Biome variation, not distance between populations, explains morphological variability in the orchid bee Eulaema nigrita (Hymenoptera, Apidae, Euglossini)

The sampling of orchid bees across different biomes provides an excellent opportunity to analyze morphological variability in this group. We examined the morphological variation of populations of Eulaema nigrita in the context of the determination of geographic origin. It also evaluated population variability of this group in different landscapes from two important biomes, Atlantic Forest, Brazilian Savanna, and the transition zone between them. These analyses were achieved by documenting the pattern of morphological differentiation using geometric morphometric analysis of the wings of 256 individuals, sampled from nine locations, from four different physiognomies. Results indicated that individuals from the Atlantic Forest physiognomies are larger than the ones from the Savanna. The clusterization of individuals was based on landscape features of the sampling areas. The results indicate little or even a complete absence of population structure. Overall, site-specific population differentiation is not strongly supported by wing traits, reinforcing the statement consistent with the broader pattern that orchid bees have a high migratory capacity. However, the subtle differentiation may indicate the existence of locally adapted traits kept by female philopatry or phenotypic plasticity triggered by environmental factors yet to be studied.