Surprising migration and population size dynamics in ancient Iberian brown bears (Ursus arctos) - PubMed (original) (raw)

Surprising migration and population size dynamics in ancient Iberian brown bears (Ursus arctos)

Cristina E Valdiosera et al. Proc Natl Acad Sci U S A. 2008.

Abstract

The endangered brown bear populations (Ursus arctos) in Iberia have been suggested to be the last fragments of the brown bear population that served as recolonization stock for large parts of Europe during the Pleistocene. Conservation efforts are intense, and results are closely monitored. However, the efforts are based on the assumption that the Iberian bears are a unique unit that has evolved locally for an extended period. We have sequenced mitochondrial DNA (mtDNA) from ancient Iberian bear remains and analyzed them as a serial dataset, monitoring changes in diversity and occurrence of European haplogroups over time. Using these data, we show that the Iberian bear population has experienced a dynamic, recent evolutionary history. Not only has the population undergone mitochondrial gene flow from other European brown bears, but the effective population size also has fluctuated substantially. We conclude that the Iberian bear population has been a fluid evolutionary unit, developed by gene flow from other populations and population bottlenecks, far from being in genetic equilibrium or isolated from other brown bear populations. Thus, the current situation is highly unusual and the population may in fact be isolated for the first time in its history.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

Past and current genetic diversity. (A) Bayesian phylogeny generated by using ancient and modern brown bear European sequences (long dataset) and three cave bears as outgroup. Bootstrap values are shown above the node, and posterior probabilities are shown under the nodes. The color of each square represents the geographic origin, the number in italics indicates the haplotype (see

SI Dataset 2

), and the “n” is the haplotype frequency. (B) Minimum spanning network showing the haplotype distribution of ancient and modern brown bear sequences (short dataset). Numbers inside the circles indicate the assigned haplotype from a total of 29 haplotypes obtained.

Fig. 2.

Fig. 2.

Changes in gene diversity simulated between different time periods assuming a constant population size. Mutation rate: 29.8% substitution per site per million years (A) and 10.0% substitution per site per million years (B). The colors refer to the proportion of simulations leading to the corresponding shift in gene diversity. Thirteen possible effective sizes were simulated (100, 500, 1,000, 2,000, 5,000, 10,000, 15,000, 20,000, 25,000, 30,000, 35,000, 40,000, and 45,000 individuals). Red line indicates observed changes in gene diversity (large dataset).

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