Vol.:(0123456789) 1 3 Conserv Genet DOI 10.1007/s10592-017-0945-7 RESEARCH ARTICLE A complex history of introgression and vicariance in a threatened montane skink (Pseudemoia cryodroma) across an Australian sky island system Margaret L. Haines 1,2,5  · Devi Stuart‑Fox 2  · Joanna Sumner 1  · Nick Clemann 3  · David G. Chapple 4  · Jane Melville 1   Received: 19 August 2016 / Accepted: 14 February 2017 © Springer Science+Business Media Dordrecht 2017 species. We found discordance between genetic markers, indicating historical mtDNA introgression at one of the study sites between P. cryodroma and the closely related, syntopic P. entrecasteauxii. Molecular diversity was posi- tively associated with site elevation and extent of suitable habitat, with inbreeding detected in three of the fve popu- lations. These results demonstrate the complex interaction between geography and habitat in shaping the population structure and genetic diversity of P. cryodroma, and high- light the importance of minimising future habitat loss and fragmentation for the long-term persistence of this species. Keywords Australian Alps · Biogeography · Lizard · Population genetics · Scincidae · Threatened species Introduction Originally popularized by Heald (1951), the term “sky islands” refers to mountain ranges that comprise a series of peaks and plateaux isolated both geographically and eco- logically by areas of lower elevation. Sky islands have been described worldwide and include regions such as the Rocky Mountains, Ethiopian Highlands, and Western Ghats (McCormack et al. 2009). The size and connectivity of many sky island populations are thought to have fuctuated in response to Plio-Pleistocene glacial cycles (Markgraf et al. 1995; Williams et al. 1998). Specifcally, sky island habitats extended downwards during periods of glacia- tion, facilitating gene fow between populations previously restricted to higher elevations, and then contracted again during interglacial periods. This is thought to have allowed species to extend their distributions to adjacent mountains during glacial periods (Browne and Ferree 2007; Rull and Nogue 2007) and/or diversify during interglacial periods Abstract Species endemic to sky island systems are isolated to mountain peaks and high elevation plateaux both geographically and ecologically, making them par- ticularly vulnerable to the efects of climate change. Pres- sures associated with climate change have already been linked to local extinctions of montane species, emphasiz- ing the importance of understanding the genetic diversity and population connectivity within sky islands systems for the conservation management of remaining populations. Our study focuses on the endangered alpine skink Pseude- moia cryodroma, which is endemic to the Victorian Alps in south-eastern Australia, and has a disjunct distribution in montane habitats above 1100 m a.s.l. Using mitochon- drial DNA (mtDNA) and microsatellite loci, we investi- gated species delimitation, genetic connectivity and popu- lation genetic structure across the geographic range of this Electronic supplementary material The online version of this article (doi:10.1007/s10592-017-0945-7) contains supplementary material, which is available to authorized users. * Margaret L. Haines hainesm@uwm.edu 1 Sciences Department, Museum Victoria, GPO Box 666, Melbourne, VIC 3001, Australia 2 School of BioSciences, University of Melbourne, Parkville, VIC 3010, Australia 3 Department of Environment, Land, Water, and Primary Industry, Arthur Rylah Institute for Environmental Research, PO Box 137, Heidelberg, VIC 3084, Australia 4 School of Biological Sciences, Monash University, Clayton, VIC 3800, Australia 5 Present Address: Department of Biological Sciences, University of Wisconsin-Milwaukee, 3209 N. Maryland Ave., Milwaukee, WI 53212, USA