Floral hosts of leaf-cutter bees (Megachilidae) in a biodiversity hotspot revealed by pollen DNA metabarcoding of historic specimens

cultivated. When plant families detected in pollen loads from different bee species were com- pared with the list of plants on which the particular bee species were observed, it was clear that Fabaceae is an important plant family for all six of the bee species (see S7 Table). Faba- ceae was the only plant family with both observed flower visits and detection in pollen loads in all six bee species. Amaranthaceae was detected by NGS in all six bee species, but only recorded in flower visits for M. karooensis and M. venusta. Additional recorded flower visits corresponding to detected families in pollen loads in this study includes Asteraceae in M. murina, M. felina, M. maxillosa, M. niveofasciata, and M. venusta, and Solanaceae and Poa- ceae in M. venusta. The 20 plant families with the most species in each region were selected from the plant database and cross-referenced with the ITS2 sequence reference database to determine whether all these families are represented in the sequence database. Three of the top 20 most species-rich families in the Succulent Karoo, one family from the Savanna, and two widespread families were not represented at all in the ITS2 database. Discussion Metabarcoding of pollen from pollinators is a recently developed molecular tool, which will greatly impact the research questions currently addressed by the fields of pollination biology and Melissopalynology (the study of pollen in honey). Here, pollen metabarcoding was used successfully on historic specimens from a natural history collection to investigate the floral

Fig 2. Frequency distribution of plant species detected in each bee species studied. Bees from the Succulent Karoo (M. karooensis and M. murina) and Savanna (M. felina and M. maxillosa) show similar species abundances, with the two widespread bee species (M. niveofasciata and M. venusta) both detecting up to 14 different plant species each. https://doi.org/10.1371/journal.pone.0244973.g002 PLOS ONE Floral hosts of Megachilidae revealed by metabarcoding PLOS ONE | https://doi.org/10.1371/journal.pone.0244973 January 21, 2021 8 / 16