1. Introduction
Inbreeding depression is assumed to be a serious problem for the conservation of small populations (Gilpin & Soulé 1986), but has been difficult to demonstrate in nature (Caughley 1994). The main obstacle has been the construction of pedigrees necessary for calculating inbreeding coefficients. Recently, modern molecular techniques have allowed indirect genetic measurement of inbreeding depression in wild animals, including mammals (e.g. Coltman et al. 1999; Slate et al. 2000). Inbreeding measured as genetic similarity between individuals does not directly translate to inbreeding coefficients. This often prevents one from establishing the level of inbreeding responsible for the decreased fitness, as well as direct comparisons with other studies. These problems are circumvented when using pedigree analysis; however, this has rarely been done in wild populations, with some notable exceptions (e.g. Keller 1998; Loeske et al. 2002). By combining DNA techniques with ecological field data, we have constructed a complete pedigree and demonstrated severe inbreeding depression in the wild Scandinavian wolf, Canis lupus, population. The wolf became functionally extinct in Scandinavia (Norway and Sweden) at the end of the 1960s. Around 1980, at least two wolves immigrated and founded a new population in south-central Scandinavia, 900km from the edge of the large Finnish/Russian source population (Wabakken et al. 2001; Vila et al. 2003). The first reproduction occurred in 1983, and by 2002 the population included approximately 100 wolves.
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