Increasing levels of inbreeding is a threat against the viabi lity of the Scandinavian wolf population. A study just coming out in the new journal PLoS ONE now demonstrates that inbreeding is not affecting the wolves as badly as expected. The results show that it is the most genetically variable wolf individuals that are recruited into the breeding population. An important consequence of this action of natural selection is that the negative effects of inbreeding are accumulating much slower than previously believed.
The wolf was exterminated in the Scandinavian peninsula by the 1960-ies. The present Scandinavian population of approximately 150 animals was founded by three immigrants from the larger Russian-Finnish population; a pair around 1980 and a single male ten years later. With so few individuals founding the population the level of inbreeding is high. By the use of DNA-analyses the research team has previously reconstructed a pedigree of the whole population. This kind of detailed information about wild animals is quite unique, but a necessary prerequisite for calculations of so called inbreeding coefficients.
- The inbreeding coefficient is a measure of the proportion of the DNA that is inbred. It varies between 0 and 100%. If a brother and sister are mating, their offspring will have an inbreeding coefficient of 25%. This is about the average level for the present wolf population in Scandinavia. And our analyses have shown that inbreeding is negative, inbred wolves produce less number of pups, says Staffan Bensch, one of the spokespersons of the research team..
The inbreeding coefficients are calculated from the sorted out pedigree. Another way to estimate the proportion of the DNA that is inbred is with DNA-techniques. The research team used samples from blood, hair and scats and examined the DNA at several places to measure the level of genetic variation of individuals. Together with the previous analyses based on inbreeding coefficients the new direct m easures of genetic variation delivered some surprising results.
- For each level of inbreeding it appears to be the wolves with the highest amount of genetic variation that establish themselves as breeders, Staffan Bensch concludes. Whether this is because the genetically diverse wolves are more healthy and stronger and thus more likely to become reproductively active, or if they are more preferred as mates by the opposite sex, we do not know.
- Even if selection is favouring the wolves that are genetically diverse, genetic variation will inevitably be lost over time in such a small population as this one. But it will take much longer than previously thought. This is an important observation since if novel genes are added by introducing a new wolf from a nearby population, the positive effects will be maintained longer than previously estimated.
- We think our results are relevant also for other threatened populations of carnivores. Such spe cies require large areas for their territories and most natural reserves are of a size in which only a few territories can be accommodated. Without immigration inbreeding will increase. If the pattern seen in the Scandinavian wolf population holds to be general, active introductions is only required to be done at rather long intervals in order to maintain the genetic variation of populations.
The study has been carried out by Swedish and Norwegian researchers lead by Staffan Bensch (Lund University, Sweden) and Olof Liberg (Grimsö Wildlife Research Station, Sweden) as a part of the SKANDULV project.
Citation: Bensch S, Andre´n H, Hansson B, Pedersen HC, Sand H, et al (2006) Selection for Heterozygosity Gives Hope to a Wild Population of Inbred Wolves. PLoS ONE 1(1): e72. doi:10.1371/journal.pone.0000072. (http://dx.doi.org/10.1371/journal.pone.0000072)
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