Plant–pollinator interactions over time: Pollen metabarcoding from bees in a historic collection

Abstract

Pollination is a key component in agricultural food production and ecosystem maintenance, with plant–pollinator interactions an important research theme in ecological and evolutionary studies. Natural history collections provide unique access to samples collected at different spatial and temporal scales. Identification of the plant origins of pollen trapped on the bodies of pollinators in these collections provides insight into historic plant communities and pollinators’ preferred floral taxa. In this study, pollen was sampled from Megachile venusta Smith bees from the National Collection of Insects, South Africa, spanning 93 years. Three barcode regions, the internal transcribed spacer 1 and 2 (ITS1 and ITS2) and ribulose‐1,5‐biphosphate carboxylase (rbcL), were sequenced from mixed pollen samples using a next‐generation sequencing approach (MiSeq, Illumina). Sequenced reads were compared to sequence reference databases that were generated by extracting sequence and taxonomic data from GenBank. ITS1 and ITS2 were amplified successfully across all (or most) samples, while rbcL performed inconsistently. Age of sample had no impact on sequencing success. Plant classification was more informative using ITS2 than ITS1 barcode data. This study also highlights the need for comprehensive reference databases as limited local plant sequence representation in reference databases resulted in higher‐level taxon classifications being more confidently interpreted. The results showed that small, insect‐carried pollen samples from historic bee specimens collected from as early as 1914 can be used to obtain pollen metabarcodes. DNA metabarcoding of mixed origin pollen samples provided a faster, more accurate method of determining pollen provenance, without the need for expert palynologists. The use of historic collections to sample pollen directly from pollinators provided additional value to these collections. Sampling pollen from historic collections can potentially provide the spatial and temporal scales for investigations into changes in plant community structure or pollinator floral choice in the face of global climate change.

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

“…All specimens with some pollen visible on their bodies when viewed under a dissecting microscope were selected regardless of when they were collected. One of the two widespread species selected, Megachile venusta , was used in a previous pollen metabarcoding study [ 26 ], where it was shown that that DNA could be successfully sequenced from a wide temporal range of samples, including pollen sampled from specimens which were collected in 1914. The data produced in this study are also used here.…”

“…Information on all bee specimens, including accession numbers, original sampling dates of bees, sampling regions and GPS coordinates (where available) is provided as supplementary information ( S1 – S5 Tables, and S1 Table from [ 26 ]).…”

“…The DNA extraction protocol was optimized in a previous study [ 26 ] and used here to ensure even rupture of all pollen grains across taxa. The DNeasy ® Plant Mini Kit (Qiagen, Hilden, Germany) was used without bead disruption during lysis.…”

“…This untapped resource can be taken advantage of by sampling pollen from insect collection specimens for metabarcoding. Recently, research showed that plant origin identifications could be made from pollen sampled from historic insect collection specimens dating back to 1914 using the internal transcribed spacer regions (ITS1 and ITS2; [ 26 ]). In this latter study, using ITS2 as a barcode, provided much better resolution for plant classification than ITS1.…”

“…In this latter study, using ITS2 as a barcode, provided much better resolution for plant classification than ITS1. Unfortunately, the DNA barcode reference library for South African plants is not complete and species- and genus-level plant classification were problematic, although family-level classification was possible [ 26 ]. Nonetheless, cataloguing the number of plant OTUs visited by bees with different habitat preferences will provide valuable information.…”