Quantifying genetic structure and levels of genetic variation are fundamentally important to predicting the ability of populations to persist in human-altered landscapes and adapt to future environmental changes. Genetic structure reflects the dispersal of individuals over generations, which can be mediated by species-level traits or environmental factors. Dispersal distances are commonly positively associated with body size and negatively associated with the amount of degraded habitat between sites, motivating investigation of these potential drivers of dispersal concomitantly. We quantified genetic structure and genetic variability within populations of seven Euglossine bee species in the genus Euglossa across fragmented landscapes. We genotyped bees at thousands of SNP loci and tested the following predictions: (1) deforested areas restrict gene flow; (2) larger species have lower genetic structure; (3) species with greater resource specialization have higher genetic structure; and (4) sites surrounded by more intact habitat have higher genetic diversity. Contrasting with previous work on bees, we found no associations of body size and genetic structure. Genetic structure was higher for species with greater resource specialization, and the amount of intact habitat between or surrounding sites was positively associated with parameters reflecting gene flow and genetic diversity. These results challenge the dominant paradigm that individuals of larger species disperse farther. They suggest that landscape and resource requirements are important factors mediating dispersal, and they motivate further work into ecological drivers of gene flow for bees.

Quantifying genetic structure and levels of genetic variation are fundamentally important to predicting the ability of populations to persist in human-altered landscapes and adapt to future environmental changes. Genetic structure reflects the dispersal of individuals over generations, which can be mediated by species-level traits or environmental factors. Dispersal distances are commonly positively associated with body size and negatively associated with the amount of degraded habitat between sites, motivating investigation of these potential drivers of dispersal concomitantly. We quantified genetic structure and genetic variability within populations of ten bee species in the tribe Euglossini across fragmented landscapes. We genotyped bees at thousands of SNP loci and tested the following predictions: (1) larger species disperse farther; (2) species with greater resource specialization disperse farther; (3) deforested areas restrict dispersal; and (4) sites surrounded by more intact habitat have higher genetic diversity. Body size was a strong predictor of genetic structure, but, surprisingly, larger species showed higher genetic structure than smaller species. The way that deforestation affected dispersal varied with body size, such that larger species dispersed less far in areas with more forest. There was no effect of geographic distance on dispersal, and sites with more intact habitat had higher genetic diversity. These results challenge the dominant paradigm that individuals of larger species disperse farther, motivating further work into ecological drivers of dispersal for bees.