ORIGINAL PAPER Liam Nolan Æ Ian D. Hogg Æ Mark I. Stevens Martin Haase Fine scale distribution of mtDNA haplotypes for the springtail Gomphiocephalus hodgsoni (Collembola) corresponds to an ancient shoreline in Taylor Valley, continental Antarctica Received: 18 July 2005 / Revised: 27 January 2006 / Accepted: 28 January 2006 / Published online: 22 February 2006 Ó Springer-Verlag 2006 Abstract We examined the fine scale distribution of the endemic Antarctic collembolan Gomphiocephalus hodg- soni in Taylor Valley, southern Victoria Land using the mitochondrial DNA cytochrome c oxidase I gene. We found an area of sympatry in the mid-region of the valley between two common haplotype groups (2.4% sequence divergence). The area of sympatry coincided with the extent of proglacial Lake Washburn (approx. 8,000 ya). This lake existed as a result of the damming of lower Taylor Valley by the grounding of the Ross Ice Sheet and may have acted as an isolating barrier to dispersal/gene flow. We suggest that the phylogenetic break occurring in the vicinity of the ancient shoreline may be the result of previous isolation of refugial allo- patric populations, followed by recolonisation into a secondary contact zone during the Holocene. Introduction The impacts of palaeoclimatic oscillations on phyloge- ography have been extensively studied in the past 15 years (see Hewitt 2001 for review). In particular, the role of late Pleistocene glaciations in shaping the genetic structure of populations has been examined for a variety of taxa, especially in high latitudes of the Northern Hemisphere (e.g. Knowles 2001). Fragmentation of populations into local refugia during periods of glacia- tion, and subsequent recolonisation of previously unavailable habitat can lead to the formation of sec- ondary contact zones. In these zones, genetically isolated populations may overlap in an area of sympatry (e.g. Pfenninger and Posada 2002). The likelihood of observing genetic isolation in such a contact zone in- creases, as dispersal ability and population size decrease (Irwin 2002). If the populations are not reproductively isolated a hybrid zone may form (Hewitt 2001). Despite the increasing number of phylogeographic studies in the Northern Hemisphere (see Avise 1998; Hewitt 2001), comparatively fewer studies have been undertaken to determine the effect of glaciations on genetic differentiation among terrestrial invertebrate populations in Antarctica (Courtwright et al. 2000; Frati et al. 2001; Stevens and Hogg 2003; see also Stevens and Hogg 2006 for review). This is unfortunate because Antarctica provides an ideal opportunity to study such events owing to its well-studied glacial history (e.g. Denton and Hughes 2000). For example, palaeoclimatic oscillations resulted in periodic fluctuations of the sea ice level in McMurdo Sound and in lake levels in the adjacent Dry Valleys. The formation of the proglacial Lake Washburn in Taylor Valley in the late Pleistocene (Denton and Hughes 2000; Denton and Marchant 2000) is now well documented and consequently provides an historical record of terrestrial habitat availability throughout Taylor Valley at the end of the Pleistocene. The lake formed due to the grounding of the West Antarctic Ice Sheet at the mouth of the Valley during the last glacial maximum. Detailed studies of the terrestrial fauna in this region would, therefore, provide valuable information on the phylogeographic history of the re- L. Nolan Æ I. D. Hogg (&) Æ M. Haase Department of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand E-mail: hogg@waikato.ac.nz M. I. Stevens Allan Wilson Centre for Molecular Ecology and Evolution, Massey University, Private Bag 11-222, Palmerston North, New Zealand M. I. Stevens School of Biological Sciences, Monash University, 3800, Victoria, Australia M. Haase Museum Alexander Koenig, Adenauerallee 160, 53113, Bonn, Germany Polar Biol (2006) 29: 813–819 DOI 10.1007/s00300-006-0119-4