Genetic variation in two land snails, Cepaea nemoralis and Succinea putris (Gastropoda, Pulmonata), from sites differing in heavy metal content Kurt Jordaens 1 , Hans De Wolf 2 , Natalie Van Houtte 1 , Bart Vandecasteele 3 & Thierry Backeljau 1,4 1 Department of Biology, Evolutionary Biology Group, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium (Phone: +32-3-265-34-56; Fax: +32-3-265-34-74; E-mail: kurt.jordaens @ua.ac.be); 2 Department of Biology, Ecophysiology, Biochemistry & Toxicology, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium; 3 Institute for Forestry and Game Management, Gaver- straat 4, B-9500, Geraardsbergen, Belgium; 4 Royal Belgian Institute of Natural Sciences, Vautierstraat 29, B-1000, Brussels, Belgium Received 24 March 2005 Accepted 2 December 2005 Key words: allozymes, Cepaea nemoralis, Gastropoda, heavy metals, isoelectric focusing, land snails, pollution, polyacrylamide gel electrophoresis, population genetics, Succinea putris Abstract Allozyme variation was determined in two land snail species (Cepaea nemoralis and Succinea putris) from four localities in northern Belgium. In each locality we selected a polluted and a nearby, less-polluted, reference plot. We examined whether (i) genetic variability differed between the polluted and reference plots, (ii) populations from polluted plots experienced recent bottlenecks, and (iii) certain allele or genotype frequencies were associated with the pollution. Our results suggest that (i) about 13% of the genetic differentiation in C. nemoralis and 5% in S. putris was due to differences among polluted and reference plots, (ii) polluted and reference plots had comparable levels of genetic variation, but in C. nemoralis observed heterozygosities were higher in polluted plots, (iii) most plots showed significant evidence for recent bottlenecks, irrespective of the degree of pollution, so that bottlenecks seem poor indicators of pollution-induced stress in land snails, and (iv) mutagenic or pollution-induced modifications did not seem to account for new allozyme variants in polluted sites. The observed patterns of genetic variation may be explained by the action of genetic drift, pollution-mediated selection, restricted gene flow, or a combination of these processes. Introduction ‘Evolutionary toxicology’ is a relatively young re- search discipline that focuses on the dynamics of genetic variation in natural populations due to environmental contaminants, such as heavy metals (Bickham & Smolen, 1994). However, estimating the genetic and demographic effects associated with heavy metal contamination in natural popu- lations is a complex and difficult issue (e.g. Hebert & Luiker, 1996; Bickham et al., 2000; Belfiore & Anderson, 2001). Heavy metals may directly (i.e. via germ cell mutations) or indirectly (i.e. via somatic muta- tions, or physiological and ecological effects) change the genetic architecture of populations (Gillespie & Guttman, 1999; Bickham et al., 2000; Belfiore & Anderson, 2001; Theodorakis, 2003; De Wolf, Blust & Backeljau, 2004). Depending on the nature and strength of these effects, genetic var- iation may be either increased or decreased in af- fected natural populations. For example, adverse mutations may negatively affect population demography resulting in an overall loss of genetic Genetica (2006) 128:227–239 Ó Springer 2006 DOI 10.1007/s10709-005-5705-9