contemporary landscapes. These balls
 were rehydrated, stained with fuchsin jelly, and pollen grains were
 identified using light microscopy, predominantly to genus. The proportion
 of each plant taxon was assessed, with taxa representing &lt;2–5%
 excluded (depending on identifier) as these may have arisen from
 contamination (Müller, 1996). These proportions were weighted by the
 overall size of the pollen ball relative to a full load, and weightings
 were used to calculate final dietary proportions. A total of 4,136 pollen
 loads from 58 bumble bee species belonging to 13 subgenera (representing
 approximately 93% of subgenera and 24% of species that collect pollen,
 Dataset S1, Dataset S2) from 34 countries were analysed (Table S1), 1,743
 of which were published previously (Kleijn & Raemakers, 2008; Wood
 <i>et al.</i>, 2019). Specimens for which label dates were
 available (n=4,089) were collected between 1874-2020 (median=1992). Data
 of capture was not considered or controlled for in this study, as there is
 no evidence to suggest that bumble bee diets change meaningfully over time
 (Kleijn & Raemakers 2008). The most important museums were the
 Laboratory of Zoology collection, University of Mons (1,221 specimens,
 Mons, Belgium), the Naturalis Biodiversity Center (552 specimens, Leiden,
 the Netherlands), the J.B. Wallis/R.E. Roughley Museum of Entomology (369
 specimens, Winnipeg, Canada), the Royal Belgian Institute of Natural
 Sciences (341 specimens, Brussels, Belgium), the Bavarian State Collection
 of Zoology (323 specimens, Munich, Germany), the A.J. Cook Arthropod
 Research Collection (296 specimens, East Lansing, USA), and the Natural
 History Museum (239 specimens, London, UK). Full details are available in
 Dataset S2.
description: Information explaining the relevant sections for each datafile
 can be found within each file on the 'Metadata' tab.