Molecular Ecology (2004) 13, 3147–3152 doi: 10.1111/j.1365-294X.2004.02315.x © 2004 Blackwell Publishing Ltd Blackwell Publishing, Ltd. The genetic structure of adders (Vipera berus) in Fennoscandia: congruence between different kinds of genetic markers M. CARLSSON, L. SÖDERBERG and H. TEGELSTRÖM * Department of Conservation Biology and Genetics, EBC, Uppsala University, Norbyv. 18D, SE-752 36 Uppsala, Sweden Abstract In order to elucidate the colonization history of Fennoscandian adders (Vipera berus), the phylogeographical patterns of two nuclear sets of DNA markers (random amplified polymorphic DNA and microsatellite) are compared with that previously obtained from mitochondrial DNA. An eastern and a western lineage within Fennoscandian adders is readily distinguishable using both sets of nuclear markers, corroborating the hypothesis that the lineages stem from separate glacial refugia. Moreover, the same contact zones as were derived from mitochondrial data are clearly identifiable. Both sets of nuclear markers detect a high level of admixture across one zone in northern Finland, with introgression reaching far west into Sweden. Keywords: adders, assignment, microsatellites, phylogeography, RAPDs, Vipera Received 22 February 2004; revision received 9 July 2004; accepted 9 July 2004 Introduction The postglacial phylogeography of northern European fauna and flora was first addressed by Nilsson (1847) who took note of morphological differences within and among taxa and suggested different colonization routes into the region. With modern molecular genetic techniques there has been an upsurge of investigations of colonization by morphologically nondifferentiated taxa (Avise 2000). Among terrestrial vertebrates, a common colonization pattern into Fennoscandia has proven to be bidirectional, with historically isolated populations colonizing from the south and the east. For several species studied, the descendants of the separate lineages meet within a 150 km area of northern Sweden (reviewed in Jaarola et al . 1999) forming a suture zone (Remington 1968). The adder, Vipera berus , is distributed across most of temperate Eurasia and, being a cold-tolerant species, can be found in Fennoscandia north of the Arctic Circle (Schiemenz 1995). The mitochondrial phylogeography for the entire geographical distribution of the adder has recently been investigated (Carlsson 2003). The mitochondrial DNA (mtDNA) data suggest that the adders of Northern Europe originate from two separate glacial refugia situated north of the Romanian part of the Carpathian Mountains. In Romania and further south several other refugial popula- tions have prevailed (Carlsson 2003). In Fennoscandia, descendants of these two geographically widespread line- ages meet in three different areas. Colonization of main- land Fennoscandia has produced a zone of contact in the north of Finland (Carlsson & Tegelström 2002), while dispersal across dozens of kilometres of open water has resulted in mitochondrial contact zones in both south- western Finland and in the Umeå Archipelago of northern Sweden. The postglacial colonization history of Fenno- scandian adders thus appears to differ in some respects to that of other vertebrate species studied to date. Most phylogeographical studies of animals are based on mtDNA as genetic marker, as the mitochondrial genome holds several advantages compared with the use of nuclear DNA (Wilson et al . 1985). However, the mtDNA is effec- tively transmitted as a single gene, and any singular gene genealogy may not accurately describe the history of populations within a species (Pamilo & Nei 1988; Rosenberg & Nordborg 2002). It is therefore prudent to compare the phylogeographical pattern derived from mtDNA with that of nuclear markers. Random amplified polymorphic DNA (RAPD) (Williams et al . 1990) is a relatively quick and inexpensive approach to Correspondence: Martin Carlsson. Fax: +46 18 471 6424; E-mail: martin.carlsson@ebc.uu.se *Håkan Tegelström died on 20 March 2004 after a brave struggle against a long illness. He will be greatly missed.