View Program - 2022 Population, Evolutionary, and Quantitative Genetics Conference

Quantifying genetic structure and levels of genetic variation within populations are of fundamental importance to biologists seeking to predict the ability of populations to persist in human-altered landscapes and adapt to future environmental changes. Genetic structure reflects the dispersal of individuals over many generations, which can be constrained by environmental factors or mediated by species-level traits such as body size. Dispersal distances are commonly positively associated with body size and negatively associated with the amount of degraded habitat between habitat fragments, motivating investigation of these two potential drivers of dispersal concomitantly. We quantified genetic structure and levels of genetic variability within populations of nine bee species within the tribe Euglossini. Euglossine bees are important pollinators of over 700 orchid species and many other tropical plants. We tested the following predictions: (1) deforested areas restrict dispersal, (2) forested paths among sites are better predictors of dispersal than Euclidian geographic distances, (3) there is a positive association of dispersal distance and body size, (4) genetic variability is greater in sites surrounded by more intact habitat. We used RADseq and the Stacks pipeline to genotype bees at thousands of SNP loci and estimate population genetic parameters. 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 genetic structure was not mediated body size, and there was no effect of deforestation or geographic distance on dispersal. There was variability across species in the way that the amount of forest surrounding sites affected genetic variability. These results challenge the dominant paradigm that individuals of larger species disperse farther, and we discuss potential ecological drivers and implications of these results.

Drivers of dispersal and genetic variation for bee species in a fragmented tropical habitat