Museum Genomics of an Important Swedish Pollinator Reveals Population Stability Across Time.

Anthropogenic activity has driven a rapid decline in wild pollinator populations over the last several decades. Understanding the genomic consequences of these declines and their long-term effects requires establishing historical baselines for population diversity. To investigate this, we conducted temporal genomic analyses of a widespread and important pollinator, the common carder bee (Bombus pascuorum). We sequenced 102 historical, dry-pinned museum specimens collected across Sweden during the last 150 years, and analysed them alongside 59 modern individuals. While historical samples showed elevated levels of fragmentation with age (range 41.8-89 bp), they also had overall high levels of endogenous DNA (median 86.9%). Our analyses revealed that while geographically isolated populations in Gotland and the Arctic mountains exhibit localized genomic differentiation and lower diversity, the overall mainland population structure is low. We find that population structure has remained stable and genomic diversity has increased across Sweden over the past 150 years. These results challenge assumptions of decline, indicating that B. pascuorum has resisted genomic erosion even with reported declines in relative abundance. This study validates dry-pinned museum insects as a powerful resource for large-scale conservation genomics studies, providing a useful temporal perspective despite DNA degradation.