Reply to Hu and Duan (Mar Biol …): Insufficient geographical sampling could severely influence phylogeographic interpretations; comment on “Phylogeography of the seaweed Ishige okamurae (Phaeophyceae): evidence for glacial refugia in the northwest Pacific region” (Lee et al. 2012)

Abstract

Hu and Duan (2013) challenge our hypotheses that asfollows: (1) southern Korea (Jeju Island) and northernTaiwan were glacial refugia for the brown alga Ishige ok-amurae during the last glacial maximum, suggestinginstead that the high haplotype diversity we observed onJeju Island resulted from admixture of southern populations(SW Taiwan and Ryuku Islands); and (2) SW Taiwan ismore likely to be a refugium than North Taiwan because itis further away from the Asian continent. Below, weaddress these points.The concept of glacial refugia in the northern hemi-sphere postulates that, whereas populations south of thesouthern edge of an advancing ice sheet are likely to belarge and diverse, small periglacial or cryptic northernrefugia north of the leading edge of the ice sheet mayform and retain high levels of diversity (Maggs et al.2008; Coyer et al. 2011). Glacial refugia populations,therefore, are characterized by a genetic signature ofhigh within-population diversity and high dissimilaritybetween refugial populations (Hewitt 1996; Comes andKadereit 1998). However, as Hu and Duan (2013) state,these patterns of diversity also may arise from secondarycontact or admixture of populations from different refu-gia (Maggs et al. 2008). Thus, the competing interpre-tations of the diversity patterns need to be evaluated inorder to identify glacial refugia (Maggs et al. 2008).As shown in Figure 1 (based on Liu et al. 2007) of Leeet al. (2012), contemporary coasts of southern Korea andeastern Taiwan were open to the sea during the last glacialmaximum (LGM) and could have formed a single largerefugium, with extensive gene flow. For two reasons,however, we believe the high haplotype diversity observedoff southern Korea (including Jeju Island) relative to otherareas and the dissimilarity compared to northern Taiwanesepopulations are consistent with identification of each as aglacial refugium. First, the haplotype network is mostconsistent with the Model IIIA [two or more refugial-derived populations with little or no contact] (Maggs et al.2008) with private haplotype C17 for Taiwan and privatehaplotypes C3 and C4 for Jeju/southern Korea. And sec-ondly, similar patterns of exceptionally high haplotypediversity have been identified on Jeju for, the brown algaeColpomenia peregrina (Lee et al. unpublished), the redalgae, Gelidium elegans (Kim et al. 2012), and Gracilariavermiculophylla (Kim et al. 2010).