Environmental and Nutritional Drivers of Size Variation in Centris Bees.

Solitary bees exhibit morphological variation influenced by environmental conditions and larval nutrition; however, the extent to which these factors interact remains insufficiently explored, particularly in tropical dry ecosystems. In this study, we examined two species of oil-collecting bees, Centris analis and Centris tarsata, in semiarid orchards of Northeastern Brazil to assess whether seasonal and nutritional factors affect adult body size. We quantified protein concentrations in larval pollen provisions and measured morphometric traits (intertegular span, head width, and head length) in individuals reared from trap nests collected during the wet and dry seasons. Using nonparametric statistics and multivariate analysis, Multiple Factor Analysis (MFA) and Hierarchical Clustering on Principal Components (HCPC), we tested associations among protein content, morphology, sex, species, season, and sampling site. Centris tarsata individuals were consistently larger and associated with higher-protein pollen, while C. analis showed greater variation in size, particularly during the rainy season. Cluster analyses revealed four distinct phenotypic profiles, shaped by interacting ecological and physiological variables. Our results suggest that larval nutritional quality is associated with adult phenotypes and covaries with bee size across seasonal resource availability; however, because this study is observational, causality cannot be inferred. This study advances the current knowledge of intraspecific and interspecific variability in Neotropical pollinators and emphasizes the role of larval diet in shaping morphological traits. By linking seasonal pollen nutrition to variation in body size, this study provides a physiological perspective on how solitary bees respond to environmental variation.