The poor cousin: contrasting patterns of intraspecific variation among co-occurring species of Vaccinium L.

• V. myrtillus is less diverse than codistributed V. uliginosum and V. vitis-idaea . • This species experienced more severe range contractions in Pleistocene. • Polyploidy and environmental stress promoted diversification of its congeners. • V. myrtillus demonstrates peculiar large-scale patterns of genetic variation. Comparison of genetic variation among closely related species with well-known ecological preferences may provide insights into the role of specific traits in biogeographic processes. Three widely distributed bird-dispersed species of the genus Vaccinium L. provide a good model system for such inference. We report the first comprehensive range-wide dataset on genetic variation in V. myrtillus that can be directly used for interspecific comparisons. In contrast to its congeners V. uliginosum and V. vitis-idaea, V. myrtillus is characterized by extremely low plastid DNA variation, with a single haplotype occupying vast territories in Eurasia and two more haplotypes occurring in the Caucasus. We suggest that the main reason for the genetic impoverishment of V. myrtillus , which is relatively cold-intolerant, is bottlenecking during the Pleistocene glaciations. We reinforce this view using niche modeling, predicting that no suitable habitats for V. myrtillus existed during the Last Glacial Maximum in Beringia and Siberia. We aggregate our new data and published information on genetic diversity in the three species and explain the differences between them based on their ecology, reproductive biology and demographic history.