High dispersal should counteract local adaptation by continuously redistributing genetic variability. In the bryophyte Sphagnum warnstorfii, the North Atlantic may not be as formidable a barrier as expected. Spores may traverse the Atlantic Ocean to North America from Europe and vice versa.
Mikulášková et al. (2015) revisit local adaptation in this high disperser in a new paper in Ecology and Evolution. Its broad tolerance to pH and calcium (two major determinants in species distribution in fens) could be due to genetically differentiated ecotypes. Indeed, pH was an important determinant in genetic structure, but it was independent of geography.
Alternatively, broad tolerance could be due to the occurrence of cryptic species, highlighting either the problems associated with species boundaries or the occurrence of introgression with phylogenetically allied species. Species definitions are a bit of a sticky subject, but both species ID and hybridization raise intriguing questions with regard to the latter’s role in shaping the genetic structure of species and the former’s influence on patterns we describe. In either case, the addition of a free-living phase, differing in ploidy, adds a complicated twist
Mikulášková E, Hájek E, Veleba A, Johnson MG, Hájek T, Shaw JA (2015) Local adaptations in bryophytes revisited: the genetic structure of the calcium-tolerant peatmoss Sphagnum warnstorfii along geographic and pH gradients. Ecology and Evolution 5: 229-242 DOI: 10.1002/ece3.1351