Short communication Novel genes continue to enhance population growth in adders (Vipera berus) Thomas Madsen a,b, * , Beata Ujvari a,b , Mats Olsson c a School of Biological Sciences A08, University of Sydney, NSW 2006, Australia b Department of Animal Ecology, Ecology Building, Lund University, S-223 62 Lund, Sweden c Department of Zoology, Animal Ecology, University of Gothenburg, Box 463, S-405 30 Gothenburg, Sweden Received 20 August 2003; received in revised form 20 January 2004; accepted 21 January 2004 Abstract In 1999, we published a report on how an introduction of 20 males into a severely inbred and isolated population of adders (Vipera berus) halted its decline towards extinction, induced a profound change in population genetic variability, resulted in a dramatic increase in offspring viability and thus in a rapid increase in numbers. Since the publication of our paper we have received numerous inquiries as to whether we have continued to monitor this population, as this is the case we herein present population demographic data gathered between 1981 and 2003. The population has continued to increase in numbers and in 2003, we collected 39 adult male adders, more than at any time over the 23-year study. Our continued work, hence, lends strong support to the im- portance of novel genes in enhancing the viability of inbred populations and supports the importance of preserving genetic vari- ability in order to maintain viable wild populations. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Novel genes; Genetic variability; Population size; Snake; Vipera berus 1. Introduction Natural populations are increasingly becoming sub- ject to the detrimental effects of human influences (e.g. Walsh et al., 2003). Human activities have unfortunately not only resulted in the extinction of numerous species but also in a massive reduction in population numbers and severe fragmentation of former habitats of vast numbers of extant species (e.g. Frankham et al., 2002). One consequence of the two latter factors is loss of ge- netic diversity and although some authors have argued that loss of genetic variability poses only a minor threat to population survival, recent studies have demonstrated that reduced genetic diversity will indeed increase the risk of population extinction (e.g. Saccheri et al., 1998; Madsen et al., 1999; Vil a et al., 2003). In 1999, we published a report on how an introduc- tion of 20 males into a severely inbred and isolated population of adders (Vipera berus) halted its decline towards extinction, induced a profound change in pop- ulation genetic variability, resulted in a dramatic in- crease in offspring viability and thus a rapid increase in numbers (Madsen et al., 1999). This type of population recovery following translocation of animals between populations has been referred to as genetic rescue (Richards, 2000; Ingvarson, 2001). However, in a recent review Fisher and Lindenmayer (2000) demonstrated that translocations do not necessarily result in genetic rescue because translocated animals may be poor breeders or die, thus preventing their novel alleles from being incorporated into the target population. They concluded that: ÔRelocations are a commonly used, popular, and potentially powerful tool for the conser- vation of biodiversity. However, they are often carried out in an ad hoc fashion, and are not carefully moni- tored. In addition, most relocations are poorly docu- mented in the published literature.Õ Since the publication of our paper in 1999, the continued monitoring of the adder population in Smygehuk has been the subject of numerous inquiries. In this short note, we therefore * Corresponding author. Tel.: +46-46-222-3787; fax: +46-46-222- 4716. E-mail address: thomas.madsen@zooekol.lu.se (T. Madsen). 0006-3207/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2004.01.022 Biological Conservation 120 (2004) 145–147 www.elsevier.com/locate/biocon BIOLOGICAL CONSERVATION