title: Evidence of rapid change in genetic structure and diversity during range expansion in a recovering large terrestrial carnivore.
abstract: Recovery of natural populations occurs often with simultaneous or subsequent range expansions. According to population genetic theory, genetic structuring emerges at the expansion front together with decreasing genetic diversity, owing to multiple founder events. Thereupon, as the expansion proceeds and connectivity among populations is established, homogenization and a resurgence of genetic diversity are to be expected. Few studies have used a fine temporal scale combined with genetic sampling to track range expansions as they proceed in wild animal populations. As a natural experiment, the historical eradication of large terrestrial carnivores followed by their recovery and recolonization may facilitate empirical tests of these ideas. Here, using brown bear (Ursus arctos) as model species, we tested predictions from genetic theory of range expansion. Individuals from all over Finland were genotyped for every year between 1996 and 2010 using 12 validated autosomal microsatellite markers. A latitudinal shift of about 110 km was observed in the distribution and delineation of genetic clusters during this period. As the range expansion proceeded, we found, as theory predicts, that the degree of genetic structure decreased, and that both genetic variation and admixture increased. The genetic consequences of range expansions may first be detected after multiple generations, but we found major changes in genetic composition after just 1.5 generations, accompanied by population growth and increased migration. These rapid genetic changes suggest an ongoing concerted action of geographical and demographic expansion combined with substantial immigration of bears from Russia during the recovery of brown bears within the large ecosystem of northern Europe.
authors.affiliation: Bioforsk-Norwegian Institute for Agricultural and Environmental Research, 9925 Svanvik, Norway snorre.hagen@bioforsk.no.
authors.forename: Snorre B
authors.initials: SB
authors.lastname: Hagen
authors.affiliation: Bioforsk-Norwegian Institute for Agricultural and Environmental Research, 9925 Svanvik, Norway.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kopatz
authors.affiliation: Department of Biology, University of Oulu, PO Box 3000, 90014 Oulu, Finland.
authors.forename: Jouni
authors.initials: J
authors.lastname: Aspi
authors.affiliation: Luke-Natural Resources Institute, Viikinkaari 4, 00790 Helsinki, Finland.
authors.forename: Ilpo
authors.initials: I
authors.lastname: Kojola
authors.affiliation: Bioforsk-Norwegian Institute for Agricultural and Environmental Research, 9925 Svanvik, Norway.
authors.forename: Hans Geir
authors.initials: HG
authors.lastname: Eiken
mesh_terms: D063147:Animal Distribution; D000818:Animals; D060435:Carnivory; D005387:Finland; D051456:Gene Flow; D014644:Genetic Variation; D018895:Microsatellite Repeats; D011158:Population Growth; D001503:Ursidae / Q000235:genetics*
keywords: DNA; Ursus arctos; brown bear; population; spatial; temporal