1 3 RAD-seq data point to a northern origin of the arctic–alpine genus 4 Cassiope (Ericaceae) q 5 6 7 Yan Hou a,⇑ , Michael D. Nowak a,b , Virginia Mirré a , Charlotte Sletten Bjorå a , Christian Brochmann a , 8 Magnus Popp a 9 a Natural History Museum, University of Oslo, NO-0318 Oslo, Norway 10 b Science for Life Laboratory, Stockholm University, Tomtebodavägen 23, S-17165 Solna, Sweden 11 12 13 15 article info 16 Article history: 17 Received 2 June 2015 18 Revised 13 November 2015 19 Accepted 14 November 2015 20 Available online xxxx 21 Keywords: 22 Arctic/Boreal 23 Disjunction 24 Himalayan–Hengduan Mountains 25 RAD-seq 26 27 abstract 28 Many arctic–alpine plants display a highly disjunct distribution between the Arctic/Boreal regions and 29 the southern Asian mountains. Two main hypotheses have been proposed to explain the origin of this 30 biogeographic pattern: (1) south-to-north migration in the late Pliocene/early Pleistocene, and (2) 31 north-to-south migration during the Miocene. The genus Cassiope is disjunctly distributed between the 32 Arctic/Boreal regions and the Himalayan–Hengduan Mountains (HHM) and was selected to test these 33 hypotheses. We constructed a fossil-calibrated phylogeny of Ericaceae using two plastid regions to esti- 34 mate the crown group age of Cassiope, and used sequence data from thousands of loci produced by 35 restriction site associated DNA sequencing (RAD-seq) to reconstruct the phylogeny of Cassiope. We also 36 performed Bayesian divergence time analysis and biogeographic analysis. The Cassiope crown group was 37 estimated to have originated in the Miocene, which predates the onset of Northern hemisphere glacia- 38 tion. All HHM species formed a clade together with one eastern Siberian species, and this clade was sister 39 to all other Arctic/Boreal species. This topology implies a northern origin of Cassiope, which is confirmed 40 by our biogeographic analysis. Our results thus suggest that the ancient north-to-south migration 41 hypothesis is most consistent with the origin of Cassiope. 42 Ó 2015 Elsevier Inc. All rights reserved. 43 44 45 46 1. Introduction 47 Many arctic–alpine plants display a highly disjunct distribution 48 between the Arctic/Boreal regions and the southern Asian moun- 49 tains. Estimating the most likely geographic origin of these taxa 50 is important for our understanding of how the historical processes 51 of species diversification and dispersal were impacted by climatic 52 oscillations and geographic isolation. There are two main compet- 53 ing hypotheses, the ‘‘Asian origin hypothesis” and the ‘‘Arctic/Bor- 54 eal origin hypothesis”, proposed to explain the historical processes 55 that lead to these conspicuous disjunctions. The two hypotheses 56 differ primarily in the direction of lineage migration between the 57 two disjunct regions and the age of the disjunction. Both hypothe- 58 ses are based on the idea that lineages that were pre-adapted to 59 cool climates expanded their ranges in response to suitable habitat 60 made available by global climatic changes, either in the Arctic/Bor- 61 eal regions or in the Asian mountains. 62 The ‘‘Asian origin hypothesis” posits that lineages from the 63 Asian mountains dispersed to high latitudes during the expansion 64 of the Arctic and Boreal biomes in response to the onset of North- 65 ern hemisphere glaciations about 3 million years ago (late Plio- 66 cene/early Pleistocene; Brochmann et al., 2013; Murray, 1995). 67 The Himalaya and Hengduan Mountains, which we collectively 68 refer to here as the HHM, are two of the world’s biodiversity hot- 69 spots (Boufford et al., 2004; Conservation International, 2005; 70 Myers et al., 2000). The HHM and the adjacent Qinghai–Tibetan 71 Plateau (QTP) have been suggested to have served as refugia during 72 glacial/interglacial periods (e.g., Jia et al., 2011; Wang et al., 2008; 73 Wen et al., 2014; Wu et al., 2010) and may have acted as sources 74 for arctic lineages under the ‘‘Asian origin hypothesis” 75 (Brochmann et al., 2013; Murray, 1995). As exemplars of this 76 model, Koenigia (Fan et al., 2013), Lagotis (Li et al., 2014), and Rho- 77 diola (Zhang et al., 2014) all contain arctic–alpine lineages exhibit- 78 ing a disjunct distribution between the Arctic/Boreal regions and 79 the HHM/QTP. These lineages were inferred to have migrated from 80 the HHM or QTP into the Arctic/Boreal regions in the late Pliocene 81 or early Pleistocene, coincident with the expansion of the Arctic/ 82 Boreal biomes at this time. http://dx.doi.org/10.1016/j.ympev.2015.11.009 1055-7903/Ó 2015 Elsevier Inc. All rights reserved. q This paper was edited by the Associate Editor Stefanie M. Ickert-Bond. ⇑ Corresponding author. Molecular Phylogenetics and Evolution xxx (2015) xxx–xxx Contents lists available at ScienceDirect Molecular Phylogenetics and Evolution journal homepage: www.elsevier.com/locate/ympev YMPEV 5355 No. of Pages 9, Model 5G 11 December 2015 Please cite this article in press as: Hou, Y., et al. RAD-seq data point to a northern origin of the arctic–alpine genus Cassiope (Ericaceae). Mol. Phylogenet. Evol. (2015), http://dx.doi.org/10.1016/j.ympev.2015.11.009