Regional variation in Bombus vosnesenskii worker body size across California's diverse landscapes

Understanding how environmental variation influences phenotypic traits in native pollinators is essential for predicting their responses to changing landscapes, particularly with ongoing habitat loss and fragmentation. In this study, we assessed variation in body size among Bombus vosnesenskii workers across California, encompassing distinct coastal and mountainous regions. Between 2017-2025, we collected more than 800 bees, sampling 6–15 workers per site, and measured morphological features, including wing cell length and head width as proxies for body size. We examined associations between environment and worker body size, controlling for collection date, which was not a significant factor in our best-fit model. Our preliminary results reveal significant regional variation in body size, with coastal bees being notably larger than mountain bees. These patterns suggest that environmental factors, such as access to floral resources or climatic conditions, may shape regional body size variation. This observed variation could indicate local ecological adaptation or underlying genetic differentiation, underscoring the need for further research into the genetic and environmental drivers of bumble bee morphology across heterogeneous landscapes.