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Appears in Collections:Biological and Environmental Sciences Journal Articles
Peer Review Status: Refereed
Title: Survival and divergence in a small group: The extraordinary genomic history of the endangered Apennine brown bear stragglers
Author(s): Benazzo, Andrea
Trucchi, Emiliano
Cahill, James A
Maisano Delser, Pierpaolo
Mona, Stefano
Fumagalli, Matteo
Bunnefeld, Lynsey
Cornetti, Luca
Ghirotto, Silvia
Girardi, Stefano
Ometto, Lino
Panziera, Alex
Rota-Stabelli, Omar
Zanetti, Enrico
Karamanlidis, Alexandros
Keywords: balancing selection
genetic drift
genetic load
Ursus arctos
Neolithic impact
Issue Date: 7-Nov-2017
Citation: Benazzo A, Trucchi E, Cahill JA, Maisano Delser P, Mona S, Fumagalli M, Bunnefeld L, Cornetti L, Ghirotto S, Girardi S, Ometto L, Panziera A, Rota-Stabelli O, Zanetti E & Karamanlidis A (2017) Survival and divergence in a small group: The extraordinary genomic history of the endangered Apennine brown bear stragglers. Proceedings of the National Academy of Sciences, 114 (45), pp. E9589-E9597.
Abstract: About 100 km east of Rome, in the central Apennine Mountains, a critically endangered population of ∼50 brown bears live in complete isolation. Mating outside this population is prevented by several 100 km of bear-free territories. We exploited this natural experiment to better understand the gene and genomic consequences of surviving at extremely small population size. We found that brown bear populations in Europe lost connectivity since Neolithic times, when farming communities expanded and forest burning was used for land clearance. In central Italy, this resulted in a 40-fold population decline. The overall genomic impact of this decline included the complete loss of variation in the mitochondrial genome and along long stretches of the nuclear genome. Several private and deleterious amino acid changes were fixed by random drift; predicted effects include energy deficit, muscle weakness, anomalies in cranial and skeletal development, and reduced aggressiveness. Despite this extreme loss of diversity, Apennine bear genomes show nonrandom peaks of high variation, possibly maintained by balancing selection, at genomic regions significantly enriched for genes associated with immune and olfactory systems. Challenging the paradigm of increased extinction risk in small populations, we suggest that random fixation of deleterious alleles (i) can be an important driver of divergence in isolation, (ii) can be tolerated when balancing selection prevents random loss of variation at important genes, and (iii) is followed by or results directly in favorable behavioral changes.
DOI Link: 10.1073/pnas.1707279114
Rights: This paper is not the copy of record and may not exactly replicate the authoritative document published in PNAS. Please do not copy or cite without the author’s permission. The final article is available at: Users may view, reproduce, or store journal content, provided that the information is only for their personal, noncommercial use.
Notes: Additional co-authors: Claudio Groff, Ladislav Paule, Leonardo Gentile, Carles Vilà, Saverio Vicario, Luigi Boitani, Ludovic Orlando, Silvia Fuselli, Cristiano Vernesi, Beth Shapiro, Paolo Ciucci, and Giorgio Bertorelle

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