Pollen diet, more than geographic distance, shapes provision microbiome composition in two species of cavity-nesting bees

The microbial composition of stored food can influence its stability and determine the microbial species consumed by the organism feeding on it. Many bee species store nectar and pollen in provisions constructed to feed developing offspring. Yet whether microbial composition is determined by the pollen types within provisions, variation between bee species at the same nesting sites, or geographic distance was unclear. Here, we sampled two species of co-occurring cavity nesting bees in the genus Osmia at 13 sites in California and examined the composition of pollen, fungi, and bacteria in provisions. Pollen composition explained 15% of variation in bacterial composition and ~30% of variation in fungal composition, whereas spatial distance among sites explained minimal additional variation. Symbiotic microbe genera Ascosphaera, Sodalis, and Wolbachia showed contrasting patterns of association with pollen composition, suggesting distinct acquisition and transmission routes for each. Compar..., Study system
We sampled the stored nectar and pollen within brood cells of two species of cavity-nesting Osmia (mason bees, Megachilidae) that nest in early spring with partially overlapping phenology, and that often co-occur. It is common to see nests of the two species within the same piece of wood nesting substrate within a microsite. Osmia lignaria is managed as a pollinator for early-flowering orchard crops and is a diet generalist (Williams & Tepedino 2003). Osmia ribifloris is a diet specialist that forages mainly on host plants in the Ericaceae (Sampson et al. 2013). Both Osmia species are common across the western United States and restricted to North America as of 2025 (discoverlife.org). Nests of each species are distinguished by nesting material: O. lignaria constructs nest partitions using mud, while O. ribifloris uses masticated leaves (Fig. 1).
Sampling design
We sampled Osmia populations at 13 geographic locations, hereafter ‘sites’, in the foothills of the western s..., # Data from: Pollen diet, more than geographic distance, shapes provision microbiome composition in two species of cavity-nesting bees

Dataset DOI: [10.5061/dryad.crjdfn3h9](10.5061/dryad.crjdfn3h9)

## Description of the data and file structure

### Files and variables

#### File: bacterialtaxonomy.csv

**Description:** 

##### Variables

* ASV: Actual sequence variant
* X: Placeholder
* Kingdom: Assigned Kingdom
* Phylum: Assigned Phylum
* Class: Assigned Class
* Order: Assigned Order
* Family: Assigned Family
* Genus: Assigned Genus
* Species: Assigned Species

#### File: sample_data_export-mod.csv

**Description:** 

##### Variables

* SampleLabel: Sample ID
* Site: Sampling site label
* Species: Bee species, L = Osmia lignaria, R= Osmia ribifloris
* Nest: Nest ID
* CellPos: Cell position within the nest, with 1 indicating the first cell provisioned in a given nest
* Type: Indicates if samples were taken in an agricultural or natural site 
* Year: Year sampled
* FungiCode: Code for...,