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Insights into bear evolution from a Pleistocene polar bear genome.

ABSTRACT: SignificanceInterspecific hybridization is a widespread phenomenon, but measuring its extent, directionality, and adaptive importance remains challenging. Ancient genomes, however, can help illuminate the history of modern organisms. Here, we present a genome retrieved from a 130,000- to 115,000-y-old polar bear and perform genome analyses of modern polar and brown bears throughout their geographic ranges. We find that the principal direction of ancient allele sharing was from brown bear into polar bear, although gene flow between them has likely been bidirectional. This partially inverts the current paradigm of unidirectional gene flow from polar into brown bear, and it suggests that polar bears were recipients of external genetic variation prior to their extensive population decline.

SUBMITTER: Lan T

PROVIDER: S-EPMC9214488 | biostudies-literature | 2022 Jun

REPOSITORIES: biostudies-literature

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Insights into bear evolution from a Pleistocene polar bear genome.

Lan Tianying T Leppälä Kalle K Tomlin Crystal C Talbot Sandra L SL Sage George K GK Farley Sean D SD Shideler Richard T RT Bachmann Lutz L Wiig Øystein Ø Albert Victor A VA Salojärvi Jarkko J Mailund Thomas T Drautz-Moses Daniela I DI Schuster Stephan C SC Herrera-Estrella Luis L Lindqvist Charlotte C

Proceedings of the National Academy of Sciences of the United States of America 20220606 24

The polar bear (Ursus maritimus) has become a symbol of the threat to biodiversity from climate change. Understanding polar bear evolutionary history may provide insights into apex carnivore responses and prospects during periods of extreme environmental perturbations. In recent years, genomic studies have examined bear speciation and population history, including evidence for ancient admixture between polar bears and brown bears (Ursus arctos). Here, we extend our earlier studies of a 130,000- ...[more]

PMID: 35666863

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Project description:Polar bears in captivity can be exposed to opportunistic pathogens not present in their natural environments. A 4-month-old polar bear (Ursus maritimus) living in an isolated enclosure with his mother in the Tierpark Berlin, Berlin, Germany, was suffering from severe abdominal pain, mild diarrhea, and loss of appetite and died in early 2017. Histopathology revealed severe hepatic degeneration and necrosis without evidence of inflammation or inclusion bodies, although a viral infection had been suspected on the basis of the clinical signs. We searched for nucleic acids of pathogens by shotgun high-throughput sequencing (HTS) from genomic DNA and cDNA extracted from tissue and blood. We identified a novel Mastadenovirus and assembled a nearly complete genome from the shotgun sequences. Quantitative PCR (qPCR) revealed that viral DNA was present in various concentrations in all tissues examined and that the highest concentrations were found in blood. Viral culture did not yield cytopathic effects, but qPCR suggested that virus replication was sustained for up to three passages. Positive immunofluorescence staining confirmed that the virus was able to replicate in the cells during early passage. Phylogenetic analysis demonstrated that the virus is highly divergent compared to other previously identified Mastadenovirus members and basal to most known viral clades. The virus was found only in the 4-month-old bear and not in other captive polar bears tested. We surmised, therefore, that the polar bear was infected from an unknown reservoir, illustrating that adenoviral diversity remains underestimated and that cross-species transmission of viruses can occur even under conditions of relative isolation.IMPORTANCE Cross-species transmission of viral pathogens is becoming an increasing problem for captive-animal facilities. This study highlights how animals in captivity are vulnerable to novel opportunistic pathogens, many of which do not result in straightforward diagnosis from symptoms and histopathology. In this study, a novel pathogen was suspected to have contributed to the death of a juvenile polar bear. HTS techniques were employed, and a novel Mastadenovirus was isolated. The virus was present in both the tissue and blood samples. Phylogenetic analysis of the virus at both the gene and genome levels revealed that it is highly divergent to other known mastadenoviruses. Overall, this study shows that animals in isolated conditions still come into contact with novel pathogens, and for many of these pathogens, the host reservoir and mode of transmission are yet to be determined.

Dataset Information

Insights into bear evolution from a Pleistocene polar bear genome.

Publications

Insights into bear evolution from a Pleistocene polar bear genome.

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