Long‐distance dispersal during the middle–late Pleistocene explains the bipolar disjunction of Carex maritima (Cyperaceae)

Abstract

AbstractAimWe set out to explain the bipolar distribution of Carex maritima, clarifying the direction and timing of dispersal. We also tested mountain‐hopping and direct long‐distance dispersal hypotheses, as well as the relationship of C. maritima with biotic and abiotic factors that could explain the bipolar distribution.LocationArctic/boreal latitudes of both hemispheres.MethodsMolecular and bioclimatic data were obtained for C. maritima and related species from section Foetidae. We sequenced two (rps16 and 5′trnK intron) plastid DNA regions (cpDNA) and the external and internal transcribed spacers (ETS and ITS) of the nuclear ribosomal gene region (nrDNA) and inferred phylogenetic relationships, divergence time estimates and biogeographical patterns using maximum likelihood, statistical parsimony, Bayesian inference and ecological niche modelling.ResultsCarex maritima populations from the Southern Hemisphere were genetically and ecologically differentiated from their northern counterparts and formed a monophyletic group nested within a paraphyletic C. maritima. Divergence time analysis estimated a middle–late Pleistocene divergence of the southern lineage (0.23 Ma; 95% highest posterior density: 0.03–0.51 Ma). Southern Hemisphere populations are more stenotopic than the Northern Hemisphere ones, which tolerate harsher conditions.Main conclusionsOur results point to a middle–late Pleistocene migration of C. maritima by long‐distance dispersal, either directly or via mountain‐hopping, from the Northern Hemisphere to the Southern Hemisphere.