Brown bears are one of the largest terrestrial carnivores today and are widely distributed in the Northern Hemisphere. Compared to many other large carnivores (cave bears, saber-toothed tigers, cave hyenas) that faced extinction at the end of the last ice age, brown bears are one of the lucky survivors, and they have survived until now, a question that has puzzled biologists for almost a century - why is this happening?
The brown bear (ursus arctos) was one of the survivors of the extinction of megafauna in the late Quaternary period. However, although brown bears are widespread throughout the Arctic Ocean, their range has shrunk considerably, and in some geographic areas they have even become extinct. Previous studies using genetic data have provided valuable information for understanding the evolutionary history of brown bears. However, most studies have been limited to contemporary individual or mitochondrial DNA, limiting the understanding of pre-modern population processes.
The researchers present genomic data from two Late Pleistocene brown bears from Honshu, Japan and eastern Siberia, and combine them with published contemporary and ancient genomic data from the all-Arctic range of brown bears to study the spatiotemporal evolutionary relationships between brown bear populations. By including genomic data from Late Pleistocene and Holocene individuals sampled outside of their current ranges, diversity that does not exist in contemporary populations was discovered.
It is important to note that while contemporary individuals show populations that are geographically structured, most likely driven by distance isolation, this pattern varies across ancient specimens from region to region. The inclusion of ancient brown bears in the analysis provides a new perspective on the evolutionary history of brown bears, helping to understand the populations and diversity of brown bears that disappeared in the Late Quaternary.
Brown bears are ecologically adaptable and have a wide range of diets. Although brown bears are carnivores, their diet can also consist mainly of plants, which allows them to adapt to changes in their environment. However, brown bears also experienced widespread range reduction and regional extinction during the last ice age. Brown bears have lived in a wider area including Ireland, Japan's largest island, Honshu, and Quebec, Canada.
Are bear populations declining or disappearing in certain areas because bears have left these areas to go to better places where they still live, or are unique bear populations with unique genes inhabiting these areas and becoming extinct, resulting in a loss of overall species diversity?
Researchers from the University of Copenhagen in Denmark and the University of Yamanashi in Japan have sought to solve this problem by investigating the evolutionary relationships between brown bears across time and space by studying the genomes of ancient brown bears dating back to 3,800 to 60,000 years ago, including several individuals outside the current range of brown bears.
Their research shows that brown bears do not simply migrate with changes in their environment, but rather have population extinctions. Ancient brown bears represent a genetic diversity not found in today's brown bear populations. While brown bears have survived the global mass extinction, their historical ranges and genetic diversity have suffered considerable losses.
This new perspective highlights a pivotal period in the history of brown bears and the challenges they faced during and after the last ice age.
Michael Westbury, senior author of the study, added:"As we continue to grapple with the challenges of human-wildlife coexistence, insights gained from the far-reaching past will be invaluable in shaping a sustainable future. Although studying recent specimens can provide some insights, by including samples from the past and areas where a species no longer exists, we can better quantify how current patterns of diversity have arisen and inform how they respond to future environmental changes. "
References: Takahiro Segawa, Alba Rey-Iglesia, Eline DLorenzen and Michael VWestbury was published in the Proceedings of the Royal Society B on January 24, 2024, entitled:"The origin and diversification of the all-Arctic brown bear population is inferred from the genomes of past and present brown bear populations"（the origins and diversification of holarctic brown bear populations inferred from genomes of past and present populations）。
doi: 10.1098/rspb.2023.2411
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