Aquatic Toxicology 86 (2008) 426–436 Evidence of population genetic effects of long-term exposure to contaminated sediments—A multi-endpoint study with copepods Johanna Gardestr¨ om a,∗ , Ulrika Dahl b , Ola Kotsalainen a , Anders Maxson b , Tina Elfwing a , Mats Grahn c , Bengt-Erik Bengtsson b , Magnus Breitholtz b a Department of Systems Ecology, Stockholm University, SE-10691 Stockholm, Sweden b Department of Applied Environmental Science (ITM), Stockholm University, SE-10691 Stockholm, Sweden c Department of Natural Sciences, S¨ odert¨ orn University College, SE-14189 Huddinge, Sweden Received 24 October 2007; received in revised form 9 December 2007; accepted 11 December 2007 Abstract In the environment, pollution generally acts over long time scales and exerts exposure of multiple toxicants on the organisms living there. Recent findings show that pollution can alter the genetics of populations. However, few of these studies have focused on long-term exposure of mixtures of substances. The relatively short generation time (ca. 4–5 weeks in sediments) of the harpacticoid copepod Attheyella crassa makes it suitable for multigenerational exposure studies. Here, A. crassa copepods were exposed for 60 and 120 days to naturally contaminated sediments (i.e., Svindersviken and Trosa; each in a concentration series including 50% contaminated sediment mixed with 50% control sediment and 100% contaminated sediment), and for 120 days to control sediment spiked with copper. We assayed changes in F ST (fixation index), which indicates if there is any population subdivision (i.e., structure) between the samples, expected heterozygosity, percent polymorphic loci, as well as abundance. There was a significant decrease in total abundance after 60 days in both of the 100% naturally contaminated sediments. This abundance bottleneck recovered in the Trosa treatment after 120 days but not in the Svindersviken treatment. After 120 days, there were fewer males in the 100% naturally contaminated sediments compared to the control, possibly caused by smaller size of males resulting in higher surface: body volume ratio in contact with toxic chemicals. In the copper treatment there was a significant decrease in genetic diversity after 120 days, although abundance remained unchanged. Neither of the naturally contaminated sediments (50 and 100%) affected genetic diversity after 120 days but they all had high within treatment F ST values, with highest F ST in both 100% treatments. This indicates differentiation between the replicates and seems to be a consequence of multi-toxicant exposure, which likely caused selective mortality against highly sensitive genotypes. We further assayed two growth-related measures, i.e., RNA content and cephalothorax length, but none of these endpoints differed between any of the treatments and the control. In conclusion, the results of the present study support the hypothesis that toxicant exposure can reduce genetic diversity and cause population differentiation. Loss of genetic diversity is of great concern since it implies reduced adaptive potential of populations in the face of future environmental change. © 2007 Elsevier B.V. All rights reserved. Keywords: Long-term exposure; Contaminant mixtures; Biodiversity; Genetic diversity; Genetic differentiation; RNA; Environmental risk assessment 1. Introduction The conservation of biodiversity has been on both the sci- entific and the political agenda ever since the Rio de Janeiro Earth Summit in 1992. The emphasis is often on protecting particular species and habitats but the declaration also com- prises the maintenance of functional diversity of ecosystems and genetic diversity of species. Relatively little attention has, ∗ Corresponding author. Tel.: +46 8 16 37 04; fax: +46 8 15 84 17. E-mail address: johanna@ecology.su.se (J. Gardestr¨ om). however, been drawn to changes in genetic diversity, especially caused by indirect or direct exposure to toxicants (Bickham et al., 2000). Recent findings show that pollution in fact can cause rapid genetic changes in exposed populations; changes that may be complex and that may take place within very short time scales (i.e., over a few generations) (Gardestr¨ om et al., 2006; Medina et al., 2007 and references therein). Direct effects may, e.g., occur when a substance cause damages on the molecular struc- ture of the DNA, i.e., mutagenic effects, while indirect effects of exposure are population-mediated processes that include alter- ations of the genetic variability in the population (De Wolf et al., 2005). Field studies have shown that mutations accumulate 0166-445X/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.aquatox.2007.12.003