title: Tree endurance on the Tibetan Plateau marks the world's highest known tree line of the Last Glacial Maximum.
abstract: Because of heterogeneous topographies, high-mountain areas could harbor a significant pool of cryptic forest refugia (glacial microrefugia unrecognized by palaeodata), which, as a result of poor accessibility, have been largely overlooked. The juniper forests of the southern Tibetan Plateau, with one of the highest tree lines worldwide, are ideal for assessing the potential of high-mountain areas to harbor glacial refugia. Genetic evidence for Last Glacial Maximum (LGM) endurance of these microrefugia is presented using paternally inherited chloroplast markers. Five-hundred and ninety individuals from 102 populations of the Juniperus tibetica complex were sequenced at three polymorphic chloroplast regions. Significant interpopulation differentiation and phylogeographic structure were detected (G(ST) = 0.49, N(ST) = 0.72, N(ST) > G(ST), P < 0.01), indicating limited among-population gene flow. Of 62 haplotypes recovered, 40 were restricted to single populations. These private haplotypes and overall degrees of diversity were evenly spread among plateau and edge populations, strongly supporting the existence of LGM microrefugia throughout the present distribution range, partly well above 3500 m. These results mark the highest LGM tree lines known, illustrating the potential significance of high-mountain areas for glacial refugia. Furthermore, as the close vicinity of orographic rear-edge and leading-edge populations potentially allows gene flow, surviving populations could preserve the complete spectrum of rear-edge and leading-edge adaptations.
authors.affiliation: Faculty of Biology, Conservation Biology, University of Marburg, Karl-von-Frisch Strasse 8, 35032 Marburg, Germany. Lars.Opgenoorth@staff.uni-marburg.de
authors.forename: Lars
authors.initials: L
authors.lastname: Opgenoorth
authors.forename: Giovanni G
authors.initials: GG
authors.lastname: Vendramin
authors.forename: Kangshan
authors.initials: K
authors.lastname: Mao
authors.forename: Georg
authors.initials: G
authors.lastname: Miehe
authors.forename: Sabine
authors.initials: S
authors.lastname: Miehe
authors.forename: Sascha
authors.initials: S
authors.lastname: Liepelt
authors.forename: Jianquan
authors.initials: J
authors.lastname: Liu
authors.forename: Birgit
authors.initials: B
authors.lastname: Ziegenhagen
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D001483:Base Sequence; D002736:Chloroplasts / Q000235:genetics; D017753:Ecosystem; D005843:Geography; D006239:Haplotypes; D046448:Ice Cover; D018653:Juniperus / Q000235:genetics* / Q000502:physiology; D011110:Polymorphism, Genetic; D018609:Tibet; D014197:Trees / Q000502:physiology*